A potent larvicidal agent against Aedes aegypti mosquito from cardanol

Larvicidal and anti-termite activities of microbial biosurfactant produced by Enterobacter cloacae SJ2 isolated from marine sponge Clathria sp

The widespread use of synthetic pesticides has resulted in a number of issues, including a rise in insecticide-resistant organisms, environmental degradation, and a hazard to human health. As a result, new microbial derived insecticides that are safe for human health and the environment are urgently needed. In this study, rhamnolipid biosurfactants produced from Enterobacter cloacae SJ2 was used to evaluate the toxicity towards mosquito larvae (Culex quinquefasciatus) and termites (Odontotermes obesus). Results showed dose dependent mortality rate was observed between the treatments. The 48 h LC50 (median lethal concentration) values of the biosurfactant were determined for termite and mosquito larvae following the non-linear regression curve fit method. Results showed larvicidal activity and anti-termite activity of biosurfactants with 48 h LC50 value (95% confidence interval) of 26.49 mg/L (25.40 to 27.57) and 33.43 mg/L (31.09 to 35.68), respectively. According to a histopathological investigation, the biosurfactant treatment caused substantial tissue damage in cellular organelles of larvae and termites. The findings of this study suggest that the microbial biosurfactant produced by E. cloacae SJ2 is an excellent and potentially effective agent for controlling Cx. quinquefasciatus and O. obesus.

Effectiveness of Cashew Nut Shell Liquid (CNSL) with Bait Formulation Against Iridomyrmex cordatus as a Vector of Cocoa Pod Rot Disease Caused by Phytophthora palmivora

<b>Background and Objective:</b> Cashew Nut Shell Liquid (CNSL) is a biopesticide that is environment-friendly in controlling ants <i>Iridomyrmex cordatus</i> is a vector pot rot disease caused by <i>Phytophthora palmivora</i>. The research aimed to obtain the best concentration of cashew nut shell liquid formulated as smart food bait to tackle the ant population of <i>Iridomyrmex cordatus</i> due mainly to a vector of <i>Phytophthora </i>pod rot. <b>Materials and Methods:</b> The research was carried out in cocoa areas in South Sulawesi with a randomized block design consisting of six treatments. Feeding trials consisted of food bait formulation that was added with cashew husk, respectively 1, 10, 20% and 17.5 g carbaryl (recommended dose) and control (without cashew husk or carbaryl). Each trial was replicated five times and set near to petiole and ant tunnel nest. The research focused on the number of ant colonies established in the trees until food bait was given. <b>Results:</b> The trial with CNSL concentration had a positive effect on the ant population the higher concentration given, the lower the ant population was obtained. Meanwhile, the population of <i>I. cordatus</i> had a positive contribution to the increase of disease incidence of <i>Phytophthora</i> pod rot disease<i>.</i> Feeding trials with 1 and 5% CNSL concentrations were less effective to limit ant population and disease incidence according to the efficacy test. In contrast, the trials of 10 and 20% were able to control population density and disease incidence due to over 51.39% efficacy test. <b>Conclusion:</b> There was a positive trend of CNSL concentration to reduce the ant population of <i>I. cordatus</i>. There was the greatest association between the increase of ant population density and the increase in disease incidence of <i>Phytophthora </i>pod rot.

Challenges, Advances and Opportunities in Exploring Natural Products to Control Arboviral Disease Vectors

Natural products constitute an important source of molecules for product development. However, despite numerous reports of compounds and active extracts from biodiversity, poor and developing countries continue to suffer with endemic diseases caused by arboviral vectors, including dengue, Zika, chikungunya and urban yellow fever. Vector control remains the most efficient disease prevention strategy. Wide and prolonged use of insecticides has resulted in vector resistance, making the search for new chemical prototypes imperative. Considering the potential of natural products chemistry for developing natural products-based products, including insecticides, this contribution discusses the general aspects and specific characteristics involved in the development of drug leads for vector control. Throughout this work, we highlight the obstacles that need to be overcome in order for natural products compounds to be considered promising prototypes. Moreover, we analyze the bottlenecks that should be addressed, together with potential strategies, to rationalize and improve the efficiency of the drug discovery process.

Rhamnolipids on Aedes aegypti larvae: a potential weapon against resistance selection

The resistance of Aedes aegypti to chemical insecticides has been reported and our work proposes the use of biosurfactants as an alternative larvicide. We evaluated the effect of rhamnolipids against larvae of pyrethroid-resistant and susceptible A. aegypti strains. Time-mortality and sublethal effects were evaluated via survival analysis and swimming behavior, respectively. Rhamnolipids showed larvicidal effect at all tested concentrations. Rhamnolipids at 300 mg L^-1 killed 100% of both susceptible and resistant larvae within 24 h of exposure and 99% after 30-days stored (pyrethroid-susceptible larvae). Regarding the sublethal effects, the swimming rate was reduced in 50 and 100 mg L^-1 of rhamnolipids in grouped (pyrethroid-susceptible) larvae. Rhamnolipids at 50 mg L^-1 reduced the distance and speed and increased the number of stops and resting time of individualized pyrethroid-susceptible larvae. The larvicidal effect of the rhamnolipids evaluated demonstrates that these compounds represent an alternative to control A. aegypti.

Sulphonates' mixtures and emulsions obtained from technical cashew nut shell liquid and cardanol for control of Aedes aegypti (Diptera: Culicidae)

Aedes aegypti is the main mosquito vector of dengue, zika, chikungunya, and yellow fever diseases. The low effectiveness of vector control options is mainly related to the increased insect's resistance and to the toxicity of products used for non-target organisms. The development of new environmentally friendly and safer products is imperative. Technical cashew nut shell liquid (tCNSL), mostly composed by cardanol (C), is an abundant by-product of the cashew (Anacardium occidentale L.) production chain, available at low cost, and with proven larvicidal activity. However, chemical modifications in both tCNSL and cardanol were required to increase their water solubilities. Our objectives were to synthesise and characterise sustainable, low-cost and easy-to-use multiple function products based on tCNSL, cardanol, and the sulphonates obtained from both; and to evaluate all these products efficacy as surfactants, larvicidal, and antimicrobial agents. None of the sulphonates presented antimicrobial and larvicidal activities. tCNSL and cardanol were successfully emulsified with sodium technical cashew nut shell liquid sulphonate (NatCNSLS, complex mixture of surfactants). The emulsions obtained presented larvicidal activity due to the presence of tCNSL and cardanol in their composition. Our results showed that the tCNSL+NatCNSLS mixture emulsion was an effective larvicide and surfactant multiple function product, with high availability and easy-to-use, which can facilitate its large-scale use in different environments. Graphical abstract.

Action of Metarhizium brunneum (Hypocreales: Clavicipitaceae) Against Organophosphate- and Pyrethroid-Resistant Aedes aegypti (Diptera: Culicidae) and the Synergistic Effects of Phenylthiourea

Dengue, yellow fever, Zika, and chikungunya arboviruses are endemic in tropical countries and are transmitted by Aedes aegypti. Resistant populations of this mosquito against chemical insecticides are spreading worldwide. This study aimed to evaluate the biological effects of exposure of pesticide-sensitive Ae. aegypti larvae (Rockefeller) to conidia of the entomopathogen, Metarhizium brunneum, laboratory strains ARSEF 4556 and V275, and any synergistic activity of phenylthiourea (PTU). In addition, to investigate the nature of any cross-resistance mechanisms, these M. brunneum strains were tested against the Rockefeller larvae and two temephos- and deltamethrin-resistant wild mosquito populations from Rio de Janeiro. Treatment of Rockefeller larvae with 106 conidia/ml of ARSEF 4556 and V275 fungal strains resulted in significant decreased survival rates to 40 and 53.33%, respectively (P < 0.0001), compared with untreated controls. In contrast, exposure to 104 or 105 conidia/ml showed no such significant survival differences. However, the addition of PTU to the conidia in the bioassays significantly increased mortalities in all groups and induced a molt block. Experiments also showed no differences in Ae. aegypti mortalities between the fungal treated, wild pesticide-resistant populations and the Rockefeller sensitive strain. The results show the efficacy of M. brunneum in controlling Ae. aegypti larvae and the synergistic role of PTU in this process. Importantly, there was no indication of any cross-resistance mechanisms between Ae. aegypti sensitive or resistant to pesticides following treatment with the fungi. These results further support using M. brunneum as an alternative biological control agent against mosquito populations resistant to chemical insecticides.