Authors : Dipti Bhimrao Kadu
Page Nos : 50-54
Description :
Spiders are one of the dominant predatory groups found in agro-ecosystems in India. They have special adaptations towards a predatory way of life. Their distensible abdomens enable them to consume large amounts of food in relatively short periods of time, while their rate of predation may greatly increase during short periods when plentiful supply of food is available. They have an exceeding high resistance to starvation, which enables them to survive and maintain normal reproduction during periods of low prey availability. This is accomplished by an ability to decrease their metabolic rate. During their life which varies from 9 months to 25 years, all instars feed voraciously as predators. Most spiders are polyphagous and feed on a variety of prey but some are specialists. Predation is not limited to adults only but includes the egg and larval or nymphal stages as well. They can achieve equilibrium in pest control, after which their own numbers are suppressed by their territoriality and cannibalism.
The population densities and species abundance of spider communities in agricultural fields can be as high as in natural ecosystems. Spiders are important predators of pests on cotton, rice, apple, banana, citrus, soybean, and various other crops and plantations. The use of spiders as biological control agents depends mainly on the conservation and increases in numbers through the use of agricultural practices such as selective spraying rather than on mass rearing and release. The extent, to which spiders can contribute to agricultural pest control, is however limited by the disruptive effect of insecticide applications. The selective use of pesticides to prevent elimination of natural enemies; restricting insecticide usage during crucial periods in the life cycle of the pest; limiting spray application to midday when spiders are less active and shelter; application of pesticides as spot treatments to permit spiders to recolonize in treated areas immediately are important to conserve the predator spiders.
