Tuesday, April 16, 2019


Biology, ecology and control of major insect pests of crops in the field and storage. Methods of controlling pests including the use of insecticides. Formulation, equipment for application and calculation rates.
Unit 1. Biology and ecology of some major insect pests of crops in the field
Unit 2. Biology and ecology of some major insect pests of stored crops
Unit 1. Methods of controlling insect pests in the field and store
Unit 1. Formulation of insecticides
Unit 2. Different equipment for the application of insecticides
Unit 3. Calculations to determine the rate of insecticide application

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.

UNIT 1. Biology and ecology of some major insect pests of field crops
1.0 Introduction
2.0 Objectives
3.0 Main Content
3.1 Insects as pests
3.2 Some major field crops of economic importance in the tropics
3.3 Biology and ecology of some insect pests of economic importance
3.4 Conclusion
4.0 Summary
5.0 Study Questions
6.0 Further Reading / References

In this unit you would be studying the biology and ecology of some insect pests of economically important field crops with emphasis on crops grown in Nigeria.
At the end of the unit, you should be able to:
* Mention some field pests of some crops
* Discuss the biology of these pests
* State the roles the pests play in the production of the crops

3.1 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.

3.1.1 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.
3.1.2 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.
3.1.3 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.
3.1.4 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

3.2 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.

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