Pesticides make it harder for male bees to attract mates

Around the world, bees are facing many threats, including toxic pesticides, climate change, disease, and habitat loss. An international research team led by Julius-Maximilians-University (JMU) Würzburg has investigated the impact of pesticides on the reproduction of wild bees. The experts have discovered that pesticide exposure interferes with reproduction among wild bees in the very earliest phase – the mating phase. 

The results of the study revealed that exposure to agrochemicals reduces the fitness of both male and female bees. This indicates that the decline of wild bees in agricultural areas may be the result of their reduced fertility due to pesticides.

To identify the factors that may be contributing to the decline of wild bees, the researchers focused on the early stages of the insects’ reproduction. They exposed horned mason bees to a non-lethal dose of the fungicide fenbuconazole. When choosing a partner to mate with, female mason bees evaluate males based on signals such as their odor and thoracic vibrations. 

“If the fungicide has an effect on male quality signals, this should increase the likelihood that pesticide-exposed males will be rejected by females,” explained study lead author Samuel Boff. 

“We also found that the pesticide-exposed males vibrate their thoracic muscle less and also had a different odor composition than the un-exposed males. The decline in bee populations in agricultural landscapes could therefore be explained by the effect of pesticides on insect mating behavior.”

According to the researchers, this study is the first to demonstrate that a fungicide with low toxicity disrupts the reproduction of bees in the mating phase. 

“Our study shows that the early stages of bee reproduction must be included in the risk assessment of pesticides,” said study co-author Professor Thomas Schmitt.

Boff hopes for broader testing of different pesticides on bee behavior and their chemical signals so that bees can be more effectively protected.

“The results provide evidence that can help to understand how pesticides might lead to reduced bee populations world-wide, especially in crop sites,” wrote the researchers. “Our study on mating behavior and sexual signals sheds the light on a new path to explore the impact of environmental stressors on insect decline.” 

“Due to the importance of bees for pollination service provision, we stress the need for the inclusion of mating experiments on safety test programs of chemical products used in agriculture, to understand the effect of pesticides on the reproductive system of beneficial insects such as bees.”

The study is published in the Journal of Applied Ecology.

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By Chrissy Sexton, Earth.com Staff Writer