Flexible Larval Growth Allows Use of a Range of Host Sizes by a Parasitoid Wasp

Abstract

Recent optimality models of host—parasitoid associations have assumed that host quality varies with host size or age at parasitism. This is based on the fact that larger hosts provide more resources, making size a reliable indicator of the amount of resources available for parasitoid development. Few studies have examined this is parasitoids that allow their hosts to continue development after parasitism (koinobiont parasitoids). In this study we compared growth trajectories of the koinobiont ichneumonid endoparasitoid Venturia canescens developing in four larval instars of one of its host, the moth Plodia interpunctella. Hosts were reared with excess food and parasitized as late second, third, fourth, and fifth instars. Hosts were dissected at intervals after parasitism, and host and parasitoid dry mass determined. The survivorship, development time, and size of eclosing adult wasp were also monitored. Hosts parasitized by Venturia continued to grow and become prepupae, although their maximum masses were progressively smaller the earlier that the hosts were parasitized: second—instar (L2) hosts grew to 70% of control (unparasitized) size, while L4 and L5 hosts reached control size. The maximum larval dry mass, as well as eclosing adult size, varied with host instar at parasitism. Venturia larvae spent prolonged periods as first instars when developing from L2 hosts and grew most rapidly during early stages in L5 larvae.The data show that for Venturia, host quality is not a direct function of host at parasitism. Furthermore, the pattern of development shown by Venturia differs markedly from that shown by aphidiid koinobiont parasitoids.

Evaluation of floral resources for enhancement of fitness of Gonatocerus ashmeadi, an egg parasitoid of the glassy-winged sharpshooter, Homalodisca vitripennis

“…However, there was no signiWcant correlation between longevity and HTL in the current study. Previous work has demonstrated a positive relationship between HTL and parasitoid longevity (Harvey et al, 1994;Bernal et al, 1999). Conversely, Pavlík (1993) found that longevity was not correlated with size for several Trichogramma spp.…”

Morphometric indicators for quality assessment in the aphid parasitoid, Lysiphlebus fabarum (Braconidae: Aphidiinae)

“…Moreover, the use of different morphological characters as proxies of body size can result in different estimates of size variation within populations and even lead to erroneous conclusions (Gauld & Fitton, 1987;Hurlbutt, 1987;Nicol & Mackauer, 1999). As the estimation of body volume from linear measurements is not always straightforward, body mass may be the most reliable proxy of body size (Sequeira & Mackauer, 1992a, b;Harvey et al, 1994Harvey et al, , 2000Harvey & Strand, 2002). For example, van Alphen & Thunnissen (1983) reported that females of Pachycrepoideus vindemiae Rondani (Pteromalidae) had greater dry mass than males of the same head width.…”

Sexual size and development time dimorphism in a parasitoid wasp: an exception to the rule?

“…5). Because pupae do not feed or grow, they are con stantly losing mass through the combined processes of respiration (metabolic activity) and desiccation, such that pupal weight declines linearly with age prior to eclosion (Sequeira & Mackauer, 1992;Harvey et al, 1994). Female wasps presumably remain in the cocoons as pharate adults and continue to lose mass after male wasps have already eclosed.…”