Hunting behaviour of predatory wasps (Hymenoptera: Vespidae: Eumeninae): is the distribution of stinging effort phylogenetically inherited or dependent on the prey type?

Abstract

Ancistrocerus, Discoelius and Symmorphus are xylicolous predatory wasps, the former two genera hunting caterpillars, the last one using both caterpillars and larvae of Chrysomelidae beetles. One of the aims of this study was to compare the stinging pattern of species from these genera with the ancestral “complete four-sting pattern” (C4SP) and reduced “two-sting pattern” (C2SP). Another aim was to clarify whether stinging pattern of predatory wasps depends mostly on the prey type or on the systematic position of the wasp. Sting traces on 6123 paralysed prey specimens, taken from 409 fresh wasp nests made by 10 wasp species in reed (Phragmites australis) trap-nests in three localities of Lithuania, were studied. The total number of stings applied to a prey specimen, the number and the share of stings directed to its body segments and the probability of stinging the segments were considered. The main conclusions of the study are: (1) the total number of stings delivered to a prey is species-specific, in some cases it may be used to distinguish fresh nests of related wasp species, as those of Symmorphus crassicornis and S. murarius and those of Discoelius dufourii and D. zonalis. (2) The distribution of stings is significantly different from the basic patterns C4SP and C2SP in all ten studied wasps; however, four caterpillar-hunting species have the distribution close to the C2SP The stinging pattern of three Symmorphus species hunting Chrysomelidae larvae included regular stings to the throat, three thoracic and the first abdominal segment; it could be abbreviated as C5SP (a complete five-sting pattern). (3) The distribution of stings among the segments of prey was found to be more dependent on the taxonomic position of the wasp species than on the prey type, thus it might be used as a behavioural character in comparative and phylogenetic studies. (4) The stinging pattern depended on the prey type as well: in the caterpillar-hunting S. debilitatus, it was quite different from the stinging pattern of the Symmorphus that hunt Chrysomelidae larvae.