ABSTRACT
The Grey Weevil, Myllocerus subfasciatus Guerin, is an important emerging pest of quarantine significance in Solanaceae crops including the eggplant, Solanum melongena. Entomopathogenic nematodes (EPNs) have been shown to be a potential source of safe and effective control of M. subfasciatus. In this study, we determined the virulence of seven strains of EPNs (Nematoda: Rhabditida) viz. Heterorhabditis bacteriophora NBAIIHb105, H. indica NBAIIHi101, H. indica NBAIIHiMah, Steinernema abbasi NBAIISa01, Steinernema abbasi NBAIISa04, S. carpocapsae NBAIISc04 and S. glaseri NBAIISg01, with different foraging behaviour, against larvae of eggplant grey weevil, M. subfasciatus (Coleoptera: Curculionidae), and their suitability in five representative soils from the eggplant grown areas under laboratory conditions. All seven nematode strains caused >80% mortality of M. subfasciatus larvae at 40 IJs/cm2. LC90 values ranged between 21.18 and 46.41 IJs/cm2 at 96 h post-application, which corresponded to field concentrations between 2.1-4.6×109 IJs/ha. H. indica NBAIIHi101, S. glaseri NBAIISg01, S. abbasi NBAIISa01 and S. carpocapsae NBAIISc04 recorded higher grub mortality, compared to H. indica NBAIIHiMah, H. bacteriophora NBAIIHb05 and S. abbasi NBAIISa04 indicating existence of inter- and intra-specific variation in virulence. Response Surface Modelling (RSM) optimized LC and LT values for maximised larval mortality. RSM predicted a concentration of 58.05-62.54 IJs/cm2 of these EPN (corresponding to a field dose of 5.8-6.2×109 IJs/ha) required for effecting 97.10-99.67% grub mortality, at 90-97 h of exposure. EPN strains performed better in terms of larval mortality in loamy sand, alluvial, mountain soil, red laterite compared to black cotton soils. Efficacy of EPN was positively correlated with the content of sand, and negatively with the clay content. It is possibly the first report that established the potential of local strains of EPNs with different foraging ability and their dosages for suppression of subterranean root feeding larvae of M. subfasciatus in five broad soil types of eggplant grown areas. Validation of this baseline data in real-time eggplant crop situations may help in evolving EPN-based viable management schedules for M. subfasciatus.