The use of synthetic insecticides has been the main approach in mosquito control programs (MCPs) to prevent or reduce mosquito populations. The global problem of insecticide resistance and the concern of environmental impacts of synthetic insecticides have resulted in the interest of botanicals as an alternative. In this study, the botanical product BigShot Maxim, which contains cedarwood oil (14%), thyme oil (0.53%), and cinnamon oil (0.23%) as active ingredients, was examined in adulticide and larvicide bioassays against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus. In the adulticide bioassay, 100% mortality was reached at a dilution of 1:10 after 4 h of exposure for all 3 species. In the larvicide bioassay, at the highest tested concentration (30 ppm by volume) the greatest mortality was 96.44 ± 1.44% SE for Ae. aegypti, 92.44 ± 2.07% SE for Cx. quinquefasciatus, and 33.33 ± 3.61% for An. quadrimaculatus, respectively. Insecticidal properties presented in all the experiments indicate that BigShot Maxim could be a viable alternative to some synthetic insecticides used in MCPs.

Controlling nuisance and medically important mosquito species is the main goal of mosquito control programs (MCPs). Synthetic insecticides have had an important role in protecting people and animals against mosquito-borne illnesses by controlling vector mosquito populations. However, synthetic insecticides to treat adult mosquitoes in the USA are limited to pyrethroids and organophosphates (Hemingway and Ranson 2000). The limited arsenal of mosquito control products has contributed to the global problem of insecticide resistance and presents an issue for MCPs (Nauen 2001, Cui et al. 2006). Because of the limitation of insecticides and resistance situation, there has been interest in developing new active ingredients using botanicals as an alternative to some synthetic insecticides with the goal of reducing insecticide resistance and identifying more environmentally sound products (Sukumara et al. 1991, Prabhakar and Jebanesan 2004). There are several botanical products that have been traditionally used as insecticides, including essential oils (Arnason et al. 2012, Sharifi-Rad et al. 2017). In previous studies, essential oils have been demonstrated to have fumigant and contact insecticidal properties (Isman 2000). The objective of the current study was to evaluate BigShot Maxim (PreVasive USA, LLC, Oakwood, GA), a natural product, which contains cedarwood oil (14%), thyme oil (0.53%), and cinnamon oil (0.23%) as the active ingredients, as an alternative to synthetic insecticides for controlling larval and adult-stage mosquitoes.

Aedes aegypti (L.), Culex quinquefasciatus Say, and Anopheles quadrimaculatus Say were obtained from the US Department of Agriculture, Center for Medical and Veterinary Entomology, Gainesville, FL, and reared in Anastasia Mosquito Control District insectaries maintained at 80 ± 2°F, 80 ± 10% RH, and a photoperiod of 14 h light and 10 h dark. Larval mosquitoes were reared in plastic trays (22 × 17 × 3 in.) on a diet of Tetramin Tropical Flakes (fish food; Tetra, Blacksburg, VA) administered in a 1:6 food:water slurry while adult mosquitoes were provided 10% sucrose solution ad libitum. Larval studies used 3rd-stage larvae, and adult studies used nonbloodfed, 5- to 7-day-old female mosquitoes of each species in the experiments described below.

To determine the optimal application rate for BigShot Maxim for adult control, adult Ae. aegypti, Cx. quinquefasciatus, and An. quadrimaculatus were exposed to 4 dilutions of BigShot Maxim using a cup bioassay. Dilutions were selected based on the micrograms of active ingredient. The dilution 1:100 (BigShot Maxim:water) (approximately 14,000 μg) is representative of the suggested application rate. One higher concentration (1:10) and 2 lower concentrations (1:300 and 1:600) were also selected for evaluation. Each trial also had a negative (water) and positive (permethrin at 43 μg/cup) control. Three trials of 5 replicates were conducted for each species. Circular Whatman grade 1 filter papers (8.5 cm diam; Cytiva, Marlborough, MA) were inoculated with 1 ml each of a specific dilution and allowed to dry overnight. The filter papers were then placed inside of a 100 × 15-mm petri dish bottom (EZ BioResearch, St. Louis, MO) topped with a 266-ml clear plastic cup (Solo Cup Company, Lake Forest, IL). Plastic cups were fastened to the rim of the petri dishes using a strip of Parafilm (Pechiney Plastic Packaging, Chicago, IL). Prior to assembly, a hole was melted into the bottom of each plastic cup to allow for aspiration of mosquitoes. The holes were sealed with a cotton ball after 15 ± 3 adult female mosquitoes were aspirated into the cup. Mosquitoes were provided 10% sugar solution ad libitum by saturating the cotton ball. Assay cups were then stored in an incubator maintained at 80 ± 2°F, 80 ± 10% RH, and a photoperiod of 14 h light and 10 h dark. Mortality was checked immediately after aspiration and then at 1, 2, 4, 8, and 24 h postexposure.

To determine the optimal larvicide application rate of BigShot Maxim, larval Ae. aegypti, Cx. quinquefasciatus, and An. quadrimaculatus were exposed to 4 concentrations of BigShot Maxim: 30 ppm, 15 ppm, 5 ppm, and 1 ppm by volume. Treatments were prepared following Environmental Protection Agency pesticide testing guidelines. Three trials of 5 replicates per concentration and a negative control were conducted for each species. To prepare the concentrations, a 10% stock solution of BigShot Maxim in acetone was serially diluted 1:9 into reverse osmosis (RO) water. Final test concentrations were achieved by adding 0.1–1.0 ml of the appropriate serial dilution into 100 ml of RO water using 266-ml clear plastic cups (Solo Cup Company). Batches of 15 3rd-stage larvae were transferred into the test containers via plastic bulb pipettes. Mortality was recorded and dead larvae removed at 24, 48, and 72 h postexposure. Larvae were defined as dead if they were unresponsive when either probed with a needle or the water was disturbed.

For adulticide bioassays, due to limited data for the bioassay experiment only a descriptive analysis was performed. Abbott's formula (Abbott 1925) was used to correct treatment mortality with control mortality >10% and the calibrated data were used in the analysis. An independent t-test and analysis of variance were conducted for comparisons maintaining the significance level at 0.05. For larvicide bioassays data, a probit analysis was conducted to determine the lethal concentrations causing 50% mortality (LC50) and 90% mortality (LC90) of BigShot Maxim after 48 h of exposure against larvae of the 3 mosquito species.

The results from the adulticide bioassay were averaged by species. For all 3 species, BigShot Maxim at a dilution of 1:10 was more effective compared with the permethrin positive control (Fig. 1). At this dilution Ae. aegypti reached 100% mortality after 2 h of exposure, while Cx. quinquefasciatus and An. quadrimaculatus both reached 100% mortality after 4 h of exposure. The permethrin positive control did not result in 100% mortality for any of the 3 species, even after 24 h of exposure. Due to limited mortality from dilutions 1:100, 1:300, and 1:600, we were unable to conduct a probit analysis to determine an optimal concentration.

Fig. 1.

Percent mortality results from adulticidal bioassay at different dilution ratios of BigShot Maxim and permethrin (positive control): (a) Aedes aegypti, (b) Culex quinquefasciatus, and (c) Anopheles quadrimaculatus. The ratios at 1:300 and 1:600 of BigShot and water (negative control) did not result in any mortality.

Fig. 1.

Percent mortality results from adulticidal bioassay at different dilution ratios of BigShot Maxim and permethrin (positive control): (a) Aedes aegypti, (b) Culex quinquefasciatus, and (c) Anopheles quadrimaculatus. The ratios at 1:300 and 1:600 of BigShot and water (negative control) did not result in any mortality.

Close modal

For all 3 species, BigShot Maxim had a significantly higher larval mortality, with all concentrations than the controls after 48 h of exposure in all concentrations except at the lowest concentration (1 ppm by volume). At the highest tested concentration (30 ppm by volume) the results demonstrated the highest mortalities for each species (96.44 ± 1.44% SE for Ae. aegypti, 92.44 ± 2.07% for Cx. quinquefasciatus, and 33.33 ± 3.61% for An. quadrimaculatus. Aedes aegypti had the highest mortality followed by Cx. quinquefasciatus and An. quadrimaculatus. The LC50 and LC90 values for 48 h of exposure were the highest in An. quadrimaculatus (LC50: 0.0131, LC90: 0.5), followed by Cx. quinquefasciatus (LC50: 0.0012, LC90: 0.004) and Ae. aegypti (LC50: 0.0004, LC90: 0.0009) (Table 1). These findings indicate that BigShot Maxim is 32 and 4 times more toxic to Ae. aegypti than to An. quadrimaculatus and Cx. quinquefasciatus, respectively, in killing 50% of their populations.

Table 1.

Effectiveness of BigShot Maxim as a larvicide against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus after 48 h of exposure in the laboratory.1

Effectiveness of BigShot Maxim as a larvicide against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus after 48 h of exposure in the laboratory.1
Effectiveness of BigShot Maxim as a larvicide against Aedes aegypti, Culex quinquefasciatus, and Anopheles quadrimaculatus after 48 h of exposure in the laboratory.1

The MCPs have been challenged by the continuous problem of insecticide resistance to some synthetic pesticides (Sokhna et al. 2013). In this study, BigShot Maxim was evaluated to determine the product's efficacy as an alternative to some synthetic pesticides. In the literature, cedarwood oil, the main active ingredient in BigShot Maxim, is shown to have high mortality against arthropod pests (Eller et al. 2014, Khanna and Chakreaborty 2018).

In this study it can be concluded that, at a dilution of 1:10, BigShot Maxim is more effective at killing Ae. aegypti, Cx. quinquefasciatus, and An. quadrimaculatus than the permethrin positive control. This dilution of BigShot Maxim could be an effective alternative to combating permethrin resistance. However, this concentration of BigShot Maxim is significantly higher than the suggested application rate (1:100) and further testing is needed to determine the optimal concentration of BigShot Maxim between 1:10 and 1:100. Alternatively, testing with higher percentages of the AI used in BigShot Maxim could be done to find a formulation that would provide lower but effective application rate. In another study, NatureCide Pest Management (Nature-Cide, Canoga Park, CA), a botanical insecticide containing 25.3% cedarwood and 12.7% cinnamon oil, was shown to be effective against Ae. aegypti in an ultra-low volume treatment at a concentration of 70 ml/liter, which resulted in 100% mortality (Bibbs et al. 2019).

BigShot Maxim was highly effective as a larvicide against Ae. aegypti and Cx. quinquefasciatus mosquitoes, with Ae. aegypti being the most affected. Mortality data and LC50 and LC90 values indicated that BigShot Maxim is not effective as a larvicide against An. quadrimaculatus.

The study shows the potential of BigShot Maxim to be used against Ae. aegypti and Cx. quinquefasciatus as an alternative to the synthetic permethrin. Unlike synthetic pesticides, BigShot Maxim is a pesticide exempt from the Federal Insecticide, Fungicide, and Rodenticide Act, making it ideal for more frequent reapplications. However, further bioassay studies are needed to find more economical and optimal concentrations, as BigShot Maxim was effective at higher than suggested label applications.

This is a research report only. Specific mention of commercial products does not imply endorsement by the Anastasia Mosquito Control District.

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Author notes

1

PreVasive USA, 3643 Explorer Trail, Oakwood, GA 30566.