🐛 Principles of Applied

When a farmer sees an insect in the field, the first practical question is not its full taxonomy but its economic role: does it damage the crop, help protect it, improve pollination, or have no major effect? That practical viewpoint is the starting point of applied entomology.

What Is Applied Entomology?

Entomology is the scientific study of insects. Broadly, it is studied in two major ways:

1. Fundamental or general entomology
2. Applied or economic entomology

Fundamental entomology deals with the academic and biological understanding of insects. It includes:

• morphology
• anatomy
• physiology
• taxonomy and classification

In this approach, insects are studied mainly to understand their structure, life processes, and diversity.

Applied entomology deals with insects from the standpoint of human welfare. Here the central concern is their usefulness or harmfulness in agriculture, animal husbandry, storage, health, and rural economy.

In simple terms:

• fundamental entomology asks, "What is this insect?"
• applied entomology asks, "What does this insect do in relation to crops, animals, people, and production systems?"

Why Applied Entomology Matters in Agriculture

Agriculture is closely linked with insect activity. Some insects directly reduce yield, while others improve crop performance or support farm-based industries.

Applied entomology helps us:

• identify insects of agricultural importance
• distinguish pests from beneficial insects
• understand crop loss and economic damage
• choose proper pest management methods
• conserve useful insects such as pollinators and natural enemies

For example:

• a stem borer in rice is important because it can reduce yield
• a ladybird beetle is important because it feeds on aphids
• a honey bee is important because it improves pollination and gives honey

So, applied entomology is not only about controlling pests. It is equally about using and conserving beneficial insects.

Economic Classification of Insects

In fundamental entomology, insects are grouped by structure into orders, families, genera, and species. In applied entomology, insects are grouped by economic importance.

This practical classification includes:

1. insects of no economic importance
2. injurious insects
3. beneficial insects

Insects of no economic importance

Many insects present in forests, uncultivated lands, or even agricultural fields neither cause significant harm nor provide a clear measurable benefit to human beings. Such insects are placed in this category.

This group reminds us that not every insect in a field is a pest. A large proportion of insect diversity has no direct economic role in day-to-day crop management.

Injurious Insects

Injurious insects are those that cause direct or indirect losses to crops, stored produce, animals, households, or human health.

1. Pests of cultivated plants

These insects attack field and horticultural crops and reduce yield or quality.

Examples:

• cotton bollworm
• rice stem borer

They may feed on roots, stems, leaves, flowers, fruits, or seeds. Their importance depends on crop stage, season, and severity of attack.

2. Storage pests

These insects attack grains, pulses, seeds, and other stored produce after harvest.

Examples:

• rice weevil
• pulse beetle

Their damage is serious because they reduce both quantity and quality during storage.

3. Pests of cattle and domestic animals

Some insects attack livestock by sucking blood, irritating the skin, or transmitting disease.

Examples:

• horse fly
• flesh fly
• fleas
• lice

These insects weaken animals and may reduce milk production, growth, or overall health.

4. Household pests and disease carriers

Some insects damage household goods, while others bite humans or spread diseases.

Examples of household pests:

• cockroaches
• ants
• silverfish

Examples of disease-carrying insects:

• mosquitoes
• houseflies
• fleas
• bed bugs

Mosquitoes are important vectors of diseases such as malaria, dengue, and filariasis. Houseflies act as mechanical carriers of pathogens causing typhoid, cholera, and other diseases.

Beneficial Insects

Beneficial insects are those that provide direct or indirect value to agriculture and society.

They can be grouped into two broad categories:

1. productive insects
2. helpful insects

A. Productive insects

These insects produce commercially useful materials.

Silkworm

• the larva produces silk filament
• this forms the basis of sericulture

Honey bee

• provides honey
• also yields beeswax, royal jelly, propolis, and bee venom
• plays a major role in pollination

Lac insect

• secretes lac
• lac is used in varnishes, polishes, coatings, and several industrial products

Some insects are also useful in medicine, food, and decorative uses.

Examples:

• bee venom has been studied in therapeutic applications
• aquatic insects may serve as fish food
• in some regions, insects are consumed as food

B. Helpful insects

These insects support agriculture by reducing pests, assisting pollination, improving soil, or cleaning organic waste.

Parasitoids

• small insects that develop on or inside a host insect
• they complete their life cycle at the expense of the host and eventually kill it
• examples include egg, larval, and pupal parasitoids

Predators

• larger free-living insects that capture and consume harmful insects
• examples: coccinellids and mantids

Pollinators

• transfer pollen and improve fruit set and seed production
• example: honey bees in sunflower and many horticultural crops

Weed-control insects

• feed on specific weeds and suppress them
• example: Zygogramma bicolorata on parthenium

Soil-building insects

• insects such as ants, beetles, crickets, and collembolans help in soil aeration and organic matter turnover

Scavengers

• feed on dead and decaying matter
• help maintain environmental hygiene
• examples: carrion beetles and rove beetles

A Simple Field-Level Way to Remember This Lesson

When you observe an insect, classify it through four practical questions:

1. Does it damage the crop or stored product?
2. Does it help control another pest?
3. Does it improve pollination or produce a useful product?
4. Does it have no major economic effect?

This approach is the real spirit of applied entomology. It connects insect study directly with crop protection, farm economics, and sustainable agriculture.

Summary Cheat Sheet

• Entomology is studied as fundamental entomology and applied entomology.
• Fundamental entomology focuses on insect structure, physiology, and taxonomy.
• Applied entomology focuses on the usefulness or harmfulness of insects to humans and agriculture.
• Economically, insects are classified as insects of no economic importance, injurious insects, and beneficial insects.
• Injurious insects include crop pests, storage pests, livestock pests, and disease-carrying insects.
• Beneficial insects include productive insects like silkworm, honey bee, and lac insect, and helpful insects like predators, parasitoids, pollinators, weed-control insects, soil builders, and scavengers.
• Applied entomology is important because it guides both pest management and beneficial insect conservation.