Study IDs new parasite threat to honeybees

Detection could enable early intervention

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Pollinators are facing a broad range of threats, from pesticides and disease, to a new species of harmful parasites. @bberwyn photo.

Staff Report

There could be more trouble ahead for pollinators, as a new species of Varroa mite is developing the ability to parasitize European honeybees. That’s a new threat for insects already under pressure from pesticides, nutritional deficiencies and disease, according to a Purdue University study.

The scienists found some populations of Varroa jacobsoni mites are shifting from feeding and reproducing on Asian honeybees, their preferred host, to European honeybees, the primary species used for crop pollination and honey production worldwide. To bee researchers, it’s a grimly familiar story: V. destructor made the same host leap at least 60 years ago, spreading rapidly to become the most important global health threat to European honeybees.

The host-switching V. jacobsoni mites have only been found in Papua New Guinea, but Purdue researchers Gladys Andino and Greg Hunt say vigilance is needed to protect European honeybees worldwide from further risk.

“This could represent a real threat,” said Andino, a bioinformatics specialist with Information Technology at Purdue. “If this mite gets out of control and spreads, we might have another situation like V. destructor.”

The lifec ycle of Varroa mites is linked with that of their bee hosts. The mites can do serious damage to their hosts’ health due to their relatively large size – “think of a tick as big as your fist,” Hunt said.

Mites latch on to bees and feed on their hemolymph, insects’ rough equivalent to blood, leaving behind open wounds that are susceptible to infection. They can also transmit diseases such as deformed wing virus and have been linked to colony collapse disorder.

The scientists studied the host switch at the genetic level to learn  which host cues mites respond to. The genes involved could lead to potential control strategies, the researchers said.

“If we can understand the mechanism, we might be able to disrupt, block or manipulate that,” Andino said. “But first we have to understand what is happening and which genes are involved in allowing the mites to shift to a new host.”

“If you’re feeding on a new host, you’re going to be stressed. You have to adapt. The food is different and might not be optimal for development,” she said. “Potentially, European honeybees are not fulfilling the requirements these mites are used to getting from Asian honeybees.”

Andino and Hunt said the mites’ leap to European honeybees likely occurred within the last decade. Previously, V. jacobsoni mites were occasionally found on European honeybees but seemed unable to produce healthy offspring, limiting their destructive capacity.

Catching the host transition in its early stages will allow researchers to continue to investigate the complex genetic details behind the shift and monitor infected European honeybees, Hunt said.

“This happened once with one species of mite, and it looks like it’s happening again. Maybe if we catch this as it’s beginning, we’ll be able to figure out why it’s happening or, down the road, stop it.”

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