Neonicotinoid insecticides can serve as inadvertent insect contraceptives

The researchers examined the effects of two neonicotionoids, thiamethoxam and clothianidin, on male honey bees’ reproductive capacity. Twenty honey bee colonies were established and treated colonies were fed pollen paste containing either 4.5 ppb thiamethoxam or 1.5 ppb clothianidin for 50 days. Once the males emerged, they were examined for abnormalities and the presence of Varroa destructor. Workers and drones were collected from each colony for a total of six hoarding cages of bees (10 drones and 20 workers) per colony. Drones were removed from randomly selected cages (three per colony) once they reached sexual maturity for sperm quantity and viability (proportion of sperm alive) assessments. The researchers found no significant difference in drone body mass between treatment and control groups. However, the median longevity of treated drones was significantly lower than controls with close to 50% difference in survival rates. Sperm quantity in drones was not significantly different, but sperm viability was significantly lower in treatment groups. There were on average approximately 39% less living sperm in treatment groups compared to controls. Declines in drone longevity and sperm viability can affect the success of colonies and the genetic variation within them (Straub et al. 2016). While this research study is not directly related to bumble bees, it indicates that neonicotinoid insecticides, in addition to having lethal and sublethal effects on bees, may be affecting reproductive capacity of males.

Straub et al.
Proceedings of the Royal Society of Biology
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