Kairomonal effect of some saturated hydrocarbons on the egg parasitoids, Trichogramma brasiliensis (Ashmead) and Trichogramma exiguum, Pinto, Platner and Oatman (Hym., Trichogrammatidae)

Abstract

Abstract: Bioassay studies carried out on the egg parasitoids Trichogramma brasiliensis and T. exiguum with 11 straight chain‐saturated hydrocarbons, revealed that pentacosane and hexacosane recorded very high parasitoid activity index (PAI) and parasitism for both the parasitoids indicating high kairomonal activity. These were followed by docosane, tricosane, heneicosane, hexatriacontane and tetracosane, which may be grouped as favourable hydrocarbons showing varying levels of kairomonal activity for T. brasiliensis, as compared to eicosane, pentadecane, octacosane and heptadecane, which can be grouped as non‐favourable hydrocarbons. In the case of T. exiguum, pentacosane‐treated egg cards showed maximum parasitism followed by hexacosane, pentadecane, hexatriacontane, tricosane and docosane thereby indicating their kairomonal activity in comparison with heptadecane, tetracosane, eicosane, heneiocosane and octacosane which recorded low levels of parasitism. In the case of T. brasiliesnsis, tetracosane recorded the highest response at the lowest concentration, C1 (62.5 ng/cm2), which decreased as the concentration increased. Eicosane, heneicosane and docosane recorded the highest parasitism at C2 (125 ng/cm2). In heptadecane, tricosane, pentacosane and hexatriacontane the highest parasitism was recorded at the medium concentration, C3 (250 ng/cm2). Octacosane recorded the highest response at C4 (375 ng/cm2). Pentadecane and hexacosane‐treated egg cards showed their highest response at C5 (500 ng/cm2). In the case of T. exiguum, the lowest concentration, C1 evoked the highest response in hexacosane, whereas heptacosane, heneiocosane, docosane and tetracosane recorded the highest parasitism at C2. Eicosane, pentacosane and octacosane recorded maximum parasitism, at C3, whereas tricosane and hexatriacontane showed maximum parasitism at C4 and pentadecane at C5. These concentrations can be taken as the optimum concentration to increase parasitization by these parasitoids. The favourable hydrocarbons at their optimum concentration can be used for efficient management of these parasitoids in field releases.