Delayed phototoxic effects of 8-methoxypsoralen, khellin, and sphondin inAedes aegypti.

At concentrations up to 6.7 ppm, 8-methoxypsoralen, sphondin, and khellin are not toxic to first-instar larvae of the mosquitoAedes aegypti. The irradiation of sensitized larvae with long-wavelength ultraviolet light did not always produce any immediate toxicity enhancement, but delayed effects were clearly visible. These were observed over the development of the organisms from first-instar larvae to adults. No adverse effects were noted when larvae were irradiated in the absence of sensitizers, or when they were placed in solutions of sensitizers which had been previously irradiated with the same light sources. 8-Methoxypsoralen was slightly more phototoxic than its isomer sphondin. Khellin, recently reported to undergo photoinduced cyclization with DNA components, showed minimal phototoxicity in the concentration range used.