The resistance of Varroa jacobsoni Oud to pyrethroids: a laboratory assay

Abstract

Summary — A bioassay has been developed to assess the susceptibility of Varroa mites to fluvalinate, flumethrin and acrinathrin. No significant differences were found among groups of mites from the same origin but from different brood stages (capped larvae, pupae with white eyes, pupae with dark eyes and white or pale bodies), while a rather variable response was observed when mites from adult bees were assayed. The LC 50 of mites from areas where treatments with fluvalinate are no longer effective was about 25-50 times higher than that of susceptible mites; an even larger increase in the LC 95 was found. The LC 50 of flumethrin and acrinathrin on mites surviving Apistan treatments increased 10-60 times.

Determination of the LC50 in the mite Varroa jacobsoni of the active substances in Perizin® and Cekafix®

“…A technique similar to that described by Milani (1995) was used, with some modifications suggested by previous experience.…”

“…Mites were collected from bee brood as described in Milani (1995). Varroa mites from brood of different ages (spinning larvae, I5; pupae with white eyes, pw; pupae with dark eyes and white or pale body, pd) were assayed separately.…”

“…Varroa mites from brood of different ages (spinning larvae, I5; pupae with white eyes, pw; pupae with dark eyes and white or pale body, pd) were assayed separately. Mites from pupae with pigmented body and from adult bees were not used, since their response might not be uniform and the mortality in the controls higher (Milani, 1995 (Finney, 1971), and assays at 2 and 100 ppm were not replicated when respectively a mortality not exceeding that of the controls or 100% mortality were expected.…”

“…Acaricide resistance is going to be an increasing problem in the near future, and is made even worse by the low number of alternatives and by the fact that the increase of the resistant populations is often unnoticed and can lead to the unexpected collapse of the colonies and to heavy bee losses (Astuti et al, 1996). Recently, bioassays for pyrethroids (Milani, 1995;Faucon et al, 1996) and amitraz (Faucon et al, 1996) have been developed.…”

“…A modification of the technique used to assess resistance to pyrethroids (Milani, 1995) was chosen; this may seem inappropriate, since these ai and especially coumaphos have been considered 'systemic' acaricides (Ritter, 1985), however, some doubt has been cast on this mode of action (van Buren et al, 1992) and other formulations that rely upon contact action have been used (Ho and An, 1980;Gajadusková et al, 1990).…”