Host Quality Effects On Sex Ratio of the Parasitic Wasp Anisopteromalus Calandrae (Chalcidoidea, Pteromalidae)

Abstract

The pteromalid wasp Anisopteromalus calandrae (Howard) is a parasite of larval instars of several species of beetles. In our experiments we used larvae of the granary weevil (Sitophilus granarius L.) as hosts. Host size may differ considerably, older larvae being much larger than younger ones. Fitness of the wasps' offspring depends on host size but differences between small and large sons are probably less than between small and large daughters. A number of experiments were carried out to investigate the effect of host quality on sex ratio. Evidence was found for the hypothesis that in Anisopteromalus offspring sexratio depends on clutch size. On large hosts (better quality) the proportion of sons is small, on young hosts (lower quality) the proportion of sons is high but these differences are due to large numbers of female-eggs being deposited on old hosts, and far fewer on young hosts, per laying period of 24 hrs. On both categories the number of sons produced per laying period is about similar. In the course of time (i.e. with decreasing life expectancy) the initial difference between treatments disappears almost completely (i.e. more and more, sub-optimal, daughters are produced on young hosts). Evidence for a memory factor was obtained with experiments in which we offered different host sizes, either successively or simultaneously. A simple model is proposed to describe the succession of sex-ratio decisions made under different conditions of host quality. Results are compared with those obtained earlier with Lariophagus, another pteromalid parasite of granary weevils, which is supposed to change sex ratio independent of clutch size.

Host‐size‐dependent feeding behaviour and progeny sex ratio of Anisopteromalus calandrae (Hym., Pteromalidae)

“…The progeny sex ratio (male/total) on small hosts was 1.00 (one of one), 1.00 (eight of eight), and 0.83 (®ve of six) when they had experienced with no host, parasitized host and healthy host, respectively. The ratio on small hosts seemed to be higher than that reported by other authors (VAN DEN ASSEM et al, 1984). However, we obtained only a few adults emerged on the small hosts (six adults) and the higher sex ratio could hardly have any statistical signi®cance.…”

“…The preference of female A. calandrae for large hosts might lead the host population to be dominated by young hosts (small host), which might, in turn, cause the population sex ratio to be male biased. However, this explanation is not consistent with the fact that progeny sex ratio of A. calandrae was female biased except when the age distribution of the host was extremely biased to the young larvae (£ 3rd instar) ( VAN DEN ASSEM et al, 1984); a situation that is unlikely to occur in the host±parasitoid system.…”

Host species-dependent and size-dependent ecological characteristics of Ephedrus nacheri (Hymenoptera: Braconidae)

“…This suggested that E. nacheri females changed their oviposition strategy in response to their encounters with hosts. Although observations that previous experience affected offspring sex-ratio have been reported for several parasitic wasps (Cloutier et al 1991;van den Assem et al 1984), the saturated sex ratios were different from those of the host aphid species. When M. persicae was supplied as the host, the offspring sex-ratios asymptotically approached 0.5-0.6.…”

Desempenho do parasitóide Nasonia vitripennis (Walker)(Hymenoptera, Pteromalidae) utilizando como hospedeiro Cochliomyia macellaria (Fabricius) (Diptera, Calliphoridae), sob diferentes tempos de exposição

“…O aumento do tempo de exposição dificulta a visualização dos efeitos do superparasitismo, devido à ação exploratória e randômica das fêmeas adultas sobre os hospedeiros (Cardoso & Milward-de-Azevedo 1995). Outros fatores também podem influenciar na razão sexual de vespas parasitóides, como o tamanho do hospedeiro, onde os mais robustos apresentam uma tendência a um maior número de fêmeas na prole como verificado por Van den Assem et al (1984) para Anisopteromalus calandrae (Howard) (Chalcidoidae, Pteromalidae). Shuker et al (2005) testaram uma hipótese chamada Asymetrical Local mate competition, que é a extensão da teoria de Hamilton (1967), Local mate competition (LMC), que sustenta a tendência ao aumento da taxa de fêmeas na prole de espécies onde apenas as fêmeas abandonam o pupário dispersando-se.…”