Response of the Egg Parasitoid Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) to Kairomones from Three Host Insects

Abstract

Kairomones emanating from males and females of three different host insects, viz., Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) and Chilo auricilius (Dudgeon) (Crambidae: Lepidoptera) that tend to influence the parasitic potential of Trichogramma chilonis Ishii was studied. Whole body extracts of male and female moths were analysed separately by gas liquid chromatography for determining their hydrocarbon profile, which showed the presence of straight chain saturated hydrocarbons ranging from C₉ to C₅₀, Different host insects showed variation in number and concentration of these chemicals, which were responsible for influencing parasitoid activity and parasitism. The concentration of these hydrocarbons ranged from 4 ppm to 1215280 ppm. The foraging activity of the parasitoid as indicated by parasitoid activity index (PAI) was highest (14.63) in S. exigua female body extract at highest concentration (60, 0000 ppm). Per cent mean parasitism rates recorded for S. litura male and S. exigua male and female body extract were significantly different from that for the body extract of C. auricilius. Both kairomonal interactions observed in the male body extract of S. litura could be due to the presence of appreciably very high amounts of favourable hydrocarbons docosane and heneicosane and comparatively high amount of octosane and pentaeosane as compared to its female body extract. Similarly, female body extract of S. exigua also showed comparatively higher amounts of favourable hydrocarbons tricosane, docosane, pentacosane, heneicosane and hexacosane as compared to its male body extract. Based on the hydrocarbon profile of body washings of males and females of the three host insects and quantity of favourable and unfavourable hydrocarbons present in individual extract body, it may be coneluded that heneicosane and hexacosane exerted significantly higher level of kairomonal effect on the parasitoid as compared to other hydrocarbons. The response elicited by the male extract body of S. litura was significantly higher, whereas the body extract of male C. auricilius elicited the least response from T. chilonis. These favourable hydrocarbons at the appropriate concentration of body extract of spent adults of S. litura males and S. exigua females could be used for enhancing parasitization by T. chilonis