title: Benefits of self-superparasitism in a polyembryonic parasitoid.
abstract: Macrocentrus grandiiis a polyembryonic parasitoid, with embryos that divide asexually within the host (European corn borer,Ostrinia nubilalis) to produce broods of clonal offspring. From a biological control standpoint, polyembryony seems advantageous because each parasitized host yields multiple parasitoids with minimal time and egg investment. When we observedM. grandiiin the field, however, we found that the parasitoid virtually always invested additional time and, if possible, stings into hosts that it had already stung, apparently reducing some of the advantages of polyembryony. We therefore investigated and found support for two potential benefits that can be gained by self-superparasitism in this system. First, multiple stings allowed production of mixed-sex broods: 27% of multiply-stung versus 0% of singly-stung hosts produced mixed-sex broods. Second, multiple stings increased mean parasitoid progeny produced per host, primarily by reducing the chance of complete brood failure. Our results indicate substantial benefit for a second sting, but little benefit for three or more stings, even thoughM. grandiiwas sometimes observed to invest more than two stings within a single host. However, we also found that within-host larval competition is prevalent, suggesting that supernumerary stings may pay off in competition against conspecific larvae. Such additional investment within a single host would be particularly beneficial when hosts, rather than eggs, are limiting, but would decrease the overall efficacy ofM. grandiias a biological control agent.
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, 100 Ecology, 1987 Upper Buford Circle, St. Paul, MN 55108.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: White
authors.affiliation: Entomology Department, University of Minnesota, 219 Hodson Hall, 1980 Folwell Avenue, St. Paul, MN, 55108.
authors.forename: D A
authors.initials: DA
authors.lastname: Andow
keywords: Macrocentrus grandii; Ostrinia nubilalis; clutch size; foraging behavior; host utilization; intraspecific competition; polyembryony; self-superparasitism