Involvement of ligninlike compounds in toxicity of dietary alder leaf litter against mosquito larvae

The toxicological characteristics of dietary decomposed alder leaf litter a gainst mosquito larvae were further investigated through enzymatic and chem ical purification of a phenoliclike cell-wall fraction isolated from crude litter. The toxicity of the subfractions obtained was controlled by standar d bioassays on third instars of Aedes aegypti chosen as a reference target species. Enzymatic hydrolyses of the sell-wall fraction were performed with caylase, pectolyase. esterase, and beta -glycosidase. in order to release, respectively, cellulose material and phenolic compounds bound to lignins. These treatments did not affect the larvicidal activity and the phenolic ac tivity of the cell-wall fraction. Chemical alkaline and acid hydrolyses wer e carried out to break ester and glycosidic bonds of the cell-wall fraction . Comparison of HPLC profiles of the hydrolysates from both toxic and nonto xic fractions did not reveal differences between the phenolic acids release d. Aluminum chloride, known for its phenolic complexing activity, counterac ted the larvicidal activity of the cell-wall fraction. Altogether, these re sults suggest the involvement of ligninlike compounds in the toxicity of di etary alder leaf litter against larval mosquitoes. The toxicity of this fra ction. which was very sensitive to drastic and smooth oxidations, seemed to be associated with a strong oxidative potential. These results are discuss ed in relation to a possible mode of action of lignins in the plant-mosquit o interactions.