Limited protection of the parasitoid Pachycrepoideus vindemiae from Drosophila suzukii host-directed spinosad suppression
Citation
Cossentine, J.E., Ayyanath, M.M. (2017). Limited protection of the parasitoid Pachycrepoideus vindemiae from Drosophila suzukii host-directed spinosad suppression. Entomologia Experimentalis et Applicata, [online] 164(1), 78-86. http://dx.doi.org/10.1111/eea.12592
Plain language summary
The encouragement or introduction of D. suzukii pupal parasitoids in impacted agricultural ecosystems would support sustainable and environmentally sound D. suzukii suppression in both non-target and commercial fruits. Our study indicates that generally the integration of P. vindemiae parasitism into a sustainable D. suzukii management program is not compatible with spinosad treatments, although P. vindemiae in the pupal stage inside the host puparia, appear to be minimally impacted by spinosad treatments, provided that the spinosad degrades before parasitoid emergence in the field. It was evident that the timing of the spinosad sprays was an important consideration in terms of the non-target effects toward the parasitoids. The longer the period of parasitoid development after spraying prior to the adult emergence, the greater the degradation of the spinosad and the less impact on the parasitoid population. Under field conditions spinosad would degrade more quickly, thus the potential impact observed under laboratory conditions might be lessened. However, timing of spinosad sprays in the field would need to consider not only the D. suzukii population but the presence of the P. vindemiae and what stage in the parasitoids lifecycle were the majority of the population. This level of monitoring would add a considerable level of complexity to the D. suzukii management program. and therefore suggests spinosad and the biocopntrol agent may not be compatible and might work better separately. Further trials under field conditions are required to determine the optimal use of both control strategies.
Abstract
Laboratory trials were conducted to determine whether the spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), puparium can provide an effective physical barrier to protect immature stages of the pupal parasitoid Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) from spinosad treatments. Spinosad insecticides are currently an important suppression strategy for D. suzukii in organically managed fruit orchards although they are well known to cause mortality in hymenopteran parasitoids. High adult P. vindemiae female mortality (83%) occurred within 24 h of exposure to D. suzukii pupae treated with 10 mg a.i. l−1 spinosad and female parasitoids did not avoid the pupae treated with similar low levels of spinosad in choice tests that included untreated pupae. Pachycrepoideus vindemiae develops as an idiobiont ectoparasitoid on host fly pupa within the sclerotized host puparium. Significant P. vindemiae survival and emergence was recorded when parasitized D. suzukii puparia were exposed to field treatment levels of spinosad; however, the parasitoid survival was dependent on the time of the spinosad treatment of the host post-parasitization. Significant parasitoid survival occurred when the host puparia were treated at 2 weeks when the parasitoid was in the pupal stage but did not occur when the host puparia were treated at 1 week post-parasitization, when the parasitoids were still in a larval stage. The parasitoid adults consumed or otherwise came in contact with residual degrading spinosad when they exited the treated host, and consequently high and low adult parasitoid mortality occurred when the adults emerged from puparia treated at 2 and 1 week(s), respectively. Our study indicates that generally the integration of P. vindemiae parasitism into a sustainable D. suzukii management program is not compatible with spinosad treatments, although P. vindemiae in the pupal stage inside sclerotized host puparia appear to be minimally impacted by spinosad treatments, provided that the spinosad degrades before parasitoid emergence.