Semi-field testing of the solitary bee Osmia bicornis (L., 1758) (Hymenoptera, Megachilidae) in flowering Phacelia tanacetifolia – Chances, improvements and limitations

Based on the proposed test design of the ICPPR non-Apis working group, a semi-field (tunnel) study was conducted with the solitary bee Osmia bicornis (L., 1758) in flowering Phacelia using tunnels. Untreated crop was used as a control, and the insect growth regulator fenoxycarb as a test item which is intended to be used as reference item for this study type. To improve the design and to enhance the informative value of such studies our method deviated in three points: placing the cocoons in the tubes of the nesting units, performing additional brood assessments in two to three day intervals and increasing the application rate of the test item. Overall the results indicated that the proposed test design is suitable to perform studies on O. bicornis in Phacelia under semi-field conditions.Data on the reproduction performance, brood termination and hatching rate of the progenies show low variability between the replicates in both treatment groups. No impact on the flight activity, mortality, reproduction performance and hatching success of the progenies was observed, but an increased brood termination rate of larvae produced within the first days after application was recorded; in particular, placing the cocoons in the tubes lead to higher proportions of nesting established females. Moreover, due to the assessment of the cell production in 2 to 3 day intervals, it is possible to analyse time dependent effects on the reproductive performance, brood termination and hatching rate which can be expected by the decreasing exposure in the course of the study. And finally, it is shown that fenoxycarb is not a suitable reference item for such studies.