Theses and Dissertations from UMD
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Item PESTICIDE RESIDUES IN BEESWAX PREDICT THE OCCURRENCE OF VARROA WITH ALLELES THAT CONFER AMITRAZ RESISTANCE.(2024) Hartel, Eric; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Honey bees are important pollinators and are essential to modern industrial agriculture. One of the largest threats to honey bee health is the parasitic varroa mite Varroa destructor. A common method beekeepers use to control varroa is the application of synthetic varroacides. Following years of treatment, varroa have developed resistance to multiple varroacides leading to treatment failures. This project set out to examine the relationship between pesticide residues within beeswax and resistance alleles in varroa. I expected that the presence of varroacides would be positively related to the occurrence of known mutated alleles that confer varroacide resistance to varroa. We looked for 3 different known varroacide resistance alleles, and only found 2, (N87S and Y215H). Both N87s and Y215H confer resistance to amitraz and her metabolite DMPF. Only one mutation, the Y215H mutation, was widespread, occurring in 68% of the 195 mites we examined. We found that the mutation occurred more frequently in mites that were collected from apiaries that had higher DMPF levels. Surprisingly, the presence of other unrelated pesticides (e.g. not having the same mode of action as amitraz) were also positively correlated with the proportion of mutated alleles found. Both the total number of pesticides found in an apiary, and increasing concentrations of fungicides, insecticides, and varroacides (including and excluding DMPF data), predicted higher odds of finding the Y215H mutation. It is unclear if this relationship is a result of a correlation between pesticide levels, if the mutation help benefits the mites resist pesticide more generally, or if the gene has become fixed in the population. It is important to monitor resistance conferring mutations in the varroa mite population in order to help beekeepers make proper varroa management decisions.Item Feeding behavior and distribution of Varroa destructor on adult bees of Apis mellifera(2022) Lamas, Zachary Siqueira; Hawthorne, David J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Varroa destructor is a competent vector of honey bee viruses and the leading cause of colony losses worldwide. Much about its feeding behavior and distribution on adult bees remains unknown. This work shows that Varroa are promiscuous feeders of adult bees, actively switching from one host to another. Laboratory trials showed there is a large heterogeneity in the host switching rate with some Varroa switching infrequently while others switched at high rates. The consequences of Varroa feeding on adult bees is largely unknown because adult feeding has largely been overlooked. This work shows that there is a high relative risk of death from Varroa feedings. Adult workers die quickly without developing high levels of infection after being fed upon by an infectious Varroa, and confer lower risk to their non-parasitized nestmates than counterparts which were nestmates to longer lived parasitized bees. Further experiments showed communicable routes of virus transmission may explain these findings. Trophallaxis between adult workers allowed for the movement of the pathogen to naïve nestmates. These nestmates act as an infectious reservoir to naïve Varroa showing communicable transmission between hosts can influence the acquisition and subsequent vectoring of the same pathogen by the vector. Another social behavior, cannibalization, was shown to have the same influence on Varroa vectoring. Varroa were also shown to be susceptible to viral acquisition through shared feedings on adult bee and brood hosts. Naïve Varroa readily acquired and then transmitted deformed wing virus when sharing the same host with an infectious Varroa. Collectively this work exemplifies how host social behavior and Varroa-Varroa transmission routes can increase the risk of vectors becoming infectious. Varroa feedings and virus transmission on adult workers cannot describe one of the most glaring features of Varroa infestations. For a portion of the year Varroa aggregate predominantly on adult drones, largely ignoring the worker cohort. Parasite burden only shifts onto workers when drone production ceases.Item POLLEN NUTRITION, PESTICIDES, AND PATHOGENS: INTERACTIVE EFFECTS ON HONEY BEE HEALTH(2017) Garavito, Andrew; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While a variety of stressors influence honey bee (Apis mellifera) health, it is the additive and interactive effects of these factors on bee health that have been driving modern research. We devised a set of two experiments to test the effects of multiple stressors on honey bee health. First, we grew sunflowers to test the effects of drought stress and seed treatment on sunflower pollen. We fed the pollen collected from these sunflowers to cohorts of bees that were either infected or uninfected with the microsporidian pathogen Nosema ceranae to find that drought stressed pollen leads to increased mortality in infected bees. Next, we fed 37 experimental pollen diets of different floral varieties and pesticide loads to honey bees infected with N. ceranae, but we were unable to find a connection between diet variety and pesticide exposure on bee health.Item In Vitro Measures of MDR-Transporter Function and Whole-Hive Exposure Dynamics Using Fluorescent Dyes(2014) Kunkel, Grace R.; Hawthorne, David; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We need to study Apis mellifera both in vivo and ex vivo to better understand honey bee biology. In vivo synergism of chemicals can occur when xenobiotic transporters are inhibited by one chemical, allowing a second chemical to accumulate and become toxic. I have conducted assays between 2010 and 2013 that demonstrated RhB dye- a xenobiotic transporter substrate, is fed in the presence of the xenobiotic inhibitor verapamil, it is found in higher levels in the hemolymph of the Apis mellifera Two types of bee food combined with two dyes were tested in 2012 for the impact of food type, and the impact of dye type on the fate of the dye in a Apis mellifera hive. Slightly hydrophobic RhB and slightly hydrophilic UrO were used. Dyed syrup persisted longer in hives than dyed pollen patties, and dyes did not spread uniformly throughout the hive.