Semiochemicals produced by tomato varieties and their role in parasitism of Corcyra cephalonica (Lepidoptera: Pyralidae) by the egg parasitoid Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Abstract

Hexane extracts of 10 different varieties of tomato (Lycopersicon esculentum Mill) obtained in the vegetative and flowering periods were studied for synomonal response of the egg parasitoid Trichogramma chilonis Ishii. Gas chromatography of leaf extracts revealed the presence of saturated hydrocarbons ranging from C14 to C29 in varying numbers and concentrations. These hydrocarbons elicited varied synomonal responses from the parasitoid. The quantity of individual hydrocarbons varied from 72 to 34,940 ppm in the vegetative period and from 4 to 46,170 ppm in the flowering period. Hexane extracts obtained during the flowering period showed a greater synomonal response compared with those obtained during the vegetative period. A better response observed for certain varieties of tomato at a particular period could be due to the presence of higher concentrations of favourable hydrocarbons relative to unfavourable ones. Synomonal activity seems to be associated mainly with tricosane, heneicosane, pentacosane and hexacosane during the vegetative period and with heneicosane and hexacosane during the flowering period. In the vegetative period, the tomato variety To-Pant-T4 elicited the highest activity as well as parasitism at the lowest concentration of 25,000 ppm, which was higher than other varieties at all concentrations. Varieties To-BT-116-32, To-BT-20-2-1 and To-Pant-T3 in the vegetative period and To-Selection-15, To-Selection-32 and To-BT-22-2-1 in the flowering period elicited higher responses than the other varieties. To-BT-20-2-1 elicited a maximum response in the flowering period, which may be due to the presence of higher relative quantities of tricosane, heneicosane and hexacosane. In view of these findings, tomato varieties with favourable semiochemicals could be exploited in an integrated pest management programme to enhance the effectiveness of the egg parasitoid T. chilonis against the fruit borer Helicoverpa armigera (Hb).