Life in extreme habitats: the number of prepupae per nest of the crabronid wasp Pemphredon fabricii is constant even under pressure from high concentrations of toxic elements

Anthropogenic habitats that are contaminated by toxic elements were recently shown to host abundant and diverse assemblages of bees and wasps (Hymenoptera: Aculeata), including numerous threatened species. However, toxic elements adversely affect insect fitness. We address the effects of toxic elements on aculeate inquilines that occupy Lipara lucens-induced galls on the common reed, Phragmites australis. We hypothesized that contamination of potential nesting and feeding habitats is associated with adverse changes in bee and wasp populations that are attracted in these environments. To address this hypothesis, we analyzed the contents of As, Cd, Cu, Pb, Zn, Fe, and S in site-matched samples of soil, reed galls, and crabronid wasp bodies and correlated them with abundance and species richness of aculeate hymenopterans in reed galls and with the number of larvae in nests of the eudominant hymenopteran, Pemphredon fabricii. The common reed was present at all the examined sites, and L. lucens-induced galls were present at all but one sampling site; the single exception was the sampling site with the highest contents of four of the seven analyzed elements. The alpha diversity of gall-associated aculeate inquilines, abundance of P. fabricii, and number of prepupae per nest of P. fabricii were not correlated with the contents of any of the seven analyzed toxic elements. We found P. fabricii to be abundantly present in habitats with extreme concentrations of toxic elements. Exposed P. fabricii accumulated Cd, Cu, and Pb, while they eliminated Fe and Zn. The obtained data did not support the hypothesis that heavy metal contamination of anthropogenic sites affects P. fabricii and other reed gall-associated aculeates.