Chapter 5: Manage insect pests and vectors

Insect pests and vectors pose significant challenges to public health, agriculture, and stored product management in Kenya. Managing these organisms effectively requires a clear understanding of their collection, identification, classification, and the dynamics of outbreaks. This chapter equips applied biology professionals with techniques to monitor and control insect populations that threaten human health, crop production, and food security, integrating practical examples from Kenyan contexts such as county agricultural offices and hospital vector control units.

5.1 Insect pests, vectors collection and classification

An insect pest is an insect that damages crops, stored products, timber or livestock enough to cause loss, and an insect vector is an insect that carries a disease-causing organism from one host to another. Managing either begins with finding the insects and naming the group they belong to, because a control measure that works on a caterpillar does nothing against a weevil in a grain store. This topic covers how pests and vectors are collected for study and how they are classified, and the two sub-topics classify field insect pests and storage pests. The outbreaks that these insects cause are treated under Insect outbreak, and their control under Control of insect pests and vectors.

Collecting insect pests and vectors

The methods of sweeping, light traps, pitfall traps and aspirators, and the ways of preserving and identifying what is caught, are taught in Perform entomological techniques. Here the question is which method fits which target. The choice depends on where the insect lives, when it is active and which stage is needed.

Every collection must travel with its field data, because a specimen without them cannot be used to follow an outbreak:

• Date and time: the day and hour of collection show activity patterns.
• Place: the site, field or store and its position are written exactly.
• Host or substrate: the crop, grain, animal or water body where the insects were found is recorded.
• Method and effort: the number of traps, the sweeps made and the hours of trapping allow counts to be compared.
• Conditions: temperature, rain and the growth stage of the crop affect numbers and are recorded.
• Collector: the name of the collector allows later questions to be answered.

Classification of insect pests and vectors

Insects are grouped by order, using the shape of the wings and mouthparts and the type of development. The main orders that contain pests and vectors are shown below.

Ticks and mites are arachnids with eight legs in the nymph and adult stages and are not insects, although they are pests and vectors and are often collected alongside insects.

Insects are also classified by the way they carry disease. A biological vector, such as a mosquito, takes up a parasite or virus, which develops or multiplies in the insect before it is passed on in the next bite. A mechanical vector, such as a house fly, only carries germs on its legs and mouthparts from dirt to food.

Identification and preservation of pest and vector collections

Specimens are identified with keys and guides and preserved by the methods taught in Perform entomological techniques. Pest work adds these points:

• Rearing to adults: many caterpillars and grubs cannot be named in the larval stage, so some are reared in cages on their food until the adult emerges.
• Voucher specimens: at least one named and labelled specimen is kept for each pest species recorded, so that later workers can check the name.
• Separate containers: specimens from different sites and dates are kept apart, because mixed samples cannot be used for counting.
• Damage records: a photograph or a damaged leaf, kernel or timber sample is kept with the specimen, since the damage can help to confirm the identification.
• Vector specimens: adult vectors collected to test for infection are kept dry or frozen according to the planned test, and not in a preservative that harms the pathogen.

5.1.1 Insect pests

Insect pests are classified so that a worker meeting a damaged crop, timber or herd can find the group, and therefore the biology, that points to a suitable management. A pest may be grouped by what it eats, by how it feeds, by how serious it is and by how its young develop.

Insects that harm crops and timber are grouped below by how they feed, because the type of mouthparts decides the damage seen.

Insect pests are also classified in other ways:

• By crop or material attacked: field crop pests such as the maize stem borers, horticultural pests such as fruit flies, pests of timber and buildings such as termites, and pests of animals such as biting flies and lice.
• By host range: monophagous pests feed on one plant species, oligophagous pests on a few related species, and polyphagous pests, such as the fall armyworm, on many unrelated plants.
• By pest status: a key pest causes serious damage in most seasons, an occasional pest causes damage only in some seasons, a minor pest rarely reaches harmful numbers, and a potential pest could become harmful if conditions change.
• By development: insects with complete metamorphosis, such as moths and beetles, pass through egg, larva, pupa and adult, and the larva and adult often feed in different ways. Insects with incomplete metamorphosis, such as locusts and bugs, pass through egg, nymph and adult, and nymphs and adults feed on the same food.
• By origin: native pests have lived in the area for a long time, and invasive pests have arrived from other regions. How invasive pests build up is covered under Insect outbreak.

5.1.2 Storage pests

Storage pests are insects that infest harvested and stored products such as grain, pulses, flour, dried fish and dried cassava. They are classified by what they can attack, where they feed and which group of insects they belong to, because these three points determine how a store should be monitored and protected.

A primary pest can attack whole, sound grain, while a secondary pest feeds on grain already damaged by other causes, or on milled and processed products.

Storage pests are also grouped by where they feed:

• Internal feeders: the larvae of weevils, bruchids and grain moths develop inside a single kernel or seed, so the grain looks sound until the adult leaves an exit hole. Grain borers tunnel into kernels as adults and leave powdery dust, and their larvae feed in the kernel and the dust.
• External feeders: flour beetles and grain beetles feed on the surface of broken grain, flour and meal and are found in the loose material of a store.
• By commodity: pests are grouped as cereal pests, pulse pests, flour and meal pests, and pests of dried animal products, so that each commodity is watched for the right insects.
• By order: most storage pests are beetles (Coleoptera) or moths (Lepidoptera), and both groups develop through egg, larva, pupa and adult.
• By feeding stage: in weevils and grain borers both adults and larvae feed, whereas in moths only the larva eats, and the adult moth does not feed on the grain.

Example: a store keeper finds small round holes in maize kernels. Round exit holes point to an internal feeder such as a weevil or a grain borer, whereas fine flour mixed with broken grain points to an external feeder such as a flour beetle.

Chapter Summary

This chapter provided a comprehensive overview of managing insect pests and vectors, beginning with methods for their collection and classification. It distinguished between general insect pests and storage pests, emphasizing their different habitats and impacts. The discussion then moved to insect outbreaks, exploring the conditions that lead to sudden increases in pest populations and the risks they pose to agriculture and public health. Finally, the chapter examined various strategies for controlling insect pests and vectors, highlighting integrated approaches that combine chemical, biological, and environmental methods. Understanding these techniques is essential for effective management to reduce damage and disease transmission. The chapter underscored the importance of accurate identification and timely intervention to maintain ecological balance and protect economic interests.