Nutritional Ecology of an Insect Host‐Parasitoid Association: The Pea Aphid‐Aphidius Ervi System

Abstract

Evolutionary host—size models assume that host quality for parasitoid growth and development is a linear function of host size. To test this assumption, we compared the growth patterns of the hymenopteran parasitoid Aphidius ervi when it developed in different nymphal instars of apterous pea aphids, Acyrthosiphon pisum. At daily intervals, unparasitized aphids and aphids that were parasitized at age 24, 48, 72, and 120 h (corresponding to nymphal instars L1—L4) were dissected. We weighed parasitoid larvae and host remains to determine changes in their relative growth rates, based on wet mass (WM) and dry mass (DM). The growth in DM of unparasitized aphids followed a sigmoid curve. Aphids that were parasitized by A. ervi continued to grow for 5—7 d before their DM started to decline. Trajectories of the parasitoid's growth during its larval and pupal stages could be described by nonlinear equations. The maximum larval DM and the time for oviposition to adult eclosion of parasitoids varied with host age at parasitization, and thus suggested differences in host quality. We proposed that, for parasitoids developing in growing and feeding stages of the host, host quality is not a linear function of host size at parasitization but reflects the degree of integration of the two systems.

Silicon influence on the tritrophic interaction: wheat plants, the greenbug Schizaphis graminum (Rondani) (Hemiptera: Aphididae), and its natural enemies, Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) and Aphidius colemani viereck (Hymenoptera: Aphidiidae)

“…Larval stage and longevity of parasitoids (Vinson & Iwantsch 1980), allowing host quality to be directly evaluated, since the shortest development period can be considered as the best growth trajectory (Sequeira & Mackauer 1992). In recent studies, many authors have observed durations of the development period of A. colemani higher than 12.2 days, different from those observed in this work for that developmental stage (Gonçalves-Gervásio et al 2001).…”

Evidence for specificity in symbiont-conferred protection against parasitoids

“…Aphids are attacked by several groups of primary parasitoids, all solitary koinobiont endoparasitoids [19]. Parasitoids typically attack pre-adult aphids but their larvae do not destructively consume the host until late in development [20,21]. The fullgrown parasitoid larva pupates inside the mummified husk of its host.…”

Host-instar selection in the aphid parasitoid Monoctonus paulensis (Hymenoptera: Braconidae, Aphidiinae): a preference for small pea aphids

“…Patterns of preference are not fixed, however, but often vary with the availability and relative abundance of different host types (Chow & Mackauer, 1991) and the female's physiological state, including her egg load, previous reproductive success, and age (Weisser, 1994;Michaud & Mackauer, 1995;Mackauer et al, 1996). Older instars and adult aphids are larger than first and second instars and, potentially, con tain more nutritional resources; however, these resources may not always be accessible by the parasitoid (Sequeira & Mackauer, 1992). Moreover, large aphids can better defend themselves against attacks and therefore may be more costly to the female than small aphids (Gerling et al, 1990;Chau & Mackauer, 1997;Losey & Denno, 1998).…”