Lethal and sublethal effects of several formulations of azadirachtin on IPM Impact R&D colonies of the bumblebee Bombus terrestris (Hymenoptera: Apidae)

The effects of different dose rates of the most important commercially available formulations of azadirachtin and technical powder of azadirachtin were tested on Bombus terrestris, using a new laboratory method on full standardised IPM Impact R&D colonies, starting with a mother queen and 20 callows. The maximum field recommended concentration (MFRC) was applied in the first series of tests through topical, oral pollen and oral sugar water treatment. A sequential dilution testing scheme was used, by decreasing the dose rate each time with 1/10 of the concentration of the previous trial, if triggered, until no significant effects were recorded any more. The survival of the mother queen and initial workers, the total number of formed workers/drones at the end of the test and the number of new born gynes and queen brood were determined as the most important end points. For the evaluation of the results the data were calculated and categorized in the IOBC side-effect classes, used for laboratory trials. This study confirms the practical experience and the previous laboratory trials that no negative toxic or sublethal effects may occur in practice with legally registered formulations of azadirachtin on Bombus terrestris while spraying this botanical insecticide at the recommended and authorised dose rates. Furthermore, during this research study it was found that an illegal formulation of azadirachtin, based on a naphta petroleum which has been withdrawn several years before the study was carried out, was used in the study of Barbosa, W.F., De Meyer, L., Guedes, R.N.C. and Smagghe, G. (2015). Analysis of two samples of this applied formulation, in EU and USA laboratories, proved that only a limited amount of azadirachtin -about half of the indicated amount- was contained, while a chlorpyrifos contamination was traced in the formulation.