Potential for conservation biological control of the obliquebanded leafroller (OBLR) Choristoneura rosaceana (Harris) in orchard systems managed with reduced-risk insecticides

Natural enemy (NE) inflicted mortality of the obliquebanded leafroller, Choristoneura rosaceana (Harris), was compared in apple orchards treated with reduced-risk and conventional insecticides and in adjacent unsprayed wild habitats. We hypothesized that NE inflicted mortality would be greater in plots treated with reduced-risk insecticides and in the wild habitats. Laboratory-reared larvae were exposed to NEs by placing larvae in excised foliage into the experimental plots. Nine parasitoid species were recorded, but only Actia interrupta (Diptera: Tachinidae), and the Hymenoptera Oncophanes americanus (Braconidae) and Exochus albifrons (Ichneumonidae) were abundant. Total parasitism by Hymenoptera and Diptera was equal among treatments; however, the prevalence of Hymenopteran and Dipteran parasitoids appeared to vary among orchards. Higher numbers of predators were collected in wild habitats but predation levels were not significantly different among treatments. We found no evidence that NEs were limited by fragmentation of wild habitats. Furthermore, the wild habitats harbored several plant species that are hosts for C. rosaceana. Because NE induced mortality was similar in both insecticide treatments and in unsprayed wild habitats, it is difficult to ascertain whether these results are due to the toxicity of the insecticides in the two pesticide-programs or the ecology of the natural enemies. The combination of highly mobile natural enemies and habitats treated with toxic insecticides may have masked treatment-specific differences. Results from this study do not provide evidence that the use of reduced risk insecticides in orchard blocks interspersed among blocks treated with conventional insecticides will afford opportunities for biological control of C. rosaceana.