Greetings,

Evidently, an iridovirus was spotted in US honey bees more than ten years ago, after the collapse of hives in 1996. The suggestion was made at the time that varroa could be vectoring this virus. Interestingly, they proposed that the virus could be killing varroa mites as well as bees, which might account for low levels of varroa in hives just prior to collapse. They also mention that Bailey & Ball had seen iridovirus in Apis cerana as early as 1976.

Soon after this, CheckMite was made available and really helped stomp down varroa -- for a while. It received Section 18 registration in 1999. In the fall of 2001, a commercial beekeeper in Maine complained of high varroa populations following treatment of his colonies with CheckMite. Jeff Pettis wrote at the time: "The appearance of mites resistant to coumaphos, the active ingredient in CheckMite, in only three years of use is disturbing in light of the limited control alternatives."

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> An iridovirus, Apis iridescent virus (AIV), isolated from sick adult specimens of Apis cerana (Hymenoptera) from Kashmir. AIV multiplied when injected into adult individuals of Apis mellifera, and it multiplied abundantly when injected into young pupae. These developed more slowly than pupae injected with water, but some occasionally matured into seemingly normal adults containing much virus.

L. BAILEY, BRENDA V. BALL, R. D. WOODS. Journal of General Virology. (1976), 31, 459-461

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> A putative iridovirus infection was found in the honey bee parasitic mite Varroa jacobsoni Oudemans, sampled from a moribund colony of bees, Apis mellifera. Examination by transmission electron microscopy of the negatively stained mite extract revealed hexagonal, isometric particles resembling invertebrate iridoviruses. This is the first time that virus particles have been found associated with Varroa.

> In the spring of 1996, beekeepers across the northeastern United States reported unusually high levels of honey bee mortality. These extreme losses are believed to be the result of infestation by two introduced parasitic mites, Varroa mite (V. jacobsoni) and tracheal mite (Acarapis woodi). Some evidence indicates that viral diseases may also be involved, with the mites acting as a virus vector and activating inapparent virus infections (Ball, 1988). 

> Iridoviruses can be lethal to their host (Boucias et al., 1987). Thus we might expect viral transmission within the colony to kill both mites and honey bees. Since the honey bee colony from which these mites were obtained perished within 4 weeks after the mites were collected, we did not examine the mite extracts and discover the virus in time to determine whether honey bees in the colony were infected with the virus. 

Scott Camazine, Tsu Peng Liu. JOURNAL OF INVERTEBRATE PATHOLOGY 71, 177–178 (1998)

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Peter Loring Borst
Ithaca, NY
peterloringborst.com

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