Pesticides: inadvertent anti-aphrodisiac in male bees

A newly-published research demonstrates that a common pesticide reduces both mating success and sperm traits of male bumblebees

Sexual reproduction is common to almost all multi-cellular organisms and can be compromised by environmental pollution, thereby affecting entire populations. Even though there is consensus that neonicotinoid insecticides can impact non-target animal fertility, their possible impact on male mating success is currently unknown in bees.

A recent scientific publication, led by the University of Bern (Switzerland) and in collaboration with the Bee Health and Behaviour Lab @UNITO, shows that sublethal exposure to a neonicotinoid significantly reduces both mating success and sperm traits of male bumblebees. The data demonstrate for the first time that neonicotinoid insecticides can impair male mating behaviour and reproductive success

in bees. The field-realistic exposure of drones to thiamethoxam not only led to 32% fewer copulations, but also reduced their total living sperm quantity by 23%. This evident effect on sperm quality became further prominent in the females inseminated by exposed males, as they revealed a 50% reduction in total living sperm quantity in the spermatheca of female bumblebees compared to their respective controls (Fig. 1).

Figure 1. Spermatheca dissection of a mated bumble bee gyne, Bombus terrestris. A) Ventral view of the abdomen prior to dissection. The red arrow points to the stinger of the gyne. Bilateral incisions were made using microscopy scissors at the caudal point of the abdomen starting from the beginning of the 6th to the end of the 4th tegeral segment (indicated by the red dashed lines) to reveal the inside of the abdomen. B) Ventral view of the abdominal cavity where the red arrow points towards the stinger and the red circle indicates the spermatheca. C & D) Enlarged view of the spermatheca.

Given that holds true for the field, this provides a plausible mechanism contributing to declines of wild bee populations globally. The widespread prophylactic use of neonicotinoids may therefore have previously overlooked inadvertent anti-aphrodisiac effects on non-target animals, thereby limiting conservation efforts.

Given the apparent key role of sex and the indispensable role of functional males, the data are of particular concern in light of ubiquitous neonicotinoid contaminations and thus may constitute a possible mechanistic explanation for recent bumblebee population declines.

Reference:
Straub L, Minnameyer A, Camenzind D, Kalbermatten I, Tosi S, Van Oystaeyen A, Wäckers F, Neumann P, Strobl V (2021) Thiamethoxam as an inadvertent anti-aphrodisiac in male bees. Toxicol. Reports 9, 36–45. https://doi.org/10.1016/j.toxrep.2021.12.003