An egg parasitoid interferes with biological control of tomato leafminer by augmentation of Nesidiocoris tenuis (Hemiptera: Miridae)

Abstract

Tomato leaf miner (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is a serious pest of tomato production in many parts of the world. The TLM has demonstrated capacity to evolve resistance to insecticides, and residues of these on tomato fruit pose hazards to human health, making biological control solutions an urgent priority. We assessed the biological control potential of the predatory bug Nesidiocoris tenuis (Reuter), in combination with the egg parasitoid Trichogramma brassicae Bezdenko at various release rates (0, 10 or 30 females/m2/week). Predators were released either 10 days before, or 10 days after, pest establishment. The predator lowered pest density only when it was released before the pest, but not to levels likely to retain the population below economic threshold. The parasitoid had no direct effect on pest density, but negatively affected the predator's impact on the pest, likely by reducing prey suitability and shifting feeding behavior toward more herbivory and/or cannibalism. Both pest and predator displayed negative density dependence; their population growth rates declined with increasing conspecific density. Our results indicate that N. tenuis should be augmented using a predator-in-first approach, and without simultaneous releases of egg parasitoids. Augmentation of N. tenuis will require integration with other tactics to provide adequate control of TLM, but has the potential for ancillary impacts on other tomato pests such as whiteflies and spider mites.