PESTS - DEFINITION, CATEGORIES, CAUSES FOR OUTBREAK

• Derived from French word ‘Peste’ and Latin term ‘Pestis’ meaning plague or contagious disease 
• Pest is any animal which is noxious(ഹാനികരമായ), 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 (അലങ്കാരമായ)
• Annoyance(ഉപദ്രവം), 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(കശേരുമൃഗം) like rats, birds, etc. 

Depending upon the importance, pests can be classified as 

• agricultural pest
• forest pest
• household pest
• medical pest
• aesthetic pest
• veterinary pests

CATEGORIES OF PESTS 

Based on occurrence following are pest categories 

• Regular pest: Frequently occurs on crop - Close association e.g. Rice slem borer, Brinjal fruit borer
• Occasional pest: Infrequently occurs, no close association e.g. Caseworm on rice, Mango stem borer
• Seasonal pest: Occurs during a particular season every year e.g. Red hairy caterpillar on groundnut, Mango hoppers (തുള്ളന്)
• Persistent pests: Occurs on the crop throughout the year and is difficult to control e.g. Chilli thrips, mealy bug on guava 
• Sporadic(അപൂര്വ്വമായ) pests: Pest occurs in isolated localities during some period. e.g. Coconut slug caterpillar

Based on level of infestation 

• Pest epidemic(പടര്ന്നുപിടിക്കുന്ന): 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(പ്രത്യേക നാട്ടില് പതിവായി കണ്ടുവരുന്ന) 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 Periyakulam

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 over a long period of time, around which the pest population tends to fluctuate due to biotic and abiotic(ജീവനില്ലാത്ത) 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 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.

PEST CATEGORIES ACCORDING TO EIL, GEP AND DB 

• 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
• 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 
• 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 
• 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 
• 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 OUTBREAK 

Activity of human beings which upsets the biotic balance of ecosystem is the prime cause for pest outbreak.

The following are some human interventions - Reason for outbreak 

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 

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. 

Intensive and Extensive cultivation 

• Monoculture (Intensive) leads to multiplication of pests Extensive cultivation of susceptible variety in large area 
• No competition for food 
• multiplication increases e.g. Stem borers in rice and sugarcane 

Introduction of new varieties and crops. 

Varieties with favourable physiological and morphological factors cause multiplication of insects. e.g. 

• Succulent(നീരുള്ള), dwarf rice varieties favour leaf folder 
• Combodia cotton favours stem weevil and spotted bollworm 
• Hybrid sorghum (CSH 1), cumbu (HB1) favour shoot flies and gall midges 

Improved agronomic practices 

• Increased N fertilizer - High leaf folder incidence on rice 
• Closer planting - BPH and leaf folder increases 
• Granular insecticides - Possess phytotonic effect on rice 

Introduction of new pest in new environment 

• Pest multiplies due to absence of natural enemies in new area 
• Apple wooly aphid Eriosoma lanigerum multiplied fast due to absence of Aphelinus mali (Parasit) 

Accidental introduction of pests from foreign countries (through air/sea ports) e.g. 

• Diamondback moth on cauliflower (Plutella xylostella) 
• Potato tuber moth Phthorimaea operculella 
• Cottony cushion scale Icerya purchasi on wattle tree 
• Wooly aphid - Eriosoma lanigerum on apple 
• Psyllid - Heteropsylla cubana on subabul 
• Spiralling whitefly - Adeyrodichus dispersus on most of horticultural crops 

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 rice 
• Synthetic pyrethroids - Whitefly in cotton 
• Carbofuran - Leaf folder in rice 

Losses caused by pests 

Crop loss from all factors - 500 billion US $ annually world wide 

• Insect pests - 15.6% loss of production
•  Plant pathogens - 13.3% 
• Weeds - 13.2% 

Estimated crop loss in various crops in India

Crop         Loss in yield % 

Wheat         3.0 

Rice             10.0 

Maize(ശീമച്ചോളം) 5.0 

Sorghum(അരിച്ചോളം) 5.0 

Cotton 18.0 

Pulses(പയർവർഗ്ഗങ്ങൾ), groundnut 5.0 

Sugarcane 10.0 

Coffee 8.0 

Fruits 25.0 

Coconut 5.0 

Estimated annual crop loss in India by insect pests = Rs.29,240 crores (Dhaliwal and Arora, 1996)

General Classification of Pests

Insects:

These are important and major pests. Insects have three pairs of legs, two pairs of wings, segmented body and characteristic compound eyes and antennae. Insects are tricky and cause damage in different ways viz. sucking sap from plants, biting plant parts, boring in to fruits, twigs and leaves, attacking roots, barks and blossoms etc. The damaging stages of different insect pests are larvae, adults and nymphs.

Mites:

These are creatures like insect but have soft body and four pairs of legs. These tiny creatures have red or pale yellow colour. They suck the sap from the plant and attack the crops in huge number.

Rodents:

(എലി, അണ്ണാന്‍ തുടങ്ങി കരണ്ടുതിന്നുന്ന ഒരു ജീവിവര്‍ഗ്ഗം)

This group of pest eat away large amount of human food and also damage the crops on large scale. They are also responsible for heavy loss to stored grains on farms, in warehouses and houses.

Animals:

Animals like Wild Boar, Deer, Elephants, Wild Buffalo, Jackals, Monkeys, Squirrels cause direct damage to crop plants. They eat away the plants and by and large they waste huge amount of crops.

Birds:

Birds attack the crop plants and eat grains. Crow, Parrots and Sparrows are major among birds that attack the crops.

TYPES OF INSECT PESTS

Whether you are growing ornamentals or vegetables, your garden plants are always prone to insect infestations, particularly in monsoon season. Remember, not all insects are pests; in fact, many of them are beneficial to plants in different ways. But the insects that are well-known pests can have a nasty impact on your Hibiscus, Roses, Tomatoes, etc. Insect pests inflict lots of damage on plants & we must identify them at a very early stage if we are to take any action on controlling them.

Following are some of the most common insect pests in your garden to watch out for:

Scales: These remain covered inside a hard coating which looks like a waxy scale & infests lower surface of leaves & veins of branches.

Thrips: These are minute sucking insects that mainly attack tender leaves, twigs & flower buds, making the affected plants weak with burnt appearance.

Aphids: These brownish or green insects suck sap from tender shoots, leaves & flower buds. The affected plant becomes weak & retards in growth.

Mealybugs: These are small fleshy insects which remain covered in white, wooly & waxy secretions. Generally, older plants are affected.

Whiteflies: These are tiny insects, white in color and are very active in damp & dark conditions.

Spider-Mites: This is a minute dot sized dangerous, shoot sucking pest, red in color, almost invisible to the naked eyes, resembling the spider but not an actual spider.

Caterpillars: Various caterpillars feed on foliage, they damage the leaves by feeding continuously.

Leaf Beetles & Weevils: These leaf infesting flying insects are considered as serious pests on flowering plants like Roses.

Cut worms: This bug remains in the soil & attacks the plant at ground level.

Leaf-miners: The larvae of theses insects mine into leaves between tissue layers, leaving excreta on leaf surface & creating typical white patterns on leaves.