Varroa feeds with fat body not haemolimph

Dr. Maja Smodiš Škerl, Agricultural institute of Slovenia, Animal Production Department, Beekeeping

Scientists until now believed that the mite Varroa destructor feeds primarly with haemolimph of honey bees. This claim has never been scientifically proven, neither has anyone put an effort to study the feeding behaviour of the mites so much in detail until now. The reason was actually in a quite difficult observation methods to find out how this parasite accesses into the honey bee body and what does it feed with. Luckily, there was a doctoral student Samuel D. Ramsey from the Department for entomology, University of Maryland College Park, USA, under the leadership of dr. Denis van Engelsdorp, Head of the department, who took this challenge to look closer the feeding mechanisms of Varroa mite. Ramsey decided to put this question in his Doctoral thesis with a help of dr. Ronald Ochoa and dr. Gary Bauchan et al., Agricultural research service, USDA Maryland, dr. Allen Cohen, Entomology and plant pathology department, North Carolina State University, and dr. Jamie D. Ellis, Entomology and nematology department, University of Florida, USA.

Parasitic mite V. destructor is one of the major single driver of the global bee health decline. Th methods for varroa control are versatile and are not always successful. Varroa mite is quite impossible to exterminate and keep the bee colonies undamaged and in a full population. Wehere are the honey bees, there are Varroa mites. But there are exceptions. In Australia and on the Islands of South West Indian Ocean (Comora and Seychelles).

Varroa is remarkably adopted to its host, honey bee. Ramsey found out that Varroa mite does not primarly feed with haemolymph, but couses severe damage to its host by feeding with the fat body tissue. In comparison to humans it looks like a giant mite, sized round 17 cm, would attach to our belly and suck our liver tissue. In the meanwhile we would go to work and try to do our job. Fat body represents one of the most important tissue that regulates immune function, pesticide detoxification, storage and mobilisation of nutrients, a successful overwintering of the bees and many other important functions in healty adult bees and brood.

In a series of trials it was determined the most favourite point for Varroa mite to feed on bees, what kind of tissue do they actually feed and would be the most important for the mite to survive and to reproduce. The results show that the mite makes a wound into the intersegmental memrabe of the under part of abdomen between the sternites, where is the best place to access the fat body. Varroa mites were fed in laboratory conditions with fat body, haemolymph and combinations fat body:haemolymph (1:3; 1:1; 3:1) and a group with no food added as a control. It was found that the mites were daying much faster feeding haemolymph or starving. The logest survival was foun in the group feeding fat body of the bees.

This findings are now scientifically proven and we are now confronting the fast that we need to change our thinking about the effects of Varroa infestations on the honey bee colony health. This kind of research is very much important for the development of sustainable management practices in beekeeping.

Ramsey S.D. et al., Varroa destructor feeds primarily on honey bee fat body tissue not hemolymph. In: DE GRAAF, D.C. (Ed.), PAXTON, Robert J. (Ed.). EurBee 8. 8th Congress of Apidology,18-20 September 2018, Ghent, Belgium : Program & Abstract book, Eurbee8, 8th Congress of Apidology, 18-20 september 2018, Ghent University. 2018, p. 140.