Monday, November 17, 2008 - 9:47 AM
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Sublethal effects of imidacloprid and amitraz on Apis mellifera Linnaeus (Hymenoptera: Apidae) larval development and larval susceptibility to Varroa destructor Anderson & Trueman (Mesostigmata: Varroidae)

Tricia Toth, ptoth24@ufl.edu, University of Florida, PO Box 110620, Gainsville, FL

Managed honey bee populations have declined dramatically in the United States since 2005. Population decreases have been attributed to a number of causes including, but not limited to, pesticide exposure, parasite vectored pathogens, arthropod bee pests, and stress. Recently, there has been resurgence among researchers to investigate the possibility of pesticide effects. Pesticides of particular interest are the neonicotinoids and varroacides. Therefore, I chose to investigate how doses of two pesticides, imidacloprid and amitraz, affect bee larval development and larval susceptibility to varroa. To test this, I fed bee larvae with diet containing various concentrations of one of the two test pesticides and measured mortality at larval and pupal development as well as several sublethal variables. Secondly, I introduced pesticide treated larvae into varroa infested colonies to determine the number of mites per larva that occur in a treated cell. My results suggest amitraz fed larvae have higher larval mortality at the highest dose administered. Both amitraz and imidacloprid fed larvae had a lower percentage of adults to emerge than untreated larvae. Only imidacloprid treated larvae showed possible sublethal effects. Treated larvae had an increased larval weight at defecation and increased larval development time. There was not enough data to suggest whether or not treatment by imidacloprid or amitraz influences bee brood susceptibility to varroa. Results from my research suggest that even small doses of certain pesticides effect bee brood development, but the effects that these pesticides could have on a colony level are still unclear.


Species 1: Hymenoptera Apidae Apis mellifera (European honey bee)
Species 2: Mesostigmata Varroidae Varroa destructor (varroa mite)

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COMMENTS AND CORRECTIONS

  • From Galen Dively, Professor, University of Maryland, November 18, 2008
    Tricia, I listen to your talk and had questions but unfortunately I spent most of my time at the ESA meeting in my room due to a bad cold and lost of my voice. So it did not have the chance to meet you. As part of the CCD working group and supported by a coop. agreement with the USDA bee lab at Beltsville MD, I hive just completed a first year experiment using replicated functional hives exposed over two brood cycles to two sublethal doses of imidacloprid (5 and 20 ppb) plus a untreated control. Doses were to bees via artificial diet patties placed insdie the hives. We recorded many endpoint measurements of hive performance and foraging behavior, which showed no siginficant adverse effects. We know the larvae and new bees were exposed because the bees and bee bread contained levels of imidacloprid, although lower but in accordance with the treatments. This test examined only one stress, that of the insecticide. The next step is to challenge the exposed new bees to other stresses, such as diseases and parasitic mites, as you did. We need to communicate together on your studies because I am interested in the assay techniques that you used to expose bees to mites. You have my email and I will connect you when I return to MD and feel alot better than I do now. Galen