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During the past decade, the use of predatory mirids alone or combined with releases of egg parasitoids of the genus Trichogramma have been tested in Europe for biological control of the worldwide invasive pest, Tuta absoluta (Meyrick). Here, we evaluated the control of this pest by the release of the Neotropical mirid Macrolophus basicornis (Stal), the Neotropic/Nearctic parasitoid Trichogramma pretiosum Riley, and by combined releases of the predator and the parasitoid. Tests were conducted in greenhouse compartments during the summer and fall season. Each compartment contained 10 tomato plants in which only the pest was released or the pest with 1 or 2 natural enemies. Plant damage, and pest and natural enemy densities were checked weekly on one apical, medium, and bottom leaf of 5 plants. Both M. basicornis and T. pretiosum significantly reduced T. absoluta density when released alone. Combined releases resulted in a 10% higher reduction during the summer season, but not during the fall season. The damage caused by T. absoluta was significantly higher in control treatments than in all natural enemy treatments: at the end of the summer trial leaves were completely damaged in the control treatment, whereas only up to 25% leaf damage occurred in the natural enemy treatments. Combined releases did not result in lower damage than with releases of either M. basicornis or T. pretiosum. Practical aspects of single and combined releases are discussed.

Biological control, which uses natural enemies to reduce pest populations, is a non-polluting powerful method to manage impacts of (invasive) pests. Currently, polyphagous mirid predators are increasingly used in commercial, augmentative biological control. Information about their foraging behaviour is essential, especially if one intends to use several natural enemies for control of one or more pests in a crop, to detect if negative intraguild effects occur. We studied a case of intraguild predation (IGP) involving a predator, Macrolophus basicornis, of the worldwide invasive South American tomato leaf miner Tuta absoluta, and explored how this predator deals with prey parasitized by Trichogramma pretiosum. Behavioural observations show that M. basicornis predators contacted significantly fewer old, parasitized eggs of T. absoluta than recently parasitized ones. Olfactometer tests revealed that predators could smell differences between volatiles of tomato leaves infested with eggs of different quality to locate suitable prey. They preferred volatiles from leaflets with unparasitized eggs above control leaflets, and, moreover, preferred volatiles from leaflets with recently parasitized eggs over volatiles of leaflets with 5-day old parasitized eggs. When predators and parasitoids are used together to control T. absoluta, parasitoids should be introduced days before predators to prevent high levels of IGP.