Method/Techniques in Biological Control
Biological control practices involve three major techniques viz,
It is advisable to introduce an exotic species of a natural enemy either when there is an unoccupied a niche and is required to be displaced by a more efficient exotic species. The former is a common situation in newly introduced pest in a country. Foreign explorations for parasites and predators have been made primarily to introduce parasites from the place of origin of the pest and sometimes to introduce exotic natural enemies of the indigenous pest species.
Recently, many international organization have been established to facilitate the movement of beneficial species from one country to another and the largest of the organization is the ‘International Institute of Biological Control’ which has laboratories in Switzerland, Trinidad, Malaysia and Pakistan. About 40% of the introduced natural enemas have established in the introduced countries and provided partial to complete control of important insect pests at the global level. In India, since the launching of ‘All India Coordinated Research Project on Biological Control of Crop Pests and Weeds’ (AICRPBC) in 1977, 79 species on natural Enemies have been imported out of which 53 have successfully multiplied and 21 have been established in the field.
Conservation means the avoidance of measures that destroy natural enemies and the use of measure that increase their longevity and reproduction of the attractiveness of an area to natural enemies. If the natural enemies are properly conserved the need for other control measures is greatly reduced.
i) Preservation of Inactive Stages:
This is most critical when there is small reservoir of natural enemies outside the cropped area e.g. Pupae of Epipyrops are found in large numbers on the trashes of sugarcane leaves at the time of harvesting. These are left around harvested fields to augment the supply of natural enemies in the pre-monsoon season against pyrilla.
ii) Avoidance of Harmful Cultural Practices:
Cultural practices like burning can be harmful to natural enemies e.g. burning of sugarcane trash destroy the resting stages of Epipyrops. Such practices can be modified to avoid harmful effects.
iii) Maintenance of Diversity:
The concept more the diversity more is the stability holds true because diverse system may provide alternate hosts as source of food, ever wintering sites, refuges etc. e.g. mixed cropping, intercropping etc.
iv) Natural Food, Artificial Food Supplements and Shelters:
Many parasitoids and predators require food frequently not available in monoculture. The availability of predatory mites was related to the availability of pollen. Artificial honey dew and pollen in the form of food sprays induced early ovipositor of Chrysopera spp.
v)Protection from Pesticides:
All pesticides have adverse effects on natural enemies. The solution lies in the use of relatively resistant strains of natural enemies and selective use of pesticides.
Augmentation includes all activities designed to increase numbers or effect of existing natural enemies. These objectives may be achieved by releasing additional numbers of a natural enemy into a system or modifying the environment in such a way as to promote greater number or effectiveness. These releases differ from introduction of imported natural enemies in that these have to be repeated periodically. The periodic releases may be either Inoculative of Inundative.
i) Inoculative Release:
Inoculative release may be made as infrequently as once a year to re-establish a species of natural which is periodically killed out In an area by unfavorable conditions part of a year.
ii) Inundative Release:
Inundative release involves mass culture and release of natural enemies to suppress the pest population directly. These are most economical against pests that have only one or few discrete generations every year e.g. massive release of Trichogramma spp.