Are indigenous strains of Trichogramma sp. (Hym., Trichogrammatidae) better candidates for biological control of lepidopterous pests of the olive tree?

Abstract

Strains of the egg parasitoid, Trichogramma, indigenous in olive groves in the Mediterranean region (T. bourarachae Pintureau & Babault, T. cacoeciae Marchal, T. cordubensis Vargas & Cabello, T. euproctidis Girault, T. nerudai Pintureau & Gerding, T. oleae Voegelé & Pointel) as well as commercially available strains (T. brassicae Bezdenko, T. cacoeciae, T. evanescens Westwood), were assessed in laboratory and semi-field experiments for their attributes as biological control agents for use against lepidopterous olive pests like the olive moth (Prays oleae Bern.) and the jasmine moth (Palpita unionalis Hübn.). In a choice test, an Egyptian strain of T. cordubensis parasitized significantly more olive and jasmine moth eggs than those of the rearing host Sitotroga cerealella Olivier. This strain was also most efficient in finding eggs of the target pests on olive foliage and on potted olive trees. Survival and fecundity of a Tunisian strain of T. bourarachae was not affected when exposed to hot (35°C) and arid (< 40% relative humidity) conditions in comparison to the mild standard of 25°C and 70% relative humidity. It was concluded that indigenous strains collected from olive groves were more effective against the target pests and more tolerant to arid conditions than commercially available parasitoid species, indicating that biological control agents should preferably be isolated from the relevant pest/crop system.