The influence of host suitability on the range of grasshopper species utilized byBlaesoxipha atlanis(Diptera: Sarcophagidae) in the field

Abstract

AbstractBlaesoxipha atlanis(Aldrich) is a common parasitic fly of agriculturally important grasshoppers in Canada. The suitability ofCamnula pellucida(Scudder),Melanoplus bivittatus(Say),Melanoplus packardiiScudder, andMelanoplus sanguinipes(Fabricius) as hosts was studied in the laboratory. Grasshoppers were singly-parasitized or left unparasitized and reared for 9 days.Melanoplus bivittatusandM. packardiidid not support parasite development, i.e. were non-permissive hosts. In both species, parasite larvae were melanized and encapsulated, but development proceeded further inM. packardii.Melanoplus sanguinipesandC. pellucidawere permissive host species with, respectively, 70% and 35% of the implanted larvae emerging from their hosts of which 86% and 50% developed into adults. Parasite development time was longer inC. pellucida. AdultB. atlanisdry mass varied with host species and host mass at parasitism, but not with host sex. Parasites developing inM. sanguinipeswere larger in terms of dry mass than counterparts developing inC. pellucida. In permissive species, unparasitized grasshoppers gained in body mass while parasitized insects lost mass during the 9-day observation period. In non-permissive species, all insects gained in body mass, but parasitized females gained less mass than unparasitized conspecifics. All unparasitized grasshoppers survived while 75–95% of permissive and 30–40% of non-permissive hosts died. Variation in the intensity of field parasitism among grasshopper species may be explained, at least in part, by qualitative differences in suitability between potential host species. Novel pest management strategies emphasize preservation of a small proportion of the pest population for natural enemies. Consideration of the outcome of specific host-parasite interactions should improve the understanding of grasshopper population dynamics and increase the predictive value of models that assess potential crop losses.