Juvenile mortality of the female descendants in the ectoparasitic mite Varroa jacobsoni in worker brood of Apis mellifera

During the autumn of 1996 and 1997 in Thessaloniki (Greece) juvenile mortal ity (JM) of the mite Varroa jacobsoni was studied in worker brood cells of frozen combs from 21 Apis mellifera macedonica colonies. The infestation le vel of the colonies varied between 8% and 35%. Sealed brood cells (n = 8454 ) containing a healthy worker pupa older than the 'pale eyes stage or a res ting adult were examined. The cells examined were singly infested by a fert ile V. jacobsoni with normal offspring in 92% of the cases. A total number of 3543 developing fertile V. jacobsoni female descendants (fd) was studied . During the mobile phases the losses of the parasite in the first, second and third fd were 2.8%, 13.8%, 30.4%, respectively. Under natural condition s no death factors act against the first fd until it reaches the second imm obile phase, or deutochrysalis phase (DCHR) in the worker brood cell. For t he subsequent fd, malnutrition possibly plays the most important role durin g the pre-DCHR mobile phases. During the immobile phases the main losses of the first fd occur in the DCHR phase. On average, the death rates for the first, second and third DCHR were 6.2%, 11.3% and 14.2%, respectively, in w orker brood cells containing maturing pupae. Rates of losses for the DCHR o f the three fd determined in cells containing the resting adult were 15.8%, 37.1% and 56.9%, respectively. The general losses concerning all developin g phases of the mite, i.e. pre-DCHR and DCHR, for the first, second and thi rd fd in worker brood cells were 18.6%, 50.9% and 87.3%, respectively. Deat h of the DCHR of V. jacobsoni in the worker brood cell of A. mellifera is c onnected with aging of the host. This is based on the following: (a), pract ically no death of DCHR was observed as long as the host retained its white body colour; dead DCHR appeared first when the aging worker pupa acquired yellow body colour; and (b), the death rate of DCHR increases as the worker pupa becomes older. The possible influence of different natural or artific ial factors causing death of female DCHR is discussed.