Lethal and sublethal effects of synthetic and bio-insecticides onTrichogramma brassicaeparasitizingTuta absoluta

Abstract

The invasive tomato leaf miner (TLM), Tuta absoluta (Meyrick) is an invasive pest on tomatoes worldwide. The main control measure against the pest has been chemical insecticides, but the pest developed resistance to many chemical classes. So alternative methods, such as biological control agents, alone or combined to chemical compounds must be evaluated to validate their synergistic actions. In this study, both lethal (concentration-mortality response) and sublethal effects of three synthetic insecticides, the bioinsecticide spinosad, as well as the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin were studied on Trichogramma brassicae Bezdenko within T. absoluta eggs. To assess the sublethal effects, the lethal concentration 25% (LC25) of chlorantraniliprole, spinosad, abamectin and indoxacarb and LC50 value of M. anisopliae was sprayed on eggs and then offered at three time intervals to the parasitoids. Fertility and other life table parameters of the individuals emerged from treated eggs were estimated. The results showed that indoxacarb showed the highest deleterious sublethal effects on T. brassicae. On the other hand, M. anisopliae was the safest treatment to combine to Trichogramma with no significant effect on some parameters. The lowest LC50 value for T. brassicae was obtained for chlorantraniliprole followed by spinosad. Synergistic effect was observed when M. anisopliae and T. brassicae used together. Hence, this will be a promising integration against T. absoluta.