Effects of dietary lambda-cyhalothrin exposure on bumblebee survival, reproduction, and foraging behavior in laboratory and greenhouse

Abstract

Bumblebees of Bombus terrestris are indispensible pollinators for ecosystems and for various agricultural crops. Unfortunately, bumblebees are challenged by various stress factors including insecticide applications. Today sublethal effects of various insecticides need to be thoroughly investigated to allow their combined use with pollinators and other beneficial organisms. In this study, we used lambda-cyhalothrin as a model pyrethroid insecticide and investigated lethal and sublethal effects by different dilutions, ranging from 1/10 to 1/100 of its maximum field recommended dosage (MFRC, 37.5 ppm), with the use of a chronic toxicity tests in the laboratory and in flight cages in the greenhouse. In the laboratory, small microcolonies with five bumblebee workers with one being pseudo-queen were used, while in the greenhouse we used queen-right mini-hives where the bumblebees need to fly for pyrethroid-contaminated food. We observed strong sublethal effects in the laboratory with treatments of 1/10 and 1/20 of the MFRC: the nest reproduction was reduced by 49 and 32 %, respectively, and the sugar water consumption by 36 %. With free-flying bumblebees, the toxic effects at 1/10 of the MFRC were more pronounced. A mortality of 88 ± 8 % was observed after only 2 weeks, being twice the mortality in the laboratory microcolonies test (43 ± 11 %). Besides, it should be mentioned that in the greenhouse experiment all queens were dead and most of the workers showed signs of incoordination and convulsion and gradually became apathetic. In conclusion, our results demonstrated the pyrethroid lambda-cyhalothrin with a range of lethal and sublethal effects, both crucial for the development and survival of the B. terrestris colonies. Moreover, this study supports the demand to test insecticide compounds on their safety, especially when the bees have to perform complex tasks such as foraging for their food.