Courtship activity, copulation & insemination success in a mosquito vector fed a herbal aphrodisiac: Implications for sterile insect technology

Background & objectives: In sterile insect technology (SIT), mating competitiveness is a pre-condition for the reduction of target pest populations and a crucial parameter for judging efficacy. Still, current SIT trials are being hindered by decreased effectiveness due to reduced sexual performance of released males. Here, we explored the possible role of a herbal aphrodisiac in boosting the mating activity of Aedes aegypti. Methods: Males were fed one of two diets in this study: experimental extract of Eurycoma longifolia (MSAs) and sugar only (MSOs). Differences in life span, courtship latency, copulation activity and mating success were examined between the two groups. Results: No deaths occurred among MSA and MSO males. Life span of MSOs was similar to that of MSAs. The courtship latency of MSAs was shorter than that of MSOs (P<0.01). MSAs had greater copulation success than MSOs (P<0.001). In all female treatments, MSAs mated more than MSOs, but the differences in rate were significant only in the highest female density (P<0.05). In MSAs, mating success varied significantly with female density (P<0.01), with the 20-female group (P<0.01) having the lowest rate. Single MSA had better mating success at the two lowest female densities. In MSOs, there were no significant differences in mating success rate between the different female densities. Interpretation & conclusions: Our results suggested that the herbal aphrodisiac, E. longifolia, stimulated the sexual activity of Ae. aegypti and may be useful for improving the mating competitiveness of sterile males, thus improving SIT programmes.

Genetic structure of the dengue vector Aedes albopictus (Skuse) from different developed settlements in Penang Island, Malaysia based on microsatellite markers

@#The medically important mosquito, Aedes albopictus is native to Asia and has become a major health concern in most Asian countries including Malaysia. Being recognized as a dengue vector, a clearer understanding of how mosquito populations are geographically connected, may therefore represent a profound yet significant understanding of control strategies. There are no documented reports on the genetic structure of Ae. albopictus populations from different developed settlements inferred from microsatellite DNA markers in Malaysia, particularly in Penang Island (Northern Peninsular Malaysia). Here, we assessed the molecular population genetics of Ae. albopictus in terms of their allelic variation, genetic diversity and population structure. A total of 42 mosquitoes were sampled from Jelutong, Batu Maung and Balik Pulau which represented urban, suburban and rural areas in Penang Island respectively and analysed for polymorphism at six microsatellite loci. All of the microsatellite markers were successfully amplified and were polymorphic, showing low genetic structure among geographic populations (FST= 0.0362). It is supported with admixture individuals observed in STRUCTURE and FCA and this suggests that high gene flow has been experienced between populations. These findings implicate passive dispersal through human-aided transportation; as a factor shaping the genetic structure of Ae. albopictus populations in Penang Island.

Larvicidal and adulticidal activities of castor oil against the dengue vector, Aedes aegypti

@#Plants contain numerous bioactive compounds that can be used to develop environmentally-safe insect control agents. Castor oil is a vegetable oil derived from the seeds of castor bean and is widely used as an industrial lubricant and medicinal purgative. In search of an alternative natural insecticide, the objective of this study was to evaluate the larvicidal and adulticidal activities of castor oil against the important dengue vector, Ae. aegypti. Larvicidal and adulticidal bioassays were conducted following the World Health Organization methods. Larvicidal activity was observed at castor oil concentrations of 10, 25, 50, 75, and 100 ppm; larval mortality was checked after 48 h of exposure and the lethal concentration (LC) at LC50 and LC90 were 51.38 and 116.26 ppm, respectively. Adulticidal activity was determined by topical application at the concentrations of 1, 5, 10, 15, and 20 µg/ mg on female mosquitoes and the mortality was checked after 24 h of exposure. The effective adulticidal activity was apparent with the LD50 and LD90 values of 6.03 and 25.07 µg/mg against female mosquitoes. The results indicated that castor oil has potential in the practical control of both immature and adult stages of the mosquito vector.