Influence du climat sur le développement de la population de Varroa jacobsoni Oud dans des colonies d'Apis mellifera iberica (Goetze) dans le sud de l'Espagne

Abstract

The population dynamics of the mite Varroa jacobsoni were studied in colonies of honeybees (Apis mellifera iberica) in the south of Spain (Andalusia), a region of wide climatic contrasts. Between July 1990 and October 1992, samples and data were collected monthly from 26 beehives untreated for parasites. The colonies were located in 9 apiaries in 3 areas with different climates (fig 1). The development of the mite population was measured by determining the infestation rate of Varroa mite in adult bee, in brood cells and the mortality per month. In the 3 different climatic areas studied: mediterranean, continental and oceanic (MCO), continental mediterranean (CM) and mediterranean subtropical (MS), the mean infestation rates were 9.9, 4.1 and 6.1 mites per 100 adult bees, respectively. The mean number of mites per 100 brood cells was 34.2, 17.8, and 24.8. The overall mean of mite infestation in the study was 8.2 mites per 100 bees, ie 29.5 mites per 100 brood cells (table I). Monthly differences in maximal infestation were observed in the areas studied (fig 2). In these areas V jacobsoni speeds up its biological cycle compared with the descriptions reported by other authors in continental Europe. V jacobsoni reaches its infective maxima earlier in the sampling stations with colder climates (CM) than in those with hotter climates (CMO). The results of our study confirm the observation of Woyke (1987) that V jacobsoni stays longer in sealed cells when climates are colder. The parasitic mite thus completes more reproductive cycles in the same period of time, speeds up the population growth. Milder climates favour global infestation rates to be higher in hotter areas (CMO). This totally different behaviour can be observed on the mediterranean coast of the Iberian Peninsula (MS). The effects of the climate in this area, together with the occurrence of efflorescence (autochtonic, from subtropical cultivations or from greenhouse cultivations) throughout the year, cause fast development of the parasitic mite leading to the death of honeybee colonies within a few months. Our study shows that the phenology and climate conditions of a region are 2 main factors which affect and modify V jacobsoni population dynamics. © 1995.