New alternative weed hosts and comparative biology of the rice blue beetle Leptispa pygmaea Baly

Studies made on weed plants commonly seen growing in the rice fields at the Regional Agricultural Research Station, Pattambi, Kerala Agricultural University, indicated that Leptispa pygmaea Baly fed on five weed plants belonging to the family Poaceae, two from the family of Limnocharitaceae, one each from Cyperaceae, Pontederiaceae and Lythraceae. But oviposition of the beetle was observed only on two alternative hosts viz., Panicum repens and Isachne miliacea of Poaceae. The beetle was found to lay 12–15 eggs on P. repens and 58 eggs on I. miliacea but there was no egg hatching on I. miliacea and the beetle completed its life cycle on P. repens. Biological study of L. pygmaea on P. repens showed a shorter life cycle of 11.5 days from egg to adult in the weed host as against 14.8 days on the rice variety Jyothi. P. repens males lived longer (38.4 days) than females with a longevity of 23.7 days. Panicum repens is a new record as an important alternative host for rice blue beetle.