Effect of tomato [Lycopersicon esculentum] leaf constituents on survival of Thrips palmi Karny (Thysanoptera: Thripidae)

Adult females of Thrips palmi KARNY survived for a long period on a filter paper disc soaked in 3% aqueous sucrose solution. They also survived for a long period even if the sucrose impregnated disc had methanol extracts of cucumber or eggplant leaves applied onto it. When methanol extract of tomato leaves was applied onto the sucrose impregnated disc, however, all the insects died within a few days. These different responses of T. palmi on three plant extracts coincide completely with the previously reported responses on intact leaf discs of respective plants. It is certain that tomato leaf contains an antifeeding or a toxic substance, because the lethal effect of the tomato leaf extract does not cancel out by addition of sucrose, which has a strong phagostimulant activity and a high nutritive value for survival. The lethal activity is concentrated in the n-butanol soluble fraction by means of liquid-liquid extraction. Since the partially purified fraction expresses its activity only during exposure, and the insects escape preferentially to feed on the disc containing the fraction, the active substance seems to be an antifeedant rather than a toxic one.