Cavity-nesting bees and wasps (Hymenoptera: Aculeata) of xerothermic habitats are unable to use cavities in reed galls
Abstract
Galls induced by Lipara lucens on common reed are adopted by bees and wasps as a nesting cavity. Most of these species occur only in wetlands.
Some of them are specialised or show strong preference to nest only in reed galls. In our manipulative study, we deployed trap nests of reed galls to 16 steppic grasslands or open sandy xerothermic habitats in the Czech Republic.
Surprisingly, we reared from a total of 1,523 galls only 31 specimens of five nesting species and one predator-inquiline. Trap nests of identical design, which we previously deployed to wetlands, contained four-times more individuals of twice as many nesting species and four parasite species.
Moreover, the most abundantly reared species in reed galls deployed to the steppic habitats was Pemphredon fabricii (58% of total individuals). This species is strictly specialised for nesting in reed beds.
Therefore, this experiment revealed that bees and wasps of xerothermic habitats are likely to have difficulties in finding the gall opening. The cavities of similar size are readily occupied by xerothermophilous bees and wasps when provided.
In contrast, despite the Lipara-induced reed gall having a broad opening, it is hidden at the top of the gall in fibrous remnants of leaves, and the non-specialist bees and wasps are unable to locate it. This is the first evidence on an overlooked aspect of cavity quality - the cavity may be present and suitable but is too difficult for the insect to find.