Outcomes of intraguild interactions between two egg parasitoids in field and semi-field conditions

Intraguild interactions between two egg parasitoids, Trissolcus basalis (Wollaston) and Ooencyrtus telenomicida (Vassiliev) exploring egg masses of the Southern Green Stink Bug Nezara viridula (L.) were investigated in field and semi-field conditions. Field trials were conducted in tomato fields by using sentinel and naturally laid egg masses in 2010 and 2011. Egg parasitoids monitoring, by sentinel egg masses placed weekly on plants during the tomato growing season and recollected one week later, showed that T. basalis occurs from June to October, whereas O. telenomicida occurs mainly in July and August. In the same fields, collections of naturally laid egg masses display different types of parasitized egg masses: only by T. basalis, only by O. telenomicida and by both species. The outcomes showed that T. basalis achieves a higher impact on the host population than O. telenomicida, even when multiparasitism occurs. Semi-field trials were conducted from July to September 2011, using pepper plants covered with mesh net in order to create small cages with five plants inside. In each cage, egg masses were placed on four plants located near to the cage corners and then T. basalis and O. telenomicida were released individually or simultaneously on the central plants. Egg masses were recollected after one week. The results showed that T. basalis achieves a high parasitization level when released alone but suffers competition by O. telenomicida when both species were simultaneously released.