Hormonal modulation of reproduction and fertility signaling in polistine wasps

In social insects, it has been suggested that reproduction and the production of particular fertility-linked cuticular hydrocarbons (CHC) may be under shared juvenile hormone (JH) control, and this could have been key in predisposing such cues to later evolve into full-fledged queen pheromone signals. However, to date, only few studies have experimentally tested this “hormonal pleiotropy” hypothesis. Here, we formally test this hypothesis using data from four species of Polistine wasps, Polistes dominula, Polistes satan, Mischocyttarus metathoracicus, and Mischocyttarus cassununga, and experimental treatments with JH using the JH analogue methoprene and the anti-JH precocene. In line with reproduction being under JH control, our results show that across these four species, precocene significantly decreased ovary development when compared with both the acetone solvent-only control and the methoprene treatment. Consistent with the hormonal pleiotropy hypothesis, these effects on reproduction were further matched by subtle shifts in the CHC profiles, with univariate analyses showing that in P. dominula and P. satan the abundance of particular linear alkanes and mono-methylated alkanes were affected by ovary development and our hormonal treatments. The results indicate that in primitively eusocial wasps, and particularly in Polistes, reproduction and the production of some CHC cues are under joint JH control. We suggest that pleiotropic links between reproduction and the production of such hydrocarbon cues have been key enablers for the origin of true fertility and queen signals in more derived, advanced eusocial insects.

DNA barcodes and new primers for nature’s pest controllers: the social wasps

Globally, biodiversity is declining as a result of anthropogenic pressures, and this could lead to extinction of some species before they are discovered. The loss of insect taxa is of prime concern, given recent reports of significant declines in the populations of many taxa across the globe. Efforts to document biodiversity have met with several challenges, amongst which are the difficulties in using morphological features to discriminate species, especially in insects. DNA barcoding is a rapid and reliable method for species identification and discovery, but choosing appropriate primers to amplify the barcode region without coamplifying contaminants remains a key challenge. We developed and tested a set of primers for PCR amplification of the DNA barcode region of the COI gene in polistine wasps. We tested their efficacy in 36 species of vespid wasps, and the solitary wasp Zethus miniatus Saussure. Samples were obtained from Africa, Americas, Asia and Europe. The polistine-specific primers successfully amplified the barcode region for all polistines tested, without amplifying any Wolbachia present; they also worked with many species from the other Vespidae wasp subfamilies. The new primers are valuable for the discovery and accurate documentation of polistine wasps in the four continents.

A molecular approach to studying Hymenoptera diets using polistine wasps

The study of animal diets has benefited from the rise of high-throughput DNA sequencing applied to stomach content or faecal samples. The latter can be fresh samples used to describe recent meals, or older samples, which can inform about past feeding activities. For most invertebrates, however, it is difficult to access ‘historical’ samples, due to the small size of the animals and the absence of permanent defecation sites. Therefore, sampling must be repeated to account for seasonal variation and to capture the overall diet of a species.This study develops a method to describe the overall diet of nest-building Hymenoptera based on a single sampling event, by analysing prey DNA from faeces accumulated in brood cells. We collected 48 nests from two species of introduced paper wasps (Polistes chinensis, and P. humilis) in the urban and peri-urban areas of Auckland, New Zealand, and selected two samples per nest. One from brood cells in the outer layer of the nest to represent the most recent diet, and one from brood cells in an inner layer to represent older diet.Diet differed between species, although both fed mainly on Thysanoptera, Lepidoptera and Acariformes. Prey taxa identified to species level included both agricultural pests and native species. Prey communities consumed were significantly different between inner and outer nest samples suggesting seasonal variation in prey availability and/or a diversification of the wasps’ diet as the colony grows. We also show for the first time potential predation of marine organisms by Polistes wasps.Our study provides field evidence that polistine wasps feed on agricultural pests, supporting the hypothesis that some social wasp species could have a suppressing effect on agricultural pests. The proposed methodology is readily applicable to other nest-building Hymenoptera and has the potential to provide comprehensive knowledge about their diet with minimum sampling effort. Such knowledge is Essential to measure the ecological impact of invasive Vespidae and support the conservation of native invertebrate biodiversity.

The Thermoregulatory Behavior of Nectar Foraging Polistine Wasps (Polistes dominula and Polistes gallicus) in Different Climate Conditions

Polistine wasps collect nectar for their energetic demand and for the provision of the brood. They are mainly ectothermic during different behavioral tasks. We investigated the body temperature of two species living in differing habitats and climate regions, in order to reveal the environmental influence on their thermoregulatory behavior. The species were Polistes dominula in the temperate climate of Central Europe, and Polistes gallicus in the warm Mediterranean climate of Southern Europe. The wasp’s body temperature was measured during foraging on lovage (Levisticum officinale) and fennel (Foeniculum vulgare) by infrared thermography in the entire ambient temperature range they are usually exposed to (Ta ~ 20–40 °C). The temperature of all body parts increased nearly linearly with ambient temperature, with the thorax as the warmest part. To achieve optimal foraging temperatures, they preferably use solar radiation. An “operative temperature model” enabled the evaluation of the endothermic effort. Polistes dominula foraging on lovage exhibited no endothermic activity. However, while foraging on fennel they had a weak and almost constant endothermic performance of about 1 °C. Polistes gallicus, by contrast, exhibited mostly no or only minor endothermy during foraging. Both wasps avoid a high energetic effort and this way reduce their foraging costs.

Morphological Differences between Reproductive and Non-reproductive Females in the Social Wasp Mischocyttarus consimilis Zikán (Hymenoptera: Vespidae)

Phenotypic divergence plays an important role in establishment of the reproductive division of labor among castes in social insects; however, little is known about this subject in independent-founding polistine wasps. In this study, we investigated morphological differences among foundresses from associative and solitary foundations, as well as among females produced in different phases of the colony cycle in Mischocyttarus consimilis Zikán. Our results showed that the alpha foundress had significantly greater body size than auxiliary foundresses, although it did not differ in size from solitary foundresses. In addition, the alpha foundress had greater ovarian development than their auxiliary and solitary foundresses. We also demonstrated that gynes were significantly larger than workers. These results therefore suggest that the phenotype of females emerging in colonies M. consimilis can vary with the progress of the colony cycle, and that body size and ovarian condition are closely linked to the function performed by the foundress.