Philanthus Triangulum Research Articles

Assessment of natural enemies of honeybee (Apis mellifera jemenitica) in the Asir region, Southwestern, Saudi Arabia

The occurrence and status of natural enemies of honey bee Apis mellifera (Hymenoptera: Apidae) in the southwestern region of Saudi Arabia was conducted during 2019 and 2020. The existence of natural enemies, particularly pests and predators, is one of the most significant problem for beekeepers in the Asir region. A total of 78 apiaries were selected from two different geographical locations (Sarat and Tihama) in the Asir region. Honey bee colonies were attacked by 17 pests and predators species in the Tihama region, compared to 15 in Sarwat mountain region of southwestern Saudi Arabia. In order of significance, wasp (Philanthus triangulum), bee-eating bird (Merops apiaster), Varroa-mite (Varroa destructor), wax moth (Achroia grisella), and spider (Misumena sp.) are the most prevalent pests that inflict major harm to apiaries in southwestern Saudi Arabia. There were also some other pests and predators that had insignificant effect on bees. Generally, the recorded natural enemy’s incidences usually occurred in the months of September-October and December to February.

European beewolf (Philanthus triangulum) will expand its geographic range as a result of climate warming

Climate change is an important driver of the spread of apiary pests and honeybee predators. These impact on one of the economically most important pollinators and thus pose serious threats to the functioning of both natural ecosystems and crops. We investigated the impact of the predicted climate change in the periods 2040–2060 and 2060–2080 on the potential distribution of the European beewolf Philanthus triangulum, a specialized honeybee predator. We modelled its potential distribution using the MaxEnt method based on contemporary occurrence data and bioclimatic variables. Our model had an overall good performance (AUC = 0.864) and the threshold of occurrence probability, assessed as the point with the highest sum of sensitivity and specificity, was at 0.533. Annual temperature range (69.5%), mean temperature in the warmest quarter (12.4%), and precipitation in the warmest quarter (7.9%) were the principal bioclimatic variables significantly affecting the potential distribution of the European beewolf. We predicted the potential distribution shifts within two scenarios (optimistic RPC4.5 and pessimistic RCP8.5) and three Global Circulation Models (HadGEM2-ES, IPSL-CM5A-LR, and MPI-SM-LR). Both optimistic and pessimistic scenarios showed that climate change will significantly increase the availability of European beewolf potential niches. Losses of potential niches will only affect small areas in southern Europe. Most of the anticipated changes for the period 2060–2080 will already have occurred in 2040–2060. The predicted range expansion of European beewolf suggests that occurrence and abundance of this species should be monitored.

Гильдии жалоносных перепончатокрылых (Hymenoptera: Aculeata) - посетителей соцветий золотарников (Solidago L.) в условиях открытых биотопов Национального парка «Нарочанский»

The study of anthophilous insects carried out in 2019-2021 in open field areas in the territory of Narochansky National Park revealed 42 species for the flower visitor guild of native European goldenrod (Solidago virgaurea L.) and for the flower-visitor guild of invasive goldenrods Solidago canadensis s. l. - 50 species of Aculeata (Hymenoptera). The taxonomic structure of guilds is different: only 11 species are present in both guilds, among visitors of S. virgaurea inflorescences the species richness of Apoidea is higher (38 species, 90 % of their total number), whereas for S. canadensis inflorescences -of Vespoidea s. l. (31 species, 62 %). There were no dominant species in the studied guilds; in the guild of S. virgaurea inflorescence visitors, the group of common species included bumblebees Bombus lucorum L. and Bombus (Psithyrus) bohemicus Seidl, the group of numerous species - bumblebees Bombus humilis Ill., Bombus lapidarius L., Bombus pratorum L., Bombus terrestris L. and Cuckoo bumblebee Bombus (Psithyrus) rupestris F. Polistine wasps Polistes nimpha Christ and Polistes dominula Christ were common among visitors of S. canadensis inflorescences; Ancistrocerus trifasciatus Mull., Philanthus triangulum F., Lasioglossum varipes Morawitz, and B. terrestris were numerous. The relative abundance of B. terrestris was the highest, approaching the threshold value for assignment to the group of numerous species. It is suggested that high relative abundance of Vespoidea s. l. visiting inflorescences of invasive goldenrods is connected to the fact that adult wasps not only feed on flowers, but prey on small insects that are numerous here.

Pollen cargo structure on Aculeata – visitors of alien Solidago canadensis L. s. l. inflorescences in Belarus

Community structure of visitors to inflorescences of invasive goldenrods was investigated by sampling at 9 sites in Minsk city, Minsk and Mogilev regions in Belarus. A total 44 species of Aculeata including 1 species of Chrysioidea, 7 species of Vespoidea and 36 species of Apoidea were registered. Among them 2 species of bumblebees (Bombus terrestris L., B. lapidarius L.) were numerous, 2 species of Vespoidea (Polistes dominula Christ, P. nimpha Christ) and 3 species of Apoidea (Philanthus triangulum F., Hylaeus communis Nyl., B. ruderarius Müller) were common. Pollen cargo analysis revealed the predominance of easily lost and relatively easily lost conspecific pollen grains on the bodies of the imago of the all common and numerous species of visitors to inflorescences of invasive goldenrods.

Predicting with the pest status of two main insects that attacking honey bee colonies in Africa based on the future climatic changes

The effects of future climate changes on the prevalence of Palarus latifrons Kohl. and Philanthus triangulum Fab that attacking honey bee colonies in Africa have not been studied before. Ecological modeling using Maxent and geographical information system (GIS) was used to achieve the study objective. The highest contribution in the model was to the annual mean temperature followed by mean temperature of the coldest quarter. The model performance was high and perfect in light of the used evaluation parameters. Some areas in southern and northern parts of Africa were suitable for the prevalence of P. latifrons Kohl. and P. triangulum Fab under current conditions.The study maps for future conditions during 2050 and 2070 highlighted the negative effects of climate change on the prevalence of these pests in specific parts in Africa. The consequences of such prevalence/limitation of P. latifrons and P. triangulum on beekeeping in Africa were discussed.

Nitric oxide radicals are emitted by wasp eggs to kill mold fungi.

Detrimental microbes caused the evolution of a great diversity of antimicrobial defenses in plants and animals. Insects developing underground seem particularly threatened. Here we show that the eggs of a solitary digger wasp, the European beewolf Philanthus triangulum, emit large amounts of gaseous nitric oxide (NO⋅) to protect themselves and their provisions, paralyzed honeybees, against mold fungi. We provide evidence that a NO-synthase (NOS) is involved in the generation of the extraordinary concentrations of nitrogen radicals in brood cells (~1500 ppm NO⋅ and its oxidation product NO2⋅). Sequencing of the beewolf NOS gene revealed no conspicuous differences to related species. However, due to alternative splicing, the NOS-mRNA in beewolf eggs lacks an exon near the regulatory domain. This preventive external application of high doses of NO⋅ by wasp eggs represents an evolutionary key innovation that adds a remarkable novel facet to the array of functions of the important biological effector NO⋅.

Philanthotoxin Analogues That Selectively Inhibit Ganglionic Nicotinic Acetylcholine Receptors with Exceptional Potency.

Philanthotoxin-433 (PhTX-433) is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 nonselectively inhibits several excitatory ligand-gated ion channels, and we recently showed that its synthetic analogue, PhTX-343, exhibits strong selectivity for neuronal over muscle-type nicotinic acetylcholine receptors (nAChRs). Here, we examined the action of 17 analogues of PhTX-343 against ganglionic (α3β4) and brain (α4β2) nAChRs expressed in Xenopus oocytes by using a two-electrode voltage clamp at -100 mV. IC50 values for PhTX-343 inhibition of α3β4 and α4β2 receptors were 7.7 and 80 nM, respectively. All the studied analogues had significantly higher potency at α3β4 nAChRs with IC50 values as low as 0.16 nM and with up to 91-fold selectivity for α3β4 over α4β2 receptors. We conclude that PhTX-343 analogues displaying both a saturated ring and an aromatic moiety in the hydrophobic headgroup of the molecule demonstrate exceptional potency and selectivity for α3β4 nAChRs.

Biologically active phenol and indole derivatives of terrestrial arthropods: electrophysiological and chemical characteristics

Toxins-antagonists of glutamatergic synapses were found in venoms of different terrestrial Arthrpopodae , both Insecta and Aranei . Chemical structures of some of them were described, and a majority of such substances are derivatives of phenol and indole. They are used successfully for electrophysiological investigations of membrane structures, and present review is devoted to some results of such studies that may be useful for laboratory investigations. Here, we described chemical structure of some toxins, as well as the results of electrophysiological registration of activities of different venoms and toxins of Arthropodae . Hypotheses that explain physiological effects of the substances – antagonists of glutamate receptors depending on the peculiarities of their chemical structures are suggested. The role of different sites of toxins’ molecules in blocking of glutamate receptors is discussed. The information about venoms’ components of Insecta family Sphecidae ( Philanthus triangulum ), and of some Araneidae spider species of Argiope , Araneus , Nephila genera is also presented. Keywords: Arthropods’ venoms, toxins, receptor antagonists, transmembrane electric current

Block of nicotinic acetylcholine receptors by philanthotoxins is strongly dependent on their subunit composition.

Philanthotoxin-433 (PhTX-433) is an active component of the venom from the Egyptian digger wasp, Philanthus triangulum. PhTX-433 inhibits several excitatory ligand-gated ion channels, and to improve selectivity two synthetic analogues, PhTX-343 and PhTX-12, were developed. Previous work showed a 22-fold selectivity of PhTX-12 over PhTX-343 for embryonic muscle-type nicotinic acetylcholine receptors (nAChRs) in TE671 cells. We investigated their inhibition of different neuronal nAChR subunit combinations as well as of embryonic muscle receptors expressed in Xenopus oocytes. Whole-cell currents in response to application of acetylcholine alone or co-applied with PhTX analogue were studied by using two-electrode voltage-clamp. α3β4 nAChRs were most sensitive to PhTX-343 (IC50 = 12 nM at −80 mV) with α4β4, α4β2, α3β2, α7 and α1β1γδ being 5, 26, 114, 422 and 992 times less sensitive. In contrast α1β1γδ was most sensitive to PhTX-12 along with α3β4 (IC50 values of 100 nM) with α4β4, α4β2, α3β2 and α7 being 3, 3, 26 and 49 times less sensitive. PhTX-343 inhibition was strongly voltage-dependent for all subunit combinations except α7, whereas this was not the case for PhTX-12 for which weak voltage dependence was observed. We conclude that PhTX-343 mainly acts as an open-channel blocker of nAChRs with strong subtype selectivity.

Mycobiota in the brood cells of the European beewolf, Philanthus triangulum (Hymenoptera: Crabronidae)

Mass provisioning insects have to cope with microbial spoilage of their food supplies. As their fitness is directly linked to the availability of high quality food for their offspring, they have evolved various mechanisms for preserving these resources. The European beewolf, Philanthus triangulum, uses several mechanisms to not only preserve the food for their larvae, paralyzed workers of the European honeybee, Apis mellifera, but also protect the larvae that develop on the stored food. To assess the spectrum of fungi that pose a threat to beewolf brood cells, we manipulated brood cells by removing the insect defenses. We monitored the subsequent fungal infestations that would have been prevented by the beewolf defense mechanisms and isolated and identified the mold fungi. The cosmopolitan and highly competitive species of Aspergillus, in particular A. flavus, dominated the mold in beewolf brood cells. All other infestations could also be attributed to generalist mold fungi that are commonly found in soil and also on insects. Our findings indicate that beewolf brood cells can be colonized by a broad range of opportunistic soil mold fungi. Thus, it seems highly adaptive that beewolves employ general, broad spectrum defense mechanisms.

Subunit-Dependent Inhibition of Neuronal Nicotinic Acetylcholine Receptors by Philanthotoxins

Philanthotoxin-433 (PhTX-433) is the active component of the Egyptian solitary digger wasp, Philanthus triangulum, venom which non-selectively inhibits several excitatory ion channels. To improve selectivity two synthetic analogues, Philanthotoxin-343 (PhTX-343) and Philanthotoxin-12 (PhTX-12), were developed. Previous work showed a 22-fold selectivity for PhTX-12 on embryonic muscle-type nicotinic acetylcholine receptors (M-nAChR) naturally expressed in the TE671 cell line in comparison to PhTX-343. In this study, we investigated the pharmacological action of both analogues on different mammalian hetero-oligomeric neuronal nicotinic acetylcholine receptor (N-nAChR) subunit combinations expressed in Xenopus oocytes. Whole-cell currents in response to application of acetylcholine alone or co-applied with PhTX-analogue were studied electrophysiologically using two-electrode voltage-clamp at three different membrane holding potentials (VH = −60 mV, −80 mV and −100 mV). Concentration-inhibition curves were constructed and IC50 values estimated for each holding potential. The IC50 values for PhTX-343 inhibition of α3β4, α3β2, α4β2 and α4β4 peak currents at −100 mV were 0.077 µM (n=9), 3.20 µM (n=8), 0.170 µM (n=7) and 0.28 µM (n=6) respectively; for PhTX-12 they were 2.03 µM (n=8), 36.0 µM (n=10), 0.430 µM (n=7) and 1.82 µM (n=9) respectively; i.e. in contrast to M-nAChR, PhTX-343 was more potent than PhTX-12 in all cases. The potency of PhTX-343 was strongly augmented by holding the cell at more negative VH while this was not the case for PhTX-12 where weak voltage-dependence was observed. The variation in potency is most likely due to a single amino acid change in the β2/4 subunit pore lining region. Therefore, we conclude that PhTX-343 works as a potent open channel blocker of the mammalian heteromeric N-nAChR and has binding site deep in the channel while the PhTX-12 site is near to the outside of channel.

Morphology, Chemistry and Function of the Postpharyngeal Gland in the South American Digger Wasps Trachypus boharti and Trachypus elongatus

Microbes pose severe threats to animals as competitors or pathogens and strongly affect the evolution of life history traits like parental care. Females of the European beewolf Philanthus triangulum, a solitary digger wasp, provision their offspring with paralyzed honeybees and embalm them with the secretion from large postpharyngeal glands (PPG) that contain mainly unsaturated hydrocarbons. This coating changes the physico-chemical properties of the prey surface, causes a reduction of water condensation and retards growth of mold fungi. Here we examined the closely related South American genus Trachypus, which shows a life-history similar to Philanthus. We investigated whether Trachypus spp. also possess PPGs and embalm larval provisions. Using histological methods and 3D reconstructions we show that Trachypus boharti and T. elongatus possess PPGs that are similar to P. triangulum but somewhat smaller. The ultrastructure of the gland epithelium suggests that the gland content is at least partly sequestered from the hemolymph. Chemical analyses using gas chromatography / mass spectrometry revealed that both the cuticle and PPGs of Trachypus contain mainly unsaturated long-chain hydrocarbons. The gland of T. boharti additionally contains long-chain ketones. The hydrocarbons from the PPG of T. elongatus occurred on prey bees excavated from nests in the field but not on conspecific control bees. While the embalming only slightly elevated the amount of hydrocarbons on prey bees, the proportion of unsaturated hydrocarbons, which is crucial for the antifungal effect, was significantly increased. The Trachypus species under study possess PPGs that are very similar to the PPG of P. triangulum with regard to morphology, ultrastructure and chemistry. Moreover, we provide clear evidence that T. elongatus females embalm their prey, presumably as a means of prey preservation. The observed differences among Trachypus and Philanthus in gland size and prey embalming may have evolved in response to divergent ecological conditions.

Maternal and Environmental Effects on Symbiont-Mediated Antimicrobial Defense

Bacteria produce a remarkable diversity of bioactive molecules with antimicrobial properties. Despite the importance of such compounds for human medicine, little is known about the factors influencing antibiotic production in natural environments. Recently, several insects have been found to benefit from symbiont-produced antimicrobial compounds for defense against pathogenic microbes. In the European beewolf, Philanthus triangulum (Hymenoptera, Crabronidae), bacteria of the genus Streptomyces provide protection against pathogens by producing antimicrobials on the larval cocoon during hibernation, thereby significantly enhancing the survival probability of the beewolf larva. To investigate the effects of abiotic and biotic factors on antibiotic production, we exposed beewolf cocoons to different environmental conditions and quantified the amount of Streptomyces-produced antibiotics by using gas chromatography/mass spectrometry (GC/MS). The results revealed no significant influence of temperature, humidity, or pathogen load on the antibiotic amount, indicating that antibiotic production is not affected by current environmental conditions but rather may be optimized to serve as a reliable long-term protection during the unpredictable phase of beewolf hibernation. However, the amount of antibiotics was positively correlated with the symbiont population size on the cocoon, which in turn is affected by the number of Streptomyces cells provided by the mother into the brood cell. Additionally, we found a positive correlation between the amount of hydrocarbons and the number and length of bacterial cells in the antennal gland secretion, suggesting that maternal investment affects symbiont growth and, thus, antibiotic production on the larval cocoon.

Dynamics of symbiont-mediated antibiotic production reveal efficient long-term protection for beewolf offspring

BackgroundInsects have evolved a wide range of mechanisms to defend themselves and their offspring against antagonists. One of these strategies involves the utilization of antimicrobial compounds provided by symbiotic bacteria to protect the host or its nutritional resources from pathogens and parasites. In the symbiosis of the solitary digger wasp, Philanthus triangulum (Hymenoptera, Crabronidae), the bacterial symbiont ‘Candidatus Streptomyces philanthi’ defends the developing larvae against pathogens by producing a mixture of at least nine antimicrobial substances on the cocoon surface. This antibiotic cocktail inhibits the growth of a broad range of detrimental fungi and bacteria, thereby significantly enhancing the offspring’s survival probability.ResultsHere we show that the production of antimicrobial compounds by the beewolf symbionts is confined to the first two weeks after cocoon spinning, leading to a high concentration of piericidins and streptochlorin on the cocoon surface. Expression profiling of housekeeping, sporulation, and antibiotic biosynthesis genes indicates that antibiotic production coincides with morphological differentiation that enables the symbionts to survive the nutrient-limited conditions on the beewolf cocoon. The antibiotic substances remain stable on the cocoon surface for the entire duration of the beewolf’s hibernation period, demonstrating that the compounds are resistant against environmental influences.ConclusionsThe antibiotic production by the beewolf symbionts serves as a reliable protection for the wasp offspring against pathogenic microorganisms during the long and unpredictable developmental phase in the subterranean brood cells. Thus, the beewolf-Streptomyces symbiosis provides one of the rare examples of antibiotics serving as an efficient defense in the natural environment and may aid in devising new strategies for the utilization of antibiotic combination therapies in human medicine against increasingly resistant bacterial and fungal pathogens.

Accelerated evolution of mitochondrial but not nuclear genomes of Hymenoptera: new evidence from crabronid wasps.

Mitochondrial genes in animals are especially useful as molecular markers for the reconstruction of phylogenies among closely related taxa, due to the generally high substitution rates. Several insect orders, notably Hymenoptera and Phthiraptera, show exceptionally high rates of mitochondrial molecular evolution, which has been attributed to the parasitic lifestyle of current or ancestral members of these taxa. Parasitism has been hypothesized to entail frequent population bottlenecks that increase rates of molecular evolution by reducing the efficiency of purifying selection. This effect should result in elevated substitution rates of both nuclear and mitochondrial genes, but to date no extensive comparative study has tested this hypothesis in insects. Here we report the mitochondrial genome of a crabronid wasp, the European beewolf (Philanthus triangulum, Hymenoptera, Crabronidae), and we use it to compare evolutionary rates among the four largest holometabolous insect orders (Coleoptera, Diptera, Hymenoptera, Lepidoptera) based on phylogenies reconstructed with whole mitochondrial genomes as well as four single-copy nuclear genes (18S rRNA, arginine kinase, wingless, phosphoenolpyruvate carboxykinase). The mt-genome of P. triangulum is 16,029 bp in size with a mean A+T content of 83.6%, and it encodes the 37 genes typically found in arthropod mt genomes (13 protein-coding, 22 tRNA, and two rRNA genes). Five translocations of tRNA genes were discovered relative to the putative ancestral genome arrangement in insects, and the unusual start codon TTG was predicted for cox2. Phylogenetic analyses revealed significantly longer branches leading to the apocritan Hymenoptera as well as the Orussoidea, to a lesser extent the Cephoidea, and, possibly, the Tenthredinoidea than any of the other holometabolous insect orders for all mitochondrial but none of the four nuclear genes tested. Thus, our results suggest that the ancestral parasitic lifestyle of Apocrita is unlikely to be the major cause for the elevated substitution rates observed in hymenopteran mitochondrial genomes.

Cryptic combat against competing microbes is a costly component of parental care in a digger wasp

Microorganisms are ubiquitous and key selective agents in parental care behaviour. Various animal species have thus evolved diverse means to prevent and combat detrimental effects of microbial competitors and pathogens on their offspring. The European beewolf, Philanthus triangulum , is a solitary crabronid wasp that stores paralysed honeybees as larval provisions in subterranean nests. In the soil the highly nutritious provisions can be attacked by a large number of microorganisms. We investigated the effect of fungal infestations of larval provisions on the reproductive success of beewolves. Although fungal infestations reduced larval survival, female beewolves largely eliminated this effect by embalming larval provisions with ample amounts of hydrocarbons. However, this came at the cost of a reduced ability to apply hydrocarbons to the provisions of future offspring. This reduced investment in embalming resulted in a higher risk of mould infestations. Embalming of the prey in P. triangulum thus meets the criterion of parental investment and females have to balance this investment of hydrocarbons in current and future offspring to maximize their lifetime reproductive success.

Structure, chemical composition and putative function of the postpharyngeal gland of the emerald cockroach wasp, Ampulex compressa (Hymenoptera, Ampulicidae)

The postpharyngeal gland (PPG) plays a major role in the social integration of ant colonies. It had been thought to be restricted to ants but was recently also described for a solitary wasp, the European beewolf ( Philanthus triangulum). This finding posed the question whether the gland has evolved independently in the two taxa or has been inherited from a common ancestor and is hence homologous. The latter alternative would be supported if a PPG was found in more basal taxa. Therefore, we examined a species at the base of the Apoidea, the solitary ampulicid wasp Ampulex compressa, for the existence of a PPG. Both sexes of this species possess a cephalic gland that branches off the posterior part of the pharynx, is lined by a cuticular intima and surrounded by a monolayered epithelium with the epithelial cells bearing long hairs. Most of these morphological characteristics conform to those of the PPG of ants and beewolves. Chemical analysis of the gland content revealed that it contains mainly hydrocarbons and that there is a congruence of the pattern of hydrocarbons in the gland, on the cuticle, and in the hemolymph, as has also been reported for both ants and beewolves. Based on these morphological and chemical results we propose that the newly described cephalic gland is a PPG and discuss its possible function in A. compressa. The present study supports the view of a homologous origin of the PPG in the aculeate Hymenoptera.

Larval Rearing Temperature Influences Amount and Composition of the Marking Pheromone of the Male Beewolf,Philanthus triangulum

Pheromones play an important role for courtship and mating in many insect species, and they are shaped by a complex interaction of genetic and environmental factors. Developmental temperature is known to have a strong influence on adult life history, morphology, and physiology, but little is known about its effect on pheromone characteristics. In the present study, the influence of temperature during larval development on the amount and composition of the complex marking pheromone from the cephalic glands of the adult male beewolf, Philanthus triangulum F. (Hymenoptera: Crabronidae), was investigated. Additionally, the effects of temperature on several life-history traits were examined. European beewolf larvae were reared at three constant temperatures (20, 25, and 30° C). Males reared at 20° C showed longer development times and higher mortality, suggesting that low temperatures constitute stressful conditions for developing larvae. After eclosion, the amount and composition of the scent marking secretion of the adult males was analyzed by coupled gas chromatography-mass spectrometry. Males that had been reared at 20° C had significantly less secretion than individuals reared under warmer conditions (25° C and 30° C). Furthermore, larval rearing temperature had a significant effect on the composition of the adult males' pheromone gland content, with warmer rearing conditions leading to higher relative amounts of compounds with high molecular weight. The results show that the temperature during larval development significantly affected the amount and composition of the content of the male pheromone glands, probably due to physiological constraints and competing processes for limited energetic resources. Thus, the pheromone gland content may contain information on developmental conditions of males, which may have consequences for female mate choice decisions and male reproductive success.

Is the postpharyngeal gland of a solitary digger wasp homologous to ants? Evidence from chemistry and physiology

The postpharyngeal gland (PPG) was thought to be restricted to ants where it serves a crucial function in the generation of the colony odour. Recently, head glands that closely resemble the PPG of ants were discovered in females of a solitary digger wasp, the European beewolf. The function of this gland necessarily differs from ants: beewolf females apply the secretion of their PPG onto the bodies of paralysed honeybees that serve as larval provisions in order to delay fungus growth. Since ants and digger wasps are not closely related, the occurrence of this gland in these two taxa might either be due to convergent evolution or it is a homologous organ inherited from a common ancestor. Here we test the hypothesis that the PPGs of both taxa are homologous by comparing characteristics of chemical composition and physiology of the PPG of beewolves and ants. Based on reported characteristics of the PPG content of ants, we tested three predictions that were all met. First, the PPG of beewolves contained mainly long-chain hydrocarbons and very few compounds with functional groups. Second, the composition of hydrocarbons in the beewolf PPG was similar to that of the hemolymph. Taking the structure of the gland epithelium and the huge requirements of beewolf females for gland secretion into account this result suggests that the content of the PPG is also sequestered from the hemolymph in beewolves. Third, the chemical composition of the PPG and the cuticle was similar in beewolves since cuticular hydrocarbons derive either from the hemolymph or the PPG. Taking the considerable morphological similarities into account, our results support the hypothesis of a homologous origin of the PPG in beewolves and ants.

Do digger wasps time their provisioning activity to avoid cuckoo wasps (Hymenoptera: Crabronidae and Chrysididae)?

Strategies adopted by parasitoids and kleptoparasites co-evolve with the defensive adaptations of their hosts, and vice-versa. Hedychrum rutilans and Hedychrum nobile are brood parasites of, respectively, Philanthus triangulum and Cerceris arenaria, two digger wasps that share most aspects of their nesting biology (solitary females dig aggregated nests in the ground and mass-provision the brood with paralyzed insects). We tested the hypothesis that similarity in the hosts’ nesting habits corresponds to similar defensive strategies against these cuckoo wasps. Peak provisioning activity by P. triangulum occurred in late afternoon (and early morning in 1 year) while peak H. rutilans activity was in early afternoon. In contrast, peak provisioning by C. arenaria and peak H. nobile activity occurred in early afternoon. Thus, P. triangulum (as previously found in other populations) appears to have timed its provisioning to avoid its brood parasite whereas C. arenaria did not, rejecting our hypothesis. The daily activity of both chrysidid wasps was positively correlated to air temperature. Host nest density positively affected only H. rutilans activity, in agreement with previous reports for other populations of this species, whereas the daily pattern of activity of the host was the key correlate with the activity of H. nobile. Mortality due to cuckoo wasps was low for both digger wasps, although it was somewhat higher at sites with many nests of P. triangulum. We suggest that perhaps the degree to which digger wasps time their activity to avoid cuckoo wasps is related to the degree of specialization in host choice by their brood parasite. H. rutilans is more highly dependent on P. triangulum, which may have had a greater effect on the timing of provision by its host.