Newly imported larval parasitoids pose minimal competitive risk to extant egg-larval parasitoid of tephritid fruit flies in Hawaii.

Competitive displacement of fruit fly parasitoids has been a serious issue in the history of fruit fly biological control in Hawaii. This concern regarding competitive risk of new parasitoids has led to an overall tightening of regulations against the use of classical biological control to manage fruit flies. Fopius arisanus (Sonan), an egg-larval parasitoid, is the most effective natural enemy of tephritid fruit flies in Hawaii. This study evaluated the competitive risk of two recently introduced larval parasitoids, Diachasmimorpha kraussii Fullaway and Psyttalia concolor (Szépligeti), to F. arisanus attacking the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Fopius arisanus won almost all intrinsic competitions against both larval parasitoids through physiological suppression of egg development. 83.3% of D. kraussii eggs and 80.2% of P. concolor eggs were killed within three days in the presence of F. arisanus larvae within the bodies of multi-parasitized hosts. The mechanism that F. arisanusemploys to eliminate both larval parasitoids is similar to that it uses against three other early established larval fruit fly parasitoids: F. vandenboschi (Fullaway), D. longicaudata (Ashmead) and D. tryoni (Cameron). It suggests that introduction of these larval parasitoids poses minimal competitive risk to F. arisanus in Hawaii.