Low efficiency of four indigenous Trichogramma wasp populations, collected from tomato crops, in controlling the invasive pest Tuta absoluta in Iran

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera Gelechiidae), has become a major pest in both greenhouse and outdoor tomato crops in Iran since its accidental introduction in 2010. In line with the biological control program of T. absoluta, recently developed in Iran, this study investigated the efficiency of four indigenous Trichogramma (Hymenoptera Trichogrammatidae) populations to control this pest. Two populations of Trichogramma brassicae Bezdenko, i.e. with and without Wolbachia Hertig et Burt infection, one population of Trichogramma evanescens Westwood, and one population of Trichogramma principium Sugonyaev et Sorokina were collected from the Helicoverpa armigera (Hubner) eggs in the tomato fields of Isfahan, Iran. The fertility life-table parameters were initially calculated on Ephestia kuehniella (Zeller) as a factitious host under laboratory conditions. Accordingly, the highest intrinsic rate of increase, the largest finite capacity for increase, and the greatest net reproductive rate were found in T. evanescens and T. principium populations, and all of which were positively affected by Wolbachia infection in T. brassicae population. The parasitism ability of these populations was then evaluated on T. absoluta eggs on the tomato leaves. T. evanescens showed the highest parasitism ability (26.82%), the rate of which was affected by female age in all populations. The efficiency of these populations was subsequently assessed on a larger scale in cages in the greenhouse under cropping conditions. The highest (7.82%) and lowest (3.17%) parasitism percentages were observed in T. brassicae, regardless of Wolbachia infection, and T. principium, respectively. Because the rates of the parasitism ability recorded from all populations were considerably low (less than 8%), it seems that these indigenous populations could not alone result in efficient control of T. absoluta.