Consequences of infanticide for a gregarious ectoparasitoid of leafroller larvae

Ecological Entomology (2015), 40, 461–470 DOI: 10.1111/een.12212 Consequences of infanticide for a gregarious ectoparasitoid of leafroller larvae J U L I E V . H O P P E R and N I C H O L A S J . M I L L S Department of Environmental Science, Policy and Management, University of California, Berkeley, California, U.S.A. Abstract. 1. In this laboratory study, the clutch size and handling time of Goniozus jacintae were investigated, a comparison of its life-history performance between primary and secondary (laid after infanticide events) broods was carried out, and the lipid and protein concentrations in the haemolymph of non-parasitised and parasitised hosts were estimated. 2. It was found that G. jacintae temporarily paralysed its host larvae for 66 min and briefly guarded its brood for 66 min. The clutch size of G. jacintae increased from two to seven with increasing larval fresh weight of its host, and both ovicide and larvicide of primary clutches occurred in 81% of encounters. 3. Secondary clutches of G. jacintae were significantly larger than primary clutches in two of three ovicide treatments for the same host individuals. Secondary clutches also experienced greater brood survivorship than primary clutches. 4. Lipid concentrations were consistently higher in the haemolymph of parasitised hosts, and protein concentrations were initially higher (until egg hatch), but increased at a lower rate in parasitised hosts than in non-parasitised hosts. 5. This study is the first to provide evidence that improved nutritional quality could be an important benefit of infanticide for an insect parasitoid, allowing for larger clutch size and improved brood survivorship among secondary broods. Key words. Clutch size, competition, Epiphyas postvittana, Goniozus jacintae, han- dling time, macronutrients, nutritional quality. Introduction Exploitative competition within the broods of gregarious par- asitoids has often been minimised through the evolution of exact clutch sizes, allowing parent females to accurately assess the quality of a host and adapt their clutch size to match the availability of resources for offspring development. Clutch size in gregarious parasitoids is also known to be influenced by other factors, such as host density, host quality, energetic reserves, and the presence of competitors (Godfray, 1994). For example, superparasitism by gregarious parasitoids frequently results in the oviposition of a smaller secondary clutch, and in most cases the resultant offspring develop to become smaller adults as a consequence of resource sharing (Godfray, 1994; Visser & Rosenheim, 1998). In some cases, however, the size of a secondary clutch may not be greatly reduced in the presence of Correspondence: Julie V. Hopper, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, U.S.A. E-mail: juliehopper@berkeley.edu © 2015 The Royal Entomological Society competitors if the parent female has the ability to successfully secure the host resources through infanticide of the primary clutch. Infanticide occurs when a parent female parasitoid either removes or kills the eggs or larvae of competitors to eliminate or at least reduce competition for the remaining host resources for its own offspring (van Alphen & Visser, 1990). Infanticide is known to occur among parasitoids in the Aphelinidae (Netting & Hunter, 2000), Bethylidae, Braconidae, and Pteromalidae (God- fray, 1994; Mayhew, 1997), Dryinidae (Yamada & Kitashiro, 2002; Ito & Yamada, 2005), Encyrtidae (Tena et al., 2008), Eupelmidae (Rojas-Rousse et al., 2005), and Ichneumonidae (Takasuka & Matsumoto, 2011). In addition to infanticide, para- sitoids can respond to previously parasitised, but otherwise suit- able, hosts by rejecting them and searching for a non-parasitised host (Mayhew, 1997), by host feeding on their haemolymph to gain additional resources for search and/or egg production (Tena et al., 2008), or by superparasitizing (intraspecific) or multiparasitizing (interspecific) them by laying additional eggs (van Alphen & Visser, 1990).