Potential for direct interference between natural enemies of Tuta absoluta on tomato

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has recently invaded some Mediterranean countries and is a key agricultural threat to tomato production. Among possibilities for controlling this pest, oophagous parasitoids have shown promising potential for controlling the pest before yield decrease, and one species in particular, Trichogramma achaeae, is currently proposed in Spain and France for inundative biological control of T. absoluta. In greenhouses, Miridae predators are also common on tomato and usually used against whiteflies. Despite the fact that these predators do not attack T. achaeae adults, they may partially decrease the overall impact of the parasitoid on T. absoluta if intraguild predation occurs on T. achaeae-parasitized eggs. Indeed, it could reduce parasitoids' offspring and thus their potential additional effect on T. absoluta. In this context, in small arenas and then in laboratory microcosms (encaged plants), we tested if the predator Macrolophus pygmaeus would show preference between T. absoluta eggs and T. achaeae-parasitized T. absoluta eggs in a choice experiment, and then we tested if the predator would reduce the number of T. achaeae-parasitized T. absoluta eggs on whole tomato plants. We also assessed if the predator and the parasitoids could impact the T. absoluta population dynamics. Combined use of T. achaeae and predators in tomato greenhouses has proven efficient in limiting T. absoluta population growth (better than predators alone). However, our findings suggest the importance of integrating the M. pygmaeus presence in the greenhouse tomato crop when using oophagous parasitoids for inundative biological control of T. absoluta, notably to ensure maximum efficacy of the parasitoids against T. absoluta both through (1) the inundative release, and (2) subsequent impact of parasitoids' offspring.