July 27, 2016

expert reaction to study investigating the effect of neonicotinoid pesticides on male honeybee fertility

The effect of neonicotinoids on the fertility of male honeybees is examined in a paper published in the journal Proceedings of the Royal Society B in which the authors report that the insecticide reduced lifespan of the bees in question as well as sperm viability but not sperm quantity.

All our previous output on this subject can be seen here.

Prof. Nick Birch, Senior Entomologist, James Hutton Institute, said

“This is an interesting paper with some potential implications on the long-term, sub-lethal effects of neonicotinoids, but it needs follow up research to validate and extrapolate the findings to the actual farming situations in Europe. Some caveats to make note of include the lack of proof of intake (amounts consumed) of the pesticide in feeding bees and the lack of exposure measurements, as drones typically eat three times the amount of female worker bees yet the effects of the pesticides on longevity look broadly similar between the two sexes. There is also no discussion of the genetic variation between honeybee populations in sensitivity to neonicotinoids, as previous research has demonstrated high levels of variation in sensitivity between different bee populations.”

Dr Peter Campbell, Senior Environmental Risk Assessor at Syngenta, which manufactures and sells the neonicotinoid Thiamethoxam, said:

“This is interesting new research investigating the potential effect of thiamethoxam and clothianadin on the fertility of male drone honeybees. Whilst the authors report a reduction in living sperms for neonicotinoid-fed bees the data also show that sperm production was highly variable during the experiment for both control and treated bees, and indeed, the authors themselves report that sperm quality of drones in this study was reduced in comparison with previous published studies. Interestingly in this study, the reported sperm viability of neonicotinoid-exposed drones was still well within the range reported in a previous published paper (Pettis et al 2016; Peng et al 2015) for health honeybee colonies. In the discussion of their findings, the authors do not discuss the significance and relevance of these findings from a study where bees are directly fed neonicotinoid treated pollen into the hives for 38 days, to effects on free foraging bees under realistic conditions of use. Given the multiple mating of honeybee queens it is unclear what the consequences of a reduction in sperm quality would actually have on queen fecundity.”

Dr Christopher Connolly, Reader in Neurobiology at the University of Dundee, said:

“This study examined the impact of exposure to two neonicotinoids (thiamethoxam and clothianidin) on male honeybee (drone) survival and sperm quality. This study is important, as failures in honeybee queen mating is reported to be a growing problem for beekeepers.

“Drones from insecticide treated colonies had shorter life spans and a modest, but significant, decrease in sperm viability. Honeybee queens mate with many males during a short period of orgy, followed by a lifetime of celibacy, depending on the use of stored sperm for the rest of her lifetime. Once this runs out, the queen can no longer produce worker bees and is replaced by the colony or the beekeeper. The question that arises from this study is whether honeybee queen fertility is compromised and whether she can be effectively replaced when required (this cannot be done during winter).

“Although the insecticide levels used in this study are realistic, it is unclear whether both neonicotinoids are commonly consumed together at these levels. Therefore, it will be important to investigate the impact of the neonicotinoids separately. This is also important as previous evidence indicates that different neonicotinoids may exert opposing effects on bumblebee queen production and sex ratios of colonies. Likewise, different beneficial insect species need to be investigated as thiamethoxam has been reported to differentially affect the sex ratio of different species, with fewer (honeybees), or more (bumblebees) male found.

“Importantly, this study demonstrates the complexity of the possible consequences from chronic exposure to pesticides and these are not assessed during safety testing. Therefore, this study further supports the need to adopt the precautionary principle on neonicotinoids until robust evidence is available for each chemical on selected beneficial insects that we decide to protect.

“It is important to stress that although the mechanism of this effect on bee sperm quality is unknown; if this is a receptor dependent process then it is unlikely to be responsible for a similar dysfunction in humans.”

‘Neonicotinoid insecticides serve as inadvertent insect contraceptives’ by Straub et al. published in Proceedings of the Royal Society B on Wednesday 27h July. 

Declared interests

Dr Peter Campbell: Dr Campbell’s employer, Syngenta, manufactures and sells the neonicotinoid Thiamethoxam.

Dr Christopher Connolly: No conflicts of interest