Reduced food consumption in the grasshopper Melanoplus sanguinipes (Orthoptera: Acrididae) parasitized by Blaesoxipha atlanis (Diptera: Sarcophagidae)

Blaesoxipha atlanis (Aldrich) is a common parasite of Melanoplus sanguinipes (Fabr.) in western Canada. We tested the hypothesis that parasitism by B. atlanis reduces food consumption by adult M. sangitinipes. Unparasitized grasshoppers serving as controls and grasshoppers infected with a single parasite larva were fed known quantities of freshly cut wheat (Triticum aestivum L. 'Katepwa') (Poaceae) leaves in the laboratory. The median development time in hosts of larvae of both male and female B. atlanis was 5.5 days. Two thirds of parasitized grasshoppers died within 9 days of infection, but all control insects survived. The dry mass of leaves consumed each day did not differ between parasitized insects that died and insects that survived parasitism; both groups fed less than unparasitized controls. The influence of parasitism on food consumption differed between host sexes, with feeding being depressed earlier and more severely in female than in male grasshoppers. The reduction in food consumption was most pronounced on day 6 after infection, when parasitized males and females consumed only 10% and 7%, respectively, of the food consumed by unparasitized controls. Parasite sex did not influence food consumption. Grasshoppers that survived parasitism by B. atlanis resumed feeding, consuming as much as unparasitized counterparts. Reduced food consumption limited the ability of grasshoppers to compensate for the nutritional demands of developing parasite larvae. As a consequence, parasitized grasshoppers lost body mass during the interaction. We propose that the temporary reduction in feeding by grasshoppers parasitized by B. atlanis that survive parasitism is not evidence of host regulation, but is consistent with a stress-induced alteration in host behaviour.