Toxicity of plant extracts containing trypsin inhibitor to the larvae of Aedes aegypti

Abstract

Mosquitoes are vectors of many pathogens and can transmit a range of potentially fatal diseases. Some of these diseases spread via mosquitoes belonging to the genus Aedes include Dengue, Chikungunya, Yellow fever, Zika etc. Conventional methods of mosquito control are not always completely successful. Therefore new strategies need to be adopted for mosquito control. Plant protease inhibitors are promising candidates as they prevent larval growth by inhibiting gut proteases of mosquito larvae. In this study we screened 15 plant extracts containing trypsin inhibitors for their toxicity to the larvae of Aedes aegypti. Leaf extracts from Lawsonia inermis showed the highest mortality with 100% mortality after 48 hours in second, third and in fourth instar larvae. The treatment with extract from Annona muricata leaf led to 100, 96 and 66% mortality after 48 hours in second, third and fourth instar larvae respectively. After Proteinase K treatment of Lawsonia inermis leaf extract, a reduction in the in vitro inhibition of larval gut protease activity from 82 to 6% and a decrease in mortality from 80 to 50% were observed compared to untreated. This revealed that the mortality, at least in part, is due to the presence of a protenaceous plant protease inhibitor in the extract. Expressing the gene coding for such protease inhibitors in micro organisms or algae upon which the mosquito larvae feeds will serve as an alternate method for control of mosquito population.