EFFECT OF VARROA-JACOBSONI (MESOSTIGMATA, VARROIDAE) ON FERAL APIS-MELLIFERA (HYMENOPTERA, APIDAE) IN CALIFORNIA

We studied the spread of the newly introduced parasitic mite, Varroa j acobsoni Oudemans, within California's population of the feral honey b ee, Apis mellifera L., by examining worker bees taken from 208 colonie s in 1990, 124 of which were examined again in 1993. The samples taken in 1990 did not contain V. jacobsoni mites. In 1993, 75% of the colon ies examined in an area located near Sacramento, CA, no longer existed , and all surviving colonies were infested with V. jacobsoni. In an ar ea located near the Californian central coast, 84% of the nest sites e xamined were occupied and few colonies contained detectable levels of V. jacobsoni. The probability of survival for colonies that have not s urvived a winter yet (founder colonies) has been previously reported t o be low in areas with a temperate climate. Data collected in an area with a low level of Varroa mite infestation suggest that the probabili ty of founder colony survival is higher in California with a mostly Me diterranean climate. The data collected in areas with a high level of Varroa mite infestation suggest that the parasite reduces the mean lif e span of feral honey bee colonies in California to go between 6 mo an d 1 yr. The parasite was widely spread in areas with a high density of commercial colonies. This suggests that the fast spread of the parasi te is caused mostly by migration of commercial colonies. We discuss th e consequences of the decline of the feral honey bee population on pol lination and on the invasion of California by Africanized bees.