Reproductive biology of Fopius arisanus (Hymenoptera: Braconidae) on Ceratitis capitata and Anastrepha spp. (Diptera: Tephritidae)

The reproduction of the solitary endoparasitoid Fopius arisanus (Sonan) (Hymenoptera: Braconidae) in Anastrepha ludens (Loew), Anastrepha obliqua (Macquart), and Anastrepha serpentina (Wiedemann) was compared with that using Ceratitis capitata (Wiedemann), being the host in which it had been reared previously. Eggs of different ages (<4 h old, 1, 2, and 3 days old for Anastrepha spp., and ⩽4 h, 1 and 2 days old for C. capitata) of each host species were placed in pieces of papaya, exposed to parasitism for 24 h and then reared through to the adult stage. Host species had a marked effect on parasitoid reproduction with consistently higher parasitoid emergence from C. capitata, whereas emergence from A. obliqua was negligible and this host was not studied further. Host age did not significantly affect parasitoid emergence from C. capitata whereas parasitism of A. ludens and A. serpentina was significantly greater in eggs exposed at 3 days old than those exposed at younger ages. Adult parasitoid sex ratio was male biased in all cases. Despite significant differences in host developmental time, host species did not affect parasitoid developmental time. Parasitoid life expectancy at emergence was reduced by >60% for parasitoids that emerged from A. ludens compared to those that emerged from A. serpentina or C. capitata. The reproduction of parasitoid progeny was highest in parasitoids that emerged from and reproduced on C. capitata and lowest for parasitoids reproducing on A. ludens. Parasitoids that emerged from A. ludens were often deformed, but were larger than those that emerged from A. serpentina. Parasitoids that emerged from C. capitata were smaller than those from Anastrepha spp. We conclude that F. arisanus is capable of sustained reproduction in C. capitata and A. serpentina and merits further study as an agent for the control of these fruit flies.     

Abiotic factors affecting Diachasmimorpha longicaudata (Hymenoptera: Braconidae) activity as a natural enemy of Ceratitis capitata (Diptera: Tephritidae) under semi‐natural conditions in the Mediterranean region

The larval–pupal endoparasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae) is currently the most commonly employed biological control agent against Tephritid fruit flies in the Americas. However, this parasitoid remains largely ignored and is not used in many regions, including the Mediterranean Basin. In this study, the potential of D. longicaudata as a biocontrol agent against the Mediterranean fruit fly (medfly) Ceratitis capitata (Diptera: Tephritidae) was addressed in an area of eastern Spain (the Valencian community). The parasitic activity of parasitoids and the effects of climatic conditions were evaluated throughout a 1‐year period in field‐cage experiments in which parasitoids were confined with apples artificially infested with medfly larvae. The following parameters were calculated and related statistically to several environmental conditions: the parasitism rate, the induced mortality and progeny sex ratio. The results show that D. longicaudata is able to parasitize medfly larvae throughout the year under semi‐natural conditions. Important fluctuations in the parasitism rate (from almost zero to 42%) and the induced mortality (from 6% to 80%) were partially influenced by climatic conditions. The parasitism rate increased with mean temperature and decreased with mean relative humidity, while the induced mortality decreased with minimum relative humidity. The optimal climatic conditions for the activity of the parasitoid were a mean temperature of 16–24°C combined with a relative humidity of 45%–60%. Overall, these results suggest that reduction in the medfly population due to D. longicaudata activity is feasible and provide information about the optimal time period for parasitoid release in the field. In conclusion, D. longicaudata has a significant potential to control C. capitata in the Mediterranean region.     

Response of two parasitoid species (Hymenoptera: Braconidae,Figitidae) to tephritid host and host food substrate cues

The Neotropical‐native figitid Aganaspis pelleranoi (Brèthes) and the Asian braconid Diachasmimorpha longicaudata (Ashmead) are two parasitoids of Tephritidae fruit flies with long and recent, respectively, evolutionary histories in the Neotropics. Both species experienced a recent range of overlap. In Argentina, A. pelleranoi is a potential species in biological control programs against the pestiferous tephritid species, Anastrepha fraterculus (Wiedemann) and Ceratitis capitata (Wiedemann), whereas D. longicaudata is already used in open‐field releases against Medfly in central‐western Argentina. To characterize the host‐foraging strategies of A. pelleranoi and D. longicaudata, olfactometer experiments were conducted comparing responses to C. capitata and A. fraterculus larvae, in two kinds of food substrate: fruit and artificial larval medium. To control the possible influence of host larvae used for parasitoid rearing on olfactory response, two strains of both parasitoid species, reared on both tephrtid species, were studied. Volatiles directly emanating either from A. fraterculus or C. capitata larvae may be detected by both A. pelleranoi and D. longicaudata, although chemical stimuli originating from the combination of host larvae and the habitat of the host were preferred. However, olfactory cues associated with host larvae probably play a relevant role in host searching behaviour of A. pelleranoi, whereas for D. longicaudata, the host‐habitat olfactory stimuli would be highly essential in short‐range host location. The strain of the parasitoids did not affect host search ability on the two tephritid species evaluated. These evidences are relevant for mass production of both parasitoids and their impact following open‐field augmentative releases.     

Effect of host Bactrocera dorsalis sex on yield and quality of the parasitoid Fopius arisanus

This study examines the effect of host Bactrocera dorsalis Hendel (Diptera: Tephritidae) sex on performance of the parasitoid Fopius arisanus Sonan (Hymenoptera: Braconidae) to enable use of a genetic sexing strain (GSS) to transfer this parasitoid to regions where B. dorsalis is not established with lower risk of accidental introduction of the host. Sex ratio and yield of F. arisanus did not significantly differ between the two sexes of a GSS, or between GSS and a standard colony strain. F1 parasitoids of individuals that emerged from the standard colony strain, male GSS hosts and female GSS hosts had similar hatching and parasitization rates on colony eggs. Survivorship of F1 parasitoids with parents from female hosts was significantly greater than for those from male hosts. Using GSS to improve the safety of parasitoid shipments is suggested to be viable, but there may be fitness effects of host sex on F1 parasitoid fitness.     

Parasitoid hymenopterans of Costa Rica: Geographical distribution of the species associated with fruit flies [Diptera: Tephritidae]

The geographical distribution of the parasitoid species associated with fruit flies in Costa Rica is presented. In a study of 319 fruit samples infested with larvae of fruit flies, collected from 135 localities, 8 parasitoid species were recovered from 11.0% of the fruit samples. Two species are considered to be indigenous, two were introduced for the biological control ofCeratitis capitata (Wiedemann) in this country, at least 3 unidentified species of eucoiline cynipoids and one species of uncertain origin was found for the first time. The identified parasitoids were:Doryctobracon crawfordi (Viereck) (indigenous),D. areolatus (Szépligeti) (indigenous),Biosteres longicaudatus Ashmead (introduced),Aceratoneuromyia indica (Silvestri) (introduced) andTrichopria sp. (indigenous?). The introduced species were more frequently associated withAnastrepha spp. than withC. capitata. The need for systematic monitoring of populations of released parasitoid species is suggested.     

Transgenic sexing system for Ceratitis capitata (Diptera: Tephritidae) based on female-specific embryonic lethality

Fruit fly pest species have been successfully controlled and managed via the Sterile Insect Technique (SIT), a control strategy that uses infertile matings of sterile males to wild females to reduce pest populations. Biological efficiency in the field is higher if only sterile males are released in SIT programs and production costs are also reduced. Sexing strains developed in the Mediterranean fruit fly Ceratitis capitata (medfly) through classical genetics are immensely beneficial to medfly SIT programs but exhibit reduced fertility and fitness. Moreover, transfer of such classical genetic systems to other tephritid species is difficult. Transgenic approaches can overcome this limitation of classical genetic sexing strains (GSSs), but had resulted so far in transgenic sexing strains (TSSs) with dominant lethality at late larval and pupal stages. Here we present a transgene-based female-specific lethality system for early embryonic sexing in medfly. The system utilizes the sex-specifically spliced transformer intron to restrict ectopic mRNA translation of the pro-apoptotic gene hid^Ala5 to females only. The expression of this lethal effector gene is driven by a tetracycline-repressible transactivator gene tTA that is under the control of promoters/enhancers of early-acting cellularization genes. Despite observed position effects on the sex-specific splicing, we could effectively establish this early-acting transgenic sexing system in the medfly C. capitata. After satisfactory performance in large scale tests, TSSs based on this system will offer cost-effective sexing once introduced into SIT programs. Moreover, this approach is straight forward to be developed also for other insect pest and vector species.     

The influence of the rearing host on the response of the parasitoid Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) to odours from Ephestia kuehniella and Plodia interpunctella in a Y-tube olfactometer

Venturia canescens (Gravenhorst) is an ichneumonid generalist parasitoid that successfully attacks the larvae of different lepidopteran pests that infest stored products. These pest species include Plodia interpunctella and Ephestia kuehniella. In this study, we aimed to evaluate the influence of the rearing host on the parasitoid’s ability to detect and respond to a new host different from the rearing species. For this reason, the trials tested the preference of parasitoids reared on P. interpunctella or E. kuehniella for products that were or were not infested with larvae of these hosts. The trials were conducted in a Y-tube olfactometer. Regardless of the rearing host species, the parasitoids showed no preference for uninfested products. The parasitoids were attracted to products infested with larvae of their rearing host in preference to uninfested products. They also showed preferential attraction to products infested with the new host over uninfested products. E. kuehniella was the preferred host, irrespectively of the parasitoid host rearing species. The results are discussed to develop a better understanding of the ecology of V. canescens for its application in biological control.     

Field parasitism of Ceratitis capitata larvae by Aganaspis daci in Chios, Greece

High parasitism rates were recorded in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in pupae derived from field infested figs, on the Greek island of Chios in 1999 and 2000. Adult parasitoids were identified as Aganaspis daci (Weld) (Hymenoptera:Eucoilidae), previously known as Trybliographa daci (Weld). Approximately 45%of C. capitata pupae yielded adultparasitoid in both years and the totalmortality of pupae due to the parasitoid was62–65%. Development of male A. daci at25°C, reared on 3rd instar larvaeof C. capitata, was shorter than that of the female (34 and 37 days respectively). Average adultmale longevity was 4–5 days longer than female(16–17 to 11–12 days, respectively) and almostidentical in wild and F₁ parasitoids ofboth sexes. We suggest that A. daci maybe an efficient form of biological control ofC. capitata in the Mediterranean regionand probably in other areas.     

Biosystematics of the Psyttalia concolor Species Complex (Hymenoptera: Braconidae: Opiinae): The Identity of Populations Attacking Ceratitis capitata (Diptera: Tephritidae) in Coffee in Kenya

The identity of a species of Psyttalia, a parasitoid of tephritid fruit flies in Kenya, was investigated. Individuals reared from coffee infested with Ceratitis capitata (Wiedemann) (Medfly) and two other tephritid species in Kenya were compared with individuals of Psyttalia concolor (Szépligeti) from a laboratory culture in Italy used in augmentative biological control of olive fly, Bactrocera oleae (Gmelin). Reciprocal crosses showed full compatibility, with production of viable female offspring. A preliminary morphometric analysis demonstrated that most individuals originating from Italy could be separated from most of those from Kenya based largely on differences in overall size.     

Different pepper cultivars affect performance of second (Myzus persicae) and third (Diaeretiella rapae) trophic levels

While chemical application can control aphid outbreaks, the overuse of insecticides can make aphids more resistant to these insecticides. These effects make strategies such as host plant resistance combined with biological control agents as an important part of alternative control methods. In this study, the performance of the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid wasp, Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) were determined on different pepper cultivars (California, Hamedan, Minab, Sabz-Farangi, Sabz-Ghalami, Semnan, Shahroud, and Tehran) in a growth chamber at 25 ± 1 °C, 60 ± 5% RH and a 16:8 h L:D photoperiod. The intrinsic rate of increase (r) of the aphid on the above-mentioned cultivars was 0.3203, 0.3891, 0.3594, 0.3152, 0.3512, 0.3032, 0.3352 and 0.2787 day⁻¹, respectively. Comparison of the intrinsic rate of increase (r) on different pepper cultivars revealed that Hamedan was the most susceptible and Tehran was the most resistant cultivar. The parasitoids reared on the aphids fed on the susceptible cultivar (Hamedan) had a higher intrinsic rate of increase (0.2641 day⁻¹) than those (0.2259 day⁻¹) reared on the resistant cultivar (Tehran). These results demonstrated that the quality of host plant affected the performance of M. persicae and its parasitoid D. rapae.     

Potential for classical biological control of the potato bug Closterotomus norwegicus (Hemiptera: Miridae): description, parasitism and host specificity of Peristenus closterotomae sp. n. (Hymenoptera: Braconidae)

The potato bug, Closterotomus norwegicus (Gmelin) (Hemiptera: Miridae) is an introduced pest of lucerne, white clover and lotus seed crops in New Zealand and a key pest of pistachios in California, USA. Efforts were made to identify potential biological control agents of C. norwegicus in Europe. A total of eight parasitoids, including six primary parasitoids from the genus Peristenus (Hymenoptera: Braconidae) and two hyperparasitoids from the genus Mesochorus (Hymenoptera: Ichneumonidae), were reared from C. norwegicus nymphs collected in various habitats in northern Germany. With a proportion of more than 85% of all C. norwegicus parasitoids, Peristenus closterotomae (Hymenoptera: Braconidae), a new species, was the most dominant parasitoid, whereas other parasitoid species only occurred sporadically. Peristenus closterotomae did not fit in the keys to any described species and is described as new to science. Parasitism caused by P. closterotomae was on average 24% (maximum 77%). To assess the host specificity of parasitoids associated with C. norwegicus, the parasitoid complexes of various Miridae occurring simultaneously with C. norwegicus were studied. Peristenus closterotomae was frequently reared from Calocoris affinis (Herrich-Schaeffer), and a few specimens were reared from Calocoris roseomaculatus (De Geer) and the meadow plant bug, Leptopterna dolobrata (Linnaeus) (all Hemiptera: Miridae). The remaining primary parasitoids associated with C. norwegicus were found to be dominant in hosts other than C. norwegicus. Whether nymphal parasitoids may potentially be used in a classical biological control initiative against the potato bug in countries where it is introduced and considered to be a pest is discussed.     

Host specificity of the egg pupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) in La Reunion

Fopius arisanus is a polyphagous parasitoid of Tephritidae, which has been recently introduced to La Réunion Island as part of a classical biological control programme. We carried out laboratory experiments to assess the host specificity of this parasitoid, initially reared on Bactrocera zonata, and then offered for parasitization the eight local tephritid pest species. Naive or experienced parasitoid females were given tephritid eggs in no choice tests. Fopius arisanus females parasitize all fly species but parasitism varies with host species. No adult wasps emerge from Bactrocera cucurbitae and the survival of this species is only slightly affected by parasitism. Dissections show that the late instars of this fly may eliminate the parasitoid by encapsulation. When developing on Ceratitis capitata, Ceratitis rosa, Dacus ciliatus, Dacus demmerezi, and Neoceratitis cyanescens, parasitoid survival rate ranges from 10 to 25%. Bactrocera zonata and Ceratitis catoirii are the best hosts, yielding parasitoid survival rates of more than 70% with no premature mortality. The egg-larval mortality of C. capitata, C. rosa, D. ciliatus, and N. cyanescens, and the pupal mortality of D. demmerezi, are significantly increased by parasitism. The size of emerging adults is affected by host species and is correlated to pupal weight. Bactrocera zonata would be a favorable host to support routine colonization of F. arisanus for mass production of this parasitoid.     

Female pupae of the genetic sexing strain “Tap-7” of Anastrepha ludens as hosts of Coptera haywardi

Female black pupae from the Anastrepha ludens genetic sexing strain Tapachula-7 were evaluated as hosts for Coptera haywardi. We studied the host acceptance and the effects of age, irradiation and automated mechanical separation of black pupae on the emergence, survival, fecundity and flight ability of parasitoid C. haywardi adults. Our results indicated that black pupae are viable hosts for C. haywardi. Adult emergence was greater when the exposed pupae were three and five days old. The impact that occurred during mechanical separation reduced emergence by 16 %. The tested irradiation doses (25, 35 and 45 Gy) did not significantly affect adult emergence. No significant differences in longevity, fecundity or flight ability were observed between parasitoids that emerged from the Tapachula-7 black pupae and those that emerged from the standard mass-reared strain.     

The effects of sterile males and two braconid parasitoids,Fopius arisanus (Sonan) and Diachasmimorpha krausii (Fullaway) (Hymenoptera), on caged populations of Mediterranean fruit flies,Ceratitis capitata (Wied.) (Diptera: Tephritidae) at various sites in Guatemala

Area-wide control of the Mediterranean fruit fly (=medfly), Ceratitis capitata (Wiedemann), typically involves sterile insect technique (=SIT), and at present the “Temperature Sensitive Lethal” (=TSL) strain is commonly mass-reared for such releases. In theory, and with some experimental support, the augmentative addition of parasitoids to sterile releases can suppress pest populations to a greater extent than either technique alone. The efficacies of TSL males, parasitoids, and TSL males and parasitoids were compared in large field cages erected over coffee grown at four locations and three altitudes (relatively high, medium and low for the crop) in Guatemala. Two species of opiine braconid parasitoids, the larval–pupal parasitoid Diachasmimorpha krausii (Fullaway) and the egg-pupal parasitoid Fopius arisanus (Sonan), were released either together or in combination with sterile males into cages along with fertile medflies. Results of this evaluation were assessed by comparing the number of pupae and adult insects that completed development (F1 generation) as a result of the reproduction of a parental generation released into each field cage. The TSL males significantly suppressed F1 fly populations but only in one of four study sites. However, the inclusion of F. arisanus and D. krausii always provided significant suppression and the effect was frequently substantial. In one site there was a significant interaction between the capacity of sterile males and parasitoids to suppress caged fly populations. There was no effect of host-fruit abundance on the numbers of flies recovered, however, there were significant interactions between maximum and minimum temperatures and the effects of sterile males and parasitoids, respectively. The results suggest that mass-reared sterile medflies and biological control agents should be tested for both consistent sexual-quality and their ability to perform in the various environments in which they will be released.     

Host-plant mediated effects of transgenic maize on the insect parasitoid Campoletis sonorensis (Hymenoptera: Ichneumonidae)

Determining the impact of genetically modified (GM) crops on beneficial organisms is an important aspect of the environmental risk assessment of GM crops. In the present study, the impact of Bt maize expressing Cry1Ab on the development and behaviour of the parasitoid Campoletis sonorensis was compared to individuals reared on hosts fed conventionally bred plants partially resistant to the European corn borer (Ostrinia nubilalis Hübner) and on susceptible maize hybrids. Adult parasitoids reared on Bt maize-fed Spodoptera frugiperda larvae were significantly smaller (15–30%) than those reared in hosts fed either of the conventional maize hybrids. The magnitude of this effect was dependent on the size of the host at oviposition and its subsequent growth rate. The development time of C. sonorensis was not affected by the maize treatment. In choice tests, female parasitoids displayed no preference for hosts fed a specific maize hybrid. No Cry1Ab was detected within adult parasitoids.     

Assessment of Ceratitis capitata (Diptera,Tephritidae) pupae killed by heat or cold as hosts for rearing Spalangia cameroni (Hymenoptera: Pteromalidae)

In this work, we study the suitability of using dead medfly Ceratitis capitata pupae, killed by heat- or cold-shock, for the mass rearing of Spalangia cameroni, a pupal parasitoid of key pests. 100% mortality of medfly pupae could be accomplished with cold-shock at –20°C for 60 min or with heat-shock at 55°C for 30 min. Neither parasitism percentage nor sex ratio of the offspring differed significantly among heat-shocked, cold-shocked and untreated pupae. In addition, there was no significant difference in the percentage of parasitoids that aborted (♂♂ or ♀♀) among pupal treatments. Some of the pupae were covered with peat because the third larval instar of the medfly buries itself before pupation. However, the buried pupae were not parasitised at a greater or lesser rate than those not covered with peat. The percentage of parasitism was also unaffected by whether the pupae had been killed recently or had been stored at between 4°C and 6°C over 15 or 30 days. The use of dead hosts and later storage permitted the following: (a) the use of hosts over long periods of time; (b) a rapid increase in parasitoid numbers and (c) the availability of pupae killed at the most suitable postpupation times for the production of parasitoids. Furthermore, in biological control projects, the use of dead parasitised pupae in the field avoids the risk of enhancing the pest and allows an increase in parasitism in the field through the use of pupae treated with cold- or heat-shock.     

Host preferences ofTrichogrammatoidea bactrae fumata (Hym.: Trichogrammatidae) an egg parasitoid of leafrollers (Lep.: Tortricidae)

Trichogrammatoidea bactrae fumata Nagaraja is a naturally occurring egg parasitoid of some leafrollers in New Zealand kiwifruit orchards. The parasitoid showed a distinct preference for younger host-eggs ofEpiphyas postvittana, in which it achieved a higher rate of successful development. Such a preference is not as apparent withCtenopseustis obliquana. Host-species preference experiments found that the parasitoid rarely attackedPlanotortrix octo, and successful wasp emergence from parasitised eggs of this host was low.Epiphyas postvittana was the preferred host whenT. bactrae fumata was reared on this species. When reared onC. obliquana, the parasitoid showed no preference forE. postvittana orC. obliquana.     

Bionomics of Opius bellus (Hymenoptera: Braconidae), an endoparasitoid of Anastrepha fraterculus (Diptera: Tephritidae) in fruit-growing areas of Northwestern Argentina

Opius bellus is a neotropical larval-prepupal parasitoid known to attack the pestiferous fruit fly, Anastrepha fraterculus. Due to interest in the use of native parasitoids in forthcoming fruit fly biocontrol programmes in Argentina, O. bellus was colonised for the first time using laboratory-reared A. fraterculus larvae. A series of experiments were conducted to (1) best achieve an efficient parasitoid rearing by determining optimal larval host age, host:parasitoid ratio and host exposure time and (2) assess their potential as biological control agents by determining reproductive parameters. The most productive exposure regimen was: 7–9 d-old (early and middle third-instars) A. fraterculus larvae for 4 h at a 4:1 host:parasitoid ratio; this array of factors was sufficient to achieve the highest average adult emergence (48%) and an offspring sex ratio at equitable proportion. Increasing both host:parasitoid ratio further than 4:1 and the host exposure time beyond 4 h did not significantly enhance parasitoid female offspring yield. Females produced eggs for 29.5 ± 1.4 days. At 32 days of age, 50% of the females were still alive. The majority of the progeny were produced by females between 20 and 24 d-old. At 26°C, gross fecundity rate, net reproductive rate, intrinsic rate of increase and mean generation time were 20.7 ± 4.2 offspring/female, 9.6 ± 2.5 females/newborn females, 0.06 ± 0.01 females/female/day and 8.4 ± 0.2 days, respectively. The long lifespan and reproductive parameters suggest that this parasitoid species has suitable attributes for mass-rearing.     

Comparative demography of three neotropical larval-prepupal parasitoid species associated with Anastrepha fraterculus (Diptera: Tephritidae)

The South American fruit fly, Anastrepha fraterculus (Wiedemann), is one of two fruit fly species of economic importance in Argentina, which along with the exotic Mediterranean fruit fly, Ceratitis capitata (Wiedemann) produce annual losses of nearly US$ 90 million for fruit production in this country.Biological control may contribute to integrated approaches to manage both pestiferous species.Information on survival, reproduction and population growth parameters, critical for successful augmentation of natural enemies, is provided for three fruit fly neotropical parasitoids, Aganaspis pelleranoi (Hymenoptera: Figitidae), Opius bellus and Doryctobracon crawfordi (Hymenoptera: Braconidae). A. pelleranoi had the highest intrinsic reproductive rate (r), survival time and reproductive time, followed by O. bellus. Meanwhile D. crawfordi showed the lowest values for reproductive and population growth parameters.     

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.