Sarita Kumar

Every year, millions of people are affected by mosquito-borne illnesses, which pose a serious danger to world health. To stop the spread of these diseases, it is essential to manage the population of their main vector. Growing resistance of Aedes aegypti to traditional insecticides calls for safer and more environmental-friendly solutions. This study compares the toxicity of commercial and crude extracted essential oil (by steam distillation) of Cymbopogon citratus (lemongrass) essential oil against Aedes aegypti . The study combines Thin Layer Chromatography (TLC) profiling of both the essential oils, and larvicidal bioassay and contact irritancy assays against Aedes aegypti to assess biological activity. Larvicidal efficacy was evaluated by exposing early fourth instars of Aedes aegypti larvae to different concentrations of crude and commercial essential oils. The bioassay demonstrated considerable concentration-dependent toxicity, with crude oil exhibiting higher toxicity (LC ₅₀ : 10.485 µg/mL) in comparison to the commercial oil (LC ₅₀ :43.504 µg/mL), which may be attributed to the diverse and differential array of bioactive secondary metabolites. Irritancy test showed significant behavioural effects, suggesting the potential use of the oils as repellents or irritants to interfere with mosquito-host contact. The study demonstrates the higher effectiveness of crude Cymbopogon citratus essential oil and suggests its use as a potential, natural alternative for mosquito control programs. The investigation offers insights into the action of major constituents of essential oils and their use in safe vector control strategies.

Mosquito-borne diseases continue to pose a serious threat to global health due to rapid urbanization, climate change, and the widespread emergence of insecticide resistance. Traditional chemical insecticides like pyrethroids, organophosphates, and organochlorines have lost their effectiveness because of resistance, environmental persistence, and non-target toxicity. Therefore, eco-friendly substitutes are urgently needed. This chapter emphasizes the potential of botanical extracts, phytochemicals, and formulations aided by nanotechnology as sustainable mosquito management tools. It covers over 300 plant species exhibiting larvicidal, repellent, ovicidal, and adulticidal activities, as well as their primary bioactive constituents, including alkaloids, flavonoids, terpenoids, phenolics, and organosulfur compounds. Botanicals exhibit different modes of action, including damage to midgut tissues, suppression of detoxifying enzymes, and interference with nerve transmission. Despite their potential, the use of botanicals is associated with instability, fast deterioration, and low field persistence. Hence, green-synthesized nanoparticles and nano-emulsions are becoming effective carriers that improve stability, bioavailability, and controlled release to overcome these problems. Additionally, incorporating botanicals into Attractive Toxic Sugar Baits (ATSB) offers a new behavior-based delivery method for focusing on populations of resistant mosquitoes. This chapter recommends the use of botanical-nano synergies as a feasible, safe, and effective alternative for current mosquito vector control programs.

Helicoverpa armigera is a major polyphagous pest with an immense potential to develop resistance to conventional insecticides. Emamectin benzoate (EMB), a compound derived from abamectin, is widely used for its efficacy against lepidopteran larvae. Despite several studies revealing its toxic and growth regulatory effects, information regarding its effects on midgut protein composition remains limited. In this study, we examined the midgut protein profile of H. armigera larvae following exposure to dietary EMB. Midgut proteins were separated by SDS-PAGE and differentially obtained bands were identified using liquid chromatography-mass spectrometry (LC-MS). The EMB-treated larvae showed a total of 39 differential proteins, among which 35 proteins were differentially deleted while just 4 proteins were differentially detected. The chief differentially absent proteins were found to be associated with metabolism, protein processing, signal transduction and stress response, while the differentially detected proteins were related to glycolysis and signal transduction. The differential absence/presence of these proteins indicated their plausible role in causing the disrupted metabolic and physiological processes in EMB-treated H. armigera larvae. This study provides qualitative molecular insights into the midgut-level responses of H. armigera to EMB exposure. However, further quantitative estimation of the altered levels of proteins can help formulation of an effective management strategy.

Introduction: Aedes aegypti serves as a primary vector for several arboviral diseases. The emergence of Aedes -borne diseases has raised concerns in health sectors worldwide. Despite the efficacy of synthetic insecticides, their repeated and random use in the fields has made mosquitoes resistant, reducing their effectiveness in control programs and causing environmental hazards. Hence, the present study aimed to assess the baseline susceptibility of α-cypermethrin to Ae. aegypti and understand the involvement of detoxification enzymes in its defense system. Methods: The study evaluated the susceptibility of Ae. aegypti to α-cypermethrin using the WHO bottle bioassay and investigated the enzymes involved in metabolic resistance through molecular docking and biochemical estimation. Adult females were exposed to different concentrations of α-cypermethrin using the WHO bottle bioassay to assess their susceptibility status. The effect was estimated on five detoxification enzymes, namely, glutathione-S-transferase (GST), cytochrome P450 monooxygenase (CYP450), α-esterase, β-esterase, and acetylcholinesterase (AChE), through molecular docking and biochemical assays. Results: The LC ₅₀ and LC ₉₀ values of α-cypermethrin were 0.00007% and 0.00059%, respectively. Exposure to the diagnostic dose (10 µg/bottle) caused 97.91% mortality, indicating suspected early signs of insecticide resistance development, according to WHO guidelines. Docking analysis showed the strongest binding affinity of β-esterase with α-cypermethrin (−9.4 kcal/mol), followed by CYP450 (−8.8 kcal/mol), GST (–7.5 kcal/mol), α-esterases (−7.1 kcal/mol), and AChE (–6.6 kcal/mol), suggesting their variable but significant involvement in detoxification. These results were corroborated by biochemical estimation of the enzymes, revealing an increase in the levels of all detoxification enzymes except GST, which showed decreased levels. The maximum effect was recorded on β-esterase levels, resulting in a 21.41-fold increase in activity. Conclusion: The present study shows the significant impact of α-cypermethrin on the survival and detoxification enzymes of Ae. aegypti. The molecular docking and biochemical characterization of detoxification enzymes demonstrated the major role of β-esterase, while also indicating a significant contribution of other enzymes to the activation of the defense system of Ae. aegypti. This is the first report that unravels the effects of α-cypermethrin on the detoxification enzymes of Ae. aegypti through molecular docking validated by biochemical assays. The study improves our understanding of resistance mechanisms and highlights the importance of regular resistance monitoring for effective mosquito control.

Aedes aegypti is a major vector of arboviral diseases such as dengue, chikungunya, Zika, and yellow fever. Traditional chemical insecticides have led to widespread insecticide resistance and posed risks to non-target organisms and the environment. Insect growth regulators (IGRs) offer a promising alternative by disrupting mosquito development rather than inducing immediate lethality. The present study evaluated the efficacy of methoxyfenozide, a non-steroidal ecdysteroid agonist, in disrupting the development and chitin synthesis of Ae. aegypti larvae to explore its potential as a mosquito control agent. Larvicidal activity, inhibition of adult emergence, and effects on chitin synthesis were assessed using standard bioassays and biochemical quantification techniques. Lethal concentrations and emergence inhibition dosages were determined using probit analysis. Methoxyfenozide exhibited dose-dependent larvicidal activity, with respective LC50 and LC90 values of 6.326 mg/L and 115.615 mg/L after 24 hours, and 4.180 mg/L and 119.100 mg/L after 48 hours, indicating a delayed action. The compound significantly inhibited adult emergence (p < 0.05), exhibiting an IE90 value of 1.209 mg/L. Morphological abnormalities, such as arrested moulting and structural deformities, were also observed. Biochemical analysis revealed a substantial reduction in chitin content in methoxyfenozide-treated larvae, with a greater decrease observed after longer treatment durations and at higher dosages. The study revealed that methoxyfenozide effectively disrupted Ae. aegypti development, inhibited both larval survival and adult emergence, as well as impeded chitin content deposition. The effective mode of action and minimal toxicity to non-target species highlight its potential for inclusion in integrated vector management strategies.

Introduction: Aedes aegypti, the vector of multiple arboviral diseases, is a prime health concern worldwide. The surge in Aedes-borne diseases emphasizes the urgent need for efficient vector control measures. Synthetic pesticides used traditionally, however, present environmental concerns and issues like resistance development, causing the use of higher chemical doses. Hence, alternate interventions like the use of insect growth regulators (diflubenzuron; DFB) show promise because of their unique mechanism of action and environmental safety. Nevertheless, mosquitoes have the potential to develop resistance to any chemical. Thus, the present study investigates the use of DFB in combination with verapamil (DFB-V; 1:10) as a possible mosquito intervention measure.Methods: The effects of both DFB and DFB-V were assessed on the larval development, adult emergence and expression of detoxification enzymes, non-specific esterases, glutathione S-transferase (GST), acetylcholinesterase (AChE), and monooxygenases in laboratory-reared (AND-Ae. aegypti) and wild-caught (GVD-Ae. aegypti) strains of Ae. aegypti. The effects on the survival of non-target organisms were also investigated. Results: The investigations showed that DFB-V treatment of the Ae. aegypti fourth instars caused a 1.16–1.37 fold higher adult emergence suppression than DFB alone, reducing the IE₅₀ values. The DFB treatment increased β-esterases, AChE, and monooxygenases but reduced the GST and α-esterase levels. The effects enhanced with the use of DFB-V, causing a significant decrease in α-esterase (7.7-fold) and an increase in monooxygenases (7.8-fold) (p < 0.05) in AND-Ae. aegypti compared to the wild-caught strain. The variation in enzyme levels in the two strains may be due to the stress caused by insecticides of different chemical natures used in the fields. No negative effects were observed on the non-target organisms—Gambusia affinis, Mesocyclops thermocyclopoides, and Paramecium tetraurelia.Conclusion: The studies showed the growth regulatory efficacy of DFB and probable role of GST and α-esterases in increasing the effects of DFB when synergized with verapamil. Further, the DFB-V combination did not result in any significant negative effects on the non-target organisms ascertaining its safe use. This is the first report unraveling the effects of the DFB–verapamil combination on the defense mechanism of Ae. aegypti. Further studies may assist in developing focused and eco-safe plans for managing Ae. aegypti populations effectively.