Subtle morphological changes in the visual and antennal sensory system of bees and wasps across an urbanisation gradient

Increased temperature and fragmentation of green spaces in urban areas could drive variations in functional traits of insects. Such morphological shifts may occur for sensory systems, which were previously reported to be prone to change with habitat characteristics in non-urban contexts. Here, we measured traits related to the visual and antennal sensory systems in the bees Halictus scabiosae and Osmia cornuta and the wasp Polistes dominula along an urbanisation gradient within Milan (Italy). We hypothesised that fragmentation could filter for better visual properties, and that higher temperature could filter for fewer thermoreceptors and more olfactory hairs. While controlling for body size, results show subtle but appreciable responses to urbanisation in one or more traits in all species, though not always supporting our hypotheses. O. cornuta shows marginally higher ommatidia density and smaller ommatidia diameter (associated with better visual resolution) in more fragmented sites, as well as marginally fewer thermoreceptors in hotter sites, in agreement with our two predictions. On the other hand, H. scabiosae has marginally smaller antennae and P. dominula has smaller eyes at warmer locations, and the wasp also has smaller antennae and 9th flagellomeres in more fragmented areas. Perhaps higher temperatures accelerate development of sensory system at higher speed than the rest of body in these two species. Our results represent the first evidence of urbanisation effects on the visual and antennal sensory systems of bees and wasps and underline how such effects may involve a much broader bouquet of traits then previously observed.

Parasitic and predatory behavior of Alysia manducator (Hymenoptera: Braconidae) on blow fly larvae feeding on an adult pig carcass in the Western Cape Province of South Africa: preliminary observations and forensic implications

Wasps are part of the entomofauna associated with vertebrate carrion. They are known to parasitize and prey on specific life stages of insect hosts such as eggs, larvae, pupae, and/or adults associated with vertebrate carrion. However, reports of parasitic behavior of wasps on carrion-associated insect life stages and their possible forensic implications are non-existent in the Western Cape Province of South Africa. This study is part of ongoing research investigating the entomofauna and their pattern of succession on an adult pig carcass in Cape Town, South Africa. During this study, the parasitic wasp Alysia manducator was noted parasitizing and preying on blow fly larvae associated with the decomposing carcass. The arrival of A. manducator coincides with the occurrence of blow fly eggs and/or larvae on the carcass. These wasps were seen in close association with the eggs and larvae of blow flies on various parts of the carcass and some wasps were seen dragging fly larvae attached to their ovipositors away from one part of the carcass to another. Some A. manducator were also observed walking over several larvae on the carcass while exhibiting a stabbing behavior presumably in search of a host for oviposition. We suggest that the observations recorded in this study are of considerable forensic importance as the dragging effect and predatory and stabbing behavior exhibited by A. manducator could potentially disrupt the feeding and development of the fly larvae on the carcass. This could subsequently alter the process of carcass decomposition and/or affect minimum post-mortem interval estimations.

Widespread distribution of honey bee-associated pathogens in native bees and wasps: Trends in pathogen prevalence and co-occurrence

Pollinators have experienced significant declines in the past decade, in part due to emerging infectious diseases. Historically, studies have primarily focused on pathogens in the Western honey bee, Apis mellifera. However, recent work has demonstrated that these pathogens are shared by other pollinators and can negatively affect their health. Here, we surveyed honey bees and 15 native bee and wasp species for 13 pathogens traditionally associated with honey bees. The native bee and wasp species included 11 species not previously screened for pathogens. We found at least one honey bee-associated pathogen in 53% of native bee and wasp samples. The most widely distributed and commonly detected pathogens were the microsporidian Nosema ceranae, the bacterium Melissococcus plutonius, and the viruses deformed wing virus and black queen cell virus. The prevalence of viruses was generally higher in honey bees than in native bees and wasps. However, the prevalence of M. plutonius and the brood fungus Ascosphaera apis was significantly higher in some native bee species than in honey bees. The data also reveal novel trends in the association between co-occurring pathogens in honey bees and native bees and wasps at the pathogen community level. These results can inform the assessment of risks that native pollinator species face from pathogen stress, and indicate that many non-viral pathogens, notably M. plutonius and N. ceranae, are far more widely distributed and commonly found in native bees and wasps than previously thought.

The transmittable through stinging microbiota differs between honeybees and wasps: a potentially greater microbial risk of the wasp sting for humans

The present research investigated whether accidental contact through stinging with honeybees, wasps, and hornets could represent a microbial hazard for humans. It has been previously suggested that such contact may transmit pathogens causing infections that could even be fatal for some susceptible individuals. Stinging simulation experiments were performed in the lab with live insects collected from the environment in Lemnos Island (north-eastern Greece), while different selective agar media targeting some clinically important bacteria (i.e., Staphylococcus aureus, Streptococcus pyogenes, Enterococcus faecalis/faecium, and Pseudomonas aeruginosa) were used as substrates for microbial recovery and identification. Results revealed none of the target pathogenic bacterial species in the honeybee samples, with bacilli, staphylococci, and micrococci dominating their surveyed microbiota. However, most of the suspect colonies isolated from wasps and hornets belonged to important hygienic indicators (i.e., enterococci, Proteus mirabilis, and coliforms), implying possible contact of these insects with fecal origin materials. To sum up, the microbiota that may be transmitted to humans through stinging appears to differ between honeybees and wasps/hornets, while the isolation from the latter samples of some other important opportunistic pathogens, such as Enterobacter spp. and Klebsiella spp., also known for multidrug resistance, could be an additional reason of concern.

Transcriptome profiling of venom gland from wasp species: de novo assembly, functional annotation, and discovery of molecular markers

Background

Vespa velutina, one of the most aggressive and fearful wasps in China, can cause grievous allergies and toxic reactions, leading to organ failure and even death. However, there is little evidence on molecular data regarding wasps. Therefore, we aimed to provide an insight into the transcripts expressed in the venom gland of wasps.

Results

In our study, high-throughput RNA sequencing was performed using the venom glands of four wasp species. First, the mitochondrial cytochrome C oxidase submit I (COI) barcoding and the neighbor joining (NJ) tree were used to validate the unique identity and lineage of each individual species. After sequencing, a total of 127,630 contigs were generated and 98,716 coding domain sequences (CDS) were predicted from the four species. The Gene ontology (GO) enrichment analysis of unigenes revealed their functional role in important biological processes (BP), molecular functions (MF) and cellular components (CC). In addition, c-type, p1 type, p2 type and p3 type were the most commonly found simple sequence repeat (SSR) types in the four species of wasp transcriptome. There were differences in the distribution of SSRs and single nucleotide polymorphisms (SNPs) among the four wasp species.

Conclusions

The transcriptome data generated in this study will improve our understanding on bioactive proteins and venom-related genes in wasp venom gland and provide a basis for pests control and other applications. To our knowledge, this is the first study on the identification of large-scale genomic data and the discovery of microsatellite markers from V. tropica ducalis and V. analis fabricius.

Insect pollinator diversity in four forested ecosystems of southern Punjab, Pakistan

This study investigated pollinator assemblage diversity and richness in four forested ecosystems of southern Punjab, Pakistan, with different landscape types. Pirowal is situated in the plains of irrigated Punjab, Lal Suhanra is part of a sandy desert ecosystem, Ghazi Ghat is part of the Indus River delta, and Fort Munro is located in dry hilly mountains. A yearlong survey of pollinator populations was carried out in these four forested ecosystems from January to December of 2010. Fortnightly hand netting was performed for collecting flower-visiting insects whereas, pan traps of three colors (white, blue, and yellow) were deployed for collecting the data. A total of 8,812 individuals from two orders (Lepidoptera and Diptera) were observed, including 22 families and 154 species. Bees were the most abundant, with 4,502 individuals, and the most species-rich taxa, with 70 species in five families, followed by flies having 2,509 individuals and 51species in 10 families. Wasps were the least abundant with 1,801 individuals and 33 species in seven families. The assemblage structure of pollinator communities as visualized through rank abundance curves showed that there were many species with low abundance and only a few species with a much higher abundance. The most abundant species among the bees, in order, were Nomia sp.3, Megachile bicolor, and Colletes sp.3; among flies, Syrphus sp.2, Calliphoridae sp.1, and Empididae sp.4; and among wasps, Tiphiidae sp.1, Myzininae sp.2, and Scelionidae sp.1.

Risk factors for severe systemic sting reactions in wasp (Vespula spp.) and honeybee (Apis mellifera) venom allergic patients

Background

Hymenoptera stings are a major cause of anaphylaxis. Various risk factors are discussed in literature. This study aims to investigate potential risk factors for severe sting reactions in wasp (Vespula spp.) and honeybee (Apis mellifera) venom allergic patients and analyses the correlation between diagnostic test results and the severity of the allergic reaction.

Methods

480 patients suffering from wasp or honeybee venom allergy were included in this retrospective case series. Only individuals allergic to Vespula spp. but not to other vespids such as Polistes were considered. The severity of their systemic field sting reaction was analysed with regard to the amount of specific IgE antibodies to whole venom extracts and to major allergens of honeybee and/or wasp venom. Furthermore, the following potential risk factors for severe sting reactions were examined: age, sex, latency time, skin symptoms, baseline serum tryptase levels and the concentration of venom inducing a positive intracutaneous test.

Results

The two following indicators for severe systemic sting reactions in honeybee and wasp venom allergic patients have been identified: a short latency time and the absence of skin symptoms. The patient’s age and baseline serum tryptase levels have been found to positively correlate with the grade of the sting reaction only in individuals allergic to wasp venom. No correlation could be found between the degree of sensitisation and the severity of the allergic reaction. Neither the amount of specific IgE antibodies to whole venom extracts nor to major allergens were significantly associated with the severity of the sting reaction.

Conclusion

The clinical history is essential for the allergological workup and therapeutic decision on Hymenoptera venom allergies. A short latency time and the absence of skin symptoms are indicators for severe systemic sting reactions, followed by the patient’s age and baseline serum tryptase levels.

How Not to Be Turned into a Zombie

The emerald jewel wasp (Ampulex compressa) is renowned for its ability to zombify the American cockroach (Periplaneta americana) with a sting to the brain. When the venom takes effect, the cockroach becomes passive and can be led by its antenna into a hole, where the wasp deposits an egg and then seals the exit with debris. The cockroach has the ability to walk, run, or fly if properly stimulated, but it does not try to escape as it is slowly eaten alive by the developing wasp larva. Although the composition and effects of the wasp's venom have been investigated, no studies have detailed how cockroaches might prevent this grim fate. Here it is shown that many cockroaches deter wasps with a vigorous defense. Successful cockroaches elevated their bodies, bringing their neck out of reach, and kicked at the wasp with their spiny hind legs, often striking the wasp's head multiple times. Failing this, the elevated, "on-guard" position allowed cockroaches to detect and evade the wasp's lunging attack. If grasped, the cockroaches parried the stinger with their legs, used a "stiff-arm" defense to hold back the stinger, and could stab at, and dislodge, the wasp with tibial spines. Lastly, cockroaches bit at the abdomen of wasps delivering the brain sting. An aggressive defense from the outset was most successful. Thus, for a cockroach not to become a zombie, the best strategy is: be vigilant, protect your throat, and strike repeatedly at the head of the attacker.

Foraging strategy of wasps - optimisation of intake rate or energetic efficiency?

In endothermic wasps, foraging is an expensive activity. To maximise the benefit for the colony, wasps can optimise either the intake rate or energetic efficiency of a foraging trip. We investigated the foraging behaviour of vespine wasps under variable environmental and reward conditions. We trained them to forage for 0.5 mol l^-1 sucrose solution from an artificial flower in a flow-through respiratory measurement chamber, and simultaneously measured their body temperature using infrared thermography to investigate interactions between thermoregulation and energetics. Measurement of carbon dioxide release (for energetic calculations) and load mass enabled the direct determination of foraging efficiency. An unlimited reward increased the wasps' energetic effort to increase the suction speed through high body temperatures. With reduced reward (limited flow), when an increased body temperature could not increase suction speed, the wasps decreased their body temperature to reduce the metabolic effort. Solar heat gain was used differently, either to increase body temperature without additional metabolic effort or to save energy. The foraging efficiency was mainly determined by the flow rate, ambient temperature and solar heat gain. In shade, an unlimited sucrose flow and a high ambient temperature yielded the highest energetic benefit. A limited flow reduced foraging efficiency in the shade, but only partly in sunshine. Solar radiation boosted the efficiency at all reward rates. Wasps responded flexibly to varying reward conditions by maximising intake rate at unlimited flow and switching to the optimisation of foraging efficiency when the intake rate could not be enhanced due to a limited flow rate.

Spectral cathodoluminescence analysis of hymenopteran mandibles with different levels of zinc enrichment in their teeth

The inclusion of Zn in insect mandibles affects their hardness and is functional to their use during feeding or reproducing. However, little is known on the chemical/structural base of Zn enrichment. Here, we found that cathodoluminescence (CL) technique revealed two different types of CL spectra in the mandibles of Hymenoptera, depending on the Zn enrichment level assessed by Energy Dispersive X-ray Spectroscopy (EDS). Individuals having negligible traces to low % of Zn in their mandible teeth (≤3 wt%) presented a wide band of luminescence in the visible range which resembled those observed in the CC structures of graphite. This spectrum is probably characteristic for un-enriched cuticle, since it did not differ from those obtained from the Zn-lacking inner part of mandibles. Individuals with moderate to high % of Zn in their mandible teeth (≥7 wt%), instead, presented additional CL peaks in the ultraviolet range. Comparisons with different minerals of Zn suggest that these peaks could be related with OZnO bonds, with hydroxyl groups and with zinc-chlorine links (in agreement with Cl high levels detected by the EDS). Being a non-destructive technique, CL allows large comparative studies of the chemistry of metal-enriched insect cuticle even using unique specimens, such as those deposited in Natural History Museums.

What do foraging wasps optimize in a variable environment, energy investment or body temperature?

Vespine wasps (Vespula sp.) are endowed with a pronounced ability of endothermic heat production. To show how they balance energetics and thermoregulation under variable environmental conditions, we measured the body temperature and respiration of sucrose foragers (1.5 M, unlimited flow) under variable ambient temperature (T_a = 20–35 °C) and solar radiation (20–570 W m⁻²). Results revealed a graduated balancing of metabolic efforts with thermoregulatory needs. The thoracic temperature in the shade depended on ambient temperature, increasing from ~37 to 39 °C. However, wasps used solar heat gain to regulate their thorax temperature at a rather high level at low T_a (mean T_thorax ~ 39 °C). Only at high T_a they used solar heat to reduce their metabolic rate remarkably. A high body temperature accelerated the suction speed and shortened foraging time. As the costs of foraging strongly depended on duration, the efficiency could be significantly increased with a high body temperature. Heat gain from solar radiation enabled the wasps to enhance foraging efficiency at high ambient temperature (T_a = 30 °C) by up to 63 %. The well-balanced change of economic strategies in response to environmental conditions minimized costs of foraging and optimized energetic efficiency.

The role of juvenile hormone in dominance behavior, reproduction and cuticular pheromone signaling in the caste-flexible epiponine wasp, Synoeca surinama

BACKGROUND

The popular view on insect sociality is that of a harmonious division of labor among two morphologically distinct and functionally non-overlapping castes. But this is a highly derived state and not a prerequisite for a functional society. Rather, caste-flexibility is a central feature in many eusocial wasps, where adult females have the potential to become queens or workers, depending on the social environment. In non-swarming paper wasps (e.g., Polistes), prospective queens fight one another to assert their dominance, with losers becoming workers if they remain on the nest. This aggression is fueled by juvenile hormone (JH) and ecdysteroids, major factors involved in caste differentiation in most eusocial insects. We tested whether these hormones have conserved aggression-promoting functions in Synoeca surinama, a caste-flexible swarm-founding wasp (Epiponini) where reproductive competition is high and aggressive displays are common.

RESULTS

We observed the behavioral interactions of S. surinama females in field nests before and after we had removed the egg-laying queen(s). We measured the ovarian reproductive status, hemolymph JH and ecdysteroid titers, ovarian ecdysteroid content, and analyzed the cuticular hydrocarbon (CHC) composition of females engaged in competitive interactions in both queenright and queenless contexts. These data, in combination with hormone manipulation experiments, revealed that neither JH nor ecdysteroids are necessary for the expression of dominance behaviors in S. surinama. Instead, we show that JH likely functions as a gonadotropin and directly modifies the cuticular hydrocarbon blend of young workers to match that of a reproductive. Hemolymph ecdysteroids, in contrast, are not different between queens and workers despite great differences in ovarian ecdysteroid content.

CONCLUSIONS

The endocrine profile of S. surinama shows surprising differences from those of other caste-flexible wasps, although a rise in JH titers in replacement queens is a common theme. Extensive remodeling of hormone functions is also evident in the highly eusocial bees, which has been attributed to the evolution of morphologically defined castes. Our results show that hormones which regulate caste-plasticity can lose these roles even while caste-plasticity is preserved.

Measuring individual locomotor rhythms in honey bees, paper wasps and other similar-sized insects

Circadian rhythms in social insects are highly plastic and are modulated by multiple factors. In addition, complex behaviors such as sun-compass orientation and time learning are clearly regulated by the circadian system in these organisms. Despite these unique features of social insect clocks, the mechanisms as well as the functional and evolutionary relevance of these traits remain largely unknown. Here we show a modification of the Drosophila activity monitoring (DAM) system that allowed us to measure locomotor rhythms of the honey bee, Apis mellifera (three variants; gAHB, carnica and caucasica), and two paper wasps (Polistes crinitus and Mischocyttarus phthisicus). A side-by-side comparison of the endogenous period under constant darkness (free-running period) led us to the realization that these social insects exhibit significant deviations from the Earth's 24 h rotational period as well as a large degree of inter-individual variation compared with Drosophila. Experiments at different temperatures, using honey bees as a model, revealed that testing the endogenous rhythm at 35°C, which is the hive's core temperature, results in average periods closer to 24 h compared with 25°C (23.8 h at 35°C versus 22.7 h at 25°C). This finding suggests that the degree of tuning of circadian temperature compensation varies among different organisms. We expect that the commercial availability, cost-effectiveness and integrated nature of this monitoring system will facilitate the growth of the circadian field in these social insects and catalyze our understanding of the mechanisms as well as the functional and evolutionary relevance of circadian rhythms.