Pest – Definition of Pest – Categories of Pests – Causes of Pest outbreak – Study Guide

Agricultural Study Materials Insects
PEST – Derived from French word ‘Peste’ and Latin term ‘Pestis’ meaning plague or contagious disease
  • Pest is any animal which is noxious, destructive or troublesome to man or his interests
  • A pest is any organism which occurs in large numbers and conflict with man’s welfare, convenience and profit
  • A pest is an organism which harms man or his property significantly or is likely to do so (Woods, 1976)
  • Insects are pests when they are sufficiently numerous to cause economic damage (Debacli, 1964)
  • 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 agricultural forest, household, medical, aesthetic and veterinary pests.CATEGORIES OF PESTSBased on occurrence following are pest categoriesRegular pest: Frequently occurs on crop – Close association e.g. Rice slem borer, Brinjal fruit borerOccasional pest: Infrequently occurs, no close association e.g. Caseworm on rice, Mango stem borerSeasonal pest: Occurs during a particular season every year e.g. Red hairy caterpillar on groundnut, Mango hoppersPersistent pests: Occurs on the crop throughout the year and is difficult to control e.g. Chilli thrips, mealy bug on guavaSporadic pests: Pest occurs in isolated localities during some period. e.g. Coconut slug caterpillar


Based on level of infestationPest epidemic: Sudden outbreak of a pest in a severe form in a region at a particular time e.g. BPH in Tanjore, RHC in Madurai, Pollachi
Endemic pest: Occurrence of the pest in a low level in few pockets, regularly and confined to particular area e.g. Rice gall midge in Madurai, Mango hoppers in PeriyakuParameters of insect population levelsGeneral equilibrium position (GEP)The average density of a population over a long period of time, around which the pest 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.Economic injury level (EIL)The lowest population density that will cause economic damageDamage boundary (DB)The lowest level of damage which can be measured. ETL is always less than EIL. Provides sufficient time for control measures.PEST CATEGORIES ACCORDING TO EIL, GEP AND DB(i) Key pest
  • Most severe and damaging pests
  • GEP lies above EIL always
  • Spray temporarily bring population below EIL
  • These are persistent pests
  • The environment must be changed to bring GEP below EIL
e.g. Cotton bollworm, Diamond backmoth(ii)  Major pest
  • GEP lies very close to EIL or coincides with EIL
  • Economic damage can be prevented by timely and repeated sprays e.g. Cotton jassid, Rice stem borer
  1. Minor pest/Occasional pest

-GEP is below the EIL usually-Rarely they cross EIL
  • Can be controlled by spraying e.g. Cotton stainers, Rice hispa, Ash weevils
(iv)  Sporadic pests
  • GEP generally below EIL
  • Sometimes it crosses EIL and cause severe loss in some places/periods e.g. Sugarcane pyrilla, White grub, Hairy caterpillar

(v)  Potential pests
  • They are not pests at present
  • GEP always less than EIL
  • If environment changed may cause economic loss e.g. S. litura is potentia pest in North India

CAUSES OF PEST OUTBREAKActivity of human beings which upsets the biotic balance of ecosystem is the prime cause for pest outbreak. The following are some human interventions – Reason fro outbreaki. Deforestation an bringing under cultivation
  • Pest feeding on forest trees are forced to feed on cropped
  • Biomass/unit area more in forests than agricultural land
  • Weather factors also altered – Affects insect development

ii. Destruction of natural enemies
  • Due to excess use of  insecticides, natural enemies are killed
  • This affects the natural control mechanism and pest outbreak occurs, e.g. Synthetic pyrethroid insecticides kill NE.

iii. Intensive and Extensive cultivationMonoculture (Intensive) leads to multiplication of pestsExtensive cultivation of susceptible variety in large area – No competition for food – multiplication increasese.g. Stem borers in rice and sugarcaneiv. Introduction of new varieties and crops.Varieties with favourable physiological and morphological factors cause multiplication of insects. e.g.Succulent, dwarf rice varieties favour leaf folderCombodia cotton favours stem weevil and spotted bollwormHybrid sorghum (CSH 1), cumbu (HB1) favour shoot flies and gall midgesv. Improved agronomic practicesIncreased N fertilizer -High leaf folder incidence on riceCloser planting – BPH and leaf folder increasesGranular insecticides – Possess phytotonic effect on ricevi. Introduction of new pest in new environmentPest multiplies due to absence of natural enemies in new areaApple wooly aphid Eriosoma lanigerum multiplied fast due to absence of Aphelinus mali (Parasit)
  1. Accidental introduction of pests from foreign countries (through air/sea ports) e.g.

  1. Diamondback moth on cauliflower (Plutella xylostella)
  1. Potato tuber moth Phthorimaea operculella
  1. Cottony cushion scale Icerya purchasi on wattle tree
  1. Wooly aphid – Eriosoma lanigerum on apple
  1. Psyllid – Heteropsylla cubana on subabul
  1. Spiralling whitefly – Adeyrodichus dispersus on most of horticultural crops
  1. Large scale storage of food grains Serve as reservoir for stored grain pests Urbanisation – changes ecological balance Rats found in underground drainage
Resurgence- Tremendous increase in pest population brought about by insecticides despite good initial reduction in pest population at the time of treatment. Deltamethrin, quinalphos, phorate – resurgence of bph in synthetic pyrethroids – whitefly in cotton carbofuran – leaf folder in riceLosses caused by pestCrop loss from all factors – 500 billion US $ annually world wideInsect pests – 15.6% loss of productionPlant pathogens – 13.3%Weeds – 13.2%(iv)  Sporadic pests
  • GEP generally below EIL
  • Sometimes it crosses EIL and cause severe loss in some places/periods e.g. Sugarcane pyrilla, White grub, Hairy caterpillar

(v)  Potential pests
  • They are not pests at present
  • GEP always less than EIL
  • If environment changed may cause economic loss e.g. S. litura is potentia pest in North India

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