XXX International Apicultural Congress, Apimondia, Nagoya, Japan, Oct. 10-16, 1985
ISSA, M. R. C.; DE JONG, D.:
GONCALVES, L. S. (Brazil)
The mite Varroa jacobsoni infests brood and adult honeybees (Grobov, 1977). The mite is known to enter brood cells when the larva is 5 to 6 days old (Issa and De Jong, 1981).
This research concerns the biology and behaviour of the mite with emphasis on understanding the mechanisms involved in the marked preference observed for drone brood. It has been previously demonstrated that the mite prefers drone brood to worker brood for reproduction (Haragsim, 1973; Marin, 1977). This also occurs with africanized honeybees. The percentage of infested cells was 7.55% for worker larvae and 40.57% for drone larvae; the infestation rates were 0.089 for worker larvae and 0.62 for drone larvae. Generally, about 40% of drone cells are infested, while for workers, the average is close to 10%. One, two, or three invading mites are commonly found in drone cells, while in workers, most cells have only one mite.
This preference of the mite for drone larvae has also been verified in the laboratory. When larvae of drones and workers in the same developmental phase were reared on Petri dishes whose bottom was covered with a beeswax layer with a shallow cavity in the middle where the mites were placed. The percentage of infested larvae was 15.5% for workers and 67.4% for drones; the rate of infestation (number of mites/number of larvae) was 0.24 for workers and 0.97 for drones.
Adult drones were also more infested than adult workers, with a rate of infestation of 0.291 for drones and 0.060 for workers. The adult workers were then divided into 2 groups by age: young workers (3 to 6 days old) and adult workers (17 to 21 days old). The rate of infestation was 0.103 for young workers and 0.049 for adult workers.
lnfestation was studied in hives with egg-laying workers and no difference in infestation was detected between bees with developed ovaries and bees without developed ovaries. Infestation in the worker-laying hives was lower than in hives with no laying workers. The mean infestation rate of 6 hives was 0.045 before egg-laying workers appeared.
Several substances were tested for their effect on mite preference both in hives and in the laboratory. Among these substances (juvenile hormone, hemolymph of drone larvae, drone larval extract in water, methanol and acetone, lyophilized drone larvae, and food from drone larvae) only food from drone larvae tested in the hive gave positive results.
When the behavior of the mite was studied in terms of the search for the host, we observed that the mite perceives the presence of the larva when it is quite close. Most mites perceive a larva at a distance of 3 mm, but some of them reacted to the presence of a larva at a distance of 4 to 5 mm. Perception of the larva is accompanied by agitation of the first pair of legs. This same agitation is also observed when the mite meets an obstacle in its path, when the mite may or may not climb onto it.
The mites that penetrate the brood cell reach the larval food and remain there until the larva consumes all the food (De Jong et al., 1982). When the mite are removed from the larval food and the food remains are cleaned off, they start to move again over a time varying from 2 minutes to 18 hours.
One of the stimuli to which the mites reacted most clearly was an air draft. The mite left no doubt about its positive response by making a 180º turn to reach the source of stimulation (site from which the draft came). The air drafts tested were produced by human respiration, aquarium aerator, chilled air, and draft from a container of carbon dioxide.
DE JONG, D.; MORSE, R. A.; EICKWOTH, G. S.(1982) Mite pests of honeybees. Ann. Rev. Entomol. 27: 229-252.
GROBOV, 0. F. (1977) Varroasis, in bees. In Varroasis, a honeybee disease. Bucharest. Apimondia, pp. 48-90.
HARAGSIM, 0. (1973) The mite Varroa jacobsoni as a threat to beekeeping in Europe. Imkerfreund 28: 312-317.
ISSA, M. R. C.; DE JONG, D.(1981) Estudo do peso e idade larval de abelhas Apis mellifera infestadas pelo acaro Varroa Jacobsoni. Suplemento Ciencia e Cultura 33(7): 674.
MARIN, M. (1977) Diagnostico y tratamiento de la Varroasis. In Varroasis, enfermedad de la abeja melifera. Apimondia Publishing House, Bucharest pp. 18-21.