Females of the European beewolf preserve their honeybee prey against competing fungi

1. Females of the European beewolf Philanthus triangulum (Hymenoptera, Sphecidae) provision brood cells with paralysed honeybees as larval food. Because brood cells are located in warm, humid locations there is a high risk of microbial decomposition of the provisions. Low incidence of fungus infestation (Aspergillus sp.) in nests in the field suggested the presence of an anti‐fungal adaptation. 2. To test whether the paralysis caused the protection from fungus infestation, the timing of fungus growth on bees that were freeze‐killed, paralysed but not provisioned, and provisioned regularly by beewolf females was determined. Fungus growth was first detected on freeze‐killed bees, followed by paralysed but not provisioned bees. By contrast, fungus growth on provisioned bees was delayed greatly or even absent. Thus, paralysis alone is much less efficient in delaying fungus growth than is regular provisioning. 3. Observations of beewolves in their nests revealed that females lick the body surface of their prey very thoroughly during the period of excavation of the brood cell. 4. To separate the effect of a possible anti‐fungal property of the brood cell and the licking of the bees, a second experiment was conducted. Timing of fungus growth on paralysed bees did not differ between artificial and original brood cells. By contrast, fungus growth on bees that had been provisioned by a female but were transferred to artificial brood cells was delayed significantly. Thus, the treatment of the bees by the female wasp but not the brood cell caused the delay in fungus growth. 5. Beewolf females most probably apply anti‐fungal chemicals to the cuticle of their prey. This is the first demonstration of the mechanism involved in the preservation of provisions in a hunting wasp. Some kind of preservation of prey as a component of parental care is probably widespread among hunting wasps and might have been a prerequisite for the evolution of mass provisioning.     

The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

Habitat structure components are effective predictors of trap-nesting Hymenoptera diversity

Habitat heterogeneity can be the major factor affecting species diversity in a community and measuring bee and wasp community habitat preferences in natural systems may provide insights for biodiversity management and conservation. In the present study, we investigate the effects of habitat structure components on solitary bee and wasp species richness and abundance. The research was conducted in an urban forest remnant in southeast Brazil. Our main questions were: (1) is similarity in habitat structure mirrored by similarity in Aculeate assemblage composition? and (2) what are the vegetation features that could be used as predictors of solitary bee and wasp richness and abundance? Aculeate bees and wasps were sampled using trap nests from February to November 2004. Trap nests were placed in sampling units located in 6 ha of secondary mesophytic forest. One hundred and thirty-seven trap nests were occupied by four species of wasps and seven species of bees. Altogether, our sampling units had a mean capture rate (relative to expected richness) of 72% during all the study period. The more similar sampling units were in terms of vegetation structure, the more similar they were in solitary bee and wasp species composition. The variance of tree abundance, shrub height and the abundance of wood logs were good predictors of solitary bee and wasp species richness and abundance in the study area. We demonstrate that even in a small scale it is possible to detect significant influences of habitat features on alpha diversity and that some of them are effective as predictors of trap-nesting Hymenoptera richness and abundance.     

Comparison of two Mediterranean crop systems: Polycrop favours trap-nesting solitary bees over monocrop

Landscape, in terms of crop diversity, together with spatial heterogeneity, connectivity and the proportion of natural elements all play a key role in the quality of the agricultural matrix. The abundant resources derived from the high productivity associated with cultivated lands within agricultural landscapes – formed by mosaics comprising small elements and systems of low agricultural intensity – may favour the populations and communities of certain insect species.Here, trap-nesting solitary bees have been studied to evaluate the effect of two Mediterranean crop systems: monocrops (vineyard and cereal) and polycrops (mixed vegetable crop) for two levels of farming intensity (high-intensity vs. low-intensity) on brood cells and emergent progeny of the bee population and community species richness.Polycrops proved favourable compared to monocrops, with the former proving particularly favourable for offspring production (brood cells and emergent progeny) of bees belonging to the genus Osmia. Bee populations, especially polylectic species, may benefit from the traits characterizing this polycrop, which provide plentiful and diverse resources both in space and time. Farming intensity, regardless the crop type, is also an important factor affecting bee community structure. Low farming intensity maintains essential semi-natural habitats providing shelter for species-rich communities. Crop richness, together with low farming intensity would provide heterogeneous landscapes with a variety of natural and cultivated resources, benefitting trap-nesting bee populations.     

Comparison of social and solitary nesting carpenter bees in sympatry reveals no advantage to social nesting

Facultatively social bees allow for comparisons of social and solitary behaviour under similar environmental conditions. When such bees are polymorphic within the same population it provides a special and somewhat unusual opportunity to examine factors leading to cooperative (social) behaviours where many parameters such as environment are not variable. Some species of bees in the genus Xylocopa offers such opportunities. Studies of these bees often point to guarding and resource limitation as factors leading to social nesting. The large carpenter bee Xylocopa virginica L. (Hymenoptera: Apidae) is one species that exhibits both solitary and social nesting behaviour within the same populations. This paper first compares social and solitary nests in an Ontario population of X. virginica to determine if there is a reproductive advantage to social nesting. Following this, a series of possible explanations for social nesting, and the roles of females in social nests are examined. Social nests have similar brood sizes to solitary nests and productivity as a function of colony size is reduced with increasing number of foundresses. Additional foundresses are not effective guards, do not prevent parasitism, do not likely perform significant work, and do not assume foraging with the loss of a primary foundress. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 998–1010.     

Maternal investment and size-number trade-off in a bee, Megachile apicalis, in seasonal environments

Maternal investment in offspring size and number differed between spring- and summer-emerging individual females of Megachile apicalis, a solitary multivoltine bee. Data from experimentally initiated female populations indicated that spring-emerging females produced a relatively large number of progeny but allocated a small amount of food to each, resulting in small progeny. Adult females of larger body sizes provisioned food at a greater rate than did smaller females, and this body-size effect was significant in spring-emerging females. The large body size of these females allowed them to increase the number of progeny produced under the abundant floral resources that occurred during the spring. Conversely, summer-emerging females produced fewer progeny under the diminishing resources for brood production, but allocated each with more food, producing larger progeny, most of which emerged in the spring of the following year. Field data using trap-nests also indicated the same pattern of seasonal offspring size allocation found in the experimental populations. This maternal investment strategy entails a trade-off between the size and number of progeny, so that the daughters upon emergence can best perform in their brood production under the seasonally variable environments where they reproduce.     

Contrasting Patterns of Species Richness and Composition of Solitary Wasps and Bees (Insecta: Hymenoptera) According to Land‐use

Several species of arthropods inhabiting forest fragments interact with managed areas. The importance of such areas to biodiversity conservation, however, is not well established. Communities of solitary wasps and bees (Insecta: Hymenoptera) play a key role in agroecosystem functioning and they have been used in studies of biodiversity assessment in different land‐use types. We aimed to assess patterns of species richness and composition of solitary wasps and bees over a 1‐yr period in a gradient of decreasing land‐use intensity formed by pastures, alley croppings, young fallows, and old fallows using trap nests. Old fallows had the highest species richness of wasps and bees, harboring all bee species and 86 percent of wasp species occurring in the region, while the remaining land‐uses had similar species richness. Vegetation structure (tree richness) and relative humidity explained most of the variance for the species richness of wasps. For bees, however, there was no influence of environmental factors on the community among land‐use types, indicating better adaptability of this group to environmental variations related to land‐use. The composition of solitary wasp communities (but not those of bees) differed among land‐use types, and the occurrence of rare species in most cases was restricted to old fallow sites. In conclusion, the community of solitary wasps and bees is contingent on land‐use, with solitary wasps more sensitive to anthropized areas. For both groups, less anthropized areas harbor a greater richness and number of rare species while more intensively managed land‐use types harbor higher abundances.     

Efficacy of strips coated with Metarhizium anisopliae for control of Varroa destructor (Acari: Varroidae) in honey bee colonies in Texas and Florida

Strips coated with conidia of Metarhizium anisopliae (Metschinkoff; Deuteromycetes: Hyphomycetes) to control the parasitic mite, Varroa destructor (Anderson and Trueman) in colonies of honey bees, Apis mellifera (Hymenoptera: Apidae) were compared against the miticide, tau-fluvalinate (Apistan) in field trials in Texas and Florida (USA). Apistan and the fungal treatments resulted in successful control of mite populations in both locations. At the end of the 42-day period of the experiment in Texas, the number of mites per bee was reduced by 69-fold in bee hives treated with Apistan and 25-fold in hives treated with the fungus; however mite infestations increased by 1.3-fold in the control bee hives. Similarly, the number of mites in sealed brood was 13-fold and 3.6-fold higher in the control bee hives than in those treated with Apistan and with the fungus, respectively. Like the miticide Apistan, the fungal treatments provided a significant reduction of mite populations at the end of the experimental period. The data from the broodless colonies treated with the fungus indicated that optimum mite control could be achieved when no brood is being produced, or when brood production is low, such as in the early spring or late fall. In established colonies in Florida, honey bee colony development did not increase under either Apistan or fungal treatments at the end of the experimental period, suggesting that other factors (queen health, food source, food availability) play some major role in the growth of bee colonies. Overall, microbial control of Varroa mites with fungal pathogens could be a useful component of an integrated pest management program for the honey bee industry.     

On a habitat structure-based approach to evaluating species occurrence: cavity-nesting Hymenoptera in a secondary tropical forest remnant

Measuring bee and wasp community habitat preferences in natural systems may provide insights for biodiversity management and conservation as habitat heterogeneity can be the major factor affecting species diversity in a community. Here, we present evidence that supports the use of a vegetation structure-based approach in order to predict the occurrence of common Brazilian-remnant solitary bee and wasp species. Using trap nests, we sampled Aculeate bees and wasps in a forest remnant within an urban area of southeast Brazil. We also measured eight habitat structure components in the area. Tree trunk circumference, shrub and wood log abundance were good predictors of presence or absence of the commonest solitary bee and wasp species in the study area. We demonstrated that even on a small scale it is possible to detect significant influences of habitat structural features on species occurrences and that some of them are effective as surrogates for predicting trap-nesting Hymenoptera occurrence in a given area. Our data present evidence on the potential application of a habitat structure-based approach in conservation assessments concerning cavity-nesting Hymenoptera. We caution, however, that this habitat structure-based approach must to be taken with prudence as a detailed survey of an area’s biodiversity is always preferable.     

Environmental influences on flight activity of USDA-ARS Russian and Italian stocks of honey bees (Hymenoptera: Apidae) during almond pollination

Differences in flight activity and in the percentages of pollen foragers between commercially managed honey bees, Apis mellifera L. (Hymenoptera: Apidae), of two stocks (USDA-ARS Russian, n = 41 colonies; and Italian, n = 43 colonies) were evaluated in an almond, Prunus dulcis (Miller) D. A. Webb, orchard in Kern Co., CA, during February and March 2002. Flight activity was measured by taking 1-min counts of bees exiting colonies on each of 9 d. Flight activity was best predicted with a model containing the effects of colony size (populations of adult bees and sealed brood), temperature, time of day, the interaction of adult bee population with temperature, and the interaction of adult bee population with time of day. Flight increased linearly with adult bee and brood population, had a quadratic relationship with temperature (increasing, but less so at higher temperatures), and had a quadratic relationship with time of day (decreasing, but less so at later times). Larger colonies had more response to changing temperatures and less response to different times of day than small colonies. Bee type had no direct influence on flight activity at any given colony size, temperature, or time of observation or when evaluated using a reduced data set retaining 34 Italian colonies and 32 Russian colonies whose mean sizes were equal. Overall, however, Russian colonies were less populous by about one-fourth and so fielded on average 71% of the foragers that Italian colonies did. Pollen collection was measured by capturing returning foragers on 4 d. The percentages of foragers with pollen were not different for the bee types.     

Biology of Lysiphlebus fabarum following cold storage of larvae and pupae

Cold storage is one means of preserving parasitoids prior to release in augmentation biological control programs. This study examined the feasibility of storing larval and pupal stages of a sexual population of Lysiphlebus fabarum Marshall (Hymenoptera: Braconidae: Aphidiinae) at 6 ± 1 and 8 ± 1 °C, 50–60% r.h., and L14:D10 photoperiod. These life stages were stored for periods of 1, 2, and 3 weeks under fluctuating thermal regimes (2 h daily at 21 ± 1 °C). Generally, pupae gave better results than larvae, and 6 °C was better than 8 °C, considering wasp survival, wasp size (tibial and antennal lengths), egg load, and egg size. The best results were obtained with pupae stored for 2 weeks under a fluctuating temperature regime at 6 °C. Females emerging from this treatment did not differ from controls (developing directly at 21 °C) in body size, egg size, or progeny sex ratio, and suffered less than 20% mortality. Egg loads were reduced in these wasps, but the reductions were substantially less than occurred in other 2‐week‐storage treatments. Wasps stored in this manner successfully parasitized similar numbers of aphids as controls and produced similar progeny sex ratios. These results reveal a suitable set of low‐temperature conditions that can be used to delay the development of L. fabarum for 2 weeks with minimal impact on wasp fitness.     

The power and efficiency of brood incubation in queenless microcolonies of bumble bees (Bombus terrestris L.)

1. Ground‐nesting colonies of bumble bees incubate their brood at > 30 °C if floral forage provides sufficient energy and the thermogenic power of the colony can counteract cool soil conditions. To explore the basis of incubation, the thermogenic power and sugar consumption of orphaned nests of bumble bee workers (microcolonies) were investigated under laboratory conditions. 2. This study tested experimentally the effect of variation in worker number (ranging from four to 12 adults) on a microcolony's capacity to regulate brood temperature and recover from acute cold exposure. Microcolonies were provided with ad libitum sugar syrup and minimal insulation and maintained at an ambient temperature of c. 25 °C. Energy conversion efficiency was estimated by comparing sugar consumption with the power required for artificial incubation. The joint energetics of foraging and incubation were modelled in wild colonies to explore the effect of colony size and landscape quality on thermoregulation. 3. The results showed that all sizes of microcolonies regulated brood temperature at c. 31 °C under laboratory conditions, which required 96 mW of thermogenic power. It was estimated that individual workers of B. terrestris generated an incubatory power of 35 mW. The smallest microcolonies had the highest conversion efficiency (57%), apparently because few workers were required for incubation. 4. Modelling indicated that small microcolonies of three to seven adult workers have the capacity for normal brood incubation in the wild, but that the minimum viable colony size increases as floral forage becomes poorer or more distant. 5. These preliminary findings suggest the feasibility of identifying the minimum conditions (forage quality, soil temperature, and colony size) necessary for brood incubation by queenright colonies in the wild.     

Availability and depletion of fat reserves in halictid foundress queens with a focus on solitary nest founding

Foundress queens of social Hymenoptera require considerable amounts of energy for survival, solitary nest founding, provisioning of the first brood, and egg production. Energy reserves in insects mostly consist of fat. We investigated how hibernation and the subsequent flight season, especially the solitary nest founding phase, influenced the abdominal fat content of gynes in the primitively eusocial sweat bee, Lasioglossum malachurum (Hymenoptera, Halictidae). In our study population, sexuals are produced in both the second and the third broods. Emerging gynes of the third brood had significantly more fat than those of the second brood, whereas there was no such difference in males. As expected, fat reserves in samples of female sexuals caught at emergence, after hibernation, during solitary nest founding, and at the end of the social phase of the nest cycle indicate a severe decrease of reserves that was highest during the 7 weeks of the solitary founding phase. Thus, the amount of fat reserves of foundress queens seems to be crucial, particularly for nest founding. However, investment of energy reserves in the solitary nest founding phase has probably to be balanced with the subsequent social phase in a way that maximizes the queen’s fitness. Possible consequences for the complexity and progress of the nest cycle are discussed.     

Multitrophic effects of experimental changes in plant diversity on cavity-nesting bees, wasps, and their parasitoids

Plant diversity changes can impact the abundance, diversity, and functioning of species at higher trophic levels. We used an experimental gradient in grassland plant diversity ranging from 1 to 16 plant species to study multitrophic interactions among plants, cavity-nesting bees and wasps, and their natural enemies, and analysed brood cell density, insect diversity (species richness), and bee and wasp community similarity over two consecutive years. The bee and wasp communities were more similar among the high (16 species) diversity plots than among plots of the lower diversity levels (up to 8 species), and a more similar community of bees and wasps resulted in a more similar community of their parasitoids. Plant diversity, which was closely related to flower diversity, positively and indirectly affected bee diversity and the diversity of their parasitoids via increasing brood cell density of bees. Increasing plant diversity directly led to higher wasp diversity. Parasitism rates of bees and wasps (hosts) were not affected by plant diversity, but increased with the diversity of their respective parasitoids. Decreases in parasitism rates of bees arose from increasing brood cell density of bees (hosts), whereas decreasing parasitism rates of wasps arose from increasing wasp diversity (hosts). In conclusion, decreases in plant diversity propagated through different trophic levels: from plants to insect hosts to their parasitoids, decreasing density and diversity. The positive relationship between plant diversity and the community similarity of higher trophic levels indicates a community-stabilising effect of high plant diversity.     

Adult pollen diet essential for egg maturation by a solitary Osmia bee

Reproduction is a nutritionally costly activity for many insects, as their eggs are rich in lipids and proteins. That cost seems especially acute for non-social bees, which for their size, lay enormous eggs. All adult female bees visit flowers, most of them to collect pollen and nectar, or sometimes oils, to feed their progeny. For adult bees, the need for pollen feeding has only been detailed for the honey bee, Apis mellifera. To experimentally test for the reproductive value of adult pollen feeding by a non-social bee, Osmia californica (Hymenoptera: Apiformes: Megachilidae), young female bees plus males were released into large glasshouse cages provided with either a male-fertile sunflower cultivar or a pollen-less one. Females regularly visited and drank nectar from flowers of both cultivars. Abundant orange pollen was seen regularly in guts of females confined with the male-fertile sunflowers, indicative of active pollen ingestion. All females’ terminal oocytes (next egg to be laid) were small at emergence. Oocytes of females confined with the pollen-less sunflowers remained small, despite frequent nectaring and exposure to other floral stimuli. In contrast, the basal oocytes of female O. californica with access to pollen had swelled to full size within ten days following emergence, enabling them to lay eggs in provided nest tubes. Adult females of this solitary bee required dietary pollen to reproduce; nitrogen stores acquired as larvae were inadequate. Early and regular pollen feeding in part paces the onset and maximum tempo of solitary bees’ lifetime reproductive output.     

Effects of a neonicotinoid pesticide on thermoregulation of African honey bees (Apis mellifera scutellata)

Thiamethoxam is a widely used neonicotinoid pesticide that, as agonist of the nicotinic acetylcholine receptors, has been shown to elicit a variety of sublethal effects in honey bees. However, information concerning neonicotinoid effects on honey bee thermoregulation is lacking. Thermoregulation is an essential ability for the honey bee that guarantees the success of foraging and many in-hive tasks, especially brood rearing. We tested the effects of acute exposure to thiamethoxam (0.2, 1, 2 ng/bee) on the thorax temperatures of foragers exposed to low (22 °C) and high (33 °C) temperature environments. Thiamethoxam significantly altered honey bee thorax temperature at all doses tested; the effects elicited varied depending on the environmental temperature and pesticide dose to which individuals were exposed. When bees were exposed to the high temperature environment, the high dose of thiamethoxam increased their thorax temperature 1–2 h after exposure. When bees were exposed to the low temperature, the higher doses of the neonicotinoid reduced bee thorax temperatures 60–90 min after treatment. In both experiments, the neonicotinoid decreased the temperature of bees the day following the exposure. After a cold shock (5 min at 4 °C), the two higher doses elicited a decrease of the thorax temperature, while the lower dose caused an increase, compared to the control. These alterations in thermoregulation caused by thiamethoxam may affect bee foraging activity and a variety of in-hive tasks, likely leading to negative consequences at the colony level. Our results shed light on sublethal effect of pesticides which our bees have to deal with.     

An overview of proximate factors affecting the nesting behavior of solitary wasps and bees (Hymenoptera: Aculeata) in preexisting cavities in wood

Guilds of Aculeate solitary wasps and bees that nest in preexisting cavities in wood are important components of terrestrial ecosystems because they engage in several ecological interactions (e.g. predation and pollination) with other species of plants and animals. Spatial and temporal variations in richness and abundance of solitary wasps and bees can be related to changes in environmental structure and in the diversity of other groups of organisms. The nesting period of these Aculeata is their most critical life cycle stage. Females of solitary wasp and bee species invest relatively more time constructing and provisioning their nests than do females of social species. Differently from species that nest in the soil or construct exposed nests, the main factors affecting the reproductive success of solitary species nesting in preexisting wood holes are still unknown. Our objective is to provide an overview of the role of proximate causes of nesting failure or success among solitary wasps and bees (Aculeata), for designing effective conservation and management strategies for these Hymenoptera.     

Fitness consequences of ecological constraints and implications for the evolution of sociality in an incipiently social bee

Ecological constraints such as resource limitation, unfavourable weather conditions, and parasite pressure have long been considered some of the most important selective pressures for the evolution of sociality. In the present study, we assess the fitness consequences of these three ecological factors on reproductive success of solitary nests and social colonies in the socially polymorphic small carpenter bee, Ceratina australensis, based on 982 nests collected over four reproductive periods. Nest site limitation was predicted to decrease opportunities for independent nest initiation and increase the frequency of social nesting. Nest sites were not limiting in this species and the frequency of social nesting was consistent across the four brood‐rearing periods studied. Unfavourable weather was predicted to lower the frequency of female dispersal from their natal nests and to limit the brood‐rearing season; this would increase the frequency and fitness of social colonies. Daily temperature and precipitation accumulation varied between seasons but were not correlated with reproductive success in this bee. Increased parasite pressure is predicted to increase the frequency and fitness of social colonies because solitary bees must leave the nest unattended during foraging bouts and are less able to defend the nest against parasites. Severe parasitism by a chalcid wasp (Eurytoma sp.) resulted in low reproductive success and total nest failure in solitary nests. Social colonies had higher reproductive success and were never extirpated by parasites. The high frequency of solitary nests suggests that this is the optimal strategy. However, social colonies have a selective advantage over solitary nesting females during periods of extreme parasite pressure, and we suggest that social nesting represents a form of bet‐hedging against unpredictable fluctuations in parasite number. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 57–67.     

How can cleptoparasitic drosophilid flies emerge from the closed brood cells of the red Mason bee?

Aculeate Hymenoptera provision their progeny with large amounts of food. To protect their investment against brood parasites, females of many bee and wasp species construct brood cells that are hard to penetrate when finally sealed. However, the sealed brood cells also pose a problem for parasites that oviposit in the brood cell during provisioning. Brood parasites are smaller than their host and may lack strong mandibles to break through the solid brood cell walls. Furthermore, in nests built in existing cavities, newly‐eclosed brood parasites need information about the location of the nest entrance. In the present study, the mechanisms of emergence are investigated in Cacoxenus indagator Loew (Diptera, Drosophilidae), the major cleptoparasite in nests of the red Mason bee Osmia bicornis L. (Hymenoptera, Megachilidae). Larvae of C. indagator move to brood cells closer to the nest entrance and sometimes make small emergence holes in the final closure of the nest entrance. Nevertheless, approximately one‐third of newly‐eclosed flies orientate and break through at least one intact cell partition to emerge. Flies make most of their attempts to emerge at the correct side (i.e. the one pointing to the nest entrance, probably by using the shape of the cell partition as a cue). Newly‐eclosed flies use their head blister (ptilinum) to exert hydraulic pressure on particles of the cell partitions and produce small holes. Thus, C. indagator exhibits a set of behavioural and physiological adaptations enabling them to successfully emerge even from closed brood cells of their host.     

Determination of the optimal parasitoid‐to‐host ratio for efficient mass‐rearing of the parasitoid,Sclerodermus pupariae (Hymenoptera: Bethylidae)

Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) is used as a potential biocontrol agent for several buprestid and cerambycid larvae. This study aimed to enhance the efficiency of mass‐rearing of this parasitoid by investigating the fitness gain of this bethylid wasp, including the proportion of successful parasitism and development, brood size, sex ratio, proportion of winged female offspring, body size and longevity of female offspring, under eight different maternal parasitoid density treatments using Thyestilla gebleri Faldermann as host in the laboratory. The results indicated that the foundress densities did not affect the parasitism or emergence rate of this parasitoid. Brood size of the parasitoids increased significantly when the number of maternal wasps ranged from one to four. However, further increases in foundress number did not affect the parasitoid brood size. The sex ratios of S. pupariae were always female‐biased. The proportions of male in the progeny colonies were <10% throughout all experimental treatments. The percentage of winged female progeny was not significantly influenced by the density of adult maternal parasitoids. Body sizes of parasitoids significantly declined with increasing maternal parasitoid densities. Although the parasitoid body size reduced when maternal wasp number was higher, it could be compromised by the relatively higher number of female offspring produced. Further, more than 70% of the parasitoids remained alive when they were stored at 12°C for four months throughout the experiments. These findings suggest that exposure of four female wasps to a single host larva would result in the highest fitness of S. pupariae. Our findings might provide a new approach to enhance the efficiency of mass‐rearing of this bethylid wasp.