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1.
The ability of the gregarious larval endoparasitoid Cotesia glomerata L. (Hymenoptera: Braconidae) to adjust progeny sex ratio and clutch size was investigated. The sex ratios (proportion of males) of field clusters were diverse, but many (70%) were female-biased. Nearly 10% yielded males only, suggesting a low percentage of unmated females in the field. In over half of the clusters containing females, the sex ratio was below 0.3. Superparasitism was common in the field, and females were believed to increase progeny sex ratio when attacking previously-parasitized hosts. However, in a single oviposition bout, sex allocation was not precisely controlled both in the field and laboratory. In the laboratory, the number of eggs laid in a day tended to decrease with increasing female age. For females which were offered two hosts per day and for those offered three hosts per day, this value became nearly the same several days after the start of oviposition. The total number of hosts which a female could parasitize during her lifetime was often less than 40. Some of the old females which attacked more than 40 hosts produced male-biased clutches; this was due to sperm depletion, because sperm remained viable throughout a female's lifetime. The amount of sperm used in a single oviposition bout seemed fixed and was not dependent on the number of eggs laid. Females with much oviposition experience did not produce new eggs to compensate for deposited eggs, and the efficiency of egg use (deposited eggs/total eggs) was more than 80%.  相似文献   

2.
夏诗洋  孟玲  李保平 《昆虫学报》2012,55(9):1069-1074
在寄生蜂行为生态学研究中, 通常将寄主体型大小作为寄主品质的主要性状来探究寄生蜂的搜寻行为机理, 而忽略寄生蜂体型大小的意义。为揭示聚寄生蜂雌蜂体型大小对其产卵决策的影响, 在严格控制寄主菜粉蝶Pieris rapae蛹体型大小(体重)的情况下, 于室内观察了不同体型大小的蝶蛹金小蜂Pteromalus puparum雌蜂的产卵行为, 并调查了子代蜂数量(窝卵数)、 性比和体型大小的变化。结果表明: 雌蜂在寄主上的驻留时间随其自身体型增大而缩短, 但随寄主体重增大而延长。窝卵数和余卵量受到雌蜂体型大小的显著影响, 均随雌蜂体型增大而显著增加(P<0.05); 但子代蜂性比不受雌蜂体型大小的显著影响 (P>0.05)。子代雌、 雄性体型大小均与雌蜂体型大小无关, 但子代雌蜂体型随寄主体重增大而增大。结果证实, 雌性蝶蛹金小蜂体型大小影响其部分产卵决策。因此, 在建立聚寄生蜂产卵决策模型中应考虑雌蜂体型大小这一重要变量因素。  相似文献   

3.
Fig‐pollinating wasps (Agaonidae) only reproduce within fig tree inflorescences (figs). Agaonid offspring sex ratios are usually female‐biased and often concur with local mate competition theory (LMC). LMC predicts less female‐bias when several foundresses reproduce in a fig due to reduced relatedness among intra‐sexually competing male offspring. Clutch size, the offspring produced by each foundress, is a strong predictor of agaonid sex ratios and correlates negatively with foundress number. However, clutch size variation can result from several processes including egg load (eggs within a foundress), competition among foundresses and oviposition site limitation, each of which can be used as a sex allocation cue. We introduced into individual Ficus racemosa figs single Ceratosolen fusciceps foundresses and allowed each to oviposit from zero to five hours thus variably reducing their eggs‐loads and then introduced each wasp individually into a second fig. Offspring sex ratio (proportion males) in second figs correlated negatively with clutch size, with males produced even in very small clutches. Ceratosolen fusciceps lay mainly male eggs first and then female eggs. Our results demonstrate that foundresses do not generally lay or attempt to lay a ‘fixed’ number of males, but do ‘reset to zero’ their sex allocation strategy on entering a second fig. With decreasing clutch size, gall failure increased, probably due to reduced pollen. We conclude that C. fusciceps foundresses can use their own egg loads as a cue to facultatively adjust their offspring sex ratios and that foundresses may also produce more ‘insurance’ males when they can predict increasing rates of offspring mortality.  相似文献   

4.
The role of sex-controlling behaviour at oviposition in generating primary sex ratios, and the effect of larval competition on secondary sex ratios, were studied in the gregarious endoparasitoid, Trichogramma chilonis. The production of a fertilized (female) egg is indicated by the incorporation of a pause in abdominal movements during oviposition, while the absence of it indicates the production of an unfertilized (male) egg. During each ovipositional bout, the first male egg is deposited at the second oviposition, and thereafter at intervals of about eight eggs. This simple pattern enables the wasps to adjust their progeny sex ratios under local male competition to a wide range of host size. Inexperienced wasps do not distinguish between parasitized and healthy hosts. Immature mortality is not significantly different between the sexes when a host is attacked by a single wasp, while females suffer higher immature mortality than males when superparasitism occurs.  相似文献   

5.
Oviposition behavior was used to determine the primary clutch size and sex ratio of the polyembryonic wasp Copidosoma floridanumAshmead (Hymenoptera: Encyrtidae) parasitizing Pseudoplusia includens(Walker) (Lepidoptera: Noctuidae). The laying of a female egg was associated with a pause in abdominal contractions during oviposition, while the laying of a male egg was associated with uninterrupted abdominal contractions. Although unmated females produced only male broods, they also displayed male and female egg oviposition movements. Wasps always laid a primary clutch of one or two eggs. For mated females if only one egg was laid, the emerging secondary clutch was all male or female, but if two eggs were laid a mixed brood of males and females was almost always produced. The secondary clutch of single sex broods was usually between 1000 and 1200 individuals, but the secondary clutch of mixed broods averaged 1143 females and 49 males. Thus, the primary sex ratio for mixed broods was 0.5 (frequency males), but the secondary sex ratio was 0.042. Manipulation of the sequence of male and female egg oviposition or of the primary clutch did not produce major alterations in the secondary clutch size or sex ratio.  相似文献   

6.
Sex allocation theory predicts that females should produce more sons when the reproductive success of sons is expected to be high, whereas they should produce more daughters, not daughters when the reproductive success of sons is expected to be low. The guppy (Poecilia reticulata) is a live‐bearing fish, and female guppies are known to produce broods with biased sex ratios. In this study, we examined the relationship between brood sex ratio and reproductive success of sons and daughters, to determine whether female guppies benefit from producing broods with biased sex ratios. We found that sons in male‐biased broods had greater mating success at maturity than sons in female‐biased broods when brood sizes were larger. On the other hand, the reproductive output of daughters was not significantly affected by brood sizes and sex ratios. Our results suggest that female guppies benefit from producing large, male‐biased brood when the reproductive success of sons is expected to be high.  相似文献   

7.
The impact of host age on the number of hosts killed, survival of progeny, progeny allocation, and sex allocation was examined for several Trichogrammatidae (Hymenoptera) species in laboratory choice tests. Individual female parasitoids were provided with young, medium-aged and old eggs of one of three lepidopterous host species: Trichoplusia ni (Hübner) (Noctuidae), Pieris rapae (L.) (Pieridae), or Plutella xylostella (L.) (Plutellidae). Trichogrammatid species behaved as gregarious parasitoids with the first two host species, and as solitary parasitoids with eggs of the smaller latter one. They mostly preferred young eggs of T. ni, but did not discriminate among P. rapae eggs of different ages, and often preferred young or medium-aged P. xylostella eggs over old eggs. Survival of progeny did not vary constantly with host age, although it was often very low in P. rapae eggs of any age. Clutch size frequently decreased with host age in both T. ni and P. rapae. Offspring sex ratio did not change with age of T. ni and P. rapae eggs, and rarely did so in P. xylostella eggs. In regard to host age, the results with T. ni are the ones which are the most in agreement with optimal foraging theoretical predictions, as clutch size was the highest in preferred younger eggs.  相似文献   

8.
Pollinator fig wasps (Agaonidae) are a model system for studies of sex ratio evolution. They lay their eggs in galled ovules within figs. Only one adult emerges from each gall, suggesting that only one egg is always laid per ovule, but if double oviposition occurs then the assumption that adult (realised) sex ratios of fig wasps are representative of primary sex ratios may be violated. Many galls also fail to produce any wasps. If they initially contained eggs then differential mortality rates may also modify realized sex ratios. We investigated whether Kradibia (= Liporrhopalum) tentacularis foundresses in Ficus montana figs avoid laying in ovules that already contain eggs. Comparisons of oviposition frequencies and wasp emergence frequencies showed that most galls that failed to produce wasps will have had eggs laid in them, but few occupied ovules contained two eggs. Realised sex ratios therefore do not necessarily reflect primary sex ratios in this species, but double oviposition is not responsible.  相似文献   

9.
Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub‐social, with single foundress females exhibiting post‐ovipositional maternal care via short‐term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female‐biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi‐foundress reproduction on some hosts. Here, we screen for further life‐history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1–8 Goniozus nephantidis females together with a host for 5+ days. Multi‐foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female‐biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female‐biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi‐foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi‐foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi‐foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.  相似文献   

10.
Superparasitism in solitary parasitoids results in fatal competition between the immature parasitoids, and consequently only one individual can emerge. In the semisoli- tary ovicidal parasitoid Echthrodelphaxfairchildii (Hymenoptera: Dryinidae), 2 adults can emerge under superparasitism with a short interval (〈24 h) between the first and second ovipositions. We determined the female parasitoid's behavioral responses under self- and conspecific superparasitism bouts with first-to-second oviposition intervals of 〈2 h. The self- and conspecific superparasitizing frequencies increased up to an oviposition interval of 0.75 h, with the former remaining lower than the latter, particularly for oviposition intervals of _〈0.25 h, suggesting the existence of self-/conspecific discrimination. The superparasitizing frequency plateaued for oviposition intervals of _〉0.75 h, with no dif- ference between self- and conspecific superparasitism. The ovicidal-probing frequency did not differ under self- and conspecific superparasitism, and was usually 〈20%. The females exhibited no preference for the oviposition side (i.e., ovipositing on the side with or without the first progeny) and almost always laid female eggs for any oviposition in- terval under self- and conspecific superparasitism. The sex ratio was not affected by the type of superparasitism, oviposition sides, or the occurrence of ovicidal probing. These observed results about the oviposition side, ovicidal probing, and sex ratios differed from the predictions obtained assuming that the females behave optimally. Possible reasons for the discrepancies are discussed: likely candidates include the high cost of selecting oviposition sides and ovicidal probing, and, for the sex ratio, the low frequency of encountering suitable hosts before superparasitism bouts.  相似文献   

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