Effect of mating combinations on the host parasitisation and sex allocation in solitary endoparasitoid, Aenasius arizonensis (Hymenoptera: Encyrtidae) (original) (raw)
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Sex allocation strategies in response to conspecifics' offspring sex ratio in solitary parasitoids
Behavioral Ecology, 2010
Parasitoid females adjust their offspring sex ratio in order to maximize their fitness. The optimal sex ratio they produce varies with several factors but especially with competition level. In solitary species, only one adult can emerge from a given host, whatever the number of eggs laid. In some species, the mortality of supernumerary individuals could be due to larval combats. This ability to fight could vary from one sex to another within species. In this way, when females explore an already parasitized host patch, the sex ratio of previous eggs can influence their fitness. These 2 factors could thus strongly influence females' sex allocation strategies. However, this prediction assumes that parasitoid females can assess the sex of eggs previously laid by conspecifics. We used host acceptance and sex ratio behavior to test this capacity, and our experimental data provide the first evidence for this capacity in a parasitoid species. Females of the solitary ectoparasitoid Anisopteromalus calandrae discriminated the sex of eggs already laid by a conspecific but only when these eggs had reached a certain developmental stage. They adapted their offspring sex ratio as predicted by Hamilton's ''sex ratio games'' model, allocating the sex of their eggs differentially according to the sex of eggs already on the hosts on which they oviposited. In this way they prevented a lethal larval fight between their sons and the females they could potentially mate after their own emergence, increasing their own fitness and their sons' reproductive success.
Factors influencing brood sex ratios in polyembryonic Hymenoptera
Oecologia, 1993
Copidosoma sp. is a polyembryonic encyrtid wasp which parasitizes isolated hosts. Most broods of this wasp are unisexual, but some contain both sexes and the secondary sex ratio of these is usually highly female biased. The overall population secondary sex ratio is female biased. Walter and Clarke (1992) argue that because the majority of individuals must mate outside the natal patch, the bias in the population secondary sex ratio contradicts predictions made by Hamilton's (1967) theory of local mate competition (LMC). We suggest that the primary sex ratio is unbiased and that Walter and Clarke's results do not cast doubt on LMC. Instead these results imply that ovipositing females make a combined clutch size and sex ratio decision influencing whether individuals developing from a particular brood will outbreed or largely inbreed; for each case the predictions of LMC theory are not violated. If this interpretation is correct, what is of interest is the basis on which this decision is made rather than the population secondary sex ratio. We show that host encounter rate influences the proportions of mixed and single sex broods laid by Copidosoma floridanum, a related polyembryonic parasitoid. Among single-sex broods the primary sex ratio is female biased, but our results are in agreement with LMC theory since offspring developing from these broods will probably mate with siblings from adjacent hosts. We consider the egg load of females to be of major influence on oviposition behaviour, and that the mating structure of parasitoid offspring, potentially differential costs of male and female broods and the natural distributions of hosts both at oviposition and eclosion, require further study.
Entomologia Experimentalis et Applicata, 1997
The sex-allocation behaviour of the solitary ectoparasitoid Dinarmus basalis (Hymenoptera: Pteromalidae) was investigated by examining the female's response to two proximal factors: the host-patch characteristics and the conspecific female density in the patch. The offspring sex-ratio of single females presented with unparasitised hosts was female biased (approximately three daughters to one son in the progeny) whatever the host density tested. The sex-ratio in the presence of hosts parasitised by a conspecific 48 h beforehand was male biased. The proportion of male offspring also increased when the number of conspecific females exploiting the patch changed from a single female to a group of females, whatever the group size. No sexual differences in mortality as a result of larval competition on superparasitised hosts were observed. The offspring sex-ratios observed in response to the host-patch characteristics were the result of manipulation of the egg fertilisation by the females during the oviposition phase. Thus, the variability of the sex-ratio in response to an increase in the number of conspecific females in the same patch represented a reduction in egg fertilisation. These results are analysed with regard to the predictions of Local Mate Competition theory and the females' host discrimination ability.
Annals of the Entomological Society of America, 1997
When females of Pimpla nipponica Uchida, a solitary parasitoid of various lepi dopterous pupae, were exposed to hosts for varing periods of time, percentage wasp emergence decreased; the percentage immature wasps dying at the egg or early-instar stages increased with increasing exposure periods. Factors influencing the increased wasp mortality were examined. Larval competition occurred b e t w e e n 24 and 48 h after parasitism when 1st instars fought physically with their mandibles. Also, m a n y parasitoid eggs had melanized wounds, developed abnormally and died, indicating that 1st instars attacked and killed conspecific eggs. Superparasitism did not influence the fitness of emerging wasps. Hosts used for host feeding by female wasps yielded fewer and smaller wasps. Thus, host feeding was the major factor influencing offspring survival and fitness when multiple attacks against a single host occurred. Superparasitism, larval competition, and host feeding in solitary parasitoids are discussed in the context of adaptive superparasitism theories and mass-rearing programs.
Superparasitism and sex ratio in the solitary parasitoid Epidinocarsis lopezi
Entomologia Experimentalis et Applicata, 1993
Highly variable sex ratios are found in the solitary parasitoid Epidinocarsis lopezi, both in the field and in a mass-rearing situation. Superparasitism is one of a number of factors which can influence sex ratios in parasitoid Hymenoptera. We show that superparasitism in E. lopezi is common in the field. Sex allocation decisions when parasitizing unparasitized hosts are not different from those with parasitized hosts; neither does differential mortality occur between the sexes in superparasitized hosts. Therefore superparasitism does not contribute to the variable sex ratio of E. lopezi. Both the occurrence of superparasitism and the sex produced when ovipositing are shown to be functional for E. lopezi.
Host-size-dependent sex ratio theory and improving mass-reared parasitoid sex ratios
Biological Control, 2002
Although an effective parasitoid of agromyzid leafminers, Diglyphus isaea (Walker) (Hymenoptera: Eulophidae) is an expensive biological control agent in terms of production costs. In part, these costs arise from the production of male-biased offspring sex ratios. Here, we present a mass-rearing technique that will increase the proportion of females produced and reduce the need for frequent releases in biocontrol programs. By presenting female D. isaea groups of sequentially larger leafminer hosts to attack, we are able to generate progressively more female-biased sex ratios. After three days of providing increasingly larger hosts, we were able to reduce the sex ratios produced by individual females from 57% male to 36% male; sex ratios produced by groups of females dropped from 64% male to 45% male. Several attributes of D. isaea sex allocation allow us to manipulate sex allocation behavior. First, D. isaea is a solitary idiobiont; resources available to each offspring are present at the time of attack allowing the ovipositing female to accurately assess host quality. Host size positively affects both male and female wasps. Females laid more daughters in larger hosts and more sons in smaller hosts. We show that the observed relationship between host size and offspring sex ratio is due to maternal sex allocation decisions rather than differential mortality. Furthermore, assessment of the size threshold was relative to prior host encounters rather than an absolute assessment. Our simple memory model suggests that while females are influenced most strongly by recent encounters, females also base their assessment of the host-size threshold on prior host encounters. Ó 2002 Elsevier Science (USA). All rights reserved.
PLoS ONE, 2013
Parasitoid wasps are convenient subjects for testing sex allocation theory. However, their intricate life histories are often insufficiently captured in simple analytical models. In the polyembryonic wasp Copidosoma koehleri, a clone of genetically identical offspring develops from each egg. Male clones contain fewer individuals than female clones. Some female larvae develop into soldiers that kill within-host competitors, while males do not form soldiers. These features complicate the prediction of Copidosoma's sex allocation. We developed an individual-based simulation model, where numerous random starting strategies compete and recombine until a single stable sex allocation evolves. Life-history parameter values (e.g., fecundity, clone-sizes, larval survival) are estimated from experimental data. The model predicts a male-biased sex allocation, which becomes more extreme as the probability of superparasitism (hosts parasitized more than once) increases. To test this prediction, we reared adult parasitoids at either low or high density, mated them, and presented them with unlimited hosts. As predicted, wasps produced more sons than daughters in all treatments. Males reared at high density (a potential cue for superparasitism) produced a higher male bias in their offspring than low-density males. Unexpectedly, female density did not affect offspring sex ratios. We discuss possible mechanisms for paternal control over offspring sex.