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What You Should Know About Insects

Insects are one of the most beautiful classes on earth. They attracts immense study. The first successive attempt to classify insects was do...

Insects are one of the most beautiful classes on earth. They attracts immense study. The first successive attempt to classify insects was done by a man called Linneus in 1758. This system of naming was called the binomial system of nomenclature and this system gives the insect 2 names
The first gives the Genera name, The second gives the specific name e.g. Sahlbergella singularis (cocoa mirids)
In classification we have what is called a hierarchy from the most inclusive to the least
In this scheme, the animal kingdom is divided into a number of phyla (singular Phylum). Each Phylum is divided into classes, classes into orders, orders into families, families into genera (singular, genus) and genera into species. A genus is one or more species classified; a family is one or more genera etc.
The class Insecta is divided into 2 broad subclasses, subclass I-Apterygota and subclass II- Pterygota. Apterygota is further divided into order Thysanoptera, Diplura, Protura and Collembola. Pterygota is divided into 2 groups, Exopterygota and Endopterygota.
The division Exopterygota is divided into the following orders; Dermaptera, Dictyoptera, Embioptera, Ephemeroptera, Grylloblattodea, Hemiptera, Homoptera, Isoptera, Mallophaga, Odonata, Orthoptera, Phasmida, Plecoptera, Psocoptera, Siphunculata and Thysanoptera. While the division Endopterygota is divided into the orders Coleoptera, Diptera, Hymenoptera, Lepidoptera, Mecoptera, Neuroptera, Siphonaptera, Strepsiptera and Trichoptera.
APTERYGOTA: these are insects that are primarily wingless i.e. without wings. They are characterized by ametabolus type of metamorphosis, anamorphic type of development (development by adding 1 segment to the existing segment). This is in contrast with epimorphic type of development where there is the same number of segments in the adults and the young, only the size are different e.g. collembola, thysamara (primitive insects).
PTERYGOTA: are insects that are primarily winged although in some cases the wings maybe lost at one stage of development or the other.
EXOPTERYGOTA: The wing parts are outside the body and the insects exhibit incomplete metamorphosis e.g. insects in the order orthopteran, isopteran
ENDOPTERYGOTA: Wing parts are internal and exhibit complete metamorphosis. The wings develop internally from imaginal disc which are embryonic cells from which the adult structures develop e.g. diptera, lepidoptera
Insects belong to the group arthropods (Phylum Arthropoda); other organisms in the group include spiders, crabs, centipedes etc. They all have segmentally arranged appendages in common. A typical adult insect has 3 basic body parts namely the head, thorax and abdomen. The thorax comprises of 3 segments namely prothorax, mesothorax and metathorax and each segment of the thorax has a pair of legs with the 2nd and 3rd in addition to the legs have a pair of wings. The thorax is basically the locomotion region while the head is for vision and feeding. The abdomen has the largest number of segments and it varies from one specie to another and on each segment we have a spiracle and usually the appendages of the abdomen are modified to the reproductive organs and they are usually located on the 9th, 10th or 11th segments depending on the insect. The stereotype plates covering the anterior of the abdomen is called Tergite while the posterior is called Sternite.
The insect body is covered with exoskeleton consisting of 2 parts namely the cuticle and the epidermis. The exoskeleton is light but very strong and forms the basis for muscular attachment. It protects the insect against water loss and predation, while allowing the trachea to take oxygen directly to the tissues of the body. It also permits the fast contraction of flight muscles. One problem of the exoskeleton is the fact that it is ridged and does not grow and thus has to be shed. The process of shedding is called moulting, which is a chemical process involving a lot of hormones. The insect has a lot of internal organs such as (i) tubular digestive tract (ii) heart with valves for pumping blood (iii) a system of pipe-like trachea for respiration (iv) an intricate muscular system (v) efficient nervous system

Insect pests of agricultural importance belong to different types of order. Orders with pests of agricultural importance include: Coleoptera, Diptera, Hymenoptera, Lepidoptera, Hemiptera, Homoptera, Isoptera, Odonata and Thysanoptera, Thysanoptera, Grylloblattodea and Orthoptera.

COLEOPTERA (beetles)
This is the largest insect order and contains 40% of the known species in the Hexapoda. It is made up of the beetles. One of the most distinctive features of the coleoptera is the structure of the wings. Most beetles have four wings, with the four pairs thickened, leathery, or hard and brittle, and usually meeting in a straight line down the middle of the back and covering the hind wings. The hind wings are membranous, are usually longer than the front wings, and when at rest, are usually folded up under the front wings. The beetles undergo complete metamorphosis. Many are phytophagous; many are predaceous; some are scavengers; others feed on mold or fungi; and a very few are parasitic. Many beetles feed on stored plant or animal products, including many types of foods, clothing and other organic materials. Examples include Callosobruchus maculatus (cowpea beetle), Sitophilus oryzae (maize weevil).

Most Diptera can be readily distinguished from other insects to which the term fly is applied (sawflies, stoneflies, caddisflies, dragonflies) by the fact that they possess one pair of wings. These are the front wings and the hind wings are reduced to small knobbed structures called halters, which function as organs of equilibrium. They are relatively small and soft bodied insects and some are quite minute but many are of great economic importance. The mouthparts are of the sucking type. They undergo complete metamorphosis and the larvae are called maggots, e.g. Hessian fly (Mayetiola destructor), a serious pest of wheat, Gall midges, mosquitoes Anopheles spp
HYMENOPTERA (sawflies, parasitic wasps, ants, wasps and bees)
From the human standpoint this order is probably the most beneficial in the entire insect class. It contains a great many species that are of value as parasites or predators of insect pests, and it contains the most important pollinators of plants, the bees. The Hymenoptera are a very interesting group in terms of their biology, for they exhibit a great diversity of habitats and complexity of behavior culminating in the eusocial organization of the wasps, ants and bees, e.g. Apis mellifera (honey bee)

LEPIDOPTERA (Butterflies and Moths)
The butterflies and moths are common insects and are well known to everyone. They are most readily recognized by the scales on the wings which come off like dust on one’s fingers when the insects are handled. They are of considerable economic importance; the larvae of most species are phytophagous and many are serious pests of cultivated plants e.g. cotton bollworm Helicoverpa armigera. A few feed on fabrics and a few feed on stored grain or meal. On the other hand, the adults of many species are beautiful and much sort after by collectors, and many serve as the basis of art and design.

The term bug is used by the general public for a great many different animals and by entomologists for occasional insects in other orders (for example, mealybugs, lightning bugs). When used for an insect in the order Hemiptera, the bug of the name is written as a separate word. The Hemiptera are sometimes called the “true” bugs, to distinguish them from occasional insects in other orders to which the term bug is applied. One of the most distinctive features of the Hemiptera, and one from which the order gets its name, is the structure of the front wings. In most Hemiptera the basal portion of the front wing is thickened and leathery, and the apical portion is membranous. This type of wing is called hemelytron (plural, hemelytra). The hind wings are entirely membranous and are slightly shorter than the front wings. The mouthparts of the Hemiptera are of the piercing-sucking type and are in the form of a slender, usually segmented beak that arises from  the front part of the head and generally extends back along the ventral side of the body.

HOMOPTERA (This order contains a large and diverse group of insects closely related to the Hemiptera. They exhibit considerable variation in body form, and many species are rather degenerate in structure. The life history of some Homoptera is very complex involving bisexual and parthenogenetic (reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants) generations, winged and wingless individuals and generations, and sometimes regular alternations of food plants. All Homoptera are plant feeders and many species are serious pests of cultivated plants. Some species transmit plant diseases. A few Homoptera are beneficial and serve as source of shellac, dyes or other materials. The mouthparts are similar to those of Hemiptera.

ISOPTERA (Termites)
Termites are medium sized cellulose eating social insects comprising the order Isoptera, a relatively small group of insects. They live in highly organized and integrated societies, or colonies with the individuals differentiated morphologically into distinct forms or castes-reproductives, workers, and soldiers-which perform different biological functions. The wings (present only in the reproductive caste) are four in number and membranous. The front and hind wings are almost equal in size hence the name Isoptera. Though termites are often referred to as “white ants”, they are not ants nor are they closely related to ants which are grouped with bees and wasps in the Hymenoptera, whose social system has evolved independently of that in the Isoptera.

The thrips are minute, slender-bodied insects 0.5-5.0 mm in length. Wings may be absent or present. The wings when fully developed are four in number, very long and narrow with few or no veins and fringed with long hairs. The fringe of hairs on the wings gives the order its name. The mouthparts are of the sucking type. Many trips are plant feeders, attacking flowers, leaves, fruits, twigs or buds. Many species are serious pests of cultivated plants.

ODONATA (dragonflies and damselflies)
The odonata are relatively large and often beautifully coloured insects. The immature stages are aquatic, and the adults are usually found near water. All stages are predaceous and feed on various insects and other organisms and from the human point of view, are generally very beneficial.
ORTHOPTERA (Grasshoppers, Crickets and Katydids)
Most Orthoptera are plant feeders and are important pests of cultivated plants. A few are predaceous, a few are scavenger and a few are more or less omnivorous e.g. variegated grasshopper Zonocerus variegatus. The Orthoptera may be winged or wingless and the winged forms usually have four wings. A number of insects “sing” but some of the best known insect songsters (grasshoppers and crickets) are in the order Orthoptera. The songs of the insects are produced chiefly by stridulation, that is by rubbing of one body part against another.

The lice are small wingless ectoparasites of birds and mammals. These insects are often divided into two separate orders, Mallophaga (chewing lice) and Anoplura (sucking lice). The suborder Anoplura contains several species that are parasites of domestic animals and two species that attack humans. These insects are irritating pests and some are important vectors of diseases e.g. Menopon gallinae which is specific to chicken.

Insects as pests
Insects are a class of invertebrates belonging to the phylum ARTHROPODA. They have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. The class INSECTA or HEXAPODA comprising the insects is the largest class in the phylum arthropoda as well as the most extensive class in the whole animal kingdom.
Insects are a very important group of animals because of their beneficial and adverse effects on the life of man. They have made a tremendous impact on the environment, on human activities and health. Insects can be classified as follows based on their economic importance. 

Injurious Insects 
a) Pests of cultivated plants (crop pests): Each cultivated plant harbours many insect pests which feed on them and reduce the yield of the crop. Field and horticultural crops are attacked by many insect species e.g. cotton bollworm (Helicoverpa armigera), Rice white stem borer (Maliarpha separatella). 
b) Storage pests: insects feed on stored products and cause economic loss e.g. Bean weevil (Callosobruchus maculatus), Khapra beetle (Trogoderma granarium). 
c) Pest attacking humans, cattle and domestic animals: Cattle are affected by pests like Horse fly (Tabanus atratus), humans by botfly (Dermatobia hominis) (Fleas and Lice). They suck blood and sometimes eat the flesh. 
Beneficial Insects 
A) Productive insects 
i) Silk worm (Bombyx mori): Helps in the production of silk
ii) Honey bee (Apis mellifera): provides us with honey and other products like bee wax and royal jelly.
iii) Lac insects: secretions from the body of these scale insects are called lac. It is used in the making of vanishes and polishes.
B) Insects useful as drugs, food, ornaments etc.
i) As medicine
i) Silk worm: - The silk worm filament secreted from the salivary gland of the larva helps us in producing silk. 
ii) Honey bee: - Provides us with honey and many other by-products like bees wax and royal jelly. 
iii) Lac insects: - The secretion from the body of these scale insects is called lac. Useful in making vanishes and polishes. 
b) Insects useful as drugs, food, ornaments etc. 
i) As medicine e.g. Sting of honey bees- remedy for rheumatism and arthritis, Eanthoridin extracted from blister beetle –useful as hair tonic. 
ii) As food - for animals and human being. 
For animals - aquatic insects used as fish food. 
Grass hoppers, termites, pupa of moths. They have been used as food by human beings in different parts of the world. 
(c) Ornaments, entertainers 
- Artists and designers copy colour of butterflies. 
- Beetles worn as necklace. 
- Insect collection is a hobby 
(d) Scientific research 
Drosophila and mosquitoes are useful in genetic and toxicological studies respectively. 

Helpful Insects 
(i) Parasites: These are small insects which feed and live on harmful insects by completing their life cycle in a host and kill the host insect. E.g. egg, larval and pupal parasitoids 
(ii) Predators: These are large insects which capture and devour harmful insects. E.g. Coccinellids, Preying mantis. 
(iii) Pollinators: Many cross-pollinated plants depend on insects for pollination and fruit set. E.g. Honey bees, aid in pollination of sunflower crop. 
(iv) Weed killers: Insects which feed on weeds and kill them. E.g. Parthenium beetle eats on parthenium. Cochneal insect feeds in Opuntia dillenii. 
(v) Soil builders: soil insects such as ants, beetles, larva of cutworms, crickets, collembola, make tunnels in soil and facilitate aeration in the soil. They become good manure after death and enrich soil. 
(vi) Scavengers: Insects which feed on dead and decaying matter are called scavengers. They are important for maintaining hygiene in the surroundings. E.g. Carrion beetles, Rove beetles feed on dead animals and plants. 

Household and Disease Carrying Insects 
i) Pests which cause damage to belongings of human beings like furniture, wool, paper etc. E.g. Cockroaches, furniture beetle, sliver fish, etc. 
ii) Pests which cause painful bite, inject venoms. E.g. Wasps, bees sting us. Hairy caterpillar nettling hairs are poisonous. Mosquitoes, bugs bite and suck blood from us. 
iii) Disease-causing: Mosquito - Malaria, Filariasis, Dengue fever. Housefly- Typhoid, Cholera, Leprosy, Anthrax 
We would be looking at the life cycle of insect pests associated with some important field crops namely: maize, (cereals), cowpea, (legumes), cotton (cash crops), cocoa, (tree crops), cassava, (root and tuber) and citrus, banana (fruit crops). 

MAIZE (Zea mays)
Maize belongs to a group of crops known as cereals. Cereals are an important group of crops which are a major source of carbohydrate for man and his livestock. Complexes of pests decimate cereals and drastically reduce their yield. Among the insect pests which decimate the cereals, the stem borers are the most important group. Stem borers are larvae of lepidopterous and dipterous insects. The adults of these pests are innocuous while the destructive stages are the larvae.
The lepidopterous borers of economic importance in Africa are Busseola fusca, Sesamia spp., Eldana saccharina, Chilo spp. and Maliarpha separatella. The dipterous species of concern is Diopsis thoracica.
The stem borers feed inside the plants and are therefore protected from parasites, predators, parasites and also contact insecticides when they are inside the plant. There are two important families under this group
I- Family Noctuidae
II- Family Pyralidae
The noctuids are very large moths while the pyralids are smaller in size. In Nigeria, particularly in cereal crops such as sorghum and maize, there are two important genera in the family noctuidae and these are:-
Genus Busseola
Genus Sesamia
They both attack cereals particularly maize and guinea corn. The adult of B. fusca is a dark moth, night flying with a wingspan of 35mm. The moth is widespread in maize growing areas of tropical and sub-tropical Africa. Mature and mated females lay their eggs under leaf sheaths in a long column stretching up the stem. The eggs are white when freshly laid but darken before eclosion. The eggs hatch in about 7-10 days. The larvae are pink to buff in colour characterized by one or more distinct black spots along the body. The larval period lasts between 33-35 days with 6-7 instars. The mature caterpillar cuts a hole in the side of the stem before pupating within the stem and tunnel. The pupa is dark brown and the pupa stage lasts for about 10 days being temperature dependent. The adult emerges through the hole in the stem prepared by the matured caterpillar.
When the eggs hatch the young larvae migrate to the leaf funnel and attack the young leaves leaving the holes or windows. In severe attack the central leaves dies. The larvae bore into the stem and cobs. The attack on the stem weakens the stem, hinders water and mineral nutrient transport and this results in poor plant growth and yield. The stem borer damage is as a result of their feeding on the leaves and in the leaf whorl and boring into the stems and fruit head causing the characteristic symptoms called dead hearts, chaffy-heads and whiteheads. Severe damage kills young plants while damage weakens older plants by borer larvae feeding within the stems. Usually more than one species can be present in the same stem, and stem may harbour several larvae. Borer infestations are carried over from one season to another by diapausing larvae, which remain in the cereal stalks, stubbles, cobs or in wild poaceous plants like Pennisetum spp.
Very few of the larvae which hatch from the eggs of B. fusca eventually gets into the stem because some are blown off by wind, some are fed on by predators or parasitized while wandering all over the plant unlike in Sesamia whose larvae enter directly into the stem. There is therefore no funnel damage in the case of Sesamia. This means that Sesamia is more difficult to control than B. fusca because it goes directly into the stem, however larvae of Sesamia do not go into diapause during the dry season.
Non-Chemical Control: Diapausing larvae can be killed by partial burning of harvested stalk before storing for fuel wood use. This can reduce diapausing larvae populations by up to 90%. Ploughing fields after harvesting can also help reduce populations.
Chemical Control: Treatment with carbofuran as granules, carbaryl and deltamethrin (as an emulsifiable concentrate) can be effective for control of young larvae when used 20-40 days after emergence. Lambda-cyhalothrin and monocrotophos are also effective applied 5-7 days after eggs are found on 5% of the plants. This will allow the chemical to reach the young larvae before they migrate to the stem.

COWPEA (Vigna unguiculata L. Walp)
Cowpea commonly referred to in Nigeria as beans is the most important grain legume crop throughout the tropical belt covering Asia, the far East, Africa, central and southern America and in the southern USA. It provides a major source of protein in human diets.
At the seedling stage cowpea is attacked by aphids (Aphis craccivora) beanflies (Ophiomyia phaseoli), leafhoppers e.g. Empoasca spp, leaf beetle, Ootheca mutabilis, and the arcticid defoliator, Amsacta moloneyi. Insects that decimate the crop at the early reproductive stage include the flower thrips e.g. Megalurothrips sjostedti while at the podding stage the legume pod borer Maruca testulalis and the bug complex viz Clavigralla tomentosicollis, Anoplocnemis curvipes, Mirperus jaculus, Aspavia armigera are the major pests of the crop
Pod sucking bugs cause considerable damage to cowpea. They usually migrate in large numbers to cowpea farms at the podding stage. Both the adults and nymphs suck sap from developing pods. Pods that are attacked dry up prematurely and seeds are poorly formed.

LEGUME POD BORER (Maruca testulalis) (Lepidoptera: Pyralidae)
The larvae of this insect are a regular pest. This borer damages both flowers and pods, and is found wherever cowpea is grown. Uncontrolled infestations can give a yield loss as high as 70%. The eggs are laid on the flower buds and younger leaves. The young larvae bore into the flowers feeding inside and causing the flowers to drop. Young stems, terminal shoots and penduncles are also damaged. Signs of larval feeding include webbing of flowers, leaves and pods and the presence of frass at the shoot tips and pods. Several flowers may be attacked by one larva. Larvae are active by night, during the day they shelter in flowers, pods, stems and leaf debris beneath the plants. Damage is more severe to pods which are located in the leaf canopy on short penduncles or those touching other parts of the plants.
The adult moth has a wingspan of 16-27 mm. Mature larvae are 16 mm in length, whitish in colour with a black head. They have characteristic dark spots on each body segment which form longitudinal dorsal and ventral rows along the length of the body.
Females may lay over 200 oval yellow eggs in batches of 2-16 on flowers, terminal shoots, leaves or pods. The eggs hatch in 2-3 days and there are 5 larval instars. The larval period lasts between 8-14 days depending on climatic conditions and food availability. Full grown larvae usually pupate in the pod but may also drop from the plant and pupate in a cocoon in the leaf debris beneath the plant. The larvae are active at night and during the day hide in flowers, pods and stems or in the soil around the plants. Adults emerge after 5-10 days and may live for 5-15 days.

Non-Chemical Control: Varieties of plant with long penduncles and tougher pods may be available. Monocropping should be avoided.
Chemical Control: Dimethoate combined with cypermethrin gives effective control in field trials. Mixtures of deltamethrin combined with dimethoate and lambda-cyhalothrin combined with dimethoate are also effective.

COTTON (Gossypium spp.)
Cotton is an important cash crop in Nigeria. It is a seed fibre and the lint is used in the manufacture of textiles. It is attacked by a lot of pests e.g. Earias insulana (Spiny bollworm), Aspavia armigera (Shield bug), Cosmophila flava (Cotton Semi-looper), Bemisia tabaci (Whitefly), Sylepta derogata (Cotton leaf roller), Dysdercus spp (Cotton stainer) and Helicoverpa armigera (Cotton Bollworm).

Helicoverpa armigera (Lepidoptera: Noctuidae) (Cotton Bollworm)
This is a very serious sporadic pest of cotton, legumes, maize, sorghum, tomatoes and okra. It is a minor pest on some fruits and it is widespread throughout Nigeria.
Larvae feed within the plant pod and fruits, eating the contents either partially or completely and causing damage that allows the entry of fungal pathogens. The larval feeding leaves characteristic circular holes surrounded by frass on the surface of the fruit or pod. On cotton, young larvae feed within flower buds and terminal buds, while older larvae feed on larger green bolls eating the contents and leaving characteristic circular holes and expelled frass on the surface. A single larva can feed on and destroy several bolls. Damages cause the bracteoles of the bud to open out leading to a symptom called ‘flared squares’. The larvae feed characteristically with the rear part of their body exposed outside the fruit.
The adult moths are up to 19 mm in length, stout bodied with a wingspan of about 40 mm. Female insects have pale brown wings with paler dots near the outer margins and males are usually more green-grey in colour. They are active at night. Young larvae are yellow-white to red-brown in colour and spotted with dark brown or black areas. Older larvae are up to 40 mm in length and may vary considerably in colour from brown or green to pale yellow and pink. There is a dark dorsal band along the length of the body and either side of this, a light, dark and another light band. This last pale band running along the side of the larvae is the most noticeable.
The eggs are spherical, 0.5 mm in diameter and yellow in colour at first, becoming brown near to hatching. Up to 500 eggs may be laid in a single night by the female moth, usually on the upper part of the plant canopy. Eclosion occurs 2-4 days and the first instar roam over the plant in search of food. There are six larval instars which last a total of 14-24 days. Fully grown larvae drop from the plant, burrow into the soil up to a depth of 25-175 mm and pupate in a lined cavity. Pupation lasts for about 10-14 days.
Non-Chemical Control: Numerous natural predators exist but generally they are not capable of preventing a pest outbreak
Chemical Control: Sprays of cypermethrin, lambda-cyhalothrin and endosulfan. Field scouting for eggs is recommended to enable chemicals to be applied at the correct time to kill first instar larvae.
CASSAVA (Manihot utilissima)
Cassava is one of the most important food crops of West Africa. It is a root tuber and it also produces latex, depending on the variety. The tuber is processed into garri, tapioca and cassava flour for human consumption. They may be fed raw or boiled to goats, pigs, horses and cattle. The main industrial use of cassava is in the manufacture of alcohol and starch.
Cassava is attacked by a lot of insect pests namely termites, green spider mites, whitefly, green cassava mealybug, variegated grasshopper etc. These insects bring about a reduction in yield of cassava.
CASSAVA GREEN SPIDER MITE (Mononychellus tanajoa) (Acarina: Tetranychidae)
This is a very serious pest which may cause 15-80% loss in tuber yield. The mites can be wind-dispersed from plant to plant. It prefers a humid environment and therefore occurs more commonly in the humid southern regions of Nigeria.

The mites feed by sucking fluid from plant tissue. Young cassava plants between 2-9 months old are most vulnerable to mite attack when young shoots and leaves may be severely damaged. The very young leaves become stunted and deformed as they grow. Young expanded leaves show varying degrees of yellow spotting which may be mistaken for the symptoms of cassava mosaic virus disease. Leaves eventually dry out and defoliation occurs progressively as new leaves appear. Older leaves remain intact. The leaves become covered in webbing produced by the mites. Older plants are less likely to be attacked.
The mites are green in colour when young becoming yellow as they mature. They are 0.2 mm in length and usually found feeding on new shoots and the underside of leaves. The eggs are laid individually on the underside of leaves. The mites live for 3-4 weeks and the females may produce 20-90 eggs during this period. The egg to adult stage lasts about 12-14 days. Populations vary with the seasonal rainfall pattern, probably in response to the availability of young foliage. Females disperse in the wind by floating on silken threads.
Cultural Control: Mite mortality due to rainfall is sufficient to suppress populations and maintain them at low levels. Cassava planted early in the wet season can remain mite free for several months. Declining rainfall later in the season allows the mite population to increase.
Chemical Control: Unless attack is extremely severe, chemical control is not recommended. Cuttings which are to be used for planting should be treated with insecticide to kill the mites. Chemical control is possible with methidathion or dimethoate.

CASSAVA MEALYBUG (Phenacoccus manihoti) (Homoptera: Pseudococcidae)
It is a very severe pest of cassava. It occurs in the dry season with the peak infestation in February/March. It is more important on young, less established or drought stressed plants. Its alternative hosts include sweet potato, eggplant and tomato. In the early stages of infestation the mealybug feeds on the young apical cassava shoots. During feeding, it injects toxic saliva into the plant which may cause deformation of growing tissues. As mealybug population increases the shoot becomes stunted and the stem twisted.
New growth becomes retarded and the shoot develops a ‘bunchy top’. Eventually all the new leaves on the shoot die and the infestation begins to spread to the older leaves lower down the stem. In the final stage s of attack the plant shows a candlestick appearance. Economic damage is due to loss of tuber yield.
The adult insects are 1-3 mm in length, oval in shape with short lateral and caudal filaments and are wingless. The living insects are pale pink in colour but this is not always obvious as they are covered in a white waxy layer. Male insects are rare. 400 eggs are laid together in a ‘cottony’ sack. One generation takes about 22 days to complete. Therefore infestation with one individual is sufficient to establish a new colony in the field. Adults live for about 20 days. Newly hatched larvae crawl to the tips of the plants where they are dispersed by the wind. The insects can also be spread by the movement of infected planting materials.

Cultural Control Cassava plants over 7 months old are more tolerant to damage. Hence planting at the beginning of the rainy season will allow plants time to grow sufficiently to withstand attack Fertilizer should be applied at the recommended rates to encourage healthy plant growth. Cuttings should be dipped for 10 minutes in hot water (520C) before planting to kill any infestations.
Chemical Control: Cuttings can be dipped before planting in dimethoate or methidathion solution for one minute to kill any larvae which may be present.

CITRUS (Citrus spp.)
Citrus fruits are grown in tropical areas of the world. Juices from grapefruits and sweet oranges are canned in small quantities in Nigeria both for export and local consumption. A lot of insects feed on citrus, causing a lot of damage. The most important insects are scale insects (Coccus viridis), mealybugs (Planococcus citri), fruit-flies (Drosophila spp.), aphids (Toxoptera aurantii and Toxoptera citricidus), citrus False Codling moths (Thaumatotibia leucotreta) and the larvae of swallow tail butterflies (Papilio demodocus).

FALSE CODLING MOTH (Thaumatotibia leucotreta) Lepidoptera:Tortricidae formally known as Cryptophlebia leucotreta
This is a very serious pest. It is widespread throughout Nigeria. Grapefruit and navel oranges are usually attacked. It is also a pest of avocado pear, guava, wild fruits, maturing maize ears and cotton bolls.
The larvae bore holes, usually in the base of mature fruit, where they enter and feed within. Larval damage allows secondary rots to attack the fruit and holes made by the larvae become surrounded by rotten tissues. The rotting spreads and the fruit drops before it is ripe. If the fruit is cut open the pink larva may be seen feeding inside the fruit surrounded by frass.
The adult moth has a wing span of about 16 mm and a body length of 7-8 mm. The forewings are mottled brown in colour with a prominent silver-white dot in the centre of each. The hind wings are paler with no markings and are fringed at the hind margin. Adults are nocturnal. The young larvae are white with dark spots and a black head capsule. When fully grown they are about 15 mm long and become pale pink in colour with a darker dorsal surface. The female can lay 100-400 eggs over the week long life span. Usually about 8 eggs are laid on the surface of each maturing fruit. Hatching occurs between 3-6 days. The young larvae spend some time moving about over the surface of the fruit before they penetrate. The larval period lasts for 17-19 days and there are five larval instars. Infected fruits will drop. The fifth instar larvae pupates in the fruit, in debris on the top of the soil or within the soil in a cocoon made from silk and soil particles. The pupal period lasts from 8-12 days.
Non-Chemical Control: Orchard sanitation is the main control method. Fallen infested fruits and the plant debris beneath should be gathered at weekly intervals and buried in a hole at least 50-100 cm deep, or burnt.
Chemical Control: Not economical
FRUITFLY (Drosophila spp.) Diptera: Drosophilidae
The larvae and adults attack fruits at ripening, causing fruit rot and fruit drop. Stored oranges are also attacked.
Adult Drosophila
BANANA (Musa spp.)
Banana is generally eaten in the fresh form, because of its high sugar content, but it can be dried and made into a highly nutritious flour.
It is attacked by a number of insects among which are Banana weevil (Cosmopolites sordidus), Banana aphid (Pentalonia nigronevosa), Banana thrips (Hercinothrips bicinctus), Coconut scale (Aspidiotus destructor) and the Fruit piercing moth (Achaea lienardi).
BANANA WEEVIL (Cosmopolites sordidus) Coleoptera: Curculionidae
This is a major pest of banana and it is found in all banana producing areas. Records show it is only a pest of banana. The larvae cause damage by tunnelling and feeding within the corms. This makes the plant weak and susceptible to secondary attack by other insects or micro-organisms which cause the corm to rot. Death of seedlings may occur if the larvae penetrate the growing region of the plant. Tunnelled corm sometimes break, but as the insects do not attack the roots lodged plants are not usually associated with this pest. The leaves turn yellow and die.
Adults are about 13 mm in length with a long curved proboscis. When newly hatched they are brown in colour becoming black after a few days. They are winged but rarely fly. They are very slow moving and are nocturnal. The larvae are about 20 mm long, legless with a white body and brown head. The adult female bites a small hole in the base of the corm and lays a single egg. The eggs are white, 3 mm long, elongate and oval. Oviposition is continuous throughout the year but it is most common in the rainy seasons. Each female may lay a total of 10-50 eggs. Hatching occurs in 1-3 weeks and the larval stage lasts for 2-6 weeks. Larvae bore holes in the corm where they feed and pupate. Adults emerge within 1-3 weeks and live in the soil feeding on banana plant material and visiting growing plants to lay their eggs. The adults live from a few months to 2 years and can survive several months without feeding.
Non-Chemical Control: Destroy the sheltering and feeding places for adults; old stems should be cut to the ground level and covered with packed soil and weeds around the banana plants should be destroyed. Infected land should be left fallow. Pest free planting materials should be used.
Chemical Control: HCH, isofenphos, aldicarb and carbofuran are effective in the control of the pest

FRUIT PIERCING MOTH (Achaea lienardi) Lepidoptera: Noctuidae
Adult moths feed by piercing the skin of ripening fruits to suck the sap. This allows the entry of pathogenic organisms and encourages fruit rotting
We would be looking at the life cycle of insect pests associated with some important storage crops namely: rice, (cereals) and groundnut (legumes).
* RICE (Oryza glaberrima and Oryza sativa)
Oryza glaberrima is native to West Africa and is normally grown as a dry land crop with seasonal flooding. Oryza sativa is grown as either a dry land or irrigated crop. Rice is eaten by man, cattle and poultry and is also used in the manufacture of starch and beer. Rice has good storage qualities and can be moved from one place to another easily.  It is attacked by rice weevil and maize weevil in storage.
Rice Weevil (Sitophilus oryzae)
Maize weevil (Sitophilus zeamais)
(Coleoptera: Curculionidae)
They are some of the most destructive primary insect pests of stored grain. Both adults and larvae feed on the grain, which may often be damaged beyond use. They are most active under warm humid conditions. 
Sitophilus zeamais is primarily a pest of maize but will attack rice, sorghum and other stored grains. Infestations can begin in ripening crops in the field and continue in the store. Sitophilus oryzae is primarily a pest of rice but will also attack maize, various cereals and their products, biscuit and pulses. This species is less likely than S. zeamais to infest ripening crops in the field. Both have been found in dried cassava.
DAMAGE: Adults and larvae feed on grains. Attack may start in the field and continue in the store. Larva tunnel and feed within the grain. After pupation adults cut 1.5mm diameter circular holes in the grain through which they emerge. Attack leaves the produce susceptible to moulds and caking. The grains are also tinted with insect excreta.
LIFE CYCLE: Females lay up to 150 eggs during their adult life. Oviposition occurs at temperatures between 15-35oC and at a grain moisture content of above 9.5%. The adult female bores a hole in the grain and deposits a single egg.. The hole is then sealed over with a gelatinous fluid. Each female lay 2-3 eggs per day during her life. Eggs hatch after about 8 days into legless, 4 mm long larvae. The larvae feed and develop over the next 6-8 weeks within the grain. They moult four times during this time. In small grains only one larva maybe present but larger grains such as maize can support 2-3 larvae in a single grain. Pupation takes place in the grain and can last 5-16 days. The adult emerges through a circular hole which it has cut out of the grain. The holes are characteristics of this pest. Adults may live for up to six months depending on conditions. There may be up to 7 generations in one year.
Non-Chemical Control: Sitophilus sp. cannot breed when grain moisture is 9% or less. Therefore grain stored in clean dry conditions is less likely to suffer attack. Infestation of stored maize can be reduced by storing it as unhusked cobs. 
Chemical Control: Fumigation followed by storage in insect proof containers is also effective. Grains can be treated with pirimphos-methyl by spraying prior to storage to kill weevil infestations, or admixed with pirimphos-methyl dust.
GROUNDNUT (Arachis hypogaea)
Groundnut or peanuts as they are sometimes called are one of the most valuable legume crops of the tropical and sub-tropical countries. They are exported mainly for their oil. It is also used in the making of margarine, soaps, cooking and salad oils. It is attacked by a number of pests which include, Groundnut Bruchid, Khapra beetle, Rust Red flour beetle, Confused flour beetle and Tropical Warehouse moth.

GROUNDNUT BRUCHID (Caryedon serratus) (Coleoptera: Bruchidae)
This insect is a serious pest. It is regularly found in groundnut-growing areas where nuts are attacked as soon as they are harvested and left to dry. Groundnuts are especially susceptible when stored in the shells. The insects can also breed on tree legumes including tamarind and locust bean.
DAMAGE: Larvae bore through the groundnut shell and enter the seed where they feed and develop. Before pupation larvae cut an exit hole, 3 mm in diameter to escape from the seed. Damage caused by the insect increases with each generation and after 13 weeks in store weight loss of seeds can be up to 38%. The product becomes contaminated with insect excreta and is unfit for human consumption. Adult insects do not cause damage.
Non-Chemical Control: Drying seeds to a moisture level below 9% deters beetle attack.
Chemical Control: Pirimphos-methyl, give effective control. Stores should be inspected at regular intervals and any insects present controlled as soon as possible before the population increases and causes serious damage.

KHAPRA BEETLE (Trogoderma granarium Everts) (Coleoptera: Dermestidae)
It is a serious pest of oilseeds, previously damaged cereals and some pulses. In Nigeria, they are pests of groundnuts especially in the north. It is found mainly in large scale stores. It can survive at a moisture content of less than 2%. Once this pest becomes established in a store it is difficult to remove.
DAMAGE: The larvae bore into grains where they feed leaving the grains hollow. The insects also contaminate the products with their moults and frass. Oil extracted from infested groundnut is also contaminated. 
LIFE CYCLE: Females lay about 40-70 eggs over a period of 3-12 days, depending on the temperature. Larvae take three weeks or more to develop and go through 4 or 5 moults. They live within the grain or hide in small crevices in the storage container. Two types of larvae are produced: those that are able to diapause and those that are not. In adverse conditions diapausing larvae leave their food material and seek out a sheltered position, such as crevice. While diapausing, the larvae are very resistant to effects of contact insecticides and fumigants. When diapause is complete the larvae will pupate. Pupation lasts for 3-5 days. Development from egg to adult usually takes about 4-6weeks, but under poor conditions can take as long as a year.
Non-Chemical Control: Storage areas should be free of crevices where the insects can shelter. The hair on the larvae allow it to become attached to sacks used for transporting the grain. Therefore sacks made from synthetic materials rather than rough fibres should be used for moving grain.

Methods of controlling insect pests in the field and store.
Types of insect pests control can be categorised into
1. Cultural control
This implies the purposeful manipulation of the environment to make it less favourable for insect reproduction and feeding. Cultural methods are based on modifications in time and manner of performing necessary operations in the production of crops etc. it is one of the cheapest methods of control available 
This includes the use of various farm practices which directly or indirectly reduce pest populations. e.g. 
a) Simple sanitation:-burning of refuse thereby destroying places in which the over wintering organisms may live. The proper care of garbage disposal e.g. when manure is cleaned up, housefly growth is retarded. Good drainage will help to control mosquitoes.
b) Soil tillage:-this will expose the ground insects to risks which lead to their destruction e.g. mole crickets.
c) Crop rotation:-the rotation of crops at the proper time will help to control pests of that crop. Timing of planting and harvest will often mean the between an average or a good yield. 
d) Use of resistant varieties/planting date:-we can use varieties of crops that are resistant to pests so as to minimize damage. There are times the resistant varieties are combined with planting date to achieve efficient results e.g. Mayetiola destructor called the Hessian fly or barley midge almost wiped out wheat in USA but it was successfully controlled by using a resistant variety of wheat along with late planting.
2. Mechanical/Physical Control
This includes the simple fly swat, fly screen and mosquito nets, light traps ('zappers'), exclusion methods such as packaging and sealing (e.g. against storage pests), sifting and separation in flour mills and the use of temperature, humidity and gas regimes against storage and museum pests. It also includes drainage against mosquitoes and removal of bushes against Tsetse flies
3. Biological Control
Biological control implies the use of natural enemies to control insects. This includes the application of available predators, parasites or diseases, either natural, introduced or commercially available. e.g. Introduction of Australian ladybirds to USA citrus, spray applications of bacterial diseases against caterpillars.
They have been used with a high success rate e.g. the scale insect is a pest of cotton and it also feeds on citrus. It almost wiped out citrus in the USA but it was successfully controlled by using the ladybird beetle insect.
1. each natural enemy is specific for what it is to control
2. it is non-hazardous i.e. it doesn’t constitute any danger to the environment
3.  it is economical when it is established
4. it is a more permanent kind of situation
1. it has limited usefulness i.e. limited to those organisms that have this natural predators
2. it has limited success because the natural enemies have to be identified and it has to be within ones reach.
3.  in most cases it is very slow in action although it gives a more permanent result.
4. the cost is very high

4. Genetic Control
This includes male sterilisation techniques, selective breeding and genetic modification. 
Male sterilisation techniques involve the mass rearing of a pest, laboratory sterilisation of males and their release into the wild with the purpose of swamping the wild male population leading to infertile egg laying. For this strategy to work, the females need to mate only once and not to be able to select against the sterile males.
This method worked extremely well with screw worm flies (the larvae of this insect is a very serious pest of cattle), leading to its complete eradication in USA. However, the same method did not work on sheep blow fly in Australia as the females selected against the sterilised males. The use of sterilant have certain specific advantages over the use of chemicals.
Advantages of sterilant over chemicals (insecticides)
Let us assume that a chemical is applied and it kills 90% of the male and female population, leaving 10 males and 10 females to mate and continue the next generation. Suppose on the other hand a sterilant with the same effect is applied, this means we would have 10 fertile females subject to the mating competition from 10 fertile males and 90 sterile males. Only one fertile female is left to produce the next generation.
There are certain criteria necessary for its success namely-
1) we are assuming the female will mate only once in a life time which is a right assumption
2) we are assuming the sterile males will enter into competition with the fertile males
3) we must have as much as possible, a geographically isolated population.

5. Chemical Control
Chemical control includes both behaviour modifiers and insecticides.
Behaviour modifiers
Attractants - cause insects to move towards their source. Examples include 
Pheromones - secreted by insect, species specific - may be used to lay trails, or for aggregation, swarming, alarm or sexual attraction.
Food and oviposition attractants. E.g. Old fruit fly is attracted to ammonia (NH3) , flavouring essences and protein sources 
Antifeedants – these prevent an insect from feeding and it subsequently starves to death 
Antioviposition chemicals – they prevent female insects from laying eggs. 
Repellents – these are used to ward off insects from where it is applied e.g. personal fly repellents
6. Attractants
Monitoring of pest situation. Traps give an early warning system in quarantine situations and are used in crops to monitor pest intensity to indicate when to apply insecticides e.g. coddling moth control. 
Direct control 
When baits are combined with a lethal trap or insecticide e.g. dark pots against the common fruit fly Drosophila melanogaster in orchards. 
Mating disruption occurs when the environment is saturated with mating pheromone so that the male is confused and cannot find a mate. (used in control of oriental fruit moth or peach moth Grapholita molesta).

Development of workable pheromone mixtures, traps and application methods is time consuming and costly. It requires -
Knowledge of physiology of pest for design of traps - size, shape, material, trap opening, the density of traps required and their positional placement in the crop.

Development of a substrate which will release the pheromone in a controlled, consistent rate. 
Knowledge of the active ingredients in a pheromone - the optimal concentration of each component and whether this changes over time. 
Financial investment - These chemicals also need to be registered, requiring lots of data. Since these cannot be patented, there is little money to be made from their commercial development and so it is usually left to government agencies.
7. Legal control (Quarantine)
In 1971 a viral disease called Venezuelan encephalitis of horse spread by a vector was wide spread in Central America and was introduced into North America. By restricting the movement of horses and embarking on mass immunization the disease was curtailed.
8. Integrated Pest Management (IPM)

Insects are known to reproduce in a variety of ways. This has helped in the propagation of species and survival in adverse conditions. The following are different ways by which insects reproduce
1. Parthenogenesis:- Some insects are able to reproduce without fertilization of eggs and this type of reproduction is called parthenogenesis. Insects that reproduce this way multiply rapidly e.g. aphids.
2. Paedogenesis:The immature stages of insects develop functional sex organs and reproduce. This is called reproduction by immature stages, e.g. the larvae stage. Examples of insects that reproduce this way include Micromalthus debilis of the family Ceccidomyiidae.
3. Polyembryony:-Some insects are able to bring up 2 or more embryo from a single egg and these embryos can subsequently develop into individuals. This is common among the parasitic wasps of the family Encyrtidae,Braconidae.
4. Hermaphroditism:- A single insect has both the male and the female reproductiveorgans. In this case both the production of eggs and the egg fertilization is carried out by the same individual e.g. Icerya purchasi (Stain insect of cotton).
5. Viviparity:-  This refers to reproduction of living young by insects without a prior lying of eggs. In some insects they are able to produce single egg and single embryo at the same time nourished within a special follicle within the female so that a mature larva is deposited e.g. Glossina spp
6.Oviparity: This is the most common type of reproduction. The eggs are laid by the female on a suitable site or substrate e.g. in/on the soil, on plant tissues or any other place where development can take place. The eggs are usually left to hatch but in most cases the eggs are tender enough for the insects to show maternal care.

The biological activity of a pesticide, be it chemical or biological in nature, is determined by its active ingredient (AI - also called the active substance). Pesticide products very rarely consist of pure technical material. The AI is usually formulated with other materials and this is the product that is sold, but it may be further diluted in use. Formulation improves the properties of a chemical for handling, storage, application and may substantially influence effectiveness and safety. Formulation terminology follows a 2-letter convention: (e.g. GR: granules)

Pesticides are available in various formulations". A formulation is simply the form of a specific product that you use. A pesticide formulation is a mixture of chemicals which effectively controls a pest. Formulating a pesticide involves processing it to improve its storage, handling, safety, application, or effectiveness. A pesticide formulation typically consists of an active ingredient, plus several inactive materials called adjuvants, or additives. The main purpose of additives is to increase the effectiveness of the active ingredient. Some common additives include spreaders, stickers, wetting agents, compatibility agents, and foaming agents. 
By far the most frequently used products are formulations for mixing with water then applying as sprays. Water miscible, older formulations include:
EC Emulsifiable concentrate
WP Wettable powder
SL Soluble (liquid) concentrate
SP Soluble powder


The following are some of the most common kinds of pesticide formulations available, along with a description to give you a better understanding of what they are:

1. Dusts (D) are made up of a finely ground mixture of active ingredient combined with clay, talc, or other powdered materials. Dusts are intended for dry use and should never be mixed with water. The percentage of active ingredient in a dust is generally quite low. Dusts are commonly used for interior wall void and perimeter treatments, as well as for crop-dusting.

2. Granules (GR) are hard, dry particles made up of porous materials and active ingredient. The percentage of active ingredient in a granule formulation is higher than that of a dust but lower than that of an EC. Granules are usually more safe to apply than dusts or ECs. Granular formulations are used most often for soil treatments. Granules will not cling to plant foliage, so that they may be directly applied over plants or soil.

3. Aerosols are sold in cans and contain one or more active ingredients under pressure. Aerosols pesticides are sold most often for home and garden use, not for agricultural use. The percentage of active ingredient in aerosols is usually very low. One of the main advantages of aerosols is that they are convenient and easy to use. Many aerosols are used for killing pests on contact, or for time-released control of flying pests.

4. Wettable powders (WP) A wettable powder is an insecticide or other pesticide formulation consisting of the active ingredient in a finely ground state combined with wetting agents and sometimes bulking agents. Wettable powders are designed to be applied as a dilute suspension through liquid spraying equipment. Wettable powders are dry and powdery. They appear similar to a dust but contain additional wetting and dispersing agents so that water may be added for maximum effectiveness. Wettable powders are also more highly concentrated than dusts to contain more active ingredient. Wettable powder formulations do not form a true solution when water is added, so frequent agitation of the spray tank is required to keep the formulation in suspension.

5. Emulsifiable concentrates (EC) are liquid formulations where the active ingredient is dissolved in oil and an emulsifier (a blend of active ingredient, organic solvent, and surfactants) is added so that the formulation may be mixed with water or oil for spraying. When the solution is diluted into water, a spontaneous milky emulsion forms with dispersed phase droplets in the size range of 1 to 25 μm. ECs are among the most widely used formulations, along with wettable powders. ECs typically contain two to six pounds of active ingredient per gallon. Unlike wettable powders, ECs require very little agitation and are easy to handle.

6. Flowable liquids (F or L) are made with active ingredients that cannot be dissolved completely in water or oil, so the active ingredient is ground up and suspended in a liquid with other suspending agents. The formulation is then ready to mix with water for application. Flowables are easy to handle, will not clog spray nozzles, and require only moderate agitation.

7. Solutions and water soluble concentrates (S) are liquids in their original state and are fully soluble in water and any other solvent. Solutions that are prepared the right way will not leave unsightly residues or clog spray nozzles.

8. Encapsulated pesticides are a new kind of formulation in which the active ingredient is held in a very small capsule. These capsules are then suspended in a liquid. This formulation of suspended capsules is then mixed with water and maybe applied with a sprayer. Encapsulated pesticides are safe and easy to use, but may pose a threat to bees when they carry the capsules back to their hive.

9. Soluble powders (SP), are dry formulations similar to wettable powders, but the difference is that when added to water a soluble powder will dissolve completely and form a genuine solution (whereas a wettable powder does not). Some agitation may be required to dissolve the soluble powder initially, but once a solution, agitation is not needed. The percentage of active ingredient in a soluble powder is high compared to ECs and WPs, and there are not currently many SP formulations available.

10. Dry flowables are very similar to granules in appearance, but behave in the same way as wettable powders. Dry flowables have several advantages over WPs because of their shape: they can be easily "poured" and measured just like liquid, and are safer to use because very little dust is released into the air when they are mixed and measured. Dry flowables contain very high percentages of active ingredient.

11. Poisonous baits are food-like substances mixed with a pesticide specifically designed to attract and be eaten by insects or other pests and eventually poison them to death. Baits are commonly used for rodent control, including mice and rats. However, baits are also used to control roaches, ants, flies, and other insects. Bait formulations can be used indoors or outdoors. When compared to ECs or other formulations, the percentage of active ingredient in a bait is low.

12. Ultra-Low Volume (ULV) are liquid formulations with uniform droplet sizes. The droplets are usually very small and no water is used. They come in formulations that are ready to use (RTU). Because no water is added, lower quantities are used per unit area.
Newer, non-powdery formulations with reduced or no use of hazardous solvents and improved stability include:
SC Suspension concentrate
CS Capsule suspensions
WG Water dispersible granules

How to choose a Formulation
Any given active ingredient can often be purchased in more than one formulation. For example, the active ingredient Deltamethrin is available as a granule (DeltaGard G Granules), a suspension concentrate (Suspend SC), a dust (Delta Dust), and an aerosol (D-Force HPX). Same active ingredient, four different products. The reason for this is that different formulations of the same active ingredient behave differently. Therefore, a deltamethrin dust is perfect for application into wall voids where it coats the inner wall and controls crawling pests, while a deltamethrin aerosol is more suited towards contact control of flying pests.

Knowing the characteristics of a given formulation will help you to choose the right product for your needs and use that product more effectively. 

Combining Different Formulations
Sometimes two different pesticide formulations are combined to create a more effective application. However, not all pesticides can be combined safely. Before combining various formulations, always consult the label or a pest control professional to find out whether the two formulations are compatible. The mixing of two incompatible pesticide formulations may be fatal. Incompatibility can be either chemical or physical.

These incompatibilities should be clearly indicated on the product label, however, it is still a good idea to contact a professional if you have any questions.

It is employed as a result of convenience, simplicity, effectiveness as well as flexibility
They are used when other control methods fail or an emergency situation arise e.g. locust invasion.

Insecticides have rapid curative action in preventing economic damage. Lethal action is rapid and a high population of pest population is usually accomplished or obtained within a few hours to a day or 2 days, e.g. swamps of migratory locust (Locusta migratoria) have been successfully controlled by aircraft spraying of insecticide.


Proper pest identification. The damaging insect must be properly identified to ensure that the right insecticide is used for its control.
Efficiency of the pesticide: depending on the insect to be controlled, a systemic or contact insecticide will be selected for use.
Pesticide compatibility: the compatibility status of the insecticide should be known prior to usage to ensure that there is no adverse effect, or change in insecticidal properties or change in phyto-toxicity when they are mixed.
Degree of phytotoxicity: Insecticides applied adversely affects the host crop been protected. Most insecticides are phyto toxic but usually at higher doses than required for pest control. The susceptibility of plants to chemical injury also varies from one plant to another and a term used for this is insecticide selectivity. An insecticide maybe toxic to the seedling stage and not phyto-toxic to the mature stage or it may be phyto-toxic to maize or cowpea and not phyto-toxic to okra.
Insect resistance to pesticides: This is an increasing problem in that a pesticide dose that normally controls certain insects over time can no longer control the same insects because of constant spraying which makes the insects grow resistant strains and this is countered by increasing the dose administered or changing the insecticides to one that has a different mode of action.
Synergism: refers to the interaction of chemicals. Some chemicals have the property of increasing the toxicity of another chemical so that the total effect produced when such chemicals are applied is greater than when either one is applied singly e.g. if 2 chemicals A & B 
Chemical A kills-16 pests
      B kills-14 pests
A + B will kill ----30 pests---additive
But if A & B are mixed and about 50% are killed, this is positive synergism but if the number of the pests reduces then it is negative synergism.
Pesticide persistence: Pesticides that are highly persistent in human, livestock and the environment though effective are dangerous, e.g. DDT has been banned globally due to its high level of persistence in the environment leading to contamination of soil and ground water. Insecticides with low persistence (pyrethrum) are more favoured to prevent environmental contamination.
Frequency of application: insecticide application must be timed accurately in order to prevent bad results. The timing should be done to concise with the stage of development at which the pest is most susceptible. Also the safe interval should be considered which is the last time of application before harvesting; so that we don’t have un-decomposed residual chemicals in the produce.

Different equipment for the application of insecticides

Equipment typically used for pesticide application may be divided into six general categories:
1. Ground sprayers
2. Applicators for solid formulations
3. Aerial sprayers
4. Fumigation equipment
5. Foggers
6. Chemigation

The following is an overview of the more common types of pesticide application equipment and some of the areas in which they are typically used.
Ground Sprayers for Liquids
Air blast Sprayers
Air blast sprayers are most often used on orchard crops, grapes and some berry crops. Air blast sprayers have nozzles placed in a very high speed air stream produced by a fan. The air stream propels the very fine spray droplets to the target. In addition, the air stream creates leaf movement, allowing better coverage of insecticides and fungicides.
Boom Sprayers
Boom sprayers have multiple nozzles spaced over the length of the boom. Tractor mounted booms sprayers are generally used to broadcast liquid pesticides over large areas such as agricultural crops or golf course turf. Field sprayers may have tank sizes ranging from 500 to 4000 litres and boom widths ranging from 6 to 36 metres.

Hand-held Sprayers
Hand wand sprayers are light weight and hand operated. Their name is derived from the long metal extension that ends in an adjustable nozzle. A hose attaches the "wand" to a small portable tank or larger, stationary one. These sprayers can vary widely in type and pressure capability. The most commonly seen handwands are compressed-air sprayers. They may be used in a variety of settings such as spot herbicide application on turf or along roadsides, indoor crack and crevice treatments or greenhouses.

Backpack Sprayer
A backpack sprayer has a spray tank that fits comfortably on the back like a knapsack. The applicator pumps the sprayer handle to build up pressure in the tank and applies the product through a small hose / single nozzle assembly. Some backpack sprayers are battery or gas powered. The usual tank capacity is about 15 litres so that the tank weight is not excessive to the handler. Backpack sprayers are commonly used to treat small areas and may be used for spot herbicide application such as on turf or along roadsides and in greenhouses.

Applicators for Solid Formulations

Granular Spreader
Granular spreaders are available to broadcast pesticide granules over an entire field surface or in bands that correspond to crop rows. Application equipment may use gravity or a positive metering mechanism to regulate the flow of granules. Small, hand-operated granule dispersal equipment (e.g., push rotary spreaders) may be used to treat smaller areas such as in landscaping.

Dust Applicators
Equipment used to apply products as a dust range from simple shaking devices to power dusters. Dusts may be applied to indoor residential (crack and crevice) and outdoor residential (ornamental) settings or, in some cases, in greenhouse or agricultural settings.

Aerial Sprayers
Fixed wing aircraft and helicopters may be used for applying pesticides either as a solid or liquid (including ultra-low volume spray). Fixed wing aircraft may be preferred when there are large, continuous areas that may be sprayed with a minimum number of turns. Helicopters are useful for treating discrete or isolated patches.

A fumigant is a pest control product that, at a specific temperature and pressure, can exist in the gaseous state in sufficient quantities to be lethal to a pest organism. Fumigants may move through air spaces between soil particles (soil fumigation) or through air in structures (space fumigation). Space fumigation generally requires the gas be contained within the treatment area for a specified period. Following treatment, aeration takes place under controlled conditions until fumigant levels have dropped below specified levels.
When soil is fumigated, liquid fumigants may be applied using equipment similar to small field sprayers; however, spray nozzles are replaced with hose shanks that inject the liquid fumigant into the soil where it will volatilize.

Fogging Equipment
Outdoor foggers or space sprayers can be mounted on a truck or aircraft and used to form a cloud of small droplets that are suspended in air. This application method is often used to control adult mosquitoes and black flies. Two types of ground equipment are used for space sprays.
Thermal foggers use heat to vaporize the insecticide into a highly visible dense fog. Diesel is often used as a carrier. Although used in the past, thermal fogging has been largely replaced by non-thermal fogging in Canada and the United States.

Ultra-low volume (ULV) sprayers, also known as "cold foggers", use concentrated insecticides with no carrier. Cold fogging produces small droplets of insecticide using special nozzles to break up the liquid droplets. As the droplets are microscopic in size, the spray area is increased, making it possible to effectively use very low application rates of the insecticide.
Fogging equipment may also be used indoors, such as in greenhouses, warehouses and farm buildings. A range of stationary/automatic or hand-held equipment is available for low volume applications.
Mist blowers produce very fine droplets by air blast generation. As air is the major carrier, the concentration of the pesticide in the spray mixture may be high.
Thermal foggers use heat to break up the pesticide into fine droplets. These products are usually formulated at low concentrations in an oil-based carrier.
Ultra-low volume or ultra-low dosage (ULV/ULD) equipment reduces the volume by reducing the use of water or any other liquid carrier. Pesticides must be specially formulated for this application.
Electrostatic equipment uses air to atomize or form spray droplets; the charged droplets are attracted to plants.

Chemigation is the application of chemicals, such as pesticides and fertilizers, to crops through an irrigation system (e.g., sprinkler, flood, furrow, drip or trickle) by mixing them with the irrigation water.
What Can Be Done to Reduce Exposure During and After Pesticide Applications?
Any unnecessary exposure to pesticides should be reduced or eliminated. Pesticide applicators can minimize exposure to themselves and others by carefully following all application instructions and precautionary statements on the product label.

It is good practice to minimize the presence of bystanders in the area while pesticides are being applied and immediately after. When a worker re-entry interval (the time after application at which re-entry to the treated area does not raise concerns regarding risk) is specified on the product label, it must be respected. Re-entry intervals are not specified for products applied in residential areas as it is not considered feasible to restrict entry into these spaces. As such, these products are only registered if they do not pose unacceptable risks to those working or playing in the treated area immediately after application. However, to minimize any unnecessary exposure to pesticides, it is still good practice to wait until the product has dried before re-entering the treated area to work or play.



Undisputegists : What You Should Know About Insects
What You Should Know About Insects
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