Can Interactions Between an Omnivorous Hemipteran and an Egg Parasitoid Limit the Level of Biological Control for the Tomato Pinworm?

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 (Th), 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.