Diapause behaviour of Zygogramma bicolorata (Coleoptera: Chrysomelidae), a biological control agent for Parthenium hysterophorus (Asteraceae), in Bangalore, India

摘要

Zygogramma bicolorata Pallister was introduced for biological control trials against the weed Parthenium hysterophorus (Asteraceae) in India. The insect entered diapause over an extended period of time between July and December in Bangalore. Diapausing adults burrowed into the soil, and emerged in May-June with the commencement of monsoon rains. Percentage diapause increased over time, peaking at 72% during November. Non-diapausing adults were capable of breeding, under laboratory conditions, during the winter. Some adults bred both before and after diapause, during two consecutive years. Soil moisture played an important role in providing the conditions for burrowing or emerging from the diapause chambers. The studies also showed that diapausing adults had to be exposed to the high summer temperatures, for termination of the diapause. It was possible to break diapause by continuous exposure to 30-degrees-C, 35-degrees-C and 40-degrees-C for 22 days, nine days and 10 hours, respectively, during February-March, about three months after its inception. This method can be used to initiate mass multiplication for carrying out releases early in the season.