Classification of Pests and Diseases | Agriculture Optional for UPSC PDF Download

Introduction

The term "pest" has its origins in the French word 'Peste' and the Latin term 'Pestis,' both of which refer to a plague or a contagious disease. In the context of agriculture and human interests, a pest can be defined as any animal or organism that is harmful, destructive, or troublesome.
More specifically:

• A pest is any organism that occurs in significant numbers and poses a threat to human welfare, convenience, or profitability.
• A pest is an organism that causes substantial harm to humans or their property or has the potential to do so, as stated by Woods in 1976.
• Insects are considered pests when their populations are large enough to cause economic damage, according to Debacli in 1964.
• Pests are organisms that impose burdens on human populations by causing harm to crop plants, forests, ornamental plants, annoyance, injury, or death to humans and domesticated animals, and the destruction or devaluation of stored products.
• Pests encompass a wide range of organisms, including insects, nematodes, mites, snails, slugs, as well as vertebrates like rats and birds.

Pests can be categorized based on their significance, such as agricultural, forest, household, medical, aesthetic, and veterinary pests, each of which pertains to different aspects of human life and interests.

Categories of Pests

Pests can be categorized based on their occurrence and level of infestation, leading to the following classifications:

Based on Occurrence

• Regular Pests: These pests frequently occur on specific crops and have a close association with them. Examples include the Rice slem borer and Brinjal fruit borer.
• Occasional Pests: Occasional pests infrequently occur on crops and do not have a close association. Examples include the Caseworm on rice and Mango stem borer.
• Seasonal Pests: Seasonal pests make their presence known during a specific season each year. Examples include the Red hairy caterpillar on groundnut and Mango hoppers.
• Persistent Pests: Persistent pests are present on the crop throughout the year and are challenging to control. Examples include the Chilli thrips and mealy bug on guava.
• Sporadic Pests: Sporadic pests are those that occur in isolated localities during specific periods. An example is the Coconut slug caterpillar.

Based on Level of Infestation

• Pest Epidemic: This refers to the sudden and severe outbreak of a pest in a particular region at a specific time. Examples include BPH in Tanjore, RHC in Madurai, and Pollachi.
• Endemic Pest: Endemic pests are pests that occur at a low level and are consistently found in a few pockets, often confined to particular areas. Examples include Rice gall midge in Madurai and Mango hoppers in Periyakulam.

Parameters of insect population levels

General Equilibrium Position (GEP)

• The GEP represents the average population density of a pest species over an extended period.
• It is the point around which pest populations tend to fluctuate in response to various biotic and abiotic factors.
• The GEP is the stable state of the pest population in the absence of permanent environmental changes.

Economic Threshold Level (ETL)

• The ETL is the population density at which it is deemed necessary to implement control measures.
• These control measures aim to prevent a growing pest population from reaching the Economic Injury Level (EIL), where it would cause economic damage.

Economic Injury Level (EIL)

• The EIL is the lowest population density at which pest activity will result in economic damage.
• It serves as a critical threshold beyond which the economic impact of the pest becomes unacceptable.

Damage Boundary (DB)

• The DB is the lowest level of damage that can be quantified or measured.
• The ETL is always set at a level below the EIL, ensuring that control measures are initiated before pest populations reach a point where they can cause economically significant damage.
• This approach provides adequate time for the implementation of effective control measures to manage pest populations and mitigate economic losses.

Pest Categories According to EIL, GEP, and DB

Key Pest

• Key pests are the most severe and damaging pests.
• The General Equilibrium Position (GEP) is consistently higher than the Economic Injury Level (EIL).
• Temporary control measures, such as spraying, may temporarily bring their populations below the EIL.
• Key pests are persistent and require changes in the environment to bring the GEP below the EIL.
• Examples include the Cotton bollworm and Diamond backmoth.

Major Pest

• Major pests have a GEP that is very close to or coincides with the EIL.
• Economic damage can be prevented through timely and repeated control measures, such as spraying.
• Examples of major pests include the Cotton jassid and Rice stem borer.

Minor Pest/Occasional Pest

• The GEP for minor or occasional pests is typically below the EIL.
• Rarely do these pests cross the EIL, and they can usually be controlled by spraying.
• Examples include Cotton stainers, Rice hispa, and Ash weevils.

Sporadic Pests

• Sporadic pests generally have a GEP below the EIL.
• Occasionally, they may cross the EIL and cause severe losses in certain places or during specific periods.
• Examples of sporadic pests are the Sugarcane pyrilla, White grub, and Hairy caterpillar.

Potential Pests

• Potential pests are not considered pests at the moment.
• The GEP is always lower than the EIL for potential pests.
• If the environmental conditions change, these pests may become economically significant.
• An example is S. litura, which is a potential pest in North India, but not currently recognized as a major issue.

Causes of Pest Outbreak

Human activities that disrupt the ecological balance of an ecosystem are the primary causes of pest outbreaks.
The following human interventions can lead to pest outbreaks and their associated reasons:

Deforestation and Conversion to Cropland

• Pest species that previously fed on forest trees are forced to feed on cultivated crops.
• The biomass per unit area is higher in forests than in agricultural land, altering weather factors and affecting insect development.

Destruction of Natural Enemies

• Excessive use of insecticides can kill natural enemies of pests.
• This disruption of natural control mechanisms can lead to pest outbreaks.
• For example, synthetic pyrethroid insecticides can kill natural enemies.

Intensive and Extensive Cultivation

• Monoculture (intensive cultivation) can lead to the multiplication of pests.
• Extensive cultivation of susceptible crop varieties over large areas without competition for food can also increase pest populations.
• For instance, stem borers in rice and sugarcane.

Introduction of New Varieties and Crops

• Crop varieties with favorable physiological and morphological traits can promote insect multiplication.
• For example, succulent dwarf rice varieties favor leaf folders, Cambodia cotton favors stem weevils and spotted bollworm, and hybrid sorghum varieties favor shoot flies and gall midges.

Improved Agronomic Practices

• The use of increased nitrogen fertilizer can lead to higher incidences of leaf folders on rice.
• Closer planting can increase populations of brown planthoppers (BPH) and leaf folders.
• Granular insecticides may possess phytotonic effects on rice, promoting pest infestations.

Introduction of New Pests to a New Environment

• Pests can multiply in new areas due to the absence of their natural enemies.
• For example, the apple wooly aphid (Eriosoma lanigerum) multiplied rapidly in the absence of Aphelinus mali (a parasite).

Accidental Introduction of Pests from Foreign Countries

• Pests can be unintentionally introduced through air and sea ports.
• Examples include the diamondback moth on cauliflower (Plutella xylostella), potato tuber moth (Phthorimaea operculella), cottony cushion scale (Icerya purchasi) on wattle trees, wooly aphid (Eriosoma lanigerum) on apple, psyllid (Heteropsylla cubana) on subabul, and spiraling whitefly (Adeyrodichus dispersus) on various horticultural crops.

Large-Scale Storage of Food Grains

• Food grain storage can serve as a reservoir for stored grain pests, leading to infestations.
• Urbanization can also disrupt the ecological balance, and the presence of rats in underground drainage systems can contribute to pest problems.

Resurgence

• Resurgence refers to a significant increase in the population of a pest species despite an initial substantial reduction in the pest population at the time of treatment with insecticides.
• This phenomenon is often observed with the use of specific insecticides, leading to the rebound or resurgence of pest populations.
• Examples include the resurgence of brown planthoppers (BPH) in rice due to the use of Deltamethrin, Quinalphos, and Phorate, as well as the resurgence of whitefly in cotton caused by synthetic pyrethroids and leaf folder in rice due to Carbofuran.

Losses Caused by Pests

• Pests can cause substantial economic losses in agriculture. Crop loss due to various factors amounts to approximately 500 billion US dollars annually worldwide.
• Insect pests are responsible for a 15.6% loss in production, plant pathogens cause a 13.3% loss, and weeds contribute to a 13.2% loss.

Estimated Crop Loss in Various Crops in India (in terms of yield percentage):

• Wheat: 3.0%
• Rice: 10.0%
• Maize: 5.0%
• Sorghum: 5.0%
• Cotton: 18.0%
• Pulses and Groundnut: 5.0%
• Sugarcane: 10.0%
• Coffee: 8.0%
• Fruits: 25.0%
• Coconut: 5.0%

Source: Pradhan (1964)
In India, it is estimated that annual crop losses caused by insect pests amount to Rs. 29,240 crores, as reported by Dhaliwal and Arora in 1996. These losses underscore the significant impact of pests on agricultural production and the importance of effective pest management.