Location: Bee Research Laboratory
Project Number: 8042-21000-290-27-I
Project Type: Interagency Reimbursable Agreement
Start Date: Feb 1, 2019
End Date: Sep 30, 2019
The overarching goal of research proposed here is to form an integrated effort against varroa mites using expertise in honey bees, mite biology, chemical ecology, physiology and biochemistry. There are four distinct objectives: 1) Elucidate key aspects of varroa mite ecology; 2) Identify potential chemical attractants or deterrents of varroa that may be employed in conjunction with chemical and/or non-chemical kill agents in physical varroa lures or traps; and 3) Develop tools for in vitro maintenance of varroa mites that focus on designs that disrupt mite feeding, development, and reproduction, 4) identify and characterize effects of components of mite saliva that are critical to mite feeding and disease transmission. The USDA-ARS Bee Research Laboratory has assembled a team of scientists committed to studying this pest and have produced valuable academic and applied resources for understanding and combating varroa mites and mitigating their negative effects on honey bees. Varroa mites, and the saliva they secrete can cause physical damage when feeding on pupa and adult honey bee hosts and may vector a number of honey bee viral pathogens. Components of mite saliva, including proteins/enzymes, and small molecules are likely an important aspect of their ability to obtain food, and may be important for aiding transmission of honey bee pathogens. Surprisingly, little is known about the identities of saliva constituents and their singular effects on honey bees. Understanding both the chemical constituents of saliva and their effects on honey bees and the ability of mites to acquire food, would provide key targets for effecting control of these damaging mites. Transmission of mites between individual honey bees is better understood than transmission of mites between colonies. Mites may be transmitted horizontally in several different ways, all of which may involve perception and response to pheromone and/or kairomone cues. Mites are known to overwinter with their honey bee hosts, and thus may become ‘seeds’ for the mite populations the following summer season. However, nearly nothing is known about how mites overwinter with honey bees. Our unpublished data suggest that as fall approaches, mites have significantly increased longevity compared to summer mites, similar to the pattern observed for their host honey bees. Questions such as whether mites utilize their hosts’ overwintering strategies (e.g., sequestering host-derived antioxidant vitellogenin or anti-stress heat shock proteins), or whether they have their own physiological mechanisms, have yet to be addressed. Chemical agents for controlling mites have been employed with mixed results; mites have gained resistance or tolerance to many varroacides, requiring development of novel chemical and non-chemical means of their control. Moreover, research on varroa mites and how to control them is hampered due to their decreased seasonal availability in temperate climates. Thus, developing a method to study varroa mites in vitro free of their honey bee hosts is an important step in furthering development of varroacides that are not acutely toxic.
For Objective 1, the focus will be on understanding two important aspects of varroa mite ecology—strategies used by mites for inter-colony transmission, and for overwintering with host honey bees. First, we will leverage the many colonies used as ‘mite farms’ on USDA-ARS grounds and monitor/measure mites’ behaviors and communications related to their exodus from highly infested colonies and favor successful relocation to naïve host colonies. Abundant overwintered and package honey bee colonies provide swarms, which can be caught, allowing us to monitor mite movements with colony budding. Next, metabolomic, genomic, microscopic, and biochemical analyses will elucidate the molecular and biochemical mechanisms allowing mites to overwinter with bees. For Objective 2, we will screen known and novel volatile and/or tactile odorant attractants of varroa mites. Collection and identification of chemical odorant and tactile chemical cues will be collected using established methodology employing chemical analysis of SPME and solute-extracted chemicals. For Objective 3, a robust method for maintaining mites in vitro will be improved upon that reduces reliance on live hosts. We will continue screening dietary components and odorant cues to prolong longevity and promote reproduction of mites in vitro, with the goal of developing tools for studying effects of non-acutely toxic varroacides. For Objective 4, protocols are in place for obtaining quantities of mite saliva, and for isolating and identifying its protein constituents, and microbes ‘carried’ by mite saliva. Besides identifying constituents of mite saliva, several tests will be conducted using acquired saliva, including bioassays of enzymatic activity and ability of saliva to degrade honey bee cuticle.