Toxicity of Tau-Fluvalinate, Lambda-Cyhalothrin, and Alpha-Cypermethrin to Aedes aegypti, 2019

The objective of this study was to generate baseline data for alternative adulticides to combat future outbreaks of yellowfever mosquitoes (YFM) that could transmit disease. YFM larvae were collected from water in peridomestic containers in Marathon, FL between March and August 2019. These larvae were returned to the laboratory, placed in screened cages, and reared to the adult stage in a growth chamber as described below at 27°C, 80% RH, and 11:13 (L:D) h cycle. Adults were blood-fed using defibrinated bovine blood (HemoStat Laboratories, Dixon, CA) placed in a bolus fashioned with rinsed hog sausage casings (Dewied International, Inc., San Antonio, TX). Plastic cups lined with seed germination paper and filled with 150 ml of distilled water were added to the cages for egg laying. Approximately 1,500 F1 progeny eggs were hatched out on 22 Apr 2019, 28 May 2019, and 5 Aug 2019. Larvae were added to 45.7 × 31.8 × 5.4 cm plastic larval trays (BioQuip Products, Inc., Rancho Dominguez, CA) containing 1.5-L distilled water. Larvae were provided with 0.01 g of Brewer’s yeast (Best Naturals LLC, Kenilworth, NJ) per pan on Day 1 and 0.05 g of TetraMin tropical fish flakes (Spectrum Brands Pet, LLC, Blacksburg, VA) per pan daily. On day 5, larvae were transferred from larval trays to 2-oz plastic cups with distilled water and placed in 30.5-cm³ cages. A total of 10 larvae were placed in each of 20 cups per cage for a total of 200 mosquito larvae in each screened cage. A pinch of tropical fish flakes was added to each cup every 2 d. Adult emergence occurred on 2 May 2019, 7 Jun 2019, and 16 Aug 2019, respectively. Adults were provided 10% sugar water via 2-oz plastic cup with lid and dental wick. Testing occurred on 7 May 2019 (τ-fluvalinate), 13 Jun 2019 (λ-cyhalothrin), and 21 Aug 2019 (α-cypermethrin). These three adulticides were purchased from Sigma–Aldrich (St. Louis, MO). Serial dilutions of each test material were made in acetone (Table 1). Clear glass 250-ml Wheaton bottles were used for all tests. Three bottles were used for each concentration of adulticide and three bottles were treated with acetone only as checks. One milliliter of each concentration of adulticide was placed into each bottle and the bottles were rolled and inverted to completely coat the inner surface with the adulticide solution. Caps were removed and the bottles were again rolled until all acetone had evaporated. Bottles were allowed to stand overnight in a dark room. The following day 30–50 adult mosquitoes were placed into the bottles. Three replicates of each adulticide and checks were run. Mortality was observed at 4 h. Data were analyzed using analysis of variance and means separated by Tukey’s Honestly Significant Test (P < 0.05). Dose–response (mortality) relationships were estimated with PoloJR (LeOra Software, LLC, Parma, MO). Data were analyzed assuming the probit model. Slopes, Χ², and LD₅₀ were estimated for each bioassay (Table 2). Results reported here provide baseline data for monitoring development of resistance in the future.

The highest doses of all compounds (1000 ppm) killed 100% of the YFM within 4 h of exposure (Table 1). However, a much higher concentration of tau-fluvalinate (LD50 = 32.33 ppm) was required to cause 100% mortality of YFM than lambda-cyhalothrin (LD50 = 0.91 ppm) or alpha-cypermethrin (LD50 ≤ 0.001; Table 2). Alpha-cypermethrin was toxic to YFM adults at much lower doses than were the other two chemicals tested. There was no mortality in the checks (Table 1).

This research study was entirely funded by Florida Keys Mosquito Control District.