Seemingly indestructible Varroa mites have decimated honeybee populations and are a primary cause of colony collapse disorder.
Michigan State University scientists have found genetic holes in the pests' armor that could potentially reduce or eliminate the marauding invaders. The team's results, published in the current issue of Insect Science, have identified four genes critical for survival and two that directly affect reproduction.
"The Varroa mite is the worst threat to honeybee health worldwide," Michigan State entomologist Zachary Huang said. "They have developed resistance to many pesticides, so it's urgent that we explore and target these genes to develop better control methods."
The mite sucks the blood of honeybees and transmits deadly viruses. Its life cycle consists of two phases: (1) the phoretic phase, in which they feed on adult bees, and (2) a reproductive phase that takes place within a sealed honeycomb cell, where the mites lay eggs on a developing bee larva.
This double-whammy of eating bees and spreading disease makes Varroa mites the number-one suspect of honeybee population declines worldwide, Michigan State said.
Controlling pests like Varroa mites succeeds by either eliminating them or reducing their ability to reproduce. The team used RNA interference to identify the key genes that could achieve these outcomes. They injected the mites with double-stranded RNA (dsRNA).
Interfering reduces transcription of a specific gene, which is the first step of making a gene -- a piece of DNA -- into a protein. This process, also known as "gene knockdown," has been successful in reducing the mating success and the number of eggs produced by cattle ticks, which threaten cows and other livestock around the world.
Using this approach, the team identified two genes that caused high mortality in Varroa mites: Da and Pros26S. In fact, Da killed more than 96% of mites. They also identified four genes that control reproduction: RpL8, RpL11, RpP0 and RpS13.
Earlier research has shown that a combination of dsRNAs can be fed to bees at the colony level. Varroa mites absorbed the "genetic cocktail" via bee blood, and their population was reduced. Future research will explore whether a single-gene approach can be scaled up and achieve the same effect at a colony-wide setting. Using a single gene with a known mechanism will be more cost effective and safer for the honeybees.
The results may have applications beyond honeybees, as well.
"It's worth noting that Da reduced reproduction in species of mosquitoes and Drosophila," Huang said. "Future research could help not only protect honeybees but also reduce disease-carrying mosquitoes or crop-damaging pests."