Biodiversity is the full range of variety and variability within and among living organisms, their associations and habitat oriented ecological complexes. The plant diversity with multiple odours in a poly-cropping ecosystem is unfavorable to many crop pests.
Mechanism for Reduction of Pest Population in Diversified System:
1. Resource Concentration Hypothesis: The host plants are concentrated in time and space in monoculture whereas it is diluted in intercropping systems by the intercrops, which acts as a impediments for the colonization and movement of the herbivores.
2. Natural Enemies Hypothesis: It postulates a greater functional and numerical response by predators and parasitoids in diversified habitats due to supply of alternative prey, foods and refugia.
Plant Diversity can be increased in the following ways:
1. i) Inter cropping: Intercropping greatly influences the microclimate within any given agro ecosystem which in turn has a high relevance to the crop pest management strategy, through population dynamics of insect pests and their natural enemies.
2. ii) Trap cropping: Trap crops are plant stands that are grown to attract insects or other organisms to protect target crops from pest attack. Trap crops should be highly attractive to pest, occupy a small area, planted at same time or earlier.
Trap crop reduces the cost of chemical pesticides, combat the problem of development of resistance by pest, less insecticide is sprayed in main crop, hence natural control remain fully operational and is environment friendly and compatible with other IPM tactics.
It is not possible with monophagous or passively dispersed pests, early sown trap crops may turn into pest nursery, possibility of increased evolution of pesticide resistance in pest as well as destruction of natural enemies.
iii) Barrier crop: Barriers are physical structures put in place to prevent a pest from reaching a plant. They keep pests away from a plant but do not kill them.
1. iv) Entomophage Park: Conservation of biological control agents by establishing the Entomophage Park has given a new approach of pest suppression. There are many plants that can be grown to attract natural predators and parasites which will help to keep down pests and diseases. Flowers such as marigolds (Tagetes), mint (Mentha), sunflower (Helianthus annus), sunhemp (Crotalaria juncea) as well as local legumes are useful attractant plants. Hoverflies, whose larvae feed on green fly are attracted to the flowers of herbs and vegetables such as fennel, celery, dill, carrots and parsnips (Umbelliferae family). The nectar and pollen that these flowers provide will help to increase the number of eggs that these insects lay. Umbellifers will also provide food to various parasitic wasps whose young live on aphids and some caterpillars.
2. v) Weed complex: Partial manual weeding and avoiding use of herbicides distributed the pest load and increased natural enemy population. The presence of weeds in crops affects both plant density and spacing pattern, which are known to influence pest population significantly. Some entomophagous insects are attracted to a particular weed due to chemicals released by host plants or other associated plants. Weeds may increase populations of non pestiferous herbivorous insects in crop fields, which serve as alternate hosts for prey.
CONCLUSION
Diversification of plants influence the relative abundance of arthropods in an ecosystem and can be exploited for minimizing crop damage by insect pests, encouraging the activity and abundance of natural enemies and reduce pesticides load in environment. The agro ecosystem can be manipulated to some extent to make least favorable to insect pests and more favorable to their natural enemies.
ABOUT AUTHOR :
Dr. Milind Joshi & Dr. Syed Shakir Ali
Krishi Vigyan Kendra, Baramati, Pune (Maharashtra) – 413115.
E-mail: Milindento15@rediffmail.com
