No abstract

The present study was conducted to determine whether Varroa jacobsoni can transmit American foulbrood (AFB), caused by the bacterium Paenibacillus larvae to healthy colonies by the surface transport of spores. Five two-storey Langstroth colonies of Apis mellifera ligustica were infested by placing a sealed brood comb, with 10% Varroa prevalence, between the central brood combs of each colony. Two months later the colonies were inoculated with P. larvae by adding brood comb pieces with clinical signs of AFB (45 _+ 5 scales per colony). After 60 days the brood area was completely uncapped by means of dissecting needles and tweezers, separating the Varroa mites from the larvae and the collected mites were introduced at a rate of 51 per colony into four recipient hives placed in an isolated apiary. Twenty female Varroa specimens were separated at random and observed by SEM. Paenibacillus larvae spores were found on the dorsal shield surface and on idiosomal setae. All colonies died after 4-5 months due to a high incidence of varroosis. No clinical AFB symptoms or P. larvae spores were observed in microscopic preparations. It is concluded that Varroajacobsoni does not transmit AFB from infected to healthy colonies; it does, however transport P. larvae spores on its surface.The mite Varroa jacobsoni Oud. (Acari: Varroidae) is an agent which transmits several pathogenic microorganisms to Apis mellifera L. It has been demonstrated that Varroa can transmit both sacbrood virus (SBV) (Bailey, 1991) and acute paralysis virus (APV) (Ball, 1985(Ball, , 1988 Ball and Allen, 1988) by inoculating virus particles into the haemolymph of honey 0168-8162 © 1995 Chapman & Hall 608 A.M. ALIPPI ETAL.bees. By means of SEM studies, Puerta et al. (1990) found spores of Ascosphaera apis (Maasen ex Clausen) Olive and Spiltoir and Aspergillus flares (Link ex Fries), on the cuticle of adult female Varroa. The mite is also one of the vectors of Hafnia alvei M¢ller, which causes septicaemia (Strick and Madel, 1988) and of several other bacteria Jarosz, 1990a, 1992).On the other hand, when varroosis and American foulbrood (AFB) develop simultaneously, colony death is accelerated (Grobov, 1977). SEM and cultural studies have shown that V. jacobsoni carries viable spores of PaenibaciUus larvae (White) Ash, Priest and Collins (Ash et al., 1993) which causes AFB (Alippi, 1992). However, there is no information concerning the transmission of this disease from colonies with AFB to healthy colonies. The purpose of the present work was to determine whether V. jacobsoni can transmit AFB to healthy colonies by the surface transport of P. larvae spores.Five two-storey standard Langstroth colonies of Apis mellifera ligustica L. were used. The selected hives had four brood combs each of which were treated with Fluvalinate (Apistan ®, manufactured by Sandoz-Zbecon) 40 days before the experiment was started in order to ensure the absence of Varroa. At the beginning of the austral summer (23 December 1993), a sealed brood comb with 10% Varroa prevalence (ap...