Virulence of entomopathogenic nematodes to larvae of the guava weevil, Conotrachelus psidii (Coleoptera: Curculionidae), in laboratory and greenhouse experiments

Abstract

Abstract The guava weevil, Conotrachelus psidii, is a major pest of guava in Brazil and causes severe reduction in fruit quality. This weevil is difficult to control with insecticides because adults emerge over a long period, and larvae develop to the fourth-instar inside the fruit and move to the soil for pupation. We assessed the virulence of entomopathogenic nematodes to fourth-instar larvae in soil by comparing their susceptibility to nine species or strains: Heterorhabditis bacteriophora HP88, H. baujardi LPP7, and LPP1, H. indica Hom1, Steinernema carpocapsae All and Mexican, S. feltiae SN, S. glaseri NC, and S. riobrave 355. In petri dish assays with sterile sand at a concentration of 100 infective juveniles (IJs) of a given nematode species/strain, larval mortality ranged from 33.5 to 84.5%, with the heterorhabditids being the most virulent. In sand column assays with H. baujardi LPP7, H. indica Hom1, or S. riobrave 355 at concentrations of 100, 200, and 500 IJs, mortality was greater than the control only for H. baujardi (62.7%) and H. indica (68.3%) at the highest concentration. For H. baujardi LPP7 in a petri dish assay, the time required to kill 50 and 90% of the larvae (LT50 and LT90) for 100 IJs was 6.3 and 9.9 days, whereas the lethal concentration required to kill 50 and 90% of the larvae (LC50 and LC90) over 7 days was 52 and 122.2 IJs. In a greenhouse study with guava trees in 20-L pots, 10 weevil larvae per pot, and concentrations of 500, 1000 or 2000 IJs, H. baujardi LPP7 caused 30 and 58% mortality at the two highest concentrations. These results show that H. baujardi is virulent to fourth-instar larvae and has potential as a biological control agent in IPM programs.