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Title: Changes in Honey Bee (Hymenoptera: Apidae) Colony Swarming and Survival Pre- and Post- Arrival of Varroa destructor (Acari: Varroidae) in Louisiana

item Villa, Joseph

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2008
Publication Date: 9/1/2008
Citation: Villa, J.D., Bustamante, D.M., Dunkley, J.P., Escobar, L.A. 2008. Changes in Honey Bee (Hymenoptera: Apidae) Colony Swarming and Survival Pre- and Postarrival of Varroa destructor (Acari: Varroidae) in Louisiana. Annals of the Entomological Society of America 101(5):867-871

Interpretive Summary: The parasitic varroa mite causes serious mortality of colonies maintained by beekeepers unless colonies are treated with pesticides. Treatments are expensive and require care in their timing and application. An additional negative impact of varroa mites has been mortality of wild honey bees. We analyzed swarm capture rates and survival of colonies not treated for mites from 1990 to 2005 in Louisiana. Varroa mites were first detected in the state in 1991 and had become widespread by 1995. Coinciding with this, we observed a sharp decline in swarm captures and in colony survival. In the later part of the observation period (1997-2005), both swarming rates and survival rebounded to levels similar to or better than those prior to the arrival of mites. Colonies could be surviving better in the presence of mites because of mixing with introduced and selected resistant stocks, because of natural selection, or because the virulence of mites has moderated.

Technical Abstract: The impact of Varroa destructor Anderson and Trueman on colonies of Apis mellifera L. in southern Louisiana was evaluated by analyzing changes in swarming and longevity of colonies for 17 years. Swarming rates were calculated from yearly captures of swarms in bait hives placed in five areas of Louisiana from 1991 to 2006. Colony longevity was monitored in 104 swarms established from 1990 to 2000 and followed until 2005. V. destructor was first detected in the state in 1991, and was widespread and detected in our samples in 1993. Prior to these events, average swarm capture rates ranged from 0.85-0.95 swarms per bait hive-year, and survival of colonies established from swarms averaged 14 months. In the years following the arrival of V. destructor (1993-1996), swarming rates and colony longevity decreased to 0.36-0.60 swarms per bait hive-year and longevity of 10 months, respectively. After about 5 years in the presence of V. destructor, both rates recovered to levels at least as high as those seen before varroa arrived; swarm capture rates were 0.75-1.04 swarms per bait hive-year and average longevity was 26 months. Analysis of varroa infestations in three colonies established from swarms in 1997 showed the presence of varroa at oscillating densities for five to eight years. Possible causes for this apparent recovery are natural selection for resistance in honey bees, introgression of selected resistant genetic material or reduced virulence of the mites.