Investigations on the Release of Exotic Beetle for Control of Parthenium hysterophorus in Delhi

A Mexican beetle, Zygogramma bicolbrata Pallister (Chrysomelidae: Coleoptera) was introduced in Delhi on September 15, 2001 in order to suppress the congress grass, Parthenium hysterophorus Linnaeus at a prevailing temperature of 20–38°C and 39–73% relative humidity. The beetles were also released at the research fields of the Indian Agricultural Research Institute, New Delhi. during September 2001 and were found multiplying at three out of five release sites till the end of October 2001 (l4.4–36.4°C and 41–66% R.H.). The beetle remained unnoticed with decline in day temperature during the winter, though in the laboratory, at 26±2°C and 60±10% R.H., it continued breeding without over wintering. Adults approaching over wintering laid few eggs upto 3rd week of November (temperatures ranging from 9.4 to 35.4°C and relative humidity ranging from 61–93%), which failed to hatch afterwards. No egg laying was observed during foggy and chilling weather in December with a minimum and maximum temperature between 3.5 to 8.0°C and 17.2 to 22.2°C, respectively. Non-over wintering females showed profuse egg laying continuously during chilling weather upto three days when released on Parthenium plants grown in pots. Survival of scanty adults during chilling weather at Delhi thus suggests that even though Parthenium beetle is unlikely to reproduce, its establishment can't be ruled out. Among various substrata evaluated for pupation, vermicompost, loamy soil and sawdust were superior, facilitating 75–100% pupation and 82.11 to 97.55% emergence. A focus on the biology is also covered in the present paper.