Predicting the altitudinal distribution of an introduced phytophagous insect against an invasive alien plant from laboratory controlled experiments: case of Cibdela janthina (Hymenoptera:Argidae) and Rubus alceifolius (Rosaceae) in La Réunion

The sawfly Cibdela janthina (Hymenoptera: Argidae) native to Sumatra was introduced on La Réunion (France, Indian Ocean) in 2007 to control the giant bramble Rubus alceifolius (Rosaceae), one of the most invasive plants on this island. We determined the influence of temperature on the development duration and survival of C. janthina preimaginal stages in controlled conditions in order to parameterize a survival model and to relate the predicted survival with observed patterns of defoliation of the host plant at different altitudes. We adjusted the Régnière model to survival data, combined with the Lactin-2 model on development rate of the three preimaginal stages of C. janthina. This model adequately predicts the observed defoliation and the altitudinal limit of the biological control agent. Our results also show that studies on temperature-related constraints on the biology of an agent introduced for weed control should be emphasized both in the pre-release and the post-release phases of a biological control program to evaluate the potential success of the control programme.