Wednesday, 17 November 2004

Natural dyes as novel insecticides

Elizabeth A. Cowles, cowlese@easternct.edu1, Richard Cowles, Richard.cowles@po.state.ct.us2, and Brenna Traver1. (1) Eastern Connecticut State University, Department of Biology, 83 Windham St, Willimantic, CT, (2) The CT Ag Experiment Station, 153 Cook Hill Rd, PO Box 248, Windsor, CT

Carminic acid, found in the hemolymph of the cochineal scale (Dactylopius coccus, Homoptera: Dactylopiidae) is already known to have antifeedant properties to ants, but insecticidal properties have not previously been reported. This and other insect dyes are usually found in homopteran species that also have a woolly body covering. This coincidence suggests that the insect dyes may also have photoactivated toxic properties, and that the white woolly covering could act as a natural sunscreen. The photoactive properties of carminic acid were compared with cyanosine, a synthetic red dye known as a photoactive insecticide, using wingless fruit flies as a model system. Carminic acid was insecticidal to fruit flies within 48 h in both lighted and darkened conditions; exposure to light increased its toxicity by 24%. At 48 h exposure in lighted conditions, the toxicity of carminic acid and cyanosine were very similar, causing ~70% mortality to flies ingesting bait containing 0.4% dye. Carminic acid is already accepted by U.S. FDA as a natural food coloring, suggesting that it could be tested as a substitute for cyanosine in an organically acceptable baited spray for controlling economically important Tephritid flies.

Species 1: Homoptera Dactylopiidae Dactylopius coccus (Coccineal scale)
Keywords: Carminic acid, phototoxic

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