Control of false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae), using in vitro-cultured Steinernema jeffreyense and S. yirgalemense

Abstract

False codling moth (FCM), Thaumatotibia leucotreta, is a priority pest of citrus, stone fruit and table grapes, as it causes direct crop damage. Biological control of entomopathogenic nematodes (EPNs) has not been explored for use against FCM in stone fruit and table grapes. However, EPNs have been shown to provide exceptional control against the larvae and pupae of FCM in laboratory bioassays, compared to other biocontrol agents. EPNs are particularly attractive for the control of FCM, as they attack the soil stages. In this study, the mortality, quality and age of in vitro liquid-cultured Steinernema jeffreyense was assessed in the laboratory and tested in the field. Additionally, pre- and post-application pathogenicity tests with FCM larvae were conducted to assess the EPN virulence of in vitro-cultured nematodes. Field trials were conducted by means of applying infective juveniles (IJs) to the vineyard floor. Four different Steinernema jeffreyense concentrations (0, 10, 20, and 30 IJs/cm2) were applied to 40 1 m2 experimental plots that were artificially infested with FCM larvae. The insects were retrieved from the soil 48 hrs after application, to allow for the assessment of the immediate effect. The FCM-loaded cages were replaced over a period of four weeks, to determine the persistence of the original application. In a second trial, following the same procedure, S. jeffreyense and Steinernema yirgalemense were compared with regard to virulence and persistence over a four-week period. In the laboratory, the in vitro-cultured EPNs proved to be of similar quality to the in vivo-cultured S. jeffreyense, with a high percentage mortality of >80%. The semi-field study showed promising results, with the immediate effect yielding up to 77% mortality of FCM larvae, which remained >35% over the four-week period after application. The results compare favourably with those of previous field studies, using in vivo EPN, proving that EPNs would be a valuable addition to the current integrated pest management programme aimed at the control of FCM.