Longevity of Fly Baits Exposed to Field Conditions

Insecticide Resistance Development in the Filth Fly Pupal Parasitoid, Spalangia cameroni (Hymenoptera: Pteromalidae), Using Laboratory Selections

Filth flies remain one of the most prevalent pest groups affecting the animal production industry. Spalangia spp. and Muscidifurax spp. are beneficial parasitic wasps that often are utilized to manage filth fly populations such as house flies, Musca domestica L. (Diptera: Muscidae), and stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae). These wasps search for filth fly pupae as hosts in areas potentially treated with insecticides, which may result in nontarget insecticide selection effects. However, research regarding resistance development in parasitic wasps such as S. cameroni Perkins (Hymenoptera: Pteromalidae) is limited. Therefore, a study was conducted to determine the potential of S. cameroni to develop resistance to the commonly used insecticide permethrin, as well as compare permethrin susceptibility among several S. cameroni strains. After 10 selected generations, susceptibility was significantly lower for the selected strain when compared with that of its unselected parent strain. A comparison of several parasitoid strains collected from different U.S. states indicated that permethrin susceptibility was not significantly different between a baseline strain and more recently established field strains. The potential implications of this previously unrecognized nontarget insecticide exposure effect on filth fly parasitoids are discussed.

Feeding Response to Select Monosaccharides, Sugar Alcohols, and Artificial Sweeteners Relative to Sucrose in Adult House Flies, Musca domestica (Diptera: Muscidae)

Use of insecticidal baits risks the evolution of resistance to the feeding stimulant in the bait, not just to the active ingredient (toxicant). Sucrose-based baits are widely used against house flies, Musca domestica L. The baits are applied as dry granules, but readily liquefy. The proboscis extension reflex (PER) and consumption of alternative sweeteners, dry or in solution, were examined. Fructose, glucose, and xylitol merit further study as alternatives to sucrose. Dry, fructose, glucose, and xylitol elicited PER much more than sucrose, although not when in solution. Furthermore, dry or in solution, females and males ate as much or more fructose as sucrose. In solution, flies ate as much glucose as sucrose; although when dry, consumption was much less for glucose than sucrose. Dry, xylitol elicited as much consumption as sucrose for females, though less for males. In solution, for both sexes, xylitol elicited less consumption than sucrose did. Acesulfame potassium, sodium cyclamate, and sucralose do not look promising as they did not often elicit PER, whether dry or in solution. Erythritol also does not look promising. Erythritol elicited PER no more than sucrose did when dry and elicited PER much less than sucrose when in solution. Flies ate much less erythritol than sucrose whether dry or in solution.

Development of a Mycoinsecticide Bait Formulation for the Control of House Flies, Musca domestica L

The control of house flies, Musca domestica (L.), currently relies on the use of chemical insecticide spray and bait formulations. Entomopathogenic fungi, such as Metarhiziumanisopliae, may provide an alternative to these products. This study aimed to develop and evaluate a mycoinsecticide bait formulation containing a virulent M. anisopliae isolate. Five M. anisopliae isolates were screened against M. domestica and isolate M16 was selected for bait development. Bait formulations containing a variety of additives, including (Z)-9-tricosene, were tested for their ability to increase fly visitation. A bait formulation containing M. anisopliae and skim milk powder was found to have the highest house fly visitation and was subsequently compared to a conventional chemical bait in an efficacy assay. The chemical bait (0.5% imidacloprid) caused faster mortality than the mycoinsecticide bait, however, similar levels of mortality were achieved by 4–5 days’ post exposure. These results suggest that M. anisopliae mycoinsecticide baits may offer an alternative to conventional chemical insecticides for the control of house flies in suitable areas.

Mortality Rate of House Flies (Diptera: Muscidae) Exposed to Insecticidal Granular Fly Baits Containing Indoxacarb, Dinotefuran, or Cyantraniliprole

The mortality rate of a field population of house fly (Musca domestica L.) was determined for a granular fly bait containing the active ingredient indoxacarb, which was compared to two commercially available granular fly baits containing either dinotefuran or cyantraniliprole. Indoxacarb was applied at three different application rates 0.498, 0.986, and 1.972 g/m2 (low, medium, and high). Time to 50% mortality was fastest for dinotefuran (5.7 h) and slowest for the low application rate of indoxacarb (10.3 h). Time to 90% mortality was fastest for the high application rate of indoxacarb (27.7 h) and slowest for dinotefuran (51.0 h) and cyantraniliprole (45.9 h). Among the three indoxacarb application rates, the high rate reached both 50 and 90% fly mortality significantly faster than the low rate. The medium rate did not significantly differ from either the high or low application rates. Dinotefuran bait produced greater fly mortality than all other treatments at 30-min post-exposure, with mortality for remaining baits exceeding controls by 3- to 6-h post-exposure. All insecticidal baits produced similar fly mortality by 6-h post-exposure and >94% fly mortality by 96-h post-exposure, indicating that each may be effective in a fly management program. Flies consumed a similar amount of the indoxacarb (regardless of application rate) and dinotefuran baits, but consumed less of the cyantraniliprole bait, suggesting a feeding irritancy or toxicity effect manifested during consumption. Nevertheless, flies consumed enough cyantraniliprole bait to cause mortality similar to other baits by 6-h post-exposure.

Quantitative Analysis of Houseflies-mediated Food Contamination with Bacteria

Flies play a key role as vectors in transmitting various bacteria and pose bacterial contamination risk to food. To evaluate the time- and concentration-related bacterial contamination of food by houseflies based on their attraction to the food, we determined the number of fed antimicrobial-resistant Escherichia coli transferred from houseflies to foods, sugar and milk mixture, apple, and castella (such as sponge cake). Houseflies contaminated the foods with the fed E. coli within 5 min, and the bacteria were present in high numbers on apple and castella (3.3 × 10³ and 3.5 × 10⁴ CFU/g of food, respectively). Furthermore, the number of fed E. coli on the foods increased with time, rising to 3.6 × 10⁴-1.7 × 10⁵ CFU/g. We show that the food contamination level caused by houseflies depends on the concentration of bacteria that the houseflies carry, the contact time with the food, and the attraction of the flies to the food.