The red mason bee Osmia bicornis under the influence of pesticide stress and food availability

Pollination is a key ecosystem service provided mostly by insects of which bees are the primary pollinators. In anthropogenically modified agriculture, however, bees are exposed to various stress factors that have caused a worldwide decline in both honey and wild bee populations. The drivers of bee losses named the most are increased pesticide application, pathogen and parasite infestation, landscape fragmentation and a decline in field margins that provide both food and habitat. Considering increasing concerns over honey bee losses, pollination by European wild bees, particularly the widespread red mason bee Osmia bicornis is already increasingly investigated as supplementary pollinator in fruit orchards due to their early flight activity in spring which makes them highly suitable pollinators for early blossoms like apples and cherries.

My Master's thesis deals with Osmia bicornis [1] under the stress of pesticides and [2] the influence of varying levels of food abundance.

[1] In a laboratory ring test, the acute oral and contact toxicity of the insecticide Dimethoate is investigated. Additionally wing contact exposure is tested as a new route of penetration. In the Tier I approach, the risk of pesticides to bees is usually assessed through oral and contact exposure. With application of the substance on the thorax as a worst-case exposure representing all possible contact exposure scenarios, routes of entry other than the thorax are not considered in risk assessment. We aim to investigate this new route of exposure via wing contact with the solitary bee Osmia bicornis to determine if mortality can be induced in this exposure scenario. Comparison of acute thorax and wing contact LD50 values are compared to evaluate if contact exposure through the wings is a relevant exposure scenario that should be considered in pollinator risk assessment (Poster).

[2] In a field trial we aim to investigate how food availability influences the attractiveness of nesting aids to Osmia bicornis and the subsequent brood development. Literature on the foraging behaviour of Osmia bicornis is limited and does not unequivocally demonstrate if the females are able to explore alternative food sources when these are scarce around the habitat site. Nesting aids for Osmia bicornis are placed in three different habitat types: vineyards (limited pollen), small apple orchards (sufficient pollen) and rape fields (sufficient but unattractive pollen). Microscopical analysis of the collected pollen is applied in order to determine the sources, variety and abundance of the pollen stored in the nesting aids. Brood development is evaluated to determine cell building activity depending on the study location. Preliminary results demonstrate that Osmia bicornis can establish populations in habitats like vineyards which, at first glance, seem to provide very limited food. The females do not depend on richly cultivated fruit orchards in order to nest but they are able to explore a wide variety of pollen sources. Especially in vineyards that provide very limited pollen itself, the undergrowth between the rows and around the site are sufficient for the females to provide for their larvae. Populations of Osmia bicornis can thus be established and maintained in non-agricultural landscapes if enough suitable habitats are provided, e.g. any cavities in woods, walls, even empty shells and plant stems. If not present naturally, these habitats can easily be provided by man in order to contribute to the conservation of wild pollinators (Poster).


Carsten Brühl

Claudia Wollmann