Toxicological and biological activity of kumchura (Kaempferia galanga L.) to the melon fly Bactrocera cucurbitae Coquillett

Abstract

The biological activity of kumchura (Kaempferia galanga L.) was tested against melon fly, Bactrocera cucurbitae Coquillett. Two preparations of kumchura were used for the experiments, a crude kumchura paste and a methanol extract of kumchura. Crude kumchura or its extract were administered to melon flies in two ways: by topical application to adults to determine LD50 values and its effect on adult behavior and incorporated in the larval diet at different concentration levels. The effect of kumchura as feeding and oviposition repellent was also tested. Additional experiments included the effects of kumchura on the reproductive capacity of melon flies. Complete inhibition of egg hatch was achieved at a concentration of 25% crude kumchura in the larval diet. Lower concentration of crude kumchura in the diet resulted in reduced pupation and adult emergence as well as a delay in larval development. A concentration of 6.25% crude kumchura in the diet significantly repelled larvae and adults; oviposition by females was not affected. Topical application of kumchura extract resulted in a short-term change in behavior, usually 2 hours in length. Movement was reduced to about 15% that of control flies. Sex attractancy was significantly reduced within the affected period. However, all flies recovered after two hours. Incorporation of sublethal concentration of kumchura extract in the larval diet (1.25 - 2.5%) reduced egg hatch, pupation and adult emergence, as well as lengthening the period of larval development. Analytical analysis of kumchura extract by thin layer chromatography resulted in the resolution of two components, both biologically active against melon flies. These two components were confirmed by high performance liquid chromatography on a silica based C-18 column. Gas chromatography/mass spectrometry data revealed that two components were very similar in composition, and may very well be the major compound and its degradative product. Comparison with standard indicate that the two components may be cinnamic acid derivatives. The potential of kumchura as a crude insect control agent is discussed.