Categories of Insect Pests and Diseases

PEST 

Any organism that cause significant and economic damage to crops, stored produced and animals”.

A pest is any organism which occurs in large numbers and conflict with man’s welfare, convenience and profit

Pests are organisms which impose burdens on human population by causing

• Injury to crop plants, forests and ornamentals
• Annoyance, injury and death to humans and domesticated animals
• Destruction or value depreciation of stored products.

Pests include insects, nematodes, mites, snails, slugs, etc. and vertebrates like rats, birds, etc. Depending upon the importance, pests may be classified as agricultural, forest, household, medical and veterinary pests.

Parameters of insect population levels

General equilibrium position (GEP) The average density of a population over a long period of time, around which the pest population  tends to fluctuate due to biotic and abiotic factors and in the absence of permanent environmental changes.

Economic threshold level (ETL) Population density at which control measure should be implemented to prevent an increasing pest population from reaching the ETL. It is also known as Action Threshold level

ETL= EIL – Daily reproductive rate of insects

Economic injury level (EIL) The lowest population density that will cause economic damage. 

Damage boundary (DB) The lowest level of damage which can be measured. ETL is always less than EIL. Provides sufficient time for control measures. 

Categories of Pest

i) Insect pests are classified as follows based on season and locality

• Regular pests: Occur most frequently (regularly) in a crop and have close association with that particular crop. Eg: Chilli Thrips, brinjal shoot and fruit borer, Rice stem borer. 
• Occasional pests: Here a close association with a particular crop is absent and they occur infrequently. Eg: Rice case worm, Parasa lepida, mango stem borer.
• Seasonal pests: Occur mostly during a particular part of the year, and usually the incidence is governed by climatic conditions. Eg: Red hairy caterpillar on groundnut-June – July, Rice grasshoppers –June-July.
• Persistent pests: Occur on a crop almost throughout the year. Eg. Thrips on chilies.
• Sporadic pests: Pests, which occur in a few isolated localities Eg. Rice ear head bug

ii) Insects pests are also classified as follows based on intensity of infestations

• Epidemic pests: Pest Occur in a severe form in a region or locality at a particular season or time only. Eg: Rice hispa, rice leaf roller.
• Endemic pests: Pests, which occur regularly and confined to a particular area of locality. Eg. Rice Gall midge in Madurai district and rice stem borer cauvery delta.
• Pandemic pests: The term “pandemic pest” is not commonly used in the context of pest management or agriculture. It may be a typographical error, and “endemic pests” would be the correct term to describe pests continuously present in a specific area.

iii) Pests are classified as follows based on damage potential 

• Key pests: These are the most severely damaging pests. The GEP is always above the EIL. Human intervention may bring the population temporarily below the EIL.. The environment must be changed to bring GEP below EIL. Ex. Cotton bollworm, Diamond back moth.
• Major pests: These are pests with the population crosses EIL quite frequently. Economic damage can be prevented by timely and repeated sprays e.g. Cotton jassid, Rice stem borer
• Minor pests: These are pests with population rarely crosses EIL and fluctuates around ETL. single application of insecticides is usually enough to prevent economic damage (5-10% damage).
• Potential pests: These pests normally do not cause any economic damage. Any change in the ecosystem may make them to cause economic damage .
• Sporadic pests: GEP generally below EIL The population of these pests is usually negligible but in certain years under favorable environmental conditions, they appear in a virtually epidemic form crossing many times over DB and EIL. 

These pests are highly sensitive to abiotic conditions and once the favorable season is over, only a residual population survives. Ex: White grub, hairy caterpillars, grass hoppers

• Abiotic factor: Sunlight, Temperature, Water availability, Soil composition, Air humidity.
• Biotic factor; living organisms or biological components like Predators and Herbivores, Pollinators, Plant Pathogens, Symbiotic Relationships etc.