Poor nutrition and pesticides a double whammy for bees

Research finds the effects of individual stressors are ramped up when combined. Geetanjali Rangnekar reports.

Lack of food and the presence of pesticides combine to increase survival risk for bees.
Lack of food and the presence of pesticides combine to increase survival risk for bees.
Monique Berger/Getty Images

Poor nutrition and pesticide exposure can work in a deadly combination to cut short the life of honeybees, joint research from the US and Italy has found.

The first-of-a-kind findings were published in the journal Proceedings of the Royal Society B. The study, led by Simone Tosi from the University of California, San Diego, and the University of Bologna, sheds light on what could be causing worldwide declines in bee populations.

Bees are nature’s great pollinators and foragers, but continued habitat destruction for agricultural use has reduced biodiversity, thereby diminishing the quality and quantity of nectar available to these insects. To make matters worse, bees come into contact with pesticides while feeding in the vicinity of treated fields, which seriously damages their health.

Tosi and colleagues conducted experiments to determine if the adverse effects poor nutrition and pesticide exposure were worse when both were present.

They subjected bees from five colonies to a variable diet, adjusting total food amount and sugar content – the latter important as fuel to power flight. The insects were also exposed to carefully calibrated doses of two neonicotinoid pesticides, clothainidin (CLO) and thiamethoxam (TMX). The levels were akin to what honeybees encounter when foraging for nectar.

The scientists found that nutritional stress, caused by poor or inadequate sugar intake, acts hand in hand with the neurotoxic effects caused by pesticides exposure to reduce honeybee survival by 50%.

Additionally, stores of glucose and other energy-rich sugars in the haemolymph—the equivalent of blood in insects — were reduced only two hours after exposure, potentially adversely affecting sugar metabolism.

Interestingly, a high sugar diet protected the bees against the detrimental effects of the pesticides. Even if bees were not exposed to the chemicals, but fed poorly, they still fared better than those exposed to both factors.

The most sobering thing about the findings is that the results were obtained under experimental conditions, in a controlled environment. In the real world, bees could be exposed to many additional environmental stressors.

The authors hope that the new findings will translate into better and more stringent toxicity testing of pesticides used in agricultural practices.

  1. http://rspb.royalsocietypublishing.org/content/284/1869/20171711
  2. http://rspb.royalsocietypublishing.org/content/284/1869/20171711
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