Aqueous suspension of ethanol extracts of Derris
(Leguminosae), collected in the state of Amazonas, Brazil, were tested for larvicidal activity against the mosquito Aedes aegypti (Diptera:Culicidae). The aim of this study was to observe the alterations of peritrophic matrix in Ae. aegypti larvae treated with an aqueous suspension of D. urucu
extract. Different concentrations of D. urucu
root extract were tested against fourth instar larvae. One hundred percent mortality was observed at 150 μg/ml (LC50 17.6 μg/ml) 24 h following treatment. In response to D. urucu
feeding, larvae excreted a large amount of amorphous feces, while control larvae did not produce feces during the assay period. Ultrastructural studies showed that larvae fed with 150 μg/ml of D. urucu
extract for 4 h have an imperfect peritrophic matrix and extensive damage of the midgut epithelium. Data indicate a protective role for the peritrophic matrix. The structural modification of the peritrophic matrix is intrinsically associated with larval mortality.