How long is long enough? Decreasing effects in Aedes aegypti larval mortality by plant extracts over time

Aedes aegypti has overcome all kinds of mosquito control attempts over the last century. Strategies for population control resorts to the use of synthetic insecticides, which can lead to problems like human intoxication and environmental contamination. The effects of Bacillus thuringiensis var. israelensis (Bti), Ilex paraguariensis (yerba mate), and Ilex theezans (cauna herb) extracts against A. aegypti larvae were evaluated. The bioassays were conducted under controlled laboratory conditions of temperature (27 ± 3°C) and photoperiod (12 h). Hydroalcoholic extract of the leaves of I. theezans displayed better residual effect compared to the aqueous extract of I. paraguariensis fruits. The strongest residual effect of I. theezans was probably due to the presence of certain chemicals in its leaves, such as coumarins, hemolytic saponins, and cyanogenic glucosides, which were absent in I. paraguariensis. The results herein contributed to the prospection of natural insecticides and opened the possibility for subsequent studies on the use of plant extracts in field situations in a short-time scale.