Residual efficacy of deltamethrin applied to foliage against Malaysian Aedes aegypti (L.) and Aedes albopictus (Skuse)

The spraying of insecticide on foliage to provide an insecticidal barrier may serve as part of the vector control measures to combat the increasing threat of Aedes-borne diseases. The effectiveness of insecticide barrier spraying was evaluated by assessing the residual efficacy of deltamethrin sprayed on foliage against Malaysian Ae. aegypti (L.) and Ae. albopictus (Skuse). In this semi-field study, landscape plants grown within the vicinity of the Institute for Medical Research (IMR), Malaysia, were treated with deltamethrin suspension concentrate (SC) with the dosage of 30 mg/m² and 50 mg/m² in three rounds of spraying. Deltamethrin residual activity on treated and untreated leaves was investigated using standard WHO cone bioassays. Wild Aedes populations at both deltamethrin-treated and untreated plant clusters were monitored by ovitrap surveillance. Ovitrap monitoring revealed that the mean number of Ae. albopictus larvae at deltamethrin-treated were significantly lower than the mean number of larvae of the same species at the untreated plant cluster. Cone bioassay results showed that the insecticide remained effective for up to 4 weeks (> 80% mortality), but the insecticide residual activity was affected by rainfall. These results suggest that insecticide barrier spraying is a promising tool and may be used along with other mosquito control tools such as indoor residual spray and space spraying to reduce the dengue burden.

Efficacy of Four Species of Zingiberaceae Extract Against Vectors of Dengue, Chikungunya and Filariasis

Laboratory bioassays on insecticidal activity of hexane crude extract derived from four species of Zingiber: Zingiber officinale var. rubrum (HZOR), Zingiber montanum (HZM), Zingiber spectabile (HZS) and Zingiber zerumbet (HZZ) were carried out against three mosquito larvae vector: Ae. albopictus, Ae. aegypti, and Cx. quinquefasciatus. GC/MS analysis revealed 43, 82, 50, and 51 compounds from HZO, HZM, HZS, and HZZ, respectively. The major principal constituents found in HZO extract were zingerone (14.92%) and benzaldehyde dimethyl thiol acetal (11.61%); HZM extract were dimethyl 4-methylphthalate (12.64%) and carbendazim (12.62%); HZS extract had 1,1'-ethylenebisdecalin (42.52%) and 1- pentadecyne (11.5%); and HZZ extract were humulene epoxide II (20.84%) and zerumbone (60.4%). Assessment of larvicidal efficacy demonstrated good larvicide effects towards all the crude hexanes. The mortality was observed after 24h exposure. The highest larvicidal mortality of Ae. albopictus larvae was found in HZOR, HZM, and HZS (LC₅₀= 96.86, 99.04 and 93.35 mg/L; LC₉₀= 168.65, 153.77, and 168.65 mg/L) respectively. HZM and HZZ were effective against Ae. aegypti larvae with LC₅₀= 84.95 and 82.05 mg/L and LC₉₀= 134.85 and 121.05 mg/ L, respectively. HZZ showed the most effective extract against Cx. quinquefasciatus larvae with LC₅₀= 49.28 mg/L and LC₉₀= 83.87 mg/L. No mortality was recorded in the control. Results from studies suggest that bioassay-guided effective extracts of Z. officinale var. rubrum, Z. montanum, Z. spectabile and Z. zerumbet are potential larvicidal candidates for controlling Ae. albopictus, Ae. aegypti, and Cx. quinquefasciatus.