Retrospective risk assessment reveals likelihood of potential non-target attack and parasitism by Cotesia urabae (Hymenoptera: Braconidae): A comparison between laboratory and field-cage testing results

Abstract

We conducted retrospective non-target risk assessment with the larval endoparasitoid Cotesia urabae (Hymenoptera: Braconidae), via sequential no-choice tests, to assess the potential risk posed to two New Zealand endemic species: the magpie moth, Nyctemera annulata (Lepidoptera: Erebidae), and the common forest looper Pseudocoremia suavis (Lepidoptera: Geometridae), as well as to the beneficial biological control agent, the cinnabar moth Tyria jacobaeae (Lepidoptera: Erebidae). Under no-choice laboratory conditions C. urabae did oviposit in T. jacobaeae and N. annulata, and parasitism was confirmed upon dissection of both species at a rate similar to the target host, Uraba lugens (Lepidoptera: Nolidae). Mean attack frequency differed significantly between the three non-targets tested and the target host, where only N. annulata and T. jacobaeae were found to be attacked at a similar rate to the target host U. lugens. However, time to attack was significantly faster against the target host than the non-targets. When oviposition-experienced and naïve C. urabae females were compared, both showed similar mean attack frequencies but experienced parasitoids showed a shorter mean time to attack than naïve parasitoids. Parasitism of N. annulata under semi-natural field conditions was also investigated in field cages. Dissections of N. annulata larvae from field-cages revealed significant differences in mean parasitism between the choice cage, and the non-target no-choice cage treatments. In both cases mean parasitism of N. annulata was significantly lower than on the target host U. lugens. Results of the field-cage assay in particular, suggest that non-target impacts of C. urabae on N. annulata in the field are likely to be limited. Whether the non-target impacts predicted will be of ecological significance to the species population dynamics remains to be ascertained.