Effects of host stage and number of feeding larvae on parasitism success and fitness in the coleopteran parasitoid, Dastarcus longulus Sharp (Coleoptera: Bothrideridae)

Abstract

Fitness elements (number and weight of emerging adults) and the success of parasitism (host mortality) in Dastarcus longulus were compared among three host stages (Monochamus alternatus larvae, pupae and adults). Different numbers of first-instar larvae were released onto single host individuals to determine the optimal host quality and rearing conditions needed to obtain large numbers of high-fitness individuals and to maximize the rearing efficiency of the parasitoid. Host mortality after the release of a single parasitoid larva was 88% on pupal hosts but <50% on larval and adult hosts. The numbers and weights of emerging adults per host were highest on pupal hosts. The estimated number of ovarioles in emerging adults was also the highest on pupal hosts. Pupae of M. alternatus thus provided the best host quality for rearing D. longulus. High host mortality was caused mainly by pupal immobility. A high feeding rate was associated with high parasitoid reproductive potential on pupal hosts. Although the release of 10 larvae onto a single pupal host resulted in the highest overall fitness of the rearing population of D. longulus, the release of two larvae onto each pupal host was the optimal procedure for maximizing the weight of individuals.