Potential of in vivo- and in vitro-cultured entomopathogenic nematodes to infect Lobesia vanillana (Lepidoptera: Tortricidae) under laboratory conditions

Abstract

Entomopathogenic nematodes (EPNs) have been successfully applied as biological control agents against above ground and soil stages of insect pests. However, for commercial application, it is crucial to mass culture these nematodes using in vitro liquid culture technology, as it is not attainable when using susceptible insects as hosts. Lobesia vanillana (Lepidoptera: Tortricidae) is regarded a sporadic pest of wine grapes in South Africa. The in vivo- and in vitro-cultured South African EPNs, Steinernema yirgalemense and Steinernema jeffreyense (Rhabditida: Steinernematidae), were evaluated against larvae and pupae of L. vanillana in laboratory bioassays. For larvae, high mortality was observed for all treatments: In vitro-cultured S. yirgalemense (98%) performed better than S. jeffreyense (73%), while within in vivo cultures, there was no difference between nematode species (both 83%). No significant difference was detected between in vivo- and in vitro cultures of the same nematode species. The LD50 of the in vitro-cultured S. yirgalemense, was 7.33 nematodes per larva. Mortality by infection was established by dissecting L. vanillana cadavers and confirming the presence of nematodes, which was > 90% for all treatments. Within in vitro cultures, both S. yirgalemense and S. jeffreyense were able to produce a new cohort of infective juveniles from L. vanillana larvae. Pupae, however, were found to be considerably less susceptible to EPN infection. This is the first study on the use of EPNs to control L. vanillana. The relative success of in vitro-cultured EPN species in laboratory assays, without any loss in pathogenicity, is encouraging for further research and development of this technology.

Exploring the Use of Entomopathogenic Nematodes and the Natural Products Derived from Their Symbiotic Bacteria to Control the Grapevine Moth, Lobesia botrana (Lepidoptera: Tortricidae)

“…This study showed that the EPNs could be effective biological control agents against EGVM larvae and pupae in vineyards. In agreement with previous studies against other tortricid species, including L. vanillana, EPN virulence differed among nematode species [35,38,39,41,42]. As observed for C. pomonella [38], our S. carpocapsae population resulted in being the most virulent against the various larval and pupal stages.…”

“…On the contrary, S. carpocapsae and S. feltiae registered 100% and 80% L5 mortality, respectively, at the same time exposure. Overall, the efficacy of our EPN populations at 48 IJs per host against L. botrana obtained similar results to those observed for two South African EPN species against L. vanillana but employed 100 IJs per host [39]. Indeed, the efficacy of these two EPN species in the 50% lethal concentration estimations against L5 EGVM is notorious.…”

“…Although the pupal stage is less conductive for EPNs [35,39,41,42], our results showed that when employing high IJ concentrations, EGVM adult emergences can be significantly restricted. As for the larval stages, S. carpocapsae resulted in the most virulent species, reducing the adult emergence to below 50% when applied at the concentration of 50 IJs per host (~50% pupal mortality if corrected with the control emergence).…”

“…The efficacy of various EPN species against pupa of C. pomonella using 50 IJs per host ranged from 20-75% in terms of pupal mortality [41], which is a similar pattern to the one observed for our populations at the same concentration (20-50% pupal mortality if converted from adult emergence). However, compared to the closely related species L. vanillana, with ~15% pupal mortality or less, depending on the EPN production system [39], the results obtained for L. botrana are promising. In addition, we observed that the presence of EPNs drove miniature EGVM adult emergences from the pupae (I. Vicente-Díez, personal observation).…”

“…Previous studies have shown the compatibility of EPN aerial applications against various tortricid species such as Cydia pomonella (L.) and Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) [34][35][36][37][38]. Furthermore, a recent study has shown the high virulence of two EPN species (S. yirgalemense and S. jeffreyense) against tortricid larvae in the species Lobesia vanillana (De Joannis) (Lepidoptera: Tortricidae), a sporadic pest in vineyards in South Africa [39]. However, to date, there is no information about the compatibility of EPNs against the widespread EGVM.…”