Relationships between the omnivorous predator Nesidiocoris tenuis (Reuter) and the egg parasitoid Trichogramma achaeae Nagaraja and Nagarkatti were studied in the laboratory (no-choice and choice assays, and functional responses) and in a greenhouse experiment. Both natural enemies are utilized in the biological control of tomato pinworm on greenhouse-grown tomato crops. Three different food items were offered to the predator: nonparasitized prey, prey parasitized for less than 4 d by T. achaeae, and prey parasitized for more than 4 d by the parasitoid. There were significant differences in consumption of food types, with highest consumption for nonparasitized prey, followed by parasitized (<4 d) and then parasitized (>4 d), both in no-choice and choice trials. At the same time, the predator causes a significant mortality in the prey (over 80%) regardless of previous parasitism, resulting in a very coincidental intraguild predation detrimental to the parasitoid. It has also been observed that there was a change in the functional response by the predator from Type II in presence of nonparasitized prey to Type I when there was a combination of parasitized and nonparasitized prey. This represents an increase of instantaneous search rate (a') and a decrease of handling time (T_h), which indicates a change in feeding behavior on the two prey types. Under greenhouse conditions, the intraguild predation reduced the percentage of parasitism by T. achaeae in just over 20%. However, when both natural enemies were present, a better control of pest Tuta absoluta (Meyrick) was achieved than in the case of application of any of them alone.