Hyperparasitism behaviour of the autoparasitoid <Emphasis Type="Italic">Encarsia tricolor</Emphasis> on two secondary host species

Hyperparasitism by virgin female Encarsia tricolor was studied by direct observation of its behaviour when contacting two secondary host species (Encarsia formosa and E. tricolor) at different host stages (first and second larval stage, third larval stage, and pupal stage). The searching and hyperparasitism behavioural sequence of E. tricolor was independent of the host stage of the whitefly (Aleyrodes proletella), and was similar to several related primary parasitoid species. In experiments with equal numbers of secondary hosts, encounter frequencies were equal for both secondary host species in all developmental stages observed. However, rates of hyperparastism were different according to host stage and host species. Hosts in the late larval stages were most preferred for hyperparasitization and the heterospecific E. formosa was more preferred as a secondary host than the conspecific, E. tricolor, in particular from the prepupal stage onwards. The window of vulnerability, i.e., the duration of the period in which a secondary host is susceptible to hyperparasitism, was largely determined by the occurrence and rate of melanization after the onset of pupation. The duration of a successful hyperparasitization event was longer than one that failed. Superparasitism occurred only once in all cases. The potential effect of autoparasitoids on biological control programs and the consequences for selection and release of an effective, yet ecologically safe agent are discussed. Handling editor: Torsten Meiners.     

Effects of host stage on the development of the facultative autoparasitoid Encarsia tricolor (Hymenoptera: Aphelinidae)

Encarsia tricolor is a facultative autoparasitoid of the glasshouse whitefly, Trialeurodes vaporariorum, with a potential in biological control. The rate of development, number of mature oocytes at emergence, number of ovarioles and size of the emerged adults were studied. Five nymphal instars (N1, N2, N3, N4, and pharate adult) of T. vaporariorum were used as hosts for the females. Female larvae and pupae of E. tricolor and Encarsia formosa were used as hosts for the males. Females developed faster when the egg was laid on N3 (18.0 days from egg to adult) and slower on N1 (22.3 days). Females were bigger when developing from N1 and N3 than from N4 and pharate adult. On emergence the mean number of mature oocytes was always small (0.8–2.6). Males developed faster and were smaller than females, and developed faster and were larger on larvae of E. formosa.     

Host selection by the heteronomous hyperparasitoid Encarsia pergandiella: multiple-choice tests using Bemisia argentifolii as primary host

The ovipositional patterns of the heteronomous hyperparasitoid Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) in the presence of its primary host Bemisia argentifolii Bellows & Perring (Hemiptera: Aleyrodidae), and in the presence or absence of conspecific and heterospecific secondary hosts (Encarsia formosa Gahan andEretmocerus mundus Mercet; Hymenoptera: Aphelinidae) were examined to assess host species preferences. Host preferences by heteronomous hyperparasitoids may affect the relative abundance of co-occurring parasitoid species and may influence host population suppression by the parasitoid community. Four combinations of hosts were tested: (1) B. argentifolii, E. mundus, and E. formosa, (2) B. argentifolii, E. formosa, and E. pergandiella, (3) B. argentifolii, E. mundus, and E. pergandiella, and, (4) B. argentifolii, E. mundus, E. formosa, and E. pergandiella. Arrays of hosts (24) were constructed in Petri dishes using leaf disks, each bearing one host. Thirty arrays of each host combination were exposed to single females for 6 h. All hosts were dissected to determine number of eggs per host. Encarsia pergandiella parasitized E. formosa hosts as frequently as E. mundus hosts. However, E. pergandiella parasitized either of these heterospecific hosts more frequently than conspecific hosts in treatments including two secondary host species. When a third parasitoid species was included in host arrays, E. pergandiella parasitized conspecific hosts as frequently as heterospecific hosts. Developmental stage of the hosts did not significantly influence host species selection by E. pergandiella. Our results indicate that host selection and oviposition by heteronomous hyperparasitoids like E. pergandiella, vary with the composition of hosts available for parasitization, and suggest a preference for heterospecific over conspecific secondary hosts.     

Host selection and sex ratio in a heteronomous hyperparasitoid

Abstract.

• 1 Encarsia tricolor Förster is a heteronomous hyperparasitoid: females develop as primary endoparasitoids of Homoptera, whereas males develop hyperparasitically in primary endoparasitoids, including conspecific females.
• 2 When offered pupae of Encarsia inaron (Walker) or conspecific pupae, E.tricolor showed a distinct preference to exploit E.inaron for male production.
• 3 Parasitoids were given the opportunity to gain different types of ovipositional experience on male and female hosts and were then offered patches containing mixtures of male and female hosts in various ratios. The mean sex ratio which they laid was not dependent on the relative availability of each type of host, whereas prior ovipositional experience had a significant effect.
• 4 Adaptive reasons for the observed oviposition strategies are suggested.

     

Secondary host choice by the autoparasitoid Encarsia pergandiella

Autoparasitoids are species of parasitic wasps in the family Aphelinidae which produce females as solitary primary endoparasitoids of homopterans such as whitefly and scale insects (primary hosts), and males as solitary hyperparasitoids. Males generally develop on immature conspecific females or on individuals of other primary parasitoid species (secondary hosts). Encarsia pergandiella is an autoparasitoid that has been introduced to Italy for control of greenhouse whitefly Trialeurodes vaporariorum, in greenhouses and field crops. In this study we examined the secondary host selection behaviour of this species with regard to conspecific females and females of two thelytokous species, E. formosa and E. meritoria. Encarsia formosa has been used successfully for greenhouse whitefly control in Northern Europe, but has not been effective in Southern Italy in winter crops in unheated greenhouses. E. meritoria has recently spread in Italy, and may have potential for biological control of whitefly in the greenhouse environment. In the first experiment, female E. pergandiella were exposed to one of three pair-wise combinations of the three species in petri dish arenas. Parasitism was determined by dissection of the hosts. The number of hosts parasitized by E. pergandiella females did not differ with host species. However, significantly greater numbers of eggs were laid in E. meritoria in both treatments in which it was present; these hosts were more likely to be superparasitized. In a second experiment, observations of females in arenas with equal numbers of all three host species indicated that females encountered and parasitized all host species with approximately equal frequency, although the length of time females spent in the oviposition posture differed with host species.     

Comparison of Foraging Behavior, Interspecific Host Discrimination, and Competition of Encarsia formosa and Amitus fuscipennis

The foraging behavior of Amitus fuscipennis MacGown & Nebeker and Encarsia formosa Gahan was studied on tomato leaflets with 20 Trialeurodes vaporariorum (Westwood) larvae in the first or third stage. Ten of the whitefly larvae were previously parasitized and contained a conspecific or a heterospecific parasitoid egg or larva. The host type (host stage and/or previous parasitization) did not influence the foraging behavior of either parasitoid species. The residence time on these tomato leaflets was about 0.9 h for A. fuscipennis and 1.9 h for E. formosa. Amitus fuscipennis hardly stood still and fed little, while E. formosa showed extensive standing still and feeding. As a result, the time walking while drumming was similar for both parasitoid species. The numbers of host encounters and ovipositions per leaflet were similar for both parasitoid species. However, the residence time of A. fuscipennis was half as long as that of E. formosa so the rate of encounters and ovipositions was higher for A. fuscipennis. Amitus fuscipennis is more efficient in finding and parasitizing hosts under these conditions. The walking activity and host acceptance of the synovigenic E. formosa diminished with the number of ovipositions, but not those of the proovigenic A. fuscipennis. Encarsia formosa is egg limited, while A. fuscipennis is time limited because of its short life span and high egg load. Both parasitoid species discriminated well between unparasitized larvae and self-parasitized larvae, but discriminated poorly those larvae parasitized by a conspecific and did not discriminate larvae parasitized by a heterospecific. Self-superparasitism, conspecific superparasitism, and multiparasitism were observed for both parasitoid species. Superparasitism always resulted in the emergence of one parasitoid and multiparasitism resulted in a higher emergence of one parasitoid of the species that had parasitized first. The data suggest that A. fuscipennis is a good candidate for use in biological control of high-density spots of T. vaporariorum when we consider its high encounter and oviposition rate.     

The effect of nitrogen fertilizer applied to Euphorbia pulcherrima on the parasitization of Bemisia argentifolii by the parasitoid Encarsia formosa

More wasps of Encarsia formosa Gahan (Hymenoptera: Aphelinidae) were found on fertilized poinsettias, Euphorbia pulcherrima (Willd.) (Euphorbiaceae), than on non-fertilized plants. Parasitization of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) by E. formosa was higher on plants treated with calcium nitrate than with ammonium nitrate or on control plants. In a no-choice test, host feeding by E. formosa was higher when hosts were on fertilized plants than when hosts were on control plants. The nitrogen content of whitefly pupae reared on plants treated with ammonium nitrate was higher than those on calcium nitrate-treated plants.Variability in the parasitization of B. argentifolii by E. formosa appears to be due to host plant-mediated differences in the whiteflies. E. formosa may be influenced by the nutritional suitability of the host, which influences whether wasps continue to oviposit, feed, or disperse.     

Egg Size, Intrinsic Competition, and Lethal Interference in the Parasitoids Encarsia pergandiella and Encarsia formosa

Recent population dynamic theory predicts that disruption of biological control may occur when one parasitoid species' superiority in intrinsic competition is associated with a lower ability to find and exploit hosts (i.e., ability in extrinsic competition). One might expect such a trade-off, for instance, if parasitoids with larger (and fewer) eggs are more likely to prevail in intrinsic competition than species with smaller (and more numerous) eggs. We tested the idea that relative egg size could be used to predict the outcome of intrinsic competition in two closely related endoparasitoids, Encarsia pergandiella Howard and Encarsia formosa Gahan. Contrary to expectation, the parasitoid species with smaller eggs, E. pergandiella, prevailed in intrinsic competition, regardless of the order that hosts were exposed to the two species. In a literature survey, we found four studies of competing pairs of endoparasitoid species for which: (a) egg size estimates were available and (b) one species was consistently superior in intrinsic competition. In three of the four studies, the small-egged species prevailed in intrinsic competition, as we also found. Although E. formosa lost in intrinsic competition, this species negatively affected E. pergandiella's progeny production by host feeding on and killing hosts containing E. pergandiella eggs. E. formosa females also host fed on conspecific-parasitized hosts. As a mechanism of both intra- and interspecific interference competition, host feeding on parasitized hosts contradicts assumptions about the nature of interference competition in existing population dynamics models.     

Superparasitism in mass reared Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), a parasitoid of fruit flies (Diptera: Tephritidae)

Superparasitism frequency and its effects on the quality of mass-reared Diachasmimorpha longicaudata (Ashmead) parasitoids were investigated under laboratory conditions. Percentage of adult emergence, sex ratio, survival, fecundity and flight ability of adult parasitoids that emerged from Anastrepha ludens (Loew) pupae with different levels of superparasitism were determined. A high prevalence of superparasitism was observed. The number of scars per pupa, produced by insertion of the parasitoid ovipositor, ranged from 1 to 30, with an average (±SD) of 8.3 ± 6.2. Adult parasitoid emergence decreased as the level of superparasitism increased. However, the fraction of females rose with increasing superparasitism and the flight ability was lower in adults emerging from pupae with only one scar, compared with adults emerging from superparasitized hosts. Female longevity and fecundity were not affected by superparasitism. Our results support the hypothesis that superparasitism in D. longicaudata might be adaptive, since adults emerging from hosts with moderate levels of superparasitism showed the highest percentage of emergence and there were no significant differences in the other quality control parameters tested. Our findings are relevant to the mass rearing process, where the ratio of hosts to parasitoids can be optimized as well as the distribution of eggs deposited in host larvae. This contributes to efficient mass rearing methods for augmentative biological control programs.     

Pre- and post-landing response of the parasitoid Encarsia formosa to whitefly hosts on Gerbera jamesonii

One of the factors that may complicate biological control of the greenhouse whitefly on Gerbera jamesonii by Encarsia formosa is the rosette shape of this ornamental, which differs from the vertical shape of most vegetable plants (cucumber, egg plant, tomato, etc.). Therefore, host-habitat location and the behaviour prior to landing on uninfested and infested leaves was studied. Attraction of E. formosa from a short distance by infested leaves could not be detected: the parasitoid females landed at random on uninfested and infested leaves. After the first landing, a redistribution of the wasps occurred on the leaves. After 24 h three times as many wasps were found on the infested leaves than on uninfested ones. In a dispersal experiment with four plants, E. formosa appeared to have no preference for landing on leaves of the medium age class, which is the age class on which most of the whiteflies in a suitable stage for parasitism occur. Twenty percent of the parasitoids were found on the plants 20 min after releasing them. These results were independent of the plant cultivar and the host density on the plants. In the course of 8 h, the number of E. formosa females recovered from plants increased linearly, and this increase was greater on plants where hosts were present and also greater on the plant cultivar with the lowest trichome density. After 24 h, the percentage of females was highest (56%) on plants with the highest host density. E. formosa females were arrested on leaves where hosts were present. Contrary to our expectation, the results from the two G. jamesonii cultivars that differed strongly in leaf hairiness were not significantly different in most experiments. Only at the high host density was parasitism found to be lower on the cultivar with the higher hair density. Parasitoids may walk on top of the `hair coverlet' of cultivars with high trichome density and, therefore, be hampered less than expected.     

Interspecific interference competition between Encarsia formosa and Encarsia sophia (Hymenoptera: Aphelinidae) in parasitizing Bemisia tabaci (Hemiptera: Aleyrodidae) on five tomato varieties

Abstract Interspecific competition between Encarsia formosa and Encarsia sophia, two major parasitoids of Bemisia tabaci, and the influence of five tomato varieties on competition outcome were investigated under laboratory conditions. E. formosa parasitized more B. tabaci than E. sophia when in single wasp assays on any of the tomato varieties investigated. When B. tabaci nymphs were exposed to both wasp species (either simultaneously or sequentially), the number of B. tabaci nymphs parasitized by either wasp species was significantly decreased compared to the sole access condition. Total mortality of B. tabaci was increased when B. tabaci nymphs were exposed to both wasp species compared to only one wasp species. Thus competition between E. formosa and E. sophia apparently reduced parasitoid offspring numbers, but not the efficiency of biological control. In fact, control efficiency was enhanced in some cases, particularly on tomato variety Huangtuoyuan (HTY). When wasps were allowed sequential access to hosts, interference occurred through host feeding by the second wasp, especially if it was E. sophia. The effect of different tomato varieties was not significant.     

Sex allocation and egg distribution of an autoparasitoid, Encarsia pergandiella (Hymenoptera: Aphelinidae)

Abstract. 1. Encarsia pergandiella Howard females develop as primary parasitoids on immature whiteflies, and males develop as secondary parasitoids on females of their own or a related species. The hypothesis that the sex ratio reflects the relative abundance of the two host types was tested in the laboratory using petri dish arenas with varying proportions of early fourth instar greenhouse whitefly (Trialeurodes vaporariorum (West.)) (primary hosts) and pupal female E.pergandiella (secondary hosts). Egg distribution was analysed with respect to sex ratio, super-parasitism and host discrimination.
2. The proportion of primary and secondary hosts parasitized in each treatment reflected the relative availability of each host type. Thus females presented with 75% primary hosts laid more female eggs than male. However, in all treatments, a greater proportion of secondary hosts were parasitized than would be expected from the proportion of secondary hosts available. This indicates that more male eggs were laid than expected.
3. More secondary hosts than primary hosts were superparasitized.
4. Host discrimination analysis using a new test statistic showed that females generally laid eggs at random with regard to previous parasitism of primary or secondary hosts. However, females in one treatment with 50% of each host type appeared to preferentially oviposit in secondary hosts which did not contain any eggs.     

Sex allocation in a field population of an autoparasitoid

Autoparasitoid wasps lay fertilized eggs in homopteran nymphs, and these eggs develop into female primary parasitoids. Unfertilized, male-producing eggs are laid in immatures of the wasps' own or another primary parasitoid species; males then develop as secondary or hyperparasitoids. In the population of Encarsia pergandiella studied in Ithaca, NY, fertilized eggs were laid in the nymphs of the whitefly Trialeurodes packardi (primary hosts) and unfertilized eggs were laid almost exclusively in pupal females of their own species (secondary hosts). In the two years the population was studied, secondary hosts were always much less abundant than primary hosts at both sites. However, secondary hosts were parasitized at a significantly greater rate than primary hosts. In a laboratory experiment, the encounter rate of females with primary and secondary hosts was not significantly different. Moreover, there was no evidence from the field that wasps found leaves bearing secondary hosts more frequently than leaves without secondary hosts. Dissections of field-collected females showed them to be mated, and thus capable of laying both unfertilized and fertilized eggs. These results suggest that wasps did not encounter secondary hosts at a greater rate, nor were they constrained to lay unfertilized eggs, but rather secondary hosts were preferred. The oviposition sex ratios were influenced by the proportion of secondary hosts, but were less female-biased than would be predicted from the proportion of secondary hosts alone. The results do not support the predictions of Godray and Waage (1990) for either strictly host-limited autoparasitoids (sex ratio should reflect the proportion of secondary hosts) or for egg-limited autoparasitoids (sex ratio should be equal, and independent of the proportion of secondary hosts).     

A simulation study of population interaction between the greenhouse whitefly,Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) and the parasitoidEncarsia formosa Gahan (Hymenoptera: Aphelinidae) II. Simulation analysis of population dynamics and strategy of biological control

Simulation studies were performed to analyze factors affecting the population dynamics of the system with the greenhouse whitefly (Trialeurodes vaporariorumWestwood ) and the parasitoid Encarsia formosaGahan and to develop strategies for the introduction of E. formosa. The reduction of parasitization efficiency with an increase in parasitoid density promotes the stability of the system, which coincides with the prediction from current theory. The stability of the system is also shown to be promoted by the effect of host feeding. The population levels of the system are remarkably suppressed with an increase in searching efficiency and a decrease in host oviposition. The control effect of the parasitoids is enhanced when the number of parasitoids is divided among many introductions. An optimal time, an optimal density ratio of parasitoids to hosts and optimal densities of hosts and parasitoids exist in the introduction programme of parasitoids.     

Temperature dependent functional response ofEncarsia formosa parasitizing the Poinsettia-strain of the cotton whitefly,bemisia tabaci, on Poinsettia

The control efficiency and performance ofEncarsia formosa Gahan (Hymenoptera: Aphelinidae) as influenced by the density of its host, the Poinsettia-strain ofBemisia tabaci Gennadius (Homoptera: Aleyrodidae), were investigated by laboratory experiments on Poinsettia (Euphorbia pulcherrrima Willd.).E. formosa showed a Type II functional response to fourth instar larvae ofB. tabaci, the response plateau increasing with temperature. A response model for randomly searching parasitoids incorporating temperature-dependent handling time and temperature-independent search rate was in accordance with the results, and gave an estimated search rate of 0.033 leaf·hour⁻¹ and handling times of 1.54, 2.86 and 20.1 h at 28°C, 22°C and 16°C, respectively. From the latter, the maximum number of hosts that can be parasitized at the three temperatures are 10.4, 5.6 and 0.8 larvae per day (provided the light period is 16 h). The number of hosts with ovipositor punctures was higher than the number of parasitized hosts, especially at 22°C and 28°C, implying thatE. formosa refrains from laying eggs in some of the hosts examined with the ovipositor. About 31% of the punctured larvae did not contain any eggs. Superparasitism occured during the experiment presumably originating from young, inexperienced parasitoids. Individual larvae were occasionally punctured several times, also by non-superparasitizingE. formosa. The resulting distribution of ovipositior holes was random, indicating thatE. formosa on the basis of antennal testing is unable to determine if a larva has previously been examined with the ovipositor. Almost fifty percent of the punctures were not followed by egg-depositions. Besides parasitizationE. formosa used hosts as food source. The number of hostfed larvae was independent of density, but varied with temperature being highest at 28°C (0.12 hostfed larvae per parasitoid per day).     

The parasite-host relationship betweenEncarsia formosa (Hymenoptera: Aphelinidae) andTrialeurodes vaporariorum (Homoptera: Aleyrodidae) I. Host finding by the parasite

Analysis of the searching behaviour ofEncarsia formosa showed that this parasite was not able to locate its individual hosts (Trialeurodes vaporariorum) from a certain distance. In addition, quantitative data on sizes and numbers of hosts of each stage present on the leaf parts under observation, and the number of contacts the wasp made with these showed that the host-searching behaviour ofE. formosa on a leaf is random. Since, moreover, the distribution of the hosts over the leaf is random too, the number of hosts parasitized per unit of time is entirely dependent on the walking speed of the parasite and the number and sizes of the hosts present.     

Presence of a conspecific increases superparasitism but not infanticide under self‐ and conspecific superparasitism in a semisolitary parasitoid,Echthrodelphax fairchildii (Hymenoptera: Dryinidae)

Female parasitoids are expected to avoid superparasitism (ovipositing in and/or on parasitized hosts) when unparasitized hosts are available. However, when the supply of unparasitized hosts is restricted, they are expected to self‐ as well as conspecifically superparasitize. One of the cues of a reduced availability of unparasitized hosts is the presence of a conspecific. Moreover, if the focal species can perform infanticide, after encountering a conspecific female, the females are expected to kill eggs existing in and/or on hosts when superparasitizing, because the eggs are more likely to be laid by others. In this study we investigated whether females of an infanticidal semisolitary parasitoid, Echthrodelphax fairchildii, increase their frequencies of superparasitism and infanticide after encountering a conspecific female. Echthrodelphax fairchildii females are capable of discriminating between self‐ and conspecific superparasitism until up to 0.75 h after the first egg was laid (self‐superparasitism frequency < conspecific superparasitism frequency). As expected, the female parasitoids were more likely to perform self‐ and conspecific superparasitism after they had encountered a conspecific. In particular, the self‐superparasitism frequency increased highly within a short period after the first oviposition, so that no difference between the self‐ and conspecific superparasitism frequencies was found. In contrast, the infanticidal‐probing frequency remained extremely low, irrespective of whether or not the female parasitoids had encountered a conspecific. Moreover, when superparasitizing, females usually laid female eggs. Possible causes for the low frequency of infanticidal probing and the female‐biased sex ratio are discussed.     

Sex Allocation Decision Under Superparasitism by the Parasitoid Wasp Eupelmus vuilleti

Superparasitism is a widespread phenomenon in parasitoids and may be advantageous in some circumstances. In this study, offspring sex ratio was analysed in three superparasitism situations: when the second egg was laid by a random Eupelmus vuilleti (Hymenoptera: Eupelmidae) female from a group, when an isolated female was allowed to lay two eggs on the same host (self-superparasitism) or laid one egg on a host already parasitized by a conspecific (conspecific superparasitism). Females produced a different offspring sex ratio according to the different superparasitism situations tested. These sex ratios are in line with the local mate competition theory. The results further suggest that females can discriminate between hosts parasitized by a conspecific or by themselves and adapt the sex of the eggs they lay accordingly.     

Influence of intrapatch experiences and temperature on the time allocation of the whitefly parasitoidEncarsia formosa (Hymenoptera: Aphelinidae)

The effect of experiences, such as contact with honeydew, rejections of hosts, and ovipositions in hosts, and of temperature on the time allocation of individualEncarsia formosa female parasitoids on tomato leaflets have been studied. Behavioral records were analyzed by means of the proportional hazards model. Analyses were carried out at two levels: (1) the tendency of leaving and (2) the tendency of changing from one leaf side to another. The patch-leaving behavior ofE. formosa can be described by a stochastic threshold mechanism, which is characterized by a certain tendency (probability per time) to leave. The median time from being placed on the leaflet or, if it occurred, from the latest encounter with a host until leaving was 18.6 min. The median time for changing from one leaf side to the other was initially 11.6 min and dropped to 5.7 min after both leaf sides had been visited. The effect of temperature, ranging from 20 to 30°C, was negligible. The presence of honeydew as well as the first oviposition in an unparasitized host decreased the tendency to leave, thus increasing the giving up time (GUT) since the latest encounter with a host. Encounters with parasitized hosts did not affect the GUT since latest encounter; as a result, the total residence time increased. After the first oviposition in an unparasitized host the tendency of changing from the lower leaf side on which hosts were present to the upper side was decreased. The presence of honeydew did not affect the tendency of changing leaf sides.     

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.