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 mortality (JM) of the mite Varroa jacobsoni was studied in worker brood cells of frozen combs from 21 Apis mellifera macedonica colonies. The infestation level 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 resting adult were examined. The cells examined were singly infested by a fertile 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 conditions no death factors act against the first fd until it reaches the second immobile phase, or deutochrysalis phase (DCHR) in the worker brood cell. For the subsequent fd, malnutrition possibly plays the most important role during 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 worker brood cells containing maturing pupae. Rates of losses for the DCHR of the three fd determined in cells containing the resting adult were 15.8%, 37.1% and 56.9%, respectively. The general losses concerning all developing phases of the mite, i.e. pre-DCHR and DCHR, for the first, second and third fd in worker brood cells were 18.6%, 50.9% and 87.3%, respectively. Death of the DCHR of V. jacobsoni in the worker brood cell of A. mellifera is connected with aging of the host. This is based on the following: (a), practically 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 artificial factors causing death of female DCHR is discussed.