Classic biological control of olive fruit fly in California, USA: release and recovery of introduced parasitoids

The establishment of olive fruit fly Bactrocera oleae (Rossi) in California, USA instigated a classical biological program. This study reports the release and recovery of two solitary larval endoparasitoids, Psyttalia humilis Silvestri and Psyttalia lounsburyi (Silvestri) imported from sub-Saharan Africa, and released in five coastal and three inland counties in California, USA. Both parasitoid species were recovered post-release within the same fruit season and dispersed up to 1,500 m from a release location. P. lounsburyi was recovered post-release the following fruit seasons at numerous sites, and up to 945 days after the last release at one site. It is now established in California coastal regions, but not at the inland release sites. We discuss ecological factors and aspects of parasitoid biology that could improve or impede the permanent establishment of olive fruit fly parasitoids in California.