Assessing the compatibility of filth fly pesticides with filth fly biological control parasitoids through toxicological and behavioral assays
King, Bethia H.
Ph.D. (Doctor of Philosophy)
Department of Biological Sciences
Flies--Biological control; Pesticides--Application; Flies as carriers of disease--Biological control
Filth flies are a significant pest at animal production facilities, leading to economic losses that include reductions in animal weight and milk production. Pesticides and biological control organisms are two important components of Integrated Pest Management (IPM) programs against filth flies. Biological control against filth flies frequently involves augmentative releases of pupal parasitoids. The compatibility of pesticides and the parasitoids Spalangia endius Walker and Urolepis rufipes Ashmead was examined using one of the most common filth flies, the house fly, Musca domestica L. The specific goals were to 1) assess the effects of the active ingredients of several house fly pesticides on house flies relative to S. endius using a new index, 2) examine the behavior and survival of S. endius and U. rufipes in response to three granular house fly baits and components, and 3) examine sublethal effects of exposure to a common neonicotinoid, imidacloprid, on S. endius. For the first goal, a Pesticide Compatibility Index (PCI) was created. This index allows comparison of LC₅₀ values between pest and biological control organism even when the mode of exposure to a pesticide differs, e.g., exposure by contact versus by feeding, and the index takes into account recommended pesticide dosages. Bioassays of survival were performed using five pesticides presented in the mode in which each organism was expected to be exposed to the pesticides, a surface contact bioassay for S. endius and a feeding bioassay for M. domestica. The PCI index was computed by first converting LC₅₀ values into units of prescribed dosages (LPR = LC₅₀-to-prescribed dosage ratio). Prescribed dosages from labels of granular baits were used. PCI was calculated as the ratio of LPRbiological control agent to LPRpest. Based on PCI values, order of compatibility with S. endius was spinosad > thiamethoxam > dinotefuran > methomyl > imidacloprid. That spinosad was better than imidacloprid or methomyl, both for parasitoid survival and for killing flies, was consistent with conclusions from the LC₅₀ values. Permethrin and nitenpyram were also tested, but their PCIs were not calculated, so they were compared to the other pesticides using LC₅₀ values. PCIs were not calculated because prescribed bait dosages were not available: permethrin is prescribed as a contact pesticide against flies rather than being consumed as a bait and nitenpyram has not been formulated as a fly pesticide. Permethrin was moderately toxic to S. endius but one of the most toxic of the pesticides for M. domestica; whereas nitenpyram was the least toxic of the pesticides for both S. endius and M. domestica. For the second goal, behaviors and mortality of S. endius and U. rufipes were tested in response to granular fly baits containing one of three active ingredients (AI): Golden Malrin (methomyl), QuickBayt (imidacloprid), or Quikstrike (dinotefuran). Behavioral responses to each of two components of the baits, the AIs and the fly attractant pheromone (Z)-9-tricosene, were also examined independently. S. endius avoided contact with bait granules, regardless of bait type. However, when S. endius contacted bait residue, the imidacloprid bait appeared to be the least harmful of the baits for S. endius, at least in the short term. S. endius was attracted to imidacloprid by itself. However, S. endius avoided (z)-9-tricosene. In contrast to S. endius' attraction to imidacloprid, S. endius neither avoided nor was attracted to methomyl or dinotefuran. For U. rufipes, the methomyl bait appeared to be especially harmful. U. rufipes avoided bait granules with imidacloprid or dinotefuran but not with methomyl, died quickly in the presence of methomyl bait residue, and had a methomyl LC₅₀ that was lower than that for S. endius. The avoidance by U. rufipes of granules with imidacloprid or dinotefuran appears to be related to components other than the AIs or the (Z)-9-tricosene because U. rufipes did not avoid either individually. The behavioral resistance of the parasitoids occurred despite no exposure recently, if ever, to these pesticides. For the third and final goal, I determined if imidacloprid, the most commonly used pesticide against filth flies, would impact the ability of S. endius to act as an effective biological control if they did not initially die from exposure. Exposure to an LC₅₀ of imidacloprid decreased the ability of surviving individuals of the parasitoid wasp S. endius to kill house fly pupae under some conditions. In an unburied hosts experiment, significantly more flies and fewer parasitoids emerged in the LC₅₀ imidacloprid treatment versus the LC₁₀ or controls; parasitoid sex ratio and longevity were not affected. However, in a buried hosts experiment, parasitoid and fly emergence were independent of treatment. ELISA (enzyme-linked immunosorbent assay) showed lower imidacloprid residues in or on parasitoids that had been exposed to the media in which hosts were buried. These findings suggest that substrate may reduce pesticides on biological control agents that burrow, making these agents more effective. Pesticides formulated to target filth flies are strong enough to kill S. endius and U. rufipes many times over. It is thus very important to carefully consider locations in which these pesticides are placed so as to minimize the likelihood of inadvertent exposure by biological control organisms like S. endius and U. rufipes. Based on these results, no current pesticide used for control of filth flies is 100% safe to S. endius or U. rufipes. That granular baits containing imidacloprid, methomyl, or dinotefuran were not attractive to either parasitoid is encouraging. However, use of U. rufipes with methomyl bait is not recommended. Of the parasitoids and baits tested, S. endius in conjunction with dinotefuran bait (QuikStrike) appears to be the best combination, based on the best PCI value and S. endius's burrowing habit removing pesticide. The behavioral response of filth fly parasitoids to spinosad bait and thiamethoxam bait would be worth investigating. My results reinforce the importance of looking not only at traditional physiological effects of pesticides but also at behavioral responses.
Burgess, Edwin R. IV, "Assessing the compatibility of filth fly pesticides with filth fly biological control parasitoids through toxicological and behavioral assays" (2016). Graduate Research Theses & Dissertations. 1538.
viii, 80 pages
Northern Illinois University
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Advisors: Bethia H. King.||Committee members: Nicholas A. Barber; Holly P. Jones; Richard B. King; Jon S. Miller.||Includes bibliographical references.||Includes illustrations.