The functional response of Uscana lariophaga under different egg distributions of its host Callosobruchus maculatus

The functional response of the egg parasitoid Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) was tested under three different host distributions (even, clumped and random) within clusters of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) eggs. A Holling Type II functional response was found for all three distributions. Over low host densities, less than 50% of the host clusters was parasitized. At low host densities, U. lariophaga females parasitized significantly fewer eggs in random egg clusters with many beans than in clusters with fewer beans and an even or clumped egg distribution. At higher egg densities, plateau levels of maximum number of hosts parasitized were the same for all three egg distributions. Uscana lariophaga appears to be adapted to search for even or clustered egg distributions, as can be found in the field and under storage conditions.     

Exploring the foraging environment of a natural enemy of Callosobruchus maculatus: Spatial egg distribution in stored cowpea

Knowledge of the spatial distribution of stored product insects may reduce the dependency on chemicals for control of these insects. Biological control, for instance, could be improved based on such knowledge. In this paper we describe the three-dimensional spatial oviposition pattern of Callosobruchus maculatus in stored cowpea. Individual C. maculatus females oviposited in clusters of 70±15 (SD) eggs. These clusters were variable in shape. In any cluster 90 to 95% of the eggs fitted into a volume of 19.1±3.5 cm³. The egg density was highest (0.6 eggs bean^–1) at the center of a cluster and decreased towards the periphery. A statistically significant relationship existed between the number of eggs n in a cluster and the cluster volume, V(cm³): V=11.5+0.11n. We also investigated the spatial egg distribution of beetles which emerged from egg clusters such as those produced by individual females. Their oviposition was not confined to one specific area but was scattered throughout the bean mass. A point pattern analysis showed that the density of the `parent' cluster had no effect on the spatial egg pattern. These results give insight into the foraging environment which the egg parasitoid Uscana lariophaga, a promising candidate for biological control of C. maculatus, is facing. We argue that the probability p of encountering at least one other bean with eggs after a parasitization is a function of the number n of beans that are visited: p=1–0.42 (0.37)^(n–1).     

‘Males second’ strategy in the allocation of sexes by the parasitic wasp,Gryon japonicum

Summary Patterns of the sex ratio allocation of Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae), a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Heteroptera: Alydidae), were investigated in the laboratory, and the result was checked against the field data on the sex composition of the parasitoid. When five host eggs were presented simultaneously to each of the females of G. japonicum in a laboratory experiment, they had a strong tendency to lay a male egg in second host egg and female eggs in the others. However, when four host eggs were presented to each female more than 3 h after the completion of oviposition on a host egg, most of the females laid male eggs in the third oviposition, i.e. the second host eggs after the experimental interruption of oviposition. These results indicated that there was a mechanism for G. japonicum to produce a male egg in the second host egg in consecutive ovipositions, and that the mechanism was reset by more than 3 h intervals of oviposition. By this mechanism, G. japonicum is thought to produce the precise sex ratio in response to the size of a host egg batch. Field data on the size of a host egg batch and the sex composition of the parasitoid in a host egg batch supported this view.     

Foraging Behavior and Patch Time Allocation by Fopius arisanus (Hymenoptera: Braconidae), an Egg-Larval Parasitoid of Tephritid Fruit Flies

This study quantitatively describes the host-searching behavior of Fopius arisanus (Sonan) (Hymenoptera: Braconidae), an important egg-larval parasitoid of tephritid fruit fly pests, on coffee berries infested with host eggs of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also investigate the parasitoid's response to local variation in host patch quality. The temporal pattern of behavioral organisation was examined by constructing an ethogram. The parasitoid spent over 90% of its foraging time in detecting and locating hosts after arriving on a host-infested fruit, and displayed a relatively fixed behavioral pattern leading to oviposition. Patch residence time increased in the presence of host-associated cues, following successful ovipositions, and with increasing size of host clutches per fruit, but decreased with each successive visit to the same host patch and with increasing availability of alternative host patches. The parasitoid females discriminated against previously parasitized hosts and spent significantly less time and searching effort on patches previously exploited by herself or by conspecific females. The effective host-searching behavior, perfect host discrimination ability, and success-motivated searching strategy shown by F. arisanus ensured a thorough exploitation of host resources by this parasitoid.     

Reciprocal influences and costs of parasitism on the development of Corcyra cephalonica and its endoparasitoid Venturia canescens

Many endoparasitoids develop successfully within a range of host instars. Parasitoid survival is highest when parasitism is initiated in earlier host instars, due to age-related changes in internal (physiological) host defences. Most studies examining fitness-related costs associated with differences in host instar have concentrated on the parasitoid, ignoring the effects of parasitism on the development of surviving hosts that have encapsulated parasitoid eggs. A laboratory experiment was undertaken examining fitness-related costs associated with encapsulation of Venturia canescens (Hymenoptera: Ichneumonidae) eggs by fifth (L5) instar larvae of Corcyra cephalonica (Lepidoptera: Pyralidae). Growth and development of both host and parasitoid were monitored in C. cephalonica larvae containing 0, 1, 2, or 4 parasitoid eggs. Adult size and fecundity of C. cephalonica did not vary with the number of eggs per host. However, there was a distinct increase in host mortality with egg number, although most parasitoids emerged from hosts containing a single egg. The most dramatic effect on the host was a highly significant increase in development time from parasitism to adult eclosion, with hosts containing 4 parasitoid eggs taking over 2.5 days longer to complete development than unparasitized larvae. The egg-to-adult development time and size of adult V. canescens did not vary with egg number per host, as demonstrated in a previous experiment using a different host (Plodia interpunctella). The results described here show that there are fitness-related costs to the host associated with resistance to parasitism.     

Uscana lariophaga, egg parasitoid of bruchid beetle storage pests of cowpea in West Africa: the effect of temperature and humidity

The stored-product bruchid pests,Callosobruchus maculatus (Fabricius) andBruchidius atrolineatus (Pic) cause considerable production losses in cowpea in West Africa.Uscana lariophage Steffan parasitizes the eggs of the bruchids both in the field and in storage. As chemical control of bruchids in traditional granaries is not appropriate for poor farmers, enhancement of the efficacy of the parasitoid by environmental manipulation has been investigated. The effect of temperature on the capacity ofU. lariophaga to parasitize eggs has been studied at eleven constant and three fluctuating temperatures within the range 10 to 45°C. Longevity of the female wasp decreased with increasing temperature. The rate of development increased linearly at temperatures from 17.5 to 35°C, but decreased from 35 to 40°C. Mortality of the developing wasp remained below 20% from 20 to 37.5°C, but outside this range, mortality reached 100% at 15 at 42.5°C. Most parasitization occurred at temperatures of 25 and 30°C. Sex ratio (percentage females) increased with temperature in the high temperature range. The intrinsic rate of increase (r_m) forU. lariophaga was highest in the temperature range from 30 to 37.5°C and was higher than that ofC. maculatus at all temperatures. While the r_m value ofC. maculatus did not vary much at temperatures from 25 to 35°C, the r_m value of the wasp doubled. Relative humidity did not effect longevity, egg-laying capacity, mortality, development time and sex ratio of the wasps withC. maculatus as host. However, withB. atrolineatus as the host, development time and mortality increased at lower relative humidity levels. The results indicate that temperature is the major regulating factor on the parasitoid. As the type of storage structure and its location (sun or shade) affects the temperature inside the store, ways are being investigated of manipulating the storage environment through temperature regulation to increase the impact of the parasitoid.     

Impact of the egg parasitoid Uscana lariophaga and the larval-pupal parasitoid Dinarmus basalis on Callosobruchus maculatus populations and cowpea losses

In West Africa, Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) and Dinarmus basalis (Rondani) (Hymenoptera: Pteromalidae) parasitize the eggs and larvae, respectively, of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae), an important pest of stored cowpea. The impact of the parasitoids on pest populations was evaluated in clay pots similar to the ones used in traditional storage in Niger. At the beginning of the storage period, cowpeas were infested with one density of C. maculatus and with either one or both of the parasitoid species. If the parasitoids we inoculated as single species in stores, both D. basalis and U. lariophaga significantly suppressed the bruchid population, but the former did so more effectively than the latter. A combination of D. basalis and U. lariophaga resulted in the same suppression of bruchid populations as when D. basalis was the only parasitoid. Fifteen weeks after storage, the parasitoids reduced the number of grains damaged significantly by 38–56%. The effect of inoculating single or multiple parasitoid species on C. maculatus populations in an augmentation strategy is discussed.     

Selection of Bemisia nymphal stages for oviposition or feeding,and host-handling times of arrhenotokous and thelytokous <Emphasis Type="Italic">Eretmocerus mundus</Emphasis> and arrhenotokous <Emphasis Type="Italic">E. eremicus</Emphasis>

Host-handling behavior is an important aspect of parasitoid foraging behavior. When a parasitoid encounters a potential host, the handling behavior starts with the evaluation of the host and continues if the host has been judged acceptable. Host handling is usually terminated after egg laying or host feeding and host marking. Host-handling behavior of an arrhenotokous population of two Eretmocerus species, E. mundus Mercet and E. eremicus Rose and Zolnerowich, along with a thelytokous population of E. mundus were compared under laboratory conditions. Several elements of host-handling behavior, including encountering, ascending, turning on host, descending, preening, egg laying, and host feeding were recorded. There were no correlations among the durations of these phases across parasitoid populations/species or host nymphal instars. Duration of different phases of host-handling behavior showed only slight and sometimes significant differences between different Eretmoceruspopulations/species. The actual laying of the egg had the longest duration of all host-handling behaviors, and was longer on third nymphal instars than on younger ones. Females of the three populations/species accepted the first three nymphal stages either for egg laying or for host feeding. Females spent a lot of time to make wounds in the host when preparing for host feeding, and eventually killed the host. The implications of these findings for the use of the different Eretmoceruspopulations/species in biological control are discussed.     

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.     

Egg load of lab-cultured <Emphasis Type="Italic">Anaphes iole</Emphasis> and effects of mate presence and exposure time on load depletion

Anaphes iole Girault (Hymenoptera: Mymaridae) is a solitary egg parasitoid of Lygus bugs (Heteroptera: Miridae) in North America. This research considered factors that might impact the egg load of lab-cultured A .iole females, reared from Lygus hesperus Knight egg patches. The following hypotheses were tested: (1) egg load was related to body size and not affected by female age, and (2) egg load depletion was not affected by mate presence and time (in days) that females were exposed to host patches. Initial egg load averaged 48 mature eggs and no immature eggs were detected in the ovarioles of dissected females. Egg load was neither related to body size (hind tibia or forewing length) nor affected significantly by age (0, 1 or 2days old honey-fed females). Mate presence (females with or without males) and exposure time (1, 3 or 5days on the same host patch) had no effect on egg load depletion. Females usually depleted most of their egg load within 24h. From 86 to 92% of females contained less than six mature eggs and no immature eggs after 1, 3 or 5days of exposure to host patches. The results of this study suggest that A. iole females are certainly pro-ovigenic and initial egg load does not correlate with body size or age. Since mated and unmated females deplete most of their egg load in 24h, time-efficient production of progeny may result when ovipositing parasitoids are exposed to suitable hosts for just a few days.The United States Government has the right to retain a non-exclusive, royalty-free license in and to any copyright of this article. This article reports the results of research only. Mention of a commercial or proprietary product does not constitute an endorsement of the product by the United States Department of Agriculture.     

Analysis of foraging behavior of the whitefly parasitoidEncarsia formosa (Hymenoptera: Aphelinidae) in an experimental arena: A simulation study

Foraging ofEncarsia formosa was analyzed using a stochastic simulation model of the parasitoid's behavior. Parasitoids were allowed to search during a fixed time in an experimental arena with immatures of the greenhouse whitefly,Trialeurodes vaporariorum. The model simulates host searching, selection, and handling behavior and the physiological state (egg load) of the parasitoid. The simulated number of hosts encountered, parasitized, or killed by host feeding agreed well with observations on leaf disks. The hypothesis of random host encounter seems to be correct. The number of ovipositions on the leaf at low host densities was strongly affected by the parasitoid's walking speed and walking activity, the probability of oviposition after encountering a host, and the initial egg load. At high densities, the initial and maximum egg load were most important. A strong temperature effect was found at 18°C or below. The number of encounters, ovipositions, and host feedings increased with host density to a maximum of 25, 6.5, and 1.5, respectively, during 2 h at 25°C. The shape of the curves resembled a Holling Type II, which may be the result of the experimental procedure, where a parasitoid was confined to a patch during a fixed time.     

Specificity of chemical cues used by a specialist egg parasitoid during host location

Plant synomones and host kairomones are known to guide the egg parasitoid Oomyzus gallerucae to its specific host, the elm leaf beetle Xanthogaleruca luteola (= Pyrrhalta) (Muller) feeding upon elm leaves (Ulmus spp.). In this study, we investigated whether the activities of these plant synomones and kairomones are specific for the plant and herbivore species, respectively. Olfactometer and contact bioassays were used. In habitat location, O. gallerucae (Fonscolombe) is known to use synomones from Ulmus minor (Miller) that are induced by egg depositions of X. luteola. The attractiveness of such induced volatiles was shown to be specific both for the Ulmus species and the herbivore species depositing eggs. Neither leaves of U. glabra Hudson (= U. montana) carrying eggs of X. luteola nor leaves of U. minor (= U. campestris = U. procera) carrying eggs of the chrysomelid species Galeruca tanaceti L. emitted attractive synomones. O. gallerucae is also known to be attracted by volatile kairomones from faeces of X. luteola feeding on U. minor and to show prolonged antennal drumming when contacting substrates contaminated with these faeces. The kairomonal activity of the faeces was proved to be independent of the Ulmus species, since also faeces from elm leaf beetles feeding upon U. glabra emitted attractive volatiles. However, the faecal kairomones were specific for the herbivorous species, since faeces from a lepidopteran larva (Opisthograptis luteolata L.) feeding upon elm hardly elicited any antennal drumming in O. gallerucae. The egg parasitoid studied is known to recognize host eggs of X. luteola by contact kairomones extractable from the egg shell. O. gallerucae clearly differentiated between host eggs and eggs of another closely related chrysomelid species, Galerucella lineola L., as was shown by comparing duration of antennal drumming on host eggs and eggs of G. lineola.     

Searching and Oviposition Behavior of Anagrus atomus L. (Hymenoptera: Mymaridae) on Four Host Plants of Its Host, the Green Leafhopper Empoasca decipiens Paoli (Homoptera: Cicadellidae)

Anagrus atomus L. is an important egg parasitoid of the green leafhopper Empoasca decipiens Paoli. In this study the ability of the parasitoid to locate and parasitize its host was investigated on four host plants, i.e., broad beans (Vicia faba L.), sweet pepper (Capsicum annuum L.), cucumber (Cucumis sativus L.), and French beans (Phaseolus vulgaris L.). For each plant species, the behavior of the parasitoid was observed on E. decipiens infested and noninfested plants. Searching and oviposition behavior were characterized by drumming, probing, and resting. Parasitoids spent significantly less time on non-infested than infested plants, 274.5 and 875.7 s, respectively, and no probing behavior was observed on non-infested plants. Frequency of resting behavior was significantly greater on non-infested than on infested plants. Total foraging time was significantly longer on infested than on non-infested plants, indicating that A. atomus females can efficiently discriminate between leaves with and without infestation. Parasitism of A. atomus was influenced by parasitoid density, with the highest parasitism rate (64.0%) obtained at a density of 10 A. atomus females/0.1356 m² but the number of parasitized eggs per female and the searching efficiency decreased with increasing parasitoid density.     

Influence of initial egg density and host size on the development of the gregarious parasitoid <Emphasis Type="Italic">Bracon hebetor</Emphasis> on three different host species

Bracon hebetor (Say) (Hymenoptera : Braconidae) is a gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product and in the field. In this study the effect of host species, size and larval competition on parasitoid size, survival and development were investigated. In laboratory studies, wasp eggs at a range of densities, were placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes orana (Fischer von Röslerstamm, Tortricidae), Plodia interpunctella (Hubner, Pyralidae) and, Lobesia botrana(Dennis & Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low at all densities and different host weights. On L. botrana survival progressively reduced as egg density increased at both host weights examined for this host. Survival on P. interpunctella was significantly affected by egg density but not by host weight. Initial egg density had a significant effect on the size of emerging adults from each rearing host. Smaller adult parasitoids emerged as egg density per larva increased. Larval host weight of P. interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids mainly at the higher egg densities used in these experiments. The above results of host quality on fitness of parasitoid are discussed.     

Foraging Behavior of the Parasitoid Encarsia formosa on Gerbera jamesonii Leaves

Insight into the foraging behavior of the parasitoid Encarsia formosa Gahan for whitefly hosts was gained by continuous observation of individual parasitoids on leaves of the ornamental plant Gerbera jamesonii, until females left the leaf. Comparison of the parasitoid behavior on three cultivars gave similar results. Mean searching time on uninfested G. jamesonii leaves of three cultivars was 1 h 30 min and the mean percentage of walking activity of the total observation time on those cultivars was 61%. Both parameters were not influenced by different leaf structures of Gerbera cultivars. Encounters with hosts arrested the parasitoids on the leaves. The walking activity and the percentage of host encounters that resulted in an oviposition decreased with decreasing egg load of the parasitoid. In comparison with tomato, where biological control of whiteflies is successful, only minor differences in the foraging behavior occur, except for the residence time of females, which was about three to four times longer on G. jamesonii leaves, but these leaves are about seven times larger than tomato leaves. The facts that (1) the foraging behavior of E. formosa on G. jamesonii is independant of the cultivar and (2) the foraging behavior is, in many aspects, similar to that on tomato suggest that biological control of whitefly on this ornamental plant is a potential option.     

Mortality by parasitization in the association between the egg-pupal parasitoid Fopius arisanus and Ceratitis capitata

We studied the interaction betweenthe egg-pupal parasitoid Fopius (+ Biosteres) arisanus (Sonan) (+Opius oophilus Fullaway) (Hymenoptera: Braconidae) and Ceratitis capitata (Wiedemann)(Diptera: Tephritidae) to assess the totalimpact of the parasitoid on the survival ofthis host. We tried to discover the factorsdetermining host suitability, measure actualpercent parasitism, and quantify host mortalityby parasitization. Research was carried outapplying dechorionation treatment, anon-destructive procedure that makes hosteggshells transparent to microscopicobservation, without interfering withdevelopment. We found that percent parasitismobserved at the egg stage did not correspond tothat detectable for emerging adults. In fact,parasitized host eggs were subject to a highermortality than non-parasitized ones. Moreover,a certain percentage of the parasitoid eggs didnot develop to the adult stage. Results fromour study allowed us to measure the percentmortality by parasitization per parasitizedegg. Furthermore, we analyzed the mortalityfactors due to parasitization acting during thehost egg stage. Most of them had never beenevidenced before and may help to explain thisphenomenon. In particular, we found that theage of the host eggs exposed to parasitoidsplays a fundamental role in the mortality byparasitization and that F. arisanusparasitizes C. capitata eggs moreefficiently close to the time of eclosion.     

Superparasitism in the solitary ectoparasitoid Aptesis nigrocincta: the influence of egg load and host encounter rate

Theory predicts that the acceptance of hosts already parasitized by a conspecific will depend both on egg load and the availability of hosts. In the present laboratory study, we tested the effect of egg load and host encounter rate on the propensity of superparasitism in the solitary parasitoid Aptesis nigrocincta Gravenhorst (Hymenoptera, Ichneumonidae), a synovigeneous ectoparasitoid of prepupae of the European Apple Sawfly. Parasitoid females carry few voluminous eggs at a time and the egg maturation rate is less than one egg per day. Egg load was manipulated by giving females access to hosts one week prior to the start of treatments and host availability by giving females access to either one host cocoon every day or every other day. In the first treatment where females had a high egg load of 5.3 egg in their ovaries and encountered host cocoons at low rates, we found that parasitized hosts were accepted to the same degree as healthy hosts. In females with significantly decreased egg load (3.8 eggs) encountering hosts at the same rate we found a slight but non-significant decrease in the acceptance of parasitized hosts compared with healthy hosts. In contrast, A. nigrocincta females accepted significantly fewer parasitized hosts at a high host encounter rate that would lead them to the point of egg limitation in the near future. Within the range of egg loads tested, the host encounter rate appears to be the most important determinant for a females decision to oviposit onto hosts already parasitized by a conspecific.     

Catching Ariadne by her thread: how a parasitoid exploits the herbivore's marking trails to locate its host

Chemical signals that can be associated with the presence of a host insect often work as arrestants in close range host location by parasitoids, leading to longer searching times on patches where such signals are present. Our current view of parasitoid host location is that by prolonging the search times in patches, randomly searching parasitoids enhance their chance of detecting host insects. However, prolonged search times are not necessarily the only modification in parasitoid behaviour. In this study, we examine the exploitation of host-fruit marking pheromone of rose-hip flies, Rhagoletis basiolaOsten-Sacken (Diptera: Tephritidae) by the specialized egg-larval parasitoid Halticoptera rosae Burks (Hymenoptera: Pteromalidae). We provide evidence that the instantaneous probability that a host egg will be located by a searching parasitoid wasp differs markedly between pheromone-marked and unmarked fruits. The arresting response to the marking pheromone, i.e., the prolonged time a wasp is willing to search on marked fruits, can only account for a small fraction of the difference in successful host location on marked and unmarked fruits. We further demonstrate that the time wasps require to locate the host egg is independent of the size of the rose-hip harbouring the fly egg, and thus is independent of the area the wasp potentially has to search. A comparison of our findings with results of different search algorithms for parasitoid wasps suggests that wasps use the fly's pheromone marking trail as a guide way to the fly's oviposition site and thus the host egg.     

Effect of larval host food substrate on egg load dynamics, egg size and adult female size in four species of braconid fruit fly (Diptera: Tephritidae) parasitoids

Life history theory predicts that individuals will allocate resources to different traits so as to maximize overall fitness. Because conditions experienced during early development can have strong downstream effects on adult phenotype and fitness, we investigated how four species of synovigenic, larval-pupal parasitoids that vary sharply in their degree of specialization (niche breadth) and life history (Diachasmimorpha longicaudata, Doryctobracon crawfordi, Opius hirtus and Utetes anastrephae), allocate resources acquired during the larval stage towards adult reproduction. Parasitoid larvae developed in a single host species reared on four different substrates that differed in quality. We measured parasitoid egg load at the moment of emergence and at 24 h, egg numbers over time, egg size, and also adult size. We predicted that across species the most specialized would have a lower capacity to respond to changes in host substrate quality than wasps with a broad host range, and that within species, females that emerged from hosts that developed in better quality substrates would have the most resources to invest in reproduction. Consistent with our predictions, the more specialized parasitoids were less plastic in some responses to host diet than the more generalist. However, patterns of egg load and size were variable across species. In general, there was a remarkable degree of reproductive effort-allocation constancy within parasitoid species. This may reflect more “time-limited” rather than “egg-limited” foraging strategies where the most expensive component of reproductive success is to locate and handle patchily-distributed and fruit-sequestered hosts. If so, egg costs, independent of degree of specialization, are relatively trivial and sufficient resources are available in fly larvae stemming from all of the substrates tested.     

Biology and field performance of gryon clavigrallae (Hymenoptera: Scelionidae), an egg parasitoid of Clavigralla spp. (Hemiptera: Coreidae) in India

The biology and impact of Gryon clavigrallae Mineo, an egg parasitoid of Clavigralla scutellaris Spinola and C. gibbosa (Westwood), was investigated. The calculated developmental threshold temperatures for females and males were 15.6 degrees C and 15.8 degrees C, respectively. Emergence exceeded 94% at temperatures between 22 and 30 degrees C. Adult females lived on average 28-96 days when fed with honey. Without food, adults lived < 6 days. Mean fecundity was 56.4 eggs per female. A significant trend of lower fecundity after longer periods of host deprivation was observed. Gryon clavigrallae females successfully oviposited in host eggs of all ages though eggs < 4 days old were preferred. Total host handling times were significantly longer on C. gibbosa eggs (23.5 min) than on C. scutellaris eggs (12.0 min). Females readily distinguished parasitized from non-parasitized host eggs. Superparasitism was observed when few or no unparasitized eggs were available. Eggs of the two Clavigralla species can be separated by surface structure and condition after eclosion. Clavigralla scutellaris laid significantly larger egg clusters than C. gibbosa (19.9 versus 10.5 eggs per cluster). Gryon clavigrallae was present as soon as the first Clavigralla spp. egg clusters were found on pigeonpea. The percentage of egg clusters parasitized increased early in the season with egg cluster density and remained high (up to 83%) despite fluctuations in host density. Overall, G. clavigrallae parasitized 40 and 58% of C. gibbosa and C. scutellaris eggs. The percentage of egg clusters parasitized and the number of eggs parasitized per cluster increased significantly with egg cluster size. The overall parasitoid sex ratio was highly female biased but varied with the number of eggs parasitized per cluster.