Fortuitous biological control of Parthenium hysterophorus by Zygogramma bicolorata in Nepal

Parthenium hysterophorus, a native of central America, is one of the most problematic alien invasive weed in tropical and subtropical world. Parthenium has invaded most of the urban areas and roadside vegetations including agriculture lands and community forest of tropical and sub tropical regions throughout Nepal. Zygogramma bicolorata is an effective biocontrol agent in suppressing Parthenium. Our observation showed that Z. bicolorata has already been established in some parts of southern Nepal, and an interesting phenomenon of ‘fortuitous biological control’ of Parthenium is operating. However, it has not reached to all areas where Parthenium weed has infested. The beetle may expand its area by natural dispersal, but the time duration for natural dispersal to the valleys like Kathmandu will take unnecessarily longer period. It would be better to prepare distribution map of this beetle in Nepal as soon as possible and introduce it as biocontrol agent of Parthenium weed in new areas after ecological assessment.