Comparison on the Diversity of Insect Pests and Natural Enemies in the Chinese Kale Treated with Insecticides and Bio-agents

Abstract

In recent years many of the conventional methods of vegetable insect pest control by broad-spectrum synthetic chemicals has been altered to bio-agents including insect pathogens and herbs extracted to reduce the harmful insecticide residues to human and environment. However, the supported bio-safety evident of applying bio-agents at the farm level was not available. The comparison on diversity of insect pests and natural enemies in the Chinese kale between fields treated with insecticides and bio-agents as in the usual farmer practice, therefore, was carried out 3 times in winter, summer, and rainy of 2001-2002 growing seasons at Bung Pra, Phitsanulok. The numbers of species and insects from both treated fields were collected and analyzed in order to evaluate safety of bio-agent treated in the farm level indicated by insect diversity index. The numbers of species in the bio-agent treated fields were revealed 2.00 up to 5.25 folds higher than those of the insecticide treated fields and the numbers of insects of the former also were higher than the latter around 1.96-4.12 folds. The insect pests mainly were diamondback moth (Plutella xylostella L.) and flea beetle (Phyllotreta sp.). The high potential predator obviously was the fire ant (Solenopsis geminata (F.)), whereas the most effective parasite was Cotesia plutellae (Kurdjumov), a larval parasite of the diamondback moth.