Glyphosate disrupts brood care in bumblebees

The decline of pollinators is threatening ecosystems and economies around the world. According to a new study, pollinator decline is likely the result of increased pesticide use in agriculture. The world’s most widely used herbicide, glyphosate, may contribute more to this development than was previously known.

The study was led by Dr. Anja Weidenmüller, an expert in the Centre for the Advanced Study of Collective Behaviour at the University of Konstanz. The researchers set out to investigate how bumblebee colonies regulate the temperature of their brood.

Bumblebee colonies use nectar as “fuel” to keep their broods at a temperature of about 32 degrees. “Just as we humans keep our body temperature constant, the animals in a colony collectively show homeostasis in the temperature regulation of their brood,” said Dr. Weidenmüller. 

This thermoregulation is important for colony development. The study clearly showed that glyphosate impacts the collective thermoregulatory capacity of bumblebee colonies.

Broods require high temperatures to develop from egg to bumblebee, and to develop a colony from a single queen to several hundred individuals. When these colonies are exposed to glyphosate, resources become limited and the collective thermal behavior is affected. Unfortunately, the impacts don’t stop there. 

“Bumblebee colonies are under really high pressure to grow as quickly as possible within a short period of time,” explained Dr. Weidenmüller. If the colony cannot maintain the necessary brood temperature, the brood will develop slowly or not at all. This limits the growth of the colony. “Only when they reach a certain colony size during the relatively short growth period are they able to produce the sexually reproductive individuals of a colony, i.e. queens and drones.”

Bumblebee colonies contaminated by glyphosate are less able to keep their brood warm. In Germany’s agricultural landscape, fewer wild flowers are available to insects, resulting in resource scarcity. “The combination of resource scarcity in cleared agricultural landscapes and pesticides can therefore pose a massive problem for colony reproduction.” 

According to Dr. Weidenmüller, rethinking the approval process for pesticides is critical to bumblebee survival. Current approvals only test how many animals die after coming into contact with a substance after 24 or 48 hours. 

“Sublethal effects, i.e. effects on organisms that are not lethal but can be seen, for example, in the animals’ physiology or behaviour, can have a significant negative impact and should be taken into account when pesticides are approved in future,” noted Dr. Weidenmüller. 

The study revealed that bumblebees exposed to glyphosate also lived an average of 32 days, thus reaching an average bumblebee age. This research approach can be applied to many of the commonly used pesticides, such as other herbicides and fungicides. Currently, information is lacking on the effects of pesticides on wild bees and other pollinators. 

Glyphosate is currently approved for use in the EU until 15 December 2022. The Glyphosate Renewal Group (GRG) applied for renewal in 2019.

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By Katherine Bucko, Earth.com Staff Writer