Entomopathogenic nematodes: a potential biocontrol agent against eggplant ash weevil Myllocerus subfasciatus Guerin (Coleoptera: Curculionidae)

Eggplant ash weevil, Myllocerus subfasciatus , is an important pest of eggplant that attacks other solanaceous crops in Asia and Southeast Asia. The potential efficacy of two species of entomopathogenic nematodes (EPN), Steinernema carpocapsae and Heterorhabditis indica , against third instar and pre-pupal stages of this pest was tested under laboratory and poly-greenhouse conditions. In this present study, both stages were susceptible to EPN species but the pre-pupal stage was more susceptible. Steinernema carpocapsae was the most effective species against pre-pupal stages. In a pot experiment, among the EPN species tested, S. carpocapsae caused significantly greater mortality (20-100%) than H. indica (16-92%) against pre-pupal stages and S. carpocapsae caused 16-92% mortality in third instar larvae, while H. indica caused (12-80%) mortality. Both EPN species were able to reproduce in third instar and pre-pupal stages of ash weevil, but progeny production rate for H. indica was significantly higher than those of S. carpocapsae . Our observations also revealed that efficacy of EPN against M. subfasciatus varies with developmental stages of M. subfasciatus and EPN species; therefore, no generalisation can be made. Our findings provide the first insight into the biocontrol potential of S. carpocapsae and H. indica against third instar and pre-pupal stages of M. subfasciatus .