Comparative capability to detoxify vegetable allelochemicals by larval mosquitoes.

In order to confirm the phytotoxicological basis for the ecological specialization of larval culicine fauna among different subalpine mosquito breeding sites, we compared the capability of six different Aedes larval taxa or populations of different ecological origin to detoxify dietary leaf litter originating from the environmental vegetation. Detoxification experiments were performed through in vitro digestion of a toxic leaf litter fraction using larval extracts as the enzymatic sources. Comparison of toxicological and detoxifying properties among the different larval samples indicates an association between their tolerance to leaf litter toxicants and their detoxification capability, which vary according to ecological origin. The fact that the detoxifying factor within the larval extracts appears to be a protein-like compound with a molecular weight bigger than 30 kDa suggests the possible involvement of detoxifying enzymes in larval tolerance to leaf litter toxicants. This is congruent with previous biochemical data that suggests the involvement of cytochrome P450 monooxygenase and esterase activities in the detoxification process.

Hot extraction and characterization of a ligninlike fraction involved in larvicidal effects of decomposed leaf litter against mosquito.

Hot water-extraction was performed on decomposed leaf litter in order to solubilize the toxic fraction involved in the dietary interaction against mosquito larvae in subalpine breeding sites. The toxic fraction was partially extracted by water with an optimum temperature of 60 degrees C and recovered in an insoluble form. Phytochemical characterization was achieved through differential enzymatic hydrolyses, using the laccase mediator delignifying system, and aluminum chloride chelation monitored by standard bioassays; comparative spectrophotometric analyses in ultraviolet light after solubilization in acetyl bromide; and comparative reversed-phase high-performance liquid chromatography of the phenolic aldehydes after alkaline nitrobenzene oxidation. The results suggested the involvement of ligninlike compounds in the toxicity of the isolated fraction. Toxicity of this fraction appeared far stronger than that of the crude leaf litter. The involvement of this ligninlike fraction in the dietary toxicity of leaf litter against larval mosquito was then investigated.

Dietary toxicity of decomposed arborescent leaf litter against larval mosquito: involvement of a lignin-polypeptidic complex.

To characterize the toxic compounds involved in the dietary toxicity of decomposed arborescent leaf litter against larval mosquito, a toxic fraction was extracted from crude leaf litter by using hot water. Preliminary characterization of this fraction, called the insoluble fraction (IF) because it progressively precipitates after extraction, has suggested the involvement of lignin-like compounds in the toxicity. Further analyzes are currently being performed by using additional phytotoxicity-based methods. The involvement of lignin-like compounds in the toxicity was indicated by both the comparative effects of different enzymatic oxidative treatments and reversed-phase high-performance liquid chromatography analysis of the phenolic aldehydes and acids obtained after alkaline nitrobenzene oxidation. However, these lignin-like compounds may not be involved alone in the toxicity, as no specific feature of those components was associated with the toxicity. Among the possible compounds associated with lignin-like compounds in the toxicity, peptidic compounds were suggested by comparative determination of the C/N ratio and then revealed by denaturation experiments, use of specific binding protein molecules, and thin-layer chromatography analysis. A possible role of these peptidic compounds associated with lignin-like compounds in the dietary toxicity of the leaf litter against the larval mosquito midgut is discussed.