The Varroa destructor, a parasitic mite that threatens populations of honey bees worldwide, has long been thought to feed on blood like many of its mite and tick cousins.

Findings of new research, however, provided evidence varroa mites do not have an appetite for hemolymph or the bee blood, but instead feed on an organ known as fat body.

Fat Body Organ

The organ plays a role in fat storage. It is also involved in breaking down toxins, production of antioxidants, and management of the bees' immune system. The fatty organs also serve key role in metamorphosis, regulating activities of key hormones.

In a study published in the Proceedings of the National Academy of Sciences on Jan. 14, Samuel Ramsey, from the University of Maryland, and colleagues observed where on the bodies of bees the varroa mites tend to attach themselves for feeding.

The idea is if the mites grabbed on to random locations, they were feeding on the hemolymph, which is distributed evenly throughout the bees' body. If the mites preferred a site on the body, it could lead researchers to the preferred meal of the parasites.

The researchers found that when the mites feed on immature bees, they will eat anywhere but in adult bees, the mites had strong preference for the underside of the bees' abdomen.

"Fat body tissue is spread throughout the bodies of immature bees. As the bees mature, the tissue migrates to the underside of the abdomen," Ramsey said.

Experiments Show Varroa Mites Feed On Fat Bodies

The researchers conducted further experiments. They also used a technique known as freeze fracturing to freeze the mites and their bee host so they could get a physical "snapshot" of the mites feeding habits in action. Microscopic images revealed the mites were feeding on fat body tissues.

The researchers also fed the bees with fluorescent dyes: a water-soluble yellow dye and a fat-soluble red dye. If the mites feed on hemolymph, researchers expect to see bright yellow glow in the bellies of the mites after feeding. If they were feeding on fat bodies, the mites' bellies would have red glow.

"When we saw the first mite's gut, it was glowing bright red like the sun," Ramsey said.

The researchers also placed mites on a dietary regimen. The mites that were fed a diet of pure hemolymph starved. Those fed with fat body tissues survived and even produced eggs.