A sister species of the Varroa destructor mite is developing the ability to parasitise European honeybees, threatening pollinators already hard pressed by pesticides, nutritional deficiencies and disease, a Purdue University study says.
Researchers found that 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.
While host-switching V. jacobsoni mites have not been found outside of Papua New Guinea, 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."
Varroa mites are obligate parasites, meaning their lifecycle is inextricably entwined 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.
To gain insight into the biology behind V. jacobsoni's host switch, Andino and Hunt, professor of behavioural genetics and honeybee specialist, studied the differences in gene expression between V. jacobsoni mites that fed and reproduced on Asian honeybees and those that parasitised European honeybees. Knowing which host cues mites respond to and 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."
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Image: Varroa mites are considered the biggest bee health problem worldwide. Here, a Varroa destructor mite has latched on to the upper-right side of a honeybee's abdomen to feed. Credit: Purdue University/Tom Campbell