What are the main factors limiting the distribution of Bembix rostrata (Hymenoptera: Crabronidae) at early-succession sites?
Abstrakt
Bembix rostrata (Hymenoptera: Crabronidae) is a conspicuous digger wasp, which is one of the most threatened species of bees and wasps in central Europe. Its distribution is restricted to sites with grey dunes or similar habitats, which B. rostrata needs for nesting.
In the years 2012-2014, we have studied the ecological factors influencing the presence of this species in two localities in the Czech Republic, where this species is still relatively abundant. We found that B. rostrata needs continuity in the characteristics of the locality in time because B. rostrata avoids settling in newly emerging localities with the appropriate substrate.
The decline in localities of B. rostrata in the Czech Republic correlated with habitat loss due to afforestation, incorrect conservational management, and isolation of the localities. The newly formed anthropogenic sites with fine-grained loose substrates, such as sandpits or fly ash deposits, were not colonised by B. rostrata.
This is in sharp contrast with another species of the genus, Bembix tarsata, which is also endangered, but successfully settled in many bare sand patches on former lignite spoil heaps in the north-west of the country. We found that both species hunt Diptera as a prey for their larvae; both are generalists with a preference for species of the family Syrphidae.
Unexpectedly, we found workers of the honeybee Apis mellifera captured as a prey for larvae of B. rostrata. Implications for insect conservation Newly applied management tools, such as army vehicles use, manual sand scraping, or plant cover removal, have a positive effect on populations of B. rostrata, as well as on other species with similar ecological requirements.