Understanding insect biology and behavior
4.a. Life cycle: In most of the insects which completely undergo complete metamorphosis, in the four stages of the life cycle, insects damage the crop only in larval stage and in at least two of the stages are immobile [egg and pupa]. Every insect has different behavior and different weaknesses in each of the stage. They can be easily managed if one can understand the lifecycle and their biology. The different stages in the insect life cycle are morphologically different and relating between one stage and other is difficult unless one studies/observes the life cycle.
Adult stage: Adults of RHC are attracted to light-community bonfires or light traps (electric bulbs or solar light) can be used to attract and kill them. Similarly adult insects of Spodoptera and helicoverpa can be attracted by using pheromone traps. Normally pheromone traps are used to monitor the insect population based on which pest management practices are taken up. Natural Resources Institute, UK in collaboration with Tamil Nadu Agriculture University, Gujarat Agriculture University, Centre for World Solidarity, Asian Vegetable Research and Development Centre has evolved mass trapping method to control Brinjal Fruit and Shoot borer and demonstrated on a large scale (http://www.nri.org, GAU, 2003) The adults of sucking pests can be attracted using yellow and white sticky boards.
Egg stage: Some insects like Spodoptera lay eggs in masses which can be identified and removed before hatching. Insects also have preference for ovi-position. Spodoptera prefers to lay eggs on castor leaves if available. Hence growing castor plants as trap crop is practiced. By observing the castor leaves farmers can easily estimate the Spodoptera incidence. Helicoverpa lays eggs singly, but has a preference towards Okra, Marigold (mostly towards plants with yellow flowers). Hence marigold is used as a trap crop where ever helicoverpa is a major problem. Rice Stem borer lays eggs on the tip of the leaves in nurseries; farmers remove these tips before transplanting (Vyavasaya Panchangam, 2007).
Larval Stage: The larval stage is the most damaging one in most of the insects like borers. In this stage they would be voracious feeders and if identified in the initial stages, they can be managed, otherwise we have to resort to control measures.
Pupal Stage: The larvae of Red Hairy Caterpillar burrow and pupate in the soil. Deep summer ploughing, which is a traditional practice in rainfed areas expose these larvae to hot sun which kills them. The larvae of stem borers in crops like paddy, sorghum pupate in the stubbles. So farmers are advised to cut the crop to ground level and clear the stubbles.
4.b. Biology: The larva of Red Hairy Caterpillar (Amsacta albistriga) has a dense body hair over the body hence no pesticide reaches it when sprayed. Therefore it needs to be controlled in other stages of its life cycle. For any safe and economic method of pest management one must understand how the pest live and die, where does it come from and when, where and how does it damage the crop. Knowledge of these biological attributes of pest will help farmers to use NPM methods successfully on a sustainable basis (GAU, 2003).
5 Understanding and managing crop ecosystem: The pest complex and the natural enemy complex are based on the crop ecosystem. The pest complex of cotton is completely different from that of Sorghum. The pest complex in wet rice ecosystem differs from the pest complex in dry rice. Decision about any pest management intervention should take into account the crop ecosystem which includes cropping pattern, pest-predator population, stage of the crop etc. Similarly the management practices followed in one crop cannot be practiced certain other crop. For example in to manage helicoverpa in pigeonpea, the farmers in Andhra Pradesh and Gulbarga use shake the plants and falling insects are collected over a sheet and killed (see box). Similarly in paddy there is a practice of pulling rope over the standing crop to control leaf roller.
Modifying the crop ecosystem for increasing the abundance, diversity and function of natural enemies in agricultural habitats by providing refuges and alternate or supplementary food resources is one of the best ways to keep pests under control. This includes trap crops, intercrops, cover crops or border crops in strips or in mixtures which attracts and hosts the natural predators. This is now widely called as ecological engineering or conservation biocontrol.