An Ozonolysis Based Method and Applications for the Non-Lethal Modification of Insect Cuticular Hydrocarbons

Effectiveness and biochemical impact of ozone gas and silica nanoparticles on Culex pipiens (Diptera: Culicidae)

Culex pipiens (Diptera: Culicidae) is a vector of many serious human diseases, and its control by the heavy use of chemical insecticides has led to the evolution of insecticide resistance and high environmental risks. Many safe alternatives, such as ozone gas (O3) and silica nanoparticles (silica NPs) can reduce these risks. Therefore, O3 and silica NPs were applied to 3rd larval instars of Cx. pipiens at different concentrations (100, 200, and 400 ppm) for different exposure times (1, 2, 3, and 5 min for O3 and 24, 48, and 72 h for silica NPs). The activity of some vital antioxidant enzymes as well as scanning electron microscopy of the body surface were also investigated. A positive correlation was observed between larval mortality % and the tested concentrations of O3 and silica NPs. O3 was more effective than silica NPs, it resulted in 92% mortality at 400 ppm for a short exposure time (5 min). O3-exposed larvae exhibited a significant increase in glutathione peroxidase, glutathione S-transferase, and catalase activities as well as the total antioxidant capacity. Scanning electron microscopy showing disruptive effects on the body surface morphology of ozone and silica NPs treated larvae. These results provide evidence that O3 and silica NPs have the potential for use as alternative vector control tools against Cx. pipiens.

Ozone exposure disrupts insect sexual communication

Insect sexual communication often relies upon sex pheromones. Most insect pheromones, however, contain carbon-carbon double bonds and potentially degrade by oxidation. Here, we show that frequently reported increased levels of Anthropocenic ozone can oxidize all described male-specific pheromones of Drosophila melanogaster, resulting in reduced amounts of pheromones such as cis-Vaccenyl Acetate and (Z)-7-Tricosene. At the same time female acceptance of ozone-exposed males is significantly delayed. Interestingly, groups of ozone-exposed males also exhibit significantly increased levels of male-male courtship behaviour. When repeating similar experiments with nine other drosophilid species, we observe pheromone degradation and/or disrupted sex recognition in eight of them. Our data suggest that Anthropocenic levels of ozone can extensively oxidize double bonds in a variety of insect pheromones, thereby leading to deviations in sexual recognition.

Desiccation resistance differences in Drosophila species can be largely explained by variations in cuticular hydrocarbons

Maintaining water balance is a universal challenge for organisms living in terrestrial environments, especially for insects, which have essential roles in our ecosystem. Although the high surface area to volume ratio in insects makes them vulnerable to water loss, insects have evolved different levels of desiccation resistance to adapt to diverse environments. To withstand desiccation, insects use a lipid layer called cuticular hydrocarbons (CHCs) to reduce water evaporation from the body surface. It has long been hypothesized that the water-proofing capability of this CHC layer, which can confer different levels of desiccation resistance, depends on its chemical composition. However, it is unknown which CHC components are important contributors to desiccation resistance and how these components can determine differences in desiccation resistance. In this study, we used machine-learning algorithms, correlation analyses, and synthetic CHCs to investigate how different CHC components affect desiccation resistance in 50 Drosophila and related species. We showed that desiccation resistance differences across these species can be largely explained by variation in CHC composition. In particular, length variation in a subset of CHCs, the methyl-branched CHCs (mbCHCs), is a key determinant of desiccation resistance. There is also a significant correlation between the evolution of longer mbCHCs and higher desiccation resistance in these species. Given that CHCs are almost ubiquitous in insects, we suggest that evolutionary changes in insect CHC components can be a general mechanism for the evolution of desiccation resistance and adaptation to diverse and changing environments.

Exploring the Insecticidal Potential of Gaseous and Aqueous Ozone to Control Spotted-Wing Drosophila, Drosophila suzukii (Diptera: Drosophilidae)

Over the last decade, numerous companies have marketed aqueous ozone sprayers for insect and disease management, but little to no data has been published on their efficacy. Thus, we evaluated the potential of both gaseous and aqueous ozone as a potential preharvest insecticide against the adult life stage of the invasive fruit pest, spotted-wing drosophila, Drosophila suzukii (Matsumura). Gaseous ozone was applied at two dosages, 14,600 and 30,100 ppmv, for varying durations and the respective concentration-time (CT) exposure responses were modeled for sex-specific mortalities recorded at 0, 24, 48, and 72 h following treatment. We found that gaseous ozone primarily caused mortality immediately following exposure, with slight increases 72 h following ozone treatments. The female and male lethal concentration-time (LCT) 50 estimates were significantly different at 0, 24, 48, and 72 h after 30,100 ppmv treatments, where males observed an increased mortality response. However, the LCT 99 estimates confidence intervals (95%) of adult female and male D. suzukii were similar at 0, 24, 48, and 72 h after 14,600 or 30,100 ppmv ozone treatments. In contrast, ozone dissolved in distilled water at 18.52 ppm (mg/L) did not provide any mortality after total immersion of subjects for 30 s. While gaseous ozone may have some utility as a fumigant for D. suzukii in closed vessels where concentrations could be maintained, we did not identify any insecticidal potential for ozone dissolved in aqueous solution when simulating a preharvest treatment under optimal laboratory conditions.