In vitro effects of imidacloprid on honey bee sperm: evaluation using computer-aided sperm analysis (CASA)

Abstract

Pesticides are considered as the most important factors of pollinators’ decline. Imidacloprid (IMD), belonging to Neonicotinoids class, is widely used as a powerful insecticide but generating important negative effects on honey bees. The current study investigated the direct effect of IMD on bee spermatozoa. The experimental design consisted of in vitro co-incubation of bee gametes with three different concentrations of IMD 1, 10, and 25 μM for 15 min. Conventional microscopic and Computer-aided sperm analyses (CASA) were concomitantly used with a dual goal: to evaluate objectively the effects of IMD on sperm parameters on the one hand and to report computer kinematic parameters in the control group, without IMD treatment, on the other hand. The results revealed apparent negative effects in a dose-dependent manner with motility collapsing completely at 25 μM of IMD. The current results highlighted the direct impact of IMD on bee spermatozoa and revealing the potential subsequent effects on bee reproduction. This study reported also drone computer sperm parameters that could serve as a reference in the studied region. Bee sperm velocities showed the lowest values ever reported in the different animal species. The CASA system appeared as objective and a sensitive method to detect subtle toxic effects on bee sperm, and this opens real perspectives particularly in studying existing correlations between CASA parameters and fertility outputs of different environmentally toxic molecules.