Laboratory acute contact toxicity test with the leafcutter bee <i>Megachile rotundata</i>

Abstract

So far little is known about the toxicity of Plant Protection Products (PPPs) to solitary bees other than Osmia spp. as well as the inter- and intra-species sensitivity differences of honey bees and solitary bees.
Megachile rotundata is a commercially bred solitary bee which is used worldwide mainly for the pollination of alfalfa. In general, bees can be exposed to PPPs directly by contact spray application (overspray) or indirectly via nectar and pollen. The leafcutter bees additionally can be exposed to (possibly) contaminated leaf pieces which are used for the building of brood cells. Therefore, contact toxicity might be of major importance within leafcutter bee species.
Acute contact toxicity tests with M. rotundata based on the existing honey bee testing guideline OECD No. 214 were carried out, to make a first step in the direction of the development of a standard test method and collect data for the comparison of inter- and intra-species contact toxicity sensitivity. The toxic reference substance dimethoate was used as test substance. LD50/24h values of M. rotundata were compared to values of A.mellifera generated in a similar period of time.
The low mortality observed in the control also after 96 hours, confirms the feasibility and reliability of the test method. The LD50/24h values of M. rotundata in all four tests were higher compared to those of A. mellifera. Accordingly, M. rotundata appeared to be slightly less sensitive to formulated dimethoate than A. mellifera.