Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.     

Breeding Strategies in Females of the Parasitoid Wasp Spalangia endius: Effects of Mating Status and Size

Does the mating status or body size of a female parasitoid wasp affect her host size choice or propensity to burrow? In Spalangia endius, using smaller hosts appears to reduce a female's cost of parasitization but not her son's fitness. However, virgin females, which produce only sons, did not preferentially parasitize smaller hosts. Mated females also showed no host size preference. Mated females burrowed more than virgins in the presence of hosts, although not in their absence. Burrowing may reduce a mated female's harassment from males, and not burrowing may increase a virgin female's chance of mating because males avoid burrowing. Mating did not increase female longevity. Greater female size increased the offspring production of mated females burrowing for hosts but not in the absence of burrowing and not in virgin females. A female's size had no significant effect on whether her first drill attempt was on a large or a small host or on the duration of her successful drills.     

Mating or ovipositing? A crucial decision in the life history of the cabbage aphid parasitoid Diaeretiella rapae (M’Intosh)

1. The reproductive fitness of a parasitoid depends on its mating and ovipositing success. Virgin haplodiploid females can reproduce, but produce only males, and may diminish fitness by producing more male offspring than required. Therefore, females must decide on whether to mate or oviposit first. 2. This study was conducted to assess the mating versus ovipositing decision and its impact on the reproductive fitness of Diaeretiella rapae (Hymenoptera: Aphididae), an endoparasitoid of the cabbage aphid Brevicoryne brassicae (Hemiptera: Aphididae). 3. When newly emerged females were given a choice between mating and ovipositing, about 62% of D. rapae females preferred to mate before ovipositing. Those females who oviposited before mating parasitised only 10% of the available aphids. After mating, females superparasitised their hosts with fertilised eggs, which resulted in a highly female‐biased sex ratio in the offspring. 4. Mating success was very high (91%) in the presence of hosts (cabbage aphid nymphs) compared with that in the absence of aphids. However, mating success was not influenced by the quality (size) of the hosts present in the mating arena, despite a parasitoid preference for larger hosts during oviposition. The time between pairing and mating was also shorter in the presence of host aphids. The mean number of aphids parasitised and the parasitism rate were significantly greater after mating.     

寄主大小及寄生顺序对蝇蛹佣小蜂寄生策略的影响

寄主大小模型认为寄生蜂后代性比与寄主大小相关,寄生蜂倾向于在大寄主上产出更多雌性后代,在小寄主上产出更多雄性后代.探讨了以家蝇蛹为寄主时,蝇蛹佣小蜂后代产量和性比变化;单次寄生情况下,寄主大小及寄生顺序对寄生蜂后代性比等影响.结果表明,蝇蛹佣小蜂的产卵期为(8.93±3.34)d,单头雌蜂能产雌性后代(34.11±16.34)头和雄性后代(11.04±8.87)头,且雄性百分比为0.24±0.11.随成蜂日龄的增大,寄生蜂产生雄性后代的比率显著增加.蝇蛹佣小蜂在寄生家蝇蛹时,会优先选择寄生个体较大的蛹;在单次寄生的情况下,蝇蛹佣小蜂倾向于在较大的家蝇蛹内产出更多的雌性后代.     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

Male house mice produce fewer offspring with lower viability and poorer performance when mated with females they do not prefer

We report experimental results consistent with the hypothesis that constraints on the expression of male mating preferences affect breeder fitness, offspring viability and performance. If constraints on the expression of mating preferences are common, tests of fitness variation associated with mate preferences must eliminate as many constraints on mate preferences as possible. We tested whether male mate preferences influenced breeder fitness, offspring performance and viability in typically polygynous house mice, Mus domesticus, from a feral source population. Our ‘free mate choice’ trials not only eliminated female preferences, male-male and female-female competition, but also our best guesses of the traits mediating choosers' preferences. Males mated with their preferred (P) females sired more litters than males mated with their nonpreferred (NP) females. Offspring viability was significantly lower when males' reproduced with females they did not prefer compared with females they did prefer. Adult sons of males that mated with their P females were socially dominant to sons of males that mated with their NP females. Adult offspring from P pairings built better nests than offspring from NP pairings. The slope of the survivorship curve for P offspring was significantly higher than for NP offspring. These results showed (1) males' mate preferences affected their fitness, (2) males that mated with females they preferred produced more litters than males that mated with females they did not prefer, and (3) their offspring were significantly more viable and performed significantly better on standardized performance tests. This is the first demonstration of fitness benefits of male choice behaviour in a mammal species with typical paternal investment. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Relatively large males lower reproductive success in female zebrafish

Females can adjust their reproductive effort in relation to their partner’s perceived fitness value. In zebrafish (Danio rerio), large males are typically preferred mating partners. However, females have been observed to reduce their reproductive output with exceptionally large males but it remains unknown whether it is due to sexual harassment or aggressive behavior to establish and maintain dominance. Here, we study the association between relative male size, sexual harassment and dominance behavior, female stress status (stress behaviors and whole-body cortisol concentration), and reproductive success during a 4 day spawning trial. We found female cortisol to correlate negatively with female body size and positively with female dominance behavior. However, male and female behavior as well as female cortisol level were not related to relative male size. Females mating with relatively large males produced more and most of their eggs during the first spawning day, while females with smaller males produced few eggs during the first day but then increased egg production. Despite females produced more eggs when mating with relatively larger males, their eggs had substantially lower fertilization rates compared to females mating with relatively smaller males. Hence, overall, the reproductive fitness was lowest when females mated with a relatively large male. These findings could help to explain the maintenance of male size variation under natural conditions.     

Long-term fitness benefits of polyandry in a small mammal, the bank vole Clethrionomys glareolus

Polyandry, i.e. mating with multiple males within one reproductive event, is a common female mating strategy but its adaptive function is often unclear. We tested whether polyandrous females gain genetic benefits by comparing fitness traits of monandrous (mated twice with a single male) and polyandrous (mated twice with two different males) female bank voles Clethrionomys glareolus. We raised the offspring in the laboratory until adulthood and measured their body size, before releasing them to outdoor enclosures to overwinter. At the onset of the breeding season in the following spring, we found that offspring of polyandrous females performed significantly better at reproduction than those of monandrous females. This was mainly due to sons of polyandrous females producing significantly more offspring than those of monandrous females. No significant differences were found for offspring body mass or winter survival between the two treatments. Our results appear to provide evidence that bank vole females gain long-term benefits from polyandry.     

Ultimate Drivers and Proximate Correlates of Polyandry in Predatory Mites

Polyandry is more widespread than anticipated from Bateman’s principle but its ultimate (evolutionary) causes and proximate (mechanistic) correlates are more difficult to pinpoint than those of polygyny. Here, we combined mating experiments, quantification of reproductive traits and microsatellite genotyping to determine the fitness implications of polyandry in two predatory mite species, where males are highly polygynous (up to 45 fertilized females during life), whereas females range from monandry to various polyandry levels. The medium-level polyandrous (up to eight male mates possible) Neoseiulus californicus received clear direct and indirect benefits: multiply mated females produced more offspring with higher survival chances over longer times than singly mated females. In contrast, singly and multiply mated females of the low-level polyandrous (commonly two male mates at maximum) Phytoseiulus persimilis produced similar numbers of offspring having similar survival chances. In both species, multiple mating resulted in mixed offspring paternities, opening the chance for indirect fitness benefits such as enhanced genetic compatibility, complementarity and/or variability. However, the female re-mating likelihood and the paternity chance of non-first male mates were lower in P. persimilis than in N. californicus. Regarding proximate factors, in both species first mating duration and female re-mating likelihood were negatively correlated. Based on occasional fertilization failure of first male mates in P. persimilis, and mixed offspring paternities in both species, we argue that fertilization assurance and the chance to gain indirect fitness benefits are the ultimate drivers of polyandry in P. persimilis, whereas those of N. californicus are higher offspring numbers coupled with enhanced offspring viability and possibly other indirect fitness benefits. Overall, the adaptive significance and proximate events well reflected the polyandry levels. Our study provides a key example for linking behavioral experiments, quantification of reproductive traits and paternity analysis via offspring genotyping to explain the evolution of differing levels of polyandry.     

SEX-RATIO SELECTION IN A BIVOLTINE THRIPS. I. CONDITIONAL SEX-RATIO MANIPULATION AND FITNESS VARIATION

Females of the bivoltine thrips Elaphrothrips tuberculatus (Hood) (Insecta: Thysanoptera) produce broods of either all males (by viviparity) or all females (by oviparity). Measurements of the sex-allocation ratio, ecological and physiological conditions affecting male and female offspring body size, and correlates of the relative fitnesses of adult males and females in relation to size indicate that female parents tend to be viviparous (produce males) if their offspring will become relatively large adults, and that males gain more in fitness from large size than do females. However, the conditions that link sex allocation with offspring fitness differ between the spring and summer generations. In spring, when breeding is synchronous, 1) oviparous and viviparous females do not differ in body size, 2) females tend to be viviparous where the fungus upon which they feed is relatively dense and where their offspring will become relatively large adults, and 3) fungus density is highly correlated with male and female offspring size. In summer, when breeding is relatively asynchronous, 1) viviparous females are much larger than oviparous females early (but not late) in the season, 2) large viviparous females begin breeding earlier than smaller ones, 3) offspring developing earlier in the season become larger adults, and 4) a higher proportion of females are viviparous earlier than later. Field experiments and field collections show that the covariation among sex allocation, conditions, and fitness is not caused by differential mortality by size or sex. Differences between the spring and summer generations in the cues used by females to adjust offspring sex ratio may be caused by seasonal variation in the factors that affect offspring size. However, in both generations, females tend to produce sons only when their offspring will become relatively large adults, whereas daughters are produced regardless of offspring size. These data suggest that females of E. tuberculatus avoid production of males (the sex with higher variance in expected fitness) when the size of their offspring is relatively uncertain.     

Do female Nicrophorus vespilloides reduce direct costs by choosing males that mate less frequently?

Sexual conflict occurs when selection to maximize fitness in one sex does so at the expense of the other sex. In the burying beetle Nicrophorus vespilloides, repeated mating provides assurance of paternity at a direct cost to female reproductive productivity. To reduce this cost, females could choose males with low repeated mating rates or smaller, servile males. We tested this by offering females a dichotomous choice between males from lines selected for high or low mating rate. Each female was then allocated her preferred or non-preferred male to breed. Females showed no preference for males based on whether they came from lines selected for high or low mating rates. Pairs containing males from high mating rate lines copulated more often than those with low line males but there was a negative relationship between female size and number of times she mated with a non-preferred male. When females bred with their preferred male the number of offspring reared increased with female size but there was no such increase when breeding with non-preferred males. Females thus benefited from being choosy, but this was not directly attributable to avoidance of costly male repeated mating.     

Effects of female and male size on female mating and remating decisions in a bean beetle

The body sizes of individuals of the choosing and chosen sexes in a mate choice may affect sequential mating of females. We examined the effects of the body sizes of females and their mates on attributes of female first mating, and the effects of body sizes of females and their previous and potential future mates on female remating in the adzuki bean beetle, Callosobruchus chinensis. Large- and small-sized adults were derived from larvae reared under conditions of low and high density in a bean, respectively. The speed of first mating of large females was not affected by the size of courting males, whereas small females initiated mating more rapidly when courted by small males. The remating probability of large females was not affected by first male size, whereas small females that mated first with smaller males were more likely to remate. These data suggest that pre- and post-copulatory female choices for male size depend on the female’s size, and the small females might be more willing to copulate with smaller males but prefer larger males to sire their offspring after copulation. A possible explanation for this preference is that small females may suffer greater harm from copulating with larger males.     

Colour Polymorphism and Alternative Breeding Strategies: Effects of Parent’s Colour Morph on Fitness Traits in the Common Wall Lizard

Colour polymorphism (CP) is widespread in animals, but mechanisms underlying morph evolution and maintenance are not completely resolved. In reptiles, CP is often genetically based and associated with alternative behavioural strategies, mainly in males for most cases. However, female colour morphs also display alternative reproductive strategies associated with behavioural and physiological traits, which may contribute to maintain CP in the population. Both sexes of the common wall lizard (Podarcis muralis) show three pure colour morphs, white, yellow and red. Here, we looked for the effects of male and female colour morphs on fitness traits of captive-breeding pairs. All yellow-throated females laid clutches of many small eggs and produced many light offspring, behaving as r-strategists, whereas white-throated females laid clutches of few large eggs and produced few heavy offspring, behaving as K-strategists. Red-throated females adopted a conditional Kr-strategy depending on their size/age. These basic female strategies were modulated in relation to mate morph: white females had the best fitness gain in terms of viable offspring when mated to red males; mating between yellow morphs yielded a greater breeding success than all other morph crosses, but also lighter offspring; finally, red females produced heavy progeny when paired with red or white males, and light offspring in pair with yellow males. Thus, correlation between CP and traits relevant to fitness combined with non-random mating, either assortative or disassortative, could increase the potential for CP to contribute to divergent evolution in the common wall lizard.     

Host-size-dependent sex ratio in a parasitoid wasp

Charnov's host-size model explains parasitoid host-size-dependent sex ratio as an adaptive consequence when there is a differential effect of host size on the offspring fitness of parasitoid males versus females. This article tests the predictions and the assumptions of the host-size model. The parasitoid wasp Pimpla nipponica Uchida (Hymenoptera: Ichneumonidae) laid more female eggs in larger or fresher host pupae when choice among hosts of different sizes or ages was allowed. Then, whether an asymmetrical effect of host size and age on the fitness of females versus males existed in P. nipponica was examined. Larger or fresher host pupae yielded larger wasps. Larger females lived longer, whereas male size did not influence male longevity. Large males mated successfully with relatively large females but failed with small females, whereas small males could mate successfully either with small or with large females. Thus, small-male advantages were found, and this held true even under male–male competition. Ovariole and egg numbers at any one time did not differ among females of different sizes. Larger females attained higher oviposition success and spent less time and energy for oviposition in hosts. Larger females produced more eggs from a single host meal. Taken together, females gained more, and males lost more, by being large. Host size and age thus asymmetrically affected the fitness of offspring males versus females through the relationships between host size or hast age and wasp size, which means the basic assumption of the host-size model was satisfied. Therefore, sex ratio control by P. nipponica in response to host size and age is adaptive. Received: November 13, 1998 / Accepted: January 18, 1999     

Vibratory courtship in a web-building spider: signalling quality or stimulating the female?

Courtship behaviour in spiders in the form of premating vibrations by males may function (1) as a male identity signal used for species recognition, (2) in suppression of female aggressiveness, (3) to stimulate female mating behaviour, or (4) as a quality signal used in female choice. We investigated the function of web vibration by male Stegodyphus lineatus in a series of experiments. Regardless of vibratory performance, all males mated successfully with virgin females but only 56.4% of males mated with nonvirgin females. Vibratory performance did not influence male mating success, but heavier males had a higher probability of mating with mated females. Males vibrated less often and produced fewer vibrations when introduced on the web of a mated female. Males that vibrated webs of virgin females mated faster than nonvibrating males, but there was no effect of vibration rate or body mass. There was no effect of male vibratory effort or vibration rate on female reproductive success measured as time to egg laying, clutch size, number of hatched young, number of dispersed young and offspring body mass after a single mating. Males vibrated on abandoned virgin female webs but the response decreased with increasing duration of female absence, suggesting that females produce a web-borne pheromone, which elicits male vibrating behaviour. Mated females were less receptive and not stimulated by male vibrating behaviour. We conclude that male premating vibrations in S. lineatus do not function as a male quality signal selected via female choice. Rather, the primary function of this behaviour may be to stimulate a receptive female to mate. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Sex ratios in field populations of two parasitoids (Hymenoptera: Chalcidoidea) of Coccus hesperidum L. (Homoptera: Coccidae)

We tested several assumptions and predictions of host-quality-dependent sex allocation theory (Charnov et al. 1981) with data obtained for the parasitoid Metaphycus stanleyi Compere on its host, brown soft scale (Coccus hesperidum L.), in a California citrus grove and in the laboratory. Scales ceased growing after parasitization by M.?stanleyi. Thus, M. stanleyi may gauge host quality (=size) at oviposition. Host size positively influenced adult parasitoid size, and parasitoid size in turn influenced adult longevity of M. stanleyi. However, parasitoid fitness gains with host size and adult size were similar in males versus females. Sex allocation to individual hosts by M. stanleyi depended on host size; females consistently emerged from larger hosts than males. Host size was important in a relative sense; the mean host sizes of females versus males, and of solitary versus gregarious parasitoids varied with the available host size distribution. The offspring sex ratio of M. stanleyi reflected the available host size distribution; the sex ratio of emerging parasitoids varied with the available host size distribution. We did not detect a “critical host size” below which males emerged, and above which females emerged; rather, only females emerged from hosts in the upper size range, and a variable ratio of males and females emerged from hosts in the lower size range. We conclude that the sex ratio of field populations of M.?stanleyi is driven largely by the available size distribution of C. hesperidum. In addition, we tested predictions resulting from theoretical analyses of sex allocation in autoparasitoids with data obtained on Coccophagus semicircularis (Förster) parasitizing brown soft scale in the field. The sex ratio of C. semicircularis was consistently and strongly female biased (ca. 90% females). Based on available theoretical analyses, we suggest that this sex ratio pattern may have resulted from a very low encounter rate of secondary hosts coupled with a strong time limitation in C. semicircularis females. This explanation was the most plausible given constraints stemming from the detection of secondary hosts, their variable location within primary hosts, and their handling times. Finally, the size of hosts which yielded single versus multiple parasitoids, and the sizes of these parasitoids, were compared. These comparisons suggested that: (1) M. stanleyi females gauge host sizes precisely, and in terms of female offspring; thus a fitness penalty is not incurred by females which share a host, while males benefit from sharing a host, and; (2) instances where multiple C. semicircularis emerged from a single host were probably the result of parasitism by different females, or during different encounters by a single female.     

Reproductive costs of mating with a sibling male: sperm depletion and multiple mating in Cephalonomia hyalinipennis

Polygynous parasitoid males may be limited by the amount of sperm they can transmit to females, which in turn may become sperm limited. In this study, I tested the effect of male mating history on copula duration, female fecundity, and offspring sex ratio, and the likelihood that females will have multiple mates, in the gregarious parasitoid Cephalonomia hyalinipennis Ashmead (Hymenoptera: Bethylidae: Epyrinae), a likely candidate for sperm depletion due to its local mate competition system. Males were eager to mate with the seven females presented in rapid succession. Copula duration did not differ with male mating history, but latency before a first mating was significantly longer than before consecutive matings. Male mating history had no bearing on female fecundity (number of offspring), but significantly influenced offspring sex ratio. The last female to mate with a given male produced significantly more male offspring than the first one, and eventually became sperm depleted. In contrast, the offspring sex ratio of first‐mated females was female biased, denoting a high degree of sex allocation control. Once‐mated females, whether sperm‐depleted or not, accepted a second mating after a period of oviposition. Sperm‐depleted females resumed production of fertilized eggs after a second mating. Young, recently mated females also accepted a second mating, but extended in‐copula courtship was observed. Carrying out multiple matings in this species thus seems to reduce the cost of being constrained to produce only haploid males after accepting copulation with a sperm‐depleted male. I discuss the reproductive fitness costs that females experience when mating solely with their sibling males and the reproductive fitness gain of males that persist in mating, even when almost sperm‐depleted. Behavioural observations support the hypothesis that females monitor their sperm stock. It is concluded that C. hyalinipennis is a species with a partial local mating system.     

Adaptiveness of sex ratio control by the pupal parasitoid Itoplectis naranyae (Hymenoptera: Ichneumonidae) in response to host size

Adaptiveness of sex ratio control by the solitary parasitoid wasp Itoplectis naranyae (Hymenoptera: Ichneumonidae) in response to host size was studied, by examining whether differential effects of host size on the fitness of resulting wasps are to be found between males and females. The offspring sex ratio (male ratio) decreased with increasing host size. Larger hosts yielded larger wasps. Male larvae were less efficient in consuming larger hosts than female larvae. No significant interaction in development time was found between parasitoid sex and host size. Larger female wasps lived longer than smaller females, while longevity of male wasps did not increase with increasing wasp size. Smaller males were able to mate either with small or with large females, while larger males failed to mate with small females. Larger female wasps had a greater number of ovarioles and mature eggs at any one time than smaller females, although the number of eggs produced per host-feeding was not influenced by female wasps. Thus, the differential effect of host size on the fitness of males and females exists in I. naranyae. The basic assumption of the host-size model was therefore satisfied, demonstrating that sex ratio control by I. naranyae in response to host size is adaptive.     

Adaptive Offspring Sex Ratio Depends on Male Tail Length in the Guppy

A biased sex ratio in a brood is considered to be an adaptive strategy under certain circumstances. For example, if the expected reproductive success of one sex is greater than that of the other, parents should produce more offspring of the former sex than the latter. A previous study has documented that in the guppy, Poecilia reticulata, the female offspring of males possessing proportionally longer tails exhibit smaller body sizes and show decreased reproductive outputs than those of males having shorter tails. On the other hand, the total lengths of the male offspring of the long‐tailed males are larger because of their longer tails; consequently, they exhibit greater sexual attractiveness to females. Therefore, it has been hypothesized that this asymmetry in the expected reproductive success between the male and female offspring of long‐tailed males may result in a biased sex ratio that is dependent on the tail lengths of their fathers. This hypothesis was tested in the present study. The results showed that the females that mated with long‐tailed males produced more male offspring than those that mated with short‐tailed males. Logistic regression analysis showed that the ratio of tail length to the standard length of the fathers is a determinant factor of the sex of their offspring. These results suggest that the manipulation of the offspring sex ratios by parents enhances the overall fitness of the offspring.     

Asymmetric size effect of sexes on reproductive fitness in an aphid parasitoid Aphidius ervi (Hymenoptera: Aphidiidae)

Most studies on size–fitness relationships focus on females and neglect males. Here, we investigated how body size of both sexes of an aphid parasitoid, Aphidius ervi Haliday, affected the reproductive fitness. Reproductive fitness was generally positively correlated with body size for both sexes in this species. Large individuals of both sexes had greater longevity, large males fathered more progeny, and large females had higher fecundity, parasitism, and greater ability in host searching and handling. We demonstrated in this study that size effects of males and females were asymmetric on different reproductive fitness parameters. With increasing body size females gained more than males in longevity and fecundity while males gained more than females in the number of female progeny. Regardless of female size, large males sustained a female-biased population longer than small males. These results suggest that male body size should also be considered in the quality control of mass-rearing programs and the evaluation of parasitoid population growth.