Larvicidal effect of a cell-wall fraction isolated from alder decaying leaves

Decaying alder leaves in water from Alpine Aedes breeding sites, particular ly their toxicity to larval Culicidae, were investigated and characterized with comparative toxicological and chemical methods. Bioassays that used th ird-instar Aedes aegypti as a reference species indicated that the larvicid al effect of crude leaf litter varied with decaying age of the litter, whil e no toxicity was detected from leaching water of the mosquito breeding sit es. Ten-month-old leaf litter was the most toxic. Comparison of the differe nt soluble and insoluble fractions obtained after sequential extraction of decomposed litter allowed us to localize the toxicity factor to an insolubl e cell-wall fraction. The toxicity seems to be linked to phenolic activity. It is higher than that found far tannic acid solutions used as a reference to mimic the larvicidal effects of the molecules naturally occurring in de caying litter. The pattern of establishing the larvicidal effect of alder l eaf litter in water of Alpine Aedes breeding sites is discussed.