Acute Toxicity Effects of three Pesticides and their Combinations on Bombus terrestris

Bumblebees are valuable pollinators and, like honeybees, contribute to crop production worldwide. During pollination, they come into contact with pesticides, which affect their vitality and behaviour. Moreover, the applications of pesticide mixtures in agriculture increase exposure risks to many animals, including insects. In this study, Bombus terrestris workers were fed with imidacloprid, cypermethrin and dimethoate, either as single compounds or as mixtures. Each pesticide was tested at the LD50 values found in the literature and in near concentrations to these, as well as at 1/10 of the experimentally evaluated LD50, including one to four replicates per pesticide or pesticide combination. The effect on worker mortality was documented after 24h and 48h, respectively. For these experiments, individuals from different colonies with nearly the same weights were used as subjects and were marked to trace their origin. The statistical strength of the results were verified by applying Mann-Whitney-U tests. A dramatically higher mortality rate was observed in the LD50 experiments that included combinations of the three pesticides, even at the minimal dosage of 1/10 of the full LD50 value. This study also alludes to the inherent difficulties of measuring LD50 values. LD50 values found in the present experiments were much higher than those reported in the literature. The results obtained support the hypothesis that pesticide combinations are responsible
for higher mortality rates supposedly through synergistic effects.
Waibel A., Schühly W., Hernández-López J., Riessberger-Gallé U., Strobl V. & Crailsheim K. 2016: Akute Vergiftung der Hummel Bombus terrestris (Linnaeus, 1758) durch drei Pestizide und deren Kombination. – Entomologica Austriaca 23: 97–107.