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Bee undergoing artificial insemination. © INRA, Guillaume Kairo

Bee declines: male exposure to pesticides indirectly affects queen reproductive capacity

Recent INRA research published in Scientific Reports shows that exposing male bees to fipronil, a pesticide, affects sperm quantity, mortality, and metabolism. It also revealed that virgin queens inseminated with semen from these males had 30% fewer live sperm available for fertilizing their eggs. These reproductive repercussions could be contributing to bee declines, which have been observed in bee colonies across the world over the last few decades.

Updated on 09/12/2016
Published on 09/06/2016

The use of systemic pesticides, such as fipronil and those in the neonicotinoid family, is the subject of fierce debate because such compounds have lethal and sublethal effects on pollinators, including honey bees. Although much attention has been paid to the impacts on female workers, much less is known about what is happening to reproductives, who play an essential role in the colony.

  

Fipronil exposure reduces sperm quantity and quality in male bees

Scientist capturing male bees at the end of the pesticide exposure experiment.. © INRA, Guillaume Kairo
Scientist capturing male bees at the end of the pesticide exposure experiment. © INRA, Guillaume Kairo

 

INRA researchers have become interested in the relationship between pesticide exposure and semen quality. In a recent experiment, they reared male bees, called drones, from emergence to sexual maturity under semi-field conditions. In itself, this part of the experiment was rather challenging and required the researchers to develop a unique methodology.

Each day, drones in the experimental group were given access to a syrup containing a low dose of fipronil (0.1 µg/L, or 0.1 ppb). As in colonies in the wild, they were also fed crushed pollen and water. Once the drones reached sexual maturity, they were captured so researchers could carry out further analyses. The results were clear: exposure to fibronil altered male fertility by affecting spermatozoa quantity, mortality, and metabolism.

  

 

 

 

Nearly one-third fewer live sperm found in queens inseminated with semen from fipronil-exposed males

Bee undergoing artificial insemination. © INRA, Guillaume Kairo
Bee undergoing artificial insemination © INRA, Guillaume Kairo

The researchers then went a step further: they examined the repercussions of decreased male fertility on female reproductive capacity. The queen plays a key role in the life cycle of her colony. Young, virgin queens mate with several drones and store the accumulated semen in their spermathecae. This reserve will be used to fertilize their eggs over their lifetimes and thus produce a continual supply of female workers, ensuring colony survival. In the experiment, scientists artificially inseminated virgin queens and then kept them under laboratory conditions for two weeks. They then examined the sperm that had been stored in their spermathecae. The results revealed that, in females who had been inseminated with semen from fipronil-exposed males, the number of live spermatozoa was 30% lower.

These findings suggest that when drones are exposed to fipronil and subsequently mate with virgin queens, the mechanisms involved in selective semen retention by females are altered. The effects of pesticides on bee reproductive systems could be playing a role in queen failure, which has been observed in many bee hives and which translates into premature queen death and/or problems with worker production, ultimately impairing colony development.

These INRA findings regarding the effects of pesticides on bee reproduction may help explain colony collapse disorder and bee declines, which have been observed around the globe over recent decades. They clearly show that the reproductive changes induced in males can have highly negative impacts on the colony as a whole.

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Plant Health and Environment
Associated Centre(s):
Provence-Alpes-Côte d'Azur

Reference

Kairo Get et al. Drone exposure to the systemic insecticide Fipronil indirectly impairs queen reproductive potential. Scientific Reports 6: 31904; DOI: 10.1038/srep31904 (2016)