Assessment of susceptible Culex quinquefasciatus larvae in Indonesia to different insecticides through metabolic enzymes and the histopathological midgut

Bioassay-Guided Isolation of Piplartine from Piper purusanum Yunck (Piperaceae) and Evaluation of Its Toxicity Against Aedes aegypti Linnaeus, 1762, Anopheles darlingi Root, 1926 (Culicidae), and Non-Target Animals

Aedes aegypti and Anopheles darlingi are the primary vectors of dengue and malaria in Brazil. Natural products are currently regarded as promising alternatives for their control, offering environmentally friendly solutions for larval management due to their low toxicity to non-target organisms. Thus, Piplartine, isolated for the first time from Piper purusanum, exhibited larvicidal activity against Ae. aegypti and An. darlingi (LC50 of 14.56 and 26.44 μg/mL), occasioned by the overproduction of reactive oxygen and nitrogen species (66.67 ± 7% and 86.33 ± 6%). Furthermore, piplartine enhanced the activity of key detoxifying enzymes, including catalase (87.00 ± 9 and 94.67 ± 9 μmol of H2O2 consumed per minute per mg of protein), glutathione S-transferase (76.00 ± 1 and 134.00 ± 1 μmol/min/mg), mixed-function oxidase (26.67 ± 5 and 55.00 ± 1 nmol cti mg⁻¹ protein), α-esterase, and β-esterase (27.67 ± 7 to 46.33 ± 1 nmol cti mg⁻¹ protein). In contrast, piplartine inhibited acetylcholinesterase activity (43.33 ± 7 and 48.00 ± 2 μmol/min/mg) compared to the negative control DMSO (87.33 ± 1 and 146.30 ± 3 μmol/min/mg). It is important to highlight that piplartine showed no lethal effects on non-target aquatic insects, with 100% survival observed at a concentration of 264.4 μg/mL. In contrast, α-cypermethrin demonstrated acute and rapid toxicity to non-target organisms, with only 9.1% survival. These findings highlight piplartine as a promising larvicide with selective toxicity and low environmental impact, suitable for integrated larval management strategies.

Functional analysis of novel cystatins from Haemaphysalis doenitzi and evaluation of their roles in cypermethrin and λ-cyhalothrin resistance

Currently, the primary strategy for tick control relies on chemical agents. Pyrethrins, which are botanically derived compounds, have demonstrated efficacy in controlling ticks without posing a risk to human or animal health. However, research into pyrethrins' metabolic mechanisms remains sparse. Cystatin, as a reversible binding inhibitor of cysteine protease, may be involved in the initiation of pyrethrin detoxification of Haemaphysalis doenitzi. In this study, two novel cystatins were cloned, HDcyst-3 and HDcyst-4, the relative expression of which was highest in the Malpighian tubules compared with the tick midguts, salivary glands, and ovaries. Prokaryotic expression and in vitro studies revealed that cystatins effectively inhibit the enzymatic activities of cathepsins B and S. RNAi results showed that the reduction of cystatins significantly decreased the engorgement weight, egg mass weight, and egg hatching rate of adult female ticks, and prolonged feeding time by two days. The control rate of rHDcyst-3 and rHDcyst-4 protein vaccination against female adults were 55.9% and 63.2%, respectively. In addition, the tick immersion test showed that cypermethrin and λ-cyhalothrin had significant acaricidal effects against adult unfed H. doenitzi. The qPCR result indicated that compared with the control group, the expression of HDcyst-3 and HDcyst-4 was markedly decreased in the sublethal cypermethrin and λ-cyhalothrin group at LC50. Enzyme activity showed that cypermethrin and λ-cyhalothrin could significantly induce the activities of glutathione S-transferase (GST), carboxylesterase (CarE), and acetylcholinesterase (AchE). The aforementioned results provided indirect evidence that cystatin plays an important role in pyrethrin detoxification and provides a theoretical basis for future acaricide experiments and pest management.

Essential oil and fenchone extracted from Tetradenia riparia (Hochstetter.) Codd (Lamiaceae) induce oxidative stress in Culex quinquefasciatus larvae (Diptera: Culicidae) without causing lethal effects on non-target animals

We investigated the larvicidal activity of the essential oil (EO) from Tetradenia riparia and its majority compound fenchone for controlling Culex quinquefasciatus larvae, focusing on reactive oxygen and nitrogen species (RONS), catalase (CAT), glutathione S-transferase (GST), acetylcholinesterase (AChE) activities, and total thiol content as oxidative stress indicators. Moreover, the lethal effect of EO and fenchone was evaluated against Anisops bouvieri, Diplonychus indicus, Danio rerio, and Paracheirodon axelrodi. The EO and fenchone (5 to 25 µg/mL) showed larvicidal activity (LC50 from 16.05 to 18.94 µg/mL), followed by an overproduction of RONS, and changes in the activity of CAT, GST, AChE, and total thiol content. The Kaplan-Meier followed by Log-rank (Mantel-Cox) analyses showed a 100% survival rate for A. bouvieri, D. indicus, D. rerio, and P. axelrodi when exposed to EO and fenchone (262.6 and 302.60 µg/mL), while α-cypermethrin (0.25 µg/mL) was extremely toxic to these non-target animals, causing 100% of death. These findings emphasize that the EO from T. riparia and fenchone serve as suitable larvicides for controlling C. quinquefasciatus larvae, without imposing lethal effects on the non-target animals investigated.

First report on evaluation of commercial eugenol and piperine against Aedes aegypti L (Diptera: Culicidae) larvae: Mortality, detoxifying enzyme, and histopathological changes in the midgut

Dengue fever is a worldwide public health problem, and efforts to eradicate it have focused on controlling the dengue vector, Aedes aegypti. This study aims to assess the toxicity and effect of commercial eugenol and piperine on Ae. aegypti larvae through enzyme detoxification and histopathological changes in the midgut. Laboratory-reared Ae. aegypti larvae were treated with various concentrations of commercial eugenol and piperine and observed after 24, 48, and 72 h. Biochemical methods were used to assess detoxification enzyme activity for acetylcholinesterase, glutathione S-transferase, and oxidase, and changes in the midgut were examined using routine histological examination. In terms of larvicidal activity, piperine exceeded eugenol. Piperine and eugenol had LC50 and LC90 values of 3.057 and 5.543 μM, respectively, and 6.421 and 44.722 μM at 24 h. Piperine and eugenol reduced oxidase activity significantly (p < 0.05), but increased acetylcholinesterase and glutathione S-transferase activity significantly (p < 0.05). After being exposed to piperine and eugenol, the food bolus and peritrophic membrane ruptured, the epithelial layer was interrupted and irregular, the epithelial cells shrank and formed irregularly, and the microvilli became irregular in shape. Commercial piperine and eugenol behave as potential larvicides, with processes involving altered detoxifying enzymes, specifically decreased oxidase function and increased GST activity, as well as midgut histological abnormalities.