Major efforts to control the population of Aedes aegypti mosquitoes involve the use of synthetic insecticides, which can be harmful to the environment. Most plant compounds are eco-friendly and some of them have biocontrol potential, whereas a fraction of these compounds is released into the environment through the leaf-leaching process. We evaluated the effects of secondary compounds from Ateleia glazioviana and Eucalyptus grandis senescent leaf leachates on Ae. aegypti larval mortality, adult emergence time, and wing size using a microcosm approach. The microcosms consisted of 10 larvae kept in water (control) and under four treatments with leachates from a combination of plant species and leaching time (7 or 14 days). Chemical analyses of the leachates showed the presence of carboxaldehyde and Heptatriocotanol, which have antimicrobial properties, potentially reducing the food available for larvae. β-Sitosterol, Stigmasterol, α-Amyrin, and Lupeol are compounds with inhibitory, neurotoxic, and larvicidal effects. Both plant species’ leachates increased larval mortality and decreased emergence time due to the presence of compounds toxic to the larvae. Larger organisms emerged in treatments with 7-days leachates, likely due to the high concentration of dissolved organic matter in the leachates. The higher mortality in 7-days leachates may also increase the organic matter from co-specific decomposition, improving adult size. Therefore, if the mosquito population is not locally extinct, compounds present in leaf leachates may act as a resource enhancing larvae growth, potentially increasing survivors’ fitness. In conclusion, biocontrol attempts using urban green spaces may have unexpected outcomes, such as resulting in larger pest organisms.

Fluctuations in food availability and larval density play pivotal roles in shaping the characteristics of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) mosquito populations through intraspecific competition. Competition for limited resources drives density‐dependent effects, influencing survival rates, time to pupation, and the size and lifespan of adult mosquitoes. Our study aimed to investigate the effects of competition, driven by variations in food and larval density, on the development and life cycle of A. aegypti. We examined the outcomes of nine distinct combinations of aquatic larval density and resource availability—measured in terms of per capita food and individual space—on key developmental metrics, including larval mortality, time to pupation, adult size, and lifespan. Our findings indicate that food availability had a more pronounced effect on larval mortality and development time than did larval density. Notably, intermediate levels of food availability and density were more conducive to higher survival rates and larger adult sizes than either low‐density conditions or an excess of resources. The density‐dependent effects, particularly, had a significant impact on adult size, often outweighing the influence of food availability. Furthermore, alleviation from competition among larvae emerged as a more critical factor in extending adult lifespan than the direct influence of resources or density alone. In conditions where food resources were scarce or competition was intense, larvae experienced prolonged development times and a higher likelihood of failing to pupate, resulting in smaller adults with reduced lifespans. These combined stressors significantly diminish the fitness (i.e., mortality and developmental parameters) of A. aegypti, highlighting the complex interplay between resource availability and intraspecific competition in determining the population dynamics of this species.

Mosquitoes, particularly Aedes aegypti, pose significant public health risks by transmitting diseases like dengue, zika and chikungunya. Bacillus thuringiensis var. israelensis (BTI) is a crucial larvicide targeting mosquitoes while sparing other organisms and the environment. This study evaluated the effects of sublethal BTI doses on Ae. aegypti larvae regarding mortality, development, adult emergence and size, using a wide-area spray application in an urban neighbourhood. Laboratory experiments with four BTI concentrations (0, 0.008, 0.02 and 0.04 ppm) assessed compensatory and over compensatory responses. The spray achieved over 90% larval mortality within 48 h, but accumulating sublethal doses could trigger compensatory and over compensatory effects, enhancing the fitness of survivors. A dose–response relationship was evident, with higher BTI concentrations leading to increased mortality, reduced longevity and fewer pupae. BTI exposure also skewed the sex ratio towards males and altered adult sizes, potentially affecting population dynamics and vectorial capacity. These findings highlight the effectiveness of BTI in Ae. aegypti control and the importance of understanding compensation, overcompensation and density-dependent effects. While wide-area BTI applications can reach inaccessible breeding sites and offer potent mosquito control, careful consideration of ecological and evolutionary consequences is crucial.