Honeybees age faster but bring back fattier pollen after consuming pesticide

Abstract

Fat can be a blessing and a curse, sustaining creatures through times of scarcity but also causing disease when carried in excess. However, the loss of fat carried by honeybees in the fat body triggers the insects’ transition from life as hive-bound nurses to adventurous foragers around 21 days of age, ready to embark on a search for nectar and pollen to feed the hive. The premature loss of fat caused by stress can also accelerate this ageing process, leading nurse bees to initiate the transformation sooner. Megan Deeter from the University of Arizona, USA, wondered whether these precocious foragers may also shift their choice of diet to fattier pollen, in an attempt to compensate for their loss. Joining forces with Lucy Snyder, Charlotte Meador and Vanessa Corby Harris from the Carl Hayden Bee Research Center, USA, Deeter decided to find out.‘We were interested in a group of pesticides, insect growth regulators, and their potential to affect bee ageing and behaviour’, says Deeter, who selected two pesticides, pyriproxyfen and spirodiclofen, which target different aspects of the ageing process, to discover first how dining on the chemicals affected the bees’ survival. Collecting recently emerged young adults from a hive, the team gently fed the youngsters a single 2 μl sip of sugar water laced with either pyriproxyfen or spirodiclofen, ranging from 21 to 84 ng. The researchers then monitored the bees, keeping track of those that perished, and discovered that increasing the dose of pyriproxyfen had a dramatic effect: 50% of the insects survived the weakest dose for 25 days, falling to 17 days after the strongest dose. In contrast, the size of the spirodiclofen dose seemed to have little effect on the bees’ survival.Next, the team tagged 900 bees, administered a dose of pesticide to each and monitored when the insects departed on their maiden flights – noting the insects’ ages, when they left and returned, the duration of their flight and whether they were carrying nectar or pollen when they came back, which is indicative of foraging rather than simply getting their bearings – to find out whether the pesticides affected the bees’ ageing process and behaviour. Comparing the novices’ departure ages, it was clear that all of the young adults embarked on their orientation flights around similar ages, from 5 to 15 days, regardless of the pesticide they had consumed. However, the pyriproxyfen-fed bees began foraging sooner than the insects that had been fed spirodiclofen, although when the team checked whether the insects were returning with pollen or nectar, it seemed that the pesticides did not skew the bees’ choice of diet. But were the stressful pesticides affecting the quality of the pollen that the bees returned with and the amount of fat carried by the insects in their fat bodies?Collecting returning foragers with their corbiculae (pollen baskets) crammed with pollen, the team recorded the amount of pollen they were transporting and its fat content, in addition to the mass of the insects’ fat bodies, and found that the fat stores of the spirodiclofen-fed bees dwindled significantly, causing them to age faster and collect less pollen, but the pollen they collected was fattier.So, stressed forager bees lose their fat reserves faster than unstressed bees, especially when fed spirodiclofen, which prevents the insects from producing fat, but the insects compensate for their loss by bringing back fattier pollen, whereas bees that have consumed pyriproxyfen begin ageing faster and foraging sooner. Deeter suggests that beekeepers provide hives with high calorie supplements to maintain the bees’ fat stores once the flowering season has passed.