Limited protection of the parasitoid Pachycrepoideus vindemiae from Drosophila suzukii host‐directed spinosad suppression

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.

Optimization of native biocontrol agents, with parasitoids of the invasive pest Drosophila suzukii as an example

“…Two important stress factors are temperature (Delava, Fleury, & Gibert, ; Ris, Allemand, Fouillet, & Fleury, ) and insecticides (Cossentine & Ayyanath, ; Komeza, Fouillet, Bouletreau, & Delpuech, ; Rafalimanana, Kaiser, & Delpuech, ). Parasitism of P. vindemmiae, for example, was significantly negatively affected by Spinosad, a commonly used insecticide against D. suzukii (Cossentine & Ayyanath, ). Hence, releasing P. vindemmiae as biological control agent in insecticide‐treated fields might reduce its efficiency.…”

Compatibility of Bioinsecticides with Parasitoids for Enhanced Integrated Pest Management of Drosophila suzukii and Tuta absoluta

“…Even doses more than 10,000 times lower than the label rate against D. suzukii were found to affect this parasitoid's life-history traits [70]. Thus, spinosad should not be considered compatible with G. kimorum, as it is with other key D. suzukii parasitoids, such as Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae), Trichopria drosophilae (Perkins), and T. anastrephae Lima (Hymenoptera: Diapriidae) [28,36,76]. Spinosad was extremely toxic to N. tutae, resulting in 100% adult mortality after 48 h of exposure to treated leaves, and significantly impaired the parasitoid's reproductive ability and no offspring could survive (Table 1).…”

Search for Alternative Control Strategies of Drosophila suzukii (Diptera: Drosophilidae): Laboratory Assays Using Volatile Natural Plant Compounds

“…It needs to be considered, that not only synthetic insecticides can have negative effects on natural enemies such as, e.g., hymenopteran parasitoids, but also natural products with insecticidal effects against the target pest might simultaneously affect survival of parasitoids developing within pest pupae or eggs [ 92 , 93 , 94 ]. This is of special importance in the case of a species such as D. suzukii when several generations of the target pest overlap and thus all life stages of the pest insect co-occur in an orchard.…”