Seasonal Occurrence and Bio-Control Efficacy of Zygogramma bicolorata Ballister (Coleoptera : Chrysomelidae) on Parthenium hysterophorus

Maximum population of Parthenium hysterophorus found from late March to mid May and July to mid September and Zygogramma bicolorata, a chrysomelid beetle, is an important bio-control agent of this weed. On the onset of winter in last week of November, most of the adults undergo to hibernation and pupae of this beetle proceed for diapause in the nearly soil of the weed up to the depth of Parthenium root, i.e. up to 10-15 cm depending on the moisture level. The diapausing pupae and over wintering adults come out in last week of February taking a duration of 2½ to 3 months. However, this duration was variable according to climatic conditions. The larvae and adult beetles were voracious feeder and fed on leaves, tender stem and inflorescence. The infested plants were soon defoliated and become stub and nude as well as developed blackish colouration at many parts. Perhaps this was due to the action of saliva of the adult beetles and their larvae on the host tissue. Experimental studies in potted caged plants showed 100% damage within a week. Field trials of the weed at selected places caused 90 % damage within 15 days. This damage occurred not only by feeding but also by the saliva secretion and faeces of the adults and larvae.