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Title: Influence of Varroa mite (Varroa destructor) infestation levels and management practices on insecticide sensitivity in the honey bee (Apis mellifera)

Author
item Rinkevich, Frank
item Danka, Robert
item HEALY, KRISTEN - Louisiana State University Agcenter

Submitted to: Bee World
Publication Type: Proceedings
Publication Acceptance Date: 2/7/2017
Publication Date: 3/2/2017
Citation: Rinkevich Jr, F.D., Danka, R.G., Healy, K.B. 2017. Influence of Varroa mite (Varroa destructor) infestation levels and management practices on insecticide sensitivity in the honey bee (Apis mellifera). Bee World. 93(4):104-127.

Interpretive Summary: Varroa mites are one of the leading causes of honey bee colony losses. As such, a number of methods are employed to control Varroa populations including chemical applications and non-chemical strategies. In our study, we managed mite populations with an approved miticide (Apivar), used non-chemical control methods (screened bottom boards, powdered sugar grooming stimulation, and drone brood mite trapping), or no mite management practices as a control. We monitored changes in mite populations as well as sensitivity to the insecticides phenothrin and clothianidin over the 5 month experiment. Apivar significantly reduced mite populations while non-chemical control was largely ineffective. There was no evidence of insecticide synergism by using Apivar. Varroa mite infestation did not change the sensitivity to phenothrin, but higher Varroa infestation was correlated with reduced sensitivity to clothianidin. Our results show 1) Varroa mite management practices yield significantly different results in mite populations, 2) the lack of synergism shows that not all laboratory results may translate to the field, and 3) Varroa infestation levels do no increase sensitivity to insecticides.

Technical Abstract: Because Varroa mites may cause devastating losses of honey bees through direct feeding, transmitting diseases, and increasing pathogen susceptibility, chemical and mechanical practices commonly are used to reduce mite infestation. While miticide applications are typically the most consistent and efficacious Varroa mite management method, miticide-induced insecticide synergism in honey bees and evolution of resistance in Varroa mites are reasonable concerns. We treated colonies with the miticide amitraz (Apivar®) or used non-chemical management techniques (screened bottom boards, powdered sugar grooming stimulation, and drone brood mite trapping), and left some colonies untreated and then measured the effect of different mite infestations on the sensitivity of bees to phenothrin, amitraz, and clothianidin. Amitraz treatment significant reduced mite populations compared to the control or non-chemical management methods. Sensitivity to all insecticides varied throughout the 5 month test among and within treatment groups. Clothianidin sensitivity decreased with increasing mite levels, but no such trend was seen with phenothrin or amitraz. In-hive amitraz treatment according to the labeled use did not synergize sensitivity to the pesticides tested; this finding should alleviate concern over potential synergistic effects. Non-chemical mite management methods were largely ineffective at reducing Varroa mite infestation in our tests for unknown reasons. These data demonstrate the complex and dynamic variables that contribute to honey bee colony health. The results underscore the importance of controlling for as many of these variables as possible in order to accurately determine the effects of each of these factors as they act alone or in concert with others.