Sex ratio response of the parasitoid wasp Muscidifurax raptor to other females

This study examines the sex ratio response of the parasitoid wasp Muscidifurax raptor to conspecific and confamilial females in relation to two groups of functional sex ratio models, local mate competition and host quality models. In some but not all experiments, M. raptor females produced a greater proportion of sons in the presence of a conspecific female than when alone, and this sex ratio effect carried over for a day after the females were isolated from each other M. raptor females also produced a greater proportion of sons in the presence of a female of the confamilial parasitoid Spalangia cameroni than when alone (although only on the second day of exposure to S. cameroni, not on the first). M. raptor's sex ratio increase in the presence of conspecifics is consistent with local mate competition models but not with host quality models because the presence of a conspecific female did not cause there to be more, and thus potentially smaller, offspring developing per host. In contrast, the presence of a S. cameroni female did cause there to be more offspring developing per host than when a M. raptor female was alone; thus M. raptor's sex ratio increase in the presence of S. cameroni may be explained by host quality models. An alternative explanation for the sex ratio increase in response to confamilials is that only a sex ratio response to conspecifics may be adaptive, due to local mate competition; but M. raptor females may be unable to distinguish between conspecific and S. cameroni females.     

Sex allocation by a mite parasitic on insects: local mate competition,host quality and operational sex ratio

The aim of this study was to test the predictions of local mate competition (LMC), host quality (HQ) and operational sex ratio (OSR) models, using a non-arrhenotokous parasitic mite, Hemisarcoptes coccophagus (Astigmata: Hemisarcoptidae). The life-history pattern of this mite meets the assumptions of these sex allocation models. Mating group size (LMC model), HQ and OSR affected the sex allocation of H. coccophagus females. Only young mite females adjusted the sex ratio of their progenies according to the predictions of LMC and HQ models; the sex allocation of old females was contrary to these predictions. We explain these patterns by the dynamic nature of the mite's population structure. When parents are young, their population distribution is patchy and progeny matings are local; hence sex allocation is in accordance with LMC theory. When parents become older, their populations shift towards panmixis; factors which had operated previously no longer exist. Consequently, females adjust the sex ratio of late progenies so that it can compensate for the earlier sex allocation, in order to make their total sex ratio unbiased, as expected in panmictic populations. Our data, expressed as the cumulative sex ratio, support this hypothesis.     

Effect of host density on offspring sex ratios and behavioral interactions between females in the parasitoid waspNasonia vitripennis (Hymenoptera: Pteromalidae)

Pairs of females of the parasitoid waspNasonia vitripennis were videotaped with one or two hosts. The presence of an additional host decreased the number of interactions between females but had no measured effect on the nature of the interactions, i.e., on whether the interaction involved physical contact or occurred while one of the females was parasitizing a host. The number of hosts did not itself affect offspring sex ratios but did influence which other factors were correlated with sex ratio. When there was one host, the proportion of sons was more positively correlated with utilization of previously drilled holes than with female-female interactions, whereas when there were two hosts, the reverse was true. Parasitizing an already parasitized host appeared to affect a female's sex ratio beyond any effects of the physical presence of another female: When two hosts were present, the proportion of sons was greater from hosts parasitized by both females than from hosts parasitized by only one female. The observation that parasitizations in previously drilled holes and female-female interactions are correlated with sex ratios is consistent with previous studies; however, that these relationships are host density dependent is a new result and remains unexplained.     

Combined effects of host quality and local mate competition on sex allocation inLariophagus distinguendus

Summary Many parasitoid wasps are known to adjust sex ratio in response to either local mate competition (LMC) or host quality. Nevertheless, few studies have investigated the combined effects of these two factors on sex allocation. The sex allocation pattern inLariophagus distinguendus, a parasitoid of granary weevil larvae, is contrasted to the expectations of Werren's (1984) model combining LMC and host quality. Several predictions of the model are confirmed, but others are not. Sex ratio on both large and small hosts declines with proportion of small hosts attacked in a manner consistent with the model. However, when only one host size is parasitized, sex ratio is not independent of that host size, as predicted by the model. Various possibilities for the deviation between expected and observed are discussed. A partial LMC/host quality model is developed which allows for some matings outside the natal patch, and predictions of this model conform more closely to the pattern observed inL. distinguendus. Finally, the application of parasitoid studies to basic questions in evolutionary ecology is briefly discussed.     

母体亲缘关系在杨氏榕树金小蜂后代性比调节中的作用

局域配偶竞争(local mate competition, LMC)理论问世以来在很多方面获得了发展,其中一个观点就是相互作用的繁殖母体之间的亲缘关系越近,后代性比越低,即产生更多的雌性后代。本研究以西双版纳广泛分布的钝叶榕Ficus curtipes上寄生的非传粉小蜂杨氏榕树金小蜂Diaziella yangi为研究对象,研究在同一榕果上产卵的繁殖雌蜂之间的亲缘关系对后代性比的影响。处理1：在同一榕果产卵的2头繁殖雌蜂来自蜂源1号树的同一个榕果;处理2：在同一榕果产卵的2头繁殖雌蜂来自蜂源2号树的同一个榕果,处理3：在同一榕果上产卵的2头繁殖蜂分别来自1、2号蜂源树。实验结果却显示出与理论预测值不一致。实验结果中,具有姐妹关系的2头繁殖雌蜂的2个处理的后代性比分别为0.195±0.028和0.189±0.043;亲缘关系较远的2头繁殖雌蜂的后代性比为0.240±0.030;不同处理的后代性比并没有显著差异。说明杨氏榕树金小蜂没有识别相互作用的繁殖雌蜂之间的亲缘关系以及据此调整后代性比的能力,这与其他大量研究 结果一致。     

Unisexual broods and sex ratios in a polyembryonic encyrtid parasitoid (Copidosoma sp.: Hymenoptera)

Summary We examined brood sex ratios of an undetermined species of Copidosoma. Most broods (65%) were unisexual, with a greater proportion of female broods. Some mixed broods contained extremely small proportions of wasps of the opposite sex. Our results imply that the female-biased sex rations in this species cannot be explained by local mate competition theory.     

Brood sex ratio variance,developmental mortality and virginity in a gregarious parasitoid wasp

Females of the parasitoid wasp Goniozus nephantidis paralyse host caterpillars and lay a clutch of up to 18 eggs onto the host integument. The known biology of G. nephantidis suggests that matings occur exclusively between siblings from the same brood. This leads to the prediction that brood sex ratios should be highly female-biased and have low variance. Sex ratios are indeed female-biased, with the mean proportion of males equal to 0.093. However, while sex ratio variance is significantly less than binomial, many broods contain no males at emergence. During development 28% of G. nephantidis offspring die. Male mortality offers a potential explanation for all-female (= virgin) broods. For the clutch sizes and mortality observed, theory predicts that <10% of females will emerge from all-female broods but the empirical value is much higher. The prediction that the prevalence of virginity decreases with increasing clutch size is, however, supported. We consider alternative explanations for the observed proportion of all-female broods, but this appears to be neither an artefact of the laboratory environment nor due to incorrect assumptions about G. nephantidis life history. Although its reproductive biology has been much investigated and its sex ratio matches some theoretical predictions, we conclude that a fuller understanding of G. nephantidis sex ratio requires a deeper knowledge of its field biology.     

母代雌蜂数、进果时间及非传粉小蜂对传粉榕小蜂后代数量及性比的影响

【目的】对性比的研究有助于我们理解自然界生物的选择压力及其所产生的原因和结果,榕树和榕小蜂之间的互惠共生关系以及生物学和生态学特性使其成为研究性比和局域配偶竞争模型（local mate competition）的理想材料。本研究旨在探明榕小蜂性比调节和进化机制。【方法】对分布于西双版纳地区的鸡嗉子榕Ficus semicordata进行了人工控制性放蜂实验。测定了母代雌蜂数量及其进果时间间隔、非传粉小蜂Sycoscapter trifemmensis数量对传粉榕小蜂Ceratosolen gravelyi后代数量（成蜂数量）和性比的影响,并分析了小蜂后代数量和性比的相关性。【结果】在榕果发育期一致的前提下,随着母代雌蜂数量的增加,每头雌蜂的平均后代数量明显下降(P<0.001),后代性比显著升高(P<0.001),后代数量和性比呈显著负相关(P<0.05);随着雌蜂进果间隔的延长,后代数量亦呈现下降趋势,且性比增大,放2头雌蜂和3头雌蜂的处理呈同样趋势,但差异均不显著(P=0.87; P=0.49),小蜂后代数量与性比无显著相关性(P=0.86)。此外,非传粉小蜂数量与传粉小蜂后代数量呈显著负相关(P<0.001),与传粉小蜂性比呈正相关(P<0.001),小蜂后代数量和性比同样呈现显著负相关(P<0.001)。【结论】本实验模拟了自然界中榕 蜂的相互作用,所得结果有助于我们理解自然状态下榕小蜂性比调节模式和机制,以及榕 蜂互利共生系统的进化机制。     

The effects of relatedness on progeny sex ratio in spider mites

Theory predicts that optimal sex allocation in subdivided populations is dependent on the genetic relatedness among competing offspring such that when relatedness is high, progeny sex allocation should be more biased than when relatedness is low. In the laboratory we compared the progeny sex ratio of four groups of five ovipositing females of various presumed degrees of relatedness (sisters of inbred laboratory population, sisters of outbred field population, non-sisters of the same field population and non-sisters each from a different, geographically distant field population). We found a greater female bias in the progeny of inbred sisters than for sisters from the field population; the progeny sex ratio was also more strongly female biased for sisters than for non-sisters from the field population. These differences in sex ratio are in line with theoretical predictions. Our results indicate that spider mites are capable of some method of discrimination between kin and non-kin.     

Increased male sex ratio among brachypterous progeny in Melittobia femorata, a sib-mating parasitoid wasp (Hymenoptera: Eulophidae)

Abstract Melittobia are gregarious ectoparasitoid wasps that primarily attack various solitary bees and wasps. Characterized by high levels of inbreeding and an extremely female-biased sex ratio, these wasps appear to satisfy Hamilton's criteria for local mate competition. However, previous studies of sex ratio have failed to take into account an important aspect of Melittobia life history, namely that every clutch represents the combined reproductive output of the initial foundress female plus as many as 37 non-disperser short-winged daughters. Melittobia femorata Dahms is unique among the 13 species of Melittobia in that adults emerge as two temporally distinct clutches. While the overall sex ratio of the combined progeny from both clutches (0.025 ± 0.01) is typical for that for other Melittobia species (between 0.02 - 0.04 for single foundress cultures of the five other species included in this study), the sex ratio for the brachypterous first clutch of M. femorata from field-parasitized hosts averaged about 10 times greater (0.303 ± 0.10). Laboratory experiments with single foundress M. femorata cultures on the same host species ( Trypoxylon politum Say) maintained at 25°C or 30°C produced smaller first clutch sizes compared to the field-infested hosts. While the number of brachypterous first clutch daughters was similar, significantly reduced first clutch sex ratios relative to field-parasitized hosts (0.07 - 0.10) were due to significantly fewer males being produced. Possible reasons for these differences and the elevated first clutch sex ratio in this species are discussed.     

More highly female-biased sex ratio in the fig wasp,Blastophaga nipponica Grandi (Agaonidae)

The sex ratio of the pollinator fig wasp,Blastophaga nipponica Grandi (Agaonidae), was examined in an experiment manipulating the number of foundresses. The sex ratio ofB. nipponica was conditional on the number of foundresses and corresponded to the qualitative prediction of the local mate competition (LMC) theory that the proportion of males increases as foundress number increases. However, the sex ratio ofB. nipponica was consistently more female-biased than predicted by extended LMC theories that incorporated effects of inbreeding, and these deviations were statistically significant. Plausible factors that would make predictions more female-biased are discussed.     

Antennal sensilla of male and female Telenomus reynoldsi gordh and coker (Hymenoptera : Scelionidae)

Sensilla on the antennae of both sexes of Telenomus reynoldsi (Hymenoptera : Scelionidae) were studied with the scanning electron microscope to determine their structure and possible function in mating and host recognition. Two types of setiform sensilla occur: curved, grooved sensilla trichodea and erect, stout sensilla chaetica. Horn-like sensilla trichodea curvata are abundant on the male antennae, but are less abundant and only present dorsally on the female. Sensilla basiconica are unique to the ventral surface of the apical 4 segments of the female antennae. Sensilla styloconica are located on A4 and A10 of the female and A7 and A9 of the male. Multiporous grooved sensilla are present on A4, A6, and A11 of the female and A4 and A6-A11 of the male. A possible sex gland is located on the venter of A5 of the male. The functions of sensilla trichodea curvata and sensilla basiconica in courtship and host recognition, respectively, are hypothesized by correlation with behavioral observations.     

Semiochemical and physical stimuli involved in host recognition by Telenomus podisi (Hymenoptera: Scelionidae) toward Euschistus heros (Heteroptera: Pentatomidae)

The egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short-range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a male-produced pheromone of E. heros. Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long-range kairomones, by T. podisi, is discussed. Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10-trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short-range kairomone. Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.     

Effects of host age and host availability on developmental period,adult size,sex ratio,longevity and fecundity inLariophagus distinguendus Förster (Hymenoptera: Pteromalidae)

The effects of host age on parasitoid reproductive capacity are studied using the pteromalid parasitoid Lariophagus distinguendusFörster and its bruchid hosts, Callosobruchus chinensis (L.) and C. maculatus (F.). A series of experiments were performed to investigate relationships between age and size of host parasitized and the developmental period of pre-imaginal progeny, sex ratio, female size, longevity, fecundity and oviposition rate. There was no effect of host size on preimaginal parasitoid developmental period. Sex ratio varied from less than 5% females from young (small) hosts to 60% females from mature (large) hosts. Adult size, female longevity, fecundity, and oviposition rate were also positively related to host age. Females provided mature hosts lived longer than those provided either young hosts or no hosts, possibly because of an increased ability to host-feed from the larger hosts. The implications of these findings to parasitoid population reproductive capacity and host-parasitoid synchrony are discussed.     

Even more extreme fertility insurance and the sex ratios of protozoan blood parasites

Theory developed for malaria and other protozoan parasites predicts that the evolutionarily stable gametocyte sex ratio (z*; proportion of gametocytes that are male) should be related to the inbreeding rate (f) by the equation z*=(1-f)/2. Although this equation has been applied with some success, it has been suggested that in some cases a less female biased sex ratio can be favoured to ensure female gametes are fertilized. Such fertility insurance can arise in response to two factors: (i) low numbers of gametes produced per gametocyte and (ii) the gametes of only a limited number of gametocytes being able to interact. However, previous theoretical studies have considered the influence of these two forms of fertility insurance separately. We use a stochastic analytical model to address this problem, and examine the consequences of when these two types of fertility insurance are allowed to occur simultaneously. Our results show that interactions between the two types of fertility insurance reduce the extent of female bias predicted in the sex ratio, suggesting that fertility insurance may be more important than has previously been assumed.     

Evolution of extraordinary female-biased sex ratios: the optimal schedule of sex ratio in local mate competition

Female-biased sex ratio in local mate competition has been well studied both theoretically and experimentally. However, some experimental data show more female-biased sex ratios than the theoretical predictions by Hamilton [1967. Science 156, 477-488] and its descendants. Here we consider the following two effects: (1) lethal male-male combat and (2) time-dependent control (or schedule) of sex ratio. The former is denoted by a male mortality being an increasing function of the number of males. The optimal schedule is analytically obtained as an evolutionarily stable strategy (ESS) by using Pontrjagin's maximum principle. As a result, an ESS is a schedule where only males are produced first, then the proportion of females are gradually increased, and finally only females are produced. Total sex ratio (sex ratio averaged over the whole reproduction period) is more female-biased than the Hamilton's result if and only if the two effects work together. The bias is stronger when lethal male combat is severer or a reproduction period is longer. When male-male combat is very severe, the sex ratio can be extraordinary female-biased (less than 5%). The model assumptions and the results generally agree with experimental data on Melittobia wasps in which extraordinary female-biased sex ratio is observed. Our study might provide a new basis for the evolution of female-biased sex ratios in local mate competition.     

A spatially explicit model of sex ratio evolution in response to sex-biased dispersal

Sex-biased dispersal occurs in all seed plants and many animal species. Theoretical models have shown that sex-biased dispersal can lead to evolutionarily stable biased sex ratios. Here, we use a spatially explicit chessboard model to simulate the evolution of sex ratio in response to sex-biased dispersal range and sex-biased dispersal rate. Two life cycles are represented in the model: one in which both sexes disperse before mating (DDM), the other in which males disperse before mating and mated females or zygotes disperse after mating (DMD). Model parameters include factors like dispersal rate, dispersal range, number of individuals per patch, and habitat heterogeneity.When dispersal range is sex biased, we find that, in a homogeneous environment, the sex ratio is generally biased towards the sex that disperses more widely (sex ratio range: 0.47–0.52). In a heterogeneous environment, the sex ratio is generally biased towards the more dispersive sex in good habitats, and towards the less dispersive sex in poor habitats (sex ratio range: 0–1). This is opposite to the effect of sex-biased dispersal rate, which favours the production of the more dispersive sex in poor habitats and the less dispersive sex in good habitats (sex ratio range: 0–1). To allow for a comparison with theoretical predictions, data concerning sex-biased dispersal and habitat-dependent sex ratios should thus incorporate information about the spatial scale of both dispersal and environmental heterogeneity.     

Cold storage of the egg parasitoids Trissolcus basalis (Wollaston) and Telenomus podisi Ashmead (Hymenoptera: Scelionidae)

Adults of Trissolcus basalis and Telenomus podisi were stored either at 15 or 18 °C after their immature development had been completed at 18 or 25 °C. Longevity of the parasitoids in the storage temperatures was evaluated, as well as fecundity and longevity following their return to 25 °C after different periods in reproductive diapause. Temperature during immature development influenced female longevity and highest mean longevity was obtained for females that developed to the adult stage at 25 °C and then were stored at 15 °C (ca. 13 months for T. basalis and 10 months for Te. podisi). For adults of T. basalis that developed at 25 °C, storage periods of 120 or 180 days at 15 or 18 °C did not affect fecundity. The fecundity of T. basalis females that developed at 18 °C and were stored for 120 days at 15 or 18 °C was not affected; however, after remaining for 180 days, fecundity was reduced in ca. 30 and 50%, respectively. Storage of Te. podisi adults at 15 or 18 °C significantly reduced fecundity. It is concluded that adults of T. basalis can be stored in the adult stage at 15 or 18 °C between two soybean crop seasons for mass production purposes, aiming the biological control of stink bugs.     

Inbreeding effects on progeny sex ratio and gender variation in the gynodioecious Silene vulgaris (Caryophyllaceae)

In gynodioecious species, sex expression is generally determined through cytoplasmic male sterility genes interacting with nuclear restorers of the male function. With dominant restorers, there may be an excess of females in the progeny of self-fertilized compared with cross-fertilized hermaphrodites. Moreover, the effect of inbreeding on late stages of the life cycle remains poorly explored. Here, we used hermaphrodites of the gynodioecious Silene vulgaris originating from three populations located in different valleys in the Alps to investigate the effects of two generations of self- and cross-fertilization on sex ratio and gender variation. We detected an increase in females in the progeny of selfed compared with outcrossed hermaphrodites and inbreeding depression for female and male fertility. Male fertility correlated positively with sex ratio differences between outbred and inbred progeny, suggesting that dominant restorers are likely to influence male fertility qualitatively and quantitatively in S. vulgaris. We argue that the excess of females in the progeny of selfed compared with outcrossed hermaphrodites and inbreeding depression for gamete production may contribute to the maintenance of females in gynodioecious populations of S. vulgaris because purging of the genetic load is less likely to occur.     

寄生3种夜蛾卵的夜蛾黑卵蜂种群增长潜能

夜蛾黑卵蜂是草地贪夜蛾卵期的一种重要寄生性天敌,适宜的寄主是实现其规模化繁育及应用的基础。本文应用实验种群生命表方法,分析、评价了草地贪夜蛾、斜纹夜蛾及甜菜夜蛾这3种夜蛾卵上夜蛾黑卵蜂的生长发育及种群增长潜能。结果表明,夜蛾黑卵蜂在3种夜蛾卵上均能顺利完成幼期发育且出蜂日期较为整齐,羽化当日即为产卵高峰日,羽化后3 d内的寄生卵量占总产卵量的80%以上。子代羽化率介于77.90%～85.56%之间,雌性比率介于0.53～0.59之间。不同寄主繁育的夜蛾黑卵蜂雄蜂后足胫节长度无明显差异,但以甜菜夜蛾卵繁育的雌蜂的后足胫节最长(152.00μm),斜纹夜蛾卵繁育的次之(146.33μm),草地贪夜蛾卵繁育的最短(142.67μm)。以甜菜夜蛾卵繁育的夜蛾黑卵蜂的内禀增长率(r_m)、净生殖力(R₀)及周限增长率(λ)均最高,分别为0.3486、57.94和1.4171,以斜纹夜蛾卵繁育的次之(r_m,0.3091;R₀,49.60;λ,1.3623),而以草地贪夜蛾卵繁育的最小(r_m,...