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

Abstract

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.