A neonicotinoid impairs male fertility in solitary bees

Low doses of a common pesticide reduce sperm quantity, viability, and total living sperm in solitary bees

The ongoing loss of global biodiversity is endangering ecosystem functioning and

human food security. While environmental pollutants are well known to reduce fertility,

the potential effects of common neonicotinoid insecticides on insect fertility remain

poorly understood (Fig. 1).

Figure 1. Osmia cornuta male genitalia and sperm. (A) Overview of the genitalia of an unmated male showing testis (te), vesica seminalis (vs), accessory gland (ad), glanuar gland (grd),

lateral ejaculatory duct (led), gonobase (gb), gonocoxites (gc), lateral penis valve (lpv) and the endophallus (ep). (B) Fluorescence stained male sperm, whereby living sperm are

stained blue and dead are red using Hoechst 33342 and propidium iodide, respectively.

A new publication, led by the University of Bern (Switzerland) in collaboration with the Bee Health and Behaviour Lab @UNITO, shows we show that field-realistic neonicotinoid exposure can drastically impact male insect fertility. Despite males being exposed to higher dosages of thiamethoxam, females revealed an overall increased hazard rate for survival; suggesting sex-specific differences in toxicological sensitivity. All tested sublethal concentrations (1.5, 4.5 and 10 ng/g) reduced sperm quantity by 57% and viability by 42% on average. The lowest tested concentration lead to a reduction in total living sperm by 90%.

Since the tested sublethal thiamethoxam concentrations match estimates of environmental pollution with this class of chemicals globally, the observed male infertility is almost inevitable and will certainly impact insect populations.

Taken together with similar reports from other species, including humans, it appears as if male infertility due to environmental pollutants (e.g. DDT, plastic, and neonicotinoids) may be a driving force behind the ongoing declines in biodiversity.

As the tested sublethal concentrations match estimates of global neonicotinoid pollution, this reveals a plausible mechanism for population declines, thereby reflecting a realistic concern.

An immediate reduction in environmental pollutants is required to decelerate the ongoing loss of biodiversity.

Reference:
Strobl V, Albrecht M, Villamar-Bouza L, Tosi S, Neumann P, Straub L (2021) The neonicotinoid thiamethoxam impairs male fertility in solitary bees, Osmia cornuta. Environ. Pollut. https://doi.org/10.1016/j.envpol.2021.117106