Insights into the effects of interspecific larval competition on Aedes aegypti (L.) and Aedes albopictus (Skuse) mosquitoes and dengue transmission

Abstract

In Sri Lanka, both Aedes aegypti and Aedes albopictus mosquitoes are prevalent and contribute to the transmission of dengue, a significant public health concern with high morbidity and mortality rates. Ae. aegypti predominates in urban environments and is a primary driver of dengue outbreaks, whereas Ae. albopictus, adaptable and found in both urban and rural areas, poses a persistent threat. While the effects on their life history and morphometrics when reared in isolation have been well investigated, the effects of their coexistence, which more closely reflect real-life scenarios in many parts of Sri Lanka, have not been thoroughly explored. Thus, this study addresses this gap by investigating the effects of interspecific larval competition on key biological parameters of both Ae. aegypti and Ae. albopictus, specifically focusing on larval duration, survival rates, and body size, particularly wing length. The study was conducted in the School of Entomology at the Medical Research Institute (MRI) in Colombo 08, Sri Lanka. The experimental design involved controlled laboratory settings where Ae. aegypti and Ae. albopictus larvae were reared either in isolation or in mixed-species groups. Eggs of both species, obtained from laboratory cultures, were hatched using the vacuum method to synchronize hatching times. Larvae were reared in 100 mL transparent plastic containers, with fifty larvae of each species reared separately and twenty-five larvae of each species reared together in mixed-species containers, each filled with 50 mL of distilled water. Larvae were fed with finely ground commercial fish food (Apex©), and feeding amounts were increased daily according to larval instar needs. Wing length was determined by mounting the separated wings on slides and measuring the radius vein length using a scale-mounted light microscope. Statistical analyses, including two-sample t-tests, were conducted using MINITAB 14 (Minitab Inc., 2004) to assess the effects of interspecific competition. Results indicate that both Ae. aegypti and Ae. albopictus exhibited longer larval durations when reared in mixedspecies conditions. Survival rates were not statistically significant for Ae. aegypti (p > 0.05) but increased in mixed-species environments, whereas survival of Ae. albopictus was significantly reduced in mixed-species conditions (p < 0.05). Morphometric analyses revealed significant differences in wing length between males and females of both species (p < 0.05). In males, wing length differences were not statistically significant (p > 0.05), but Ae. aegypti tended to have longer wings compared to Ae. albopictus in mixed-species environments. However, in females, wing length was significantly higher in Ae. aegypti and lower in Ae. albopictus (p < 0.05) when reared in mixed-species environments. In conclusion, interspecific competition between Ae. aegypti and Ae. albopictus influences larval development, survival rates, and body size differently for each species. Mixed-species conditions result in prolonged larval stages, altered survival rates, and distinct morphometric changes (i.e. wing length), with Ae. aegypti demonstrating characteristics suggestive of relative strength or competitive advantage compared to Ae. albopictus. The findings highlight the intricate dynamics of interspecific competition among Aedes mosquito species, emphasizing the need to consider these ecological interactions in strategies for controlling mosquito populations and mitigating dengue transmission, leading to more effective disease prevention efforts.