Nosema disease in the honey bee (Apis mellifera L) infested with varroa mites in southern Spain

Twenty-nine hives infested by Varroa jacobsoni were sampled over a 2-year period in order to find out their degree of infection by Nosema apis. The hives were situated in ten apiaries distributed throughout southern Spain. N apis has been found in 90% of the apiaries sampled and in 55.17% of the hives studied, but only 5.1% of the bees were infected. We have found a low correlation between the average number of spores per infected bee in the positive samples and the percentage of infected bees (r(2) = 0.2438; P < 0.001; n = 33), and between the average number spores in the composite samples of 60 bees and the percentage of infected bees (r(2) = 0.4557; P < 0.001, n = 33). Our results show that N apis and V jacobsoni could develop independently and that those samples which manifested a low, medium and high infestation by V jacobsoni had percentage infections with N apis of 22.6% +/- 3.6% vs 47.5% +/- 16.2% vs 16.7% +/- 10.4% respectively, without significant differences (F = 0.2817; P = 0.7567). A progressive increase in the number of spores per individual was detected with increasing levels of V jacobsoni infestation: 5.9 x 10(6) vs 9.1 x 10(6) vs 13.8 x 10(6) spores/bees, but no significant differences exist between them (F = 0.6053; P = 0.5531).