Effect of continuous laboratory rearing on the fecundity, longevity and sex ratio of the Parthenium beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae)

Continuous laboratory rearing was found to affect the quality of the population of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), a biological control agent introduced into India against the noxious weed, Parthenium hysterophorus L. (Asteraceae). Thus, continuously laboratory reared adults were found to lay fewer eggs per female (1455.1) and produced lesser number of males (12.64%) as compared to wild type individuals, viz., 2521 and 30.72%, respectively, released into the field four years earlier from the same stock. However, laboratory reared females survived longer (151.5) than the wild type individuals (129.3), while the reverse was true for the males (127.3 and 210.8 respectively). Also, it was indicated that laboratory adaptation could have delayed the population buildup of the insect under field conditions in Bangalore.