Host specificity of the tribe Chrysidini (Hymenoptera: Chrysididae) in Estonia ascertained with trap-nesting

Abstract

Cuckoo wasps (Chrysididae) are a medium-sized and widespread family of Hymenoptera whose species are generally parasitoids or cleptoparasites of solitary wasps and bees. The identities of the hosts are known from various studies and occasional records; however the utility of such data is often low due to unstable taxonomy of the species and the inappropriate methods used to determine the host species. Therefore, despite numerous publications on the subject, the host-parasite relationships of cuckoo wasps are poorly understood. Moreover, a revision of existing literature reveals that cuckoo wasps are often unreasonably considered to be unspecialized (i.e., sharing host species). In this study we use an accurate method (trap-nests) to determine the host relationships of Estonian cuckoo wasps of the genera Chrysis and Trichrysis and determine their level of specialization. 568 trap nest bundles (each containing 15-20 single reed stems) were established at 361 locations across Estonia during the vegetation periods of 2009-2011. Nests built in traps were opened and the order of cells documented in order to determine the host-parasite relationships of mason wasps and cuckoo wasps. Altogether, 5386 insects were recorded, including 12 species of Chrysidini. Hosts of all 12 cuckoo wasp species were determined and included some not previously recorded. Analysis of host-parasite relationships revealed that Estonian species of Chrysidini exhibit a greater degree of host specialization than previously thought, with only a minimal overlap in hosts between species. Such a high degree of specialization accounts for the high species diversity of cuckoo wasps, as the diversity of parasitic insects is often associated with narrow host specialization.

Keywords

• hymenoptera
• chrysididae
• cuckoo wasps
• parasite specialization
• trap nest
• chrysis
• host specificity