Katharina Merkel, Samira Mohamed, Sunday Ekesi, Thomas Hoffmeister:
Differential Immuno-Suppressive Ability of Different Morphotypes of the Invasive Fruit Fly Bactrocera invadens towards Eggs of the Parasitoid Diachasmimorpha longicaudata


1University of Bremen, Population Ecology Lab, Germany
2International Centre of Insect Physiology and Ecology (ICIPE), Plant Health Division, Kenya

In 2003, the Asian fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) was first reported in Africa. This insect is an invasive species that is to date considered to be among the major pests of mango in Sub Saharan Africa. Being an alien pest and lacking indigenous parasitoid species, the use of introduced parasitoids against B. invadens may be a promising pest management strategy. One key factor for the success of such classical biological control programs is the physiological compatibility between the parasitoid and the target pest. Preliminary work indicated that B. invadens exhibits a differential ability of immuno-suppression against the introduced endoparasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). Within the population of B. invadens there are eight distinct morphotypes based on the pattern of the scutum. We hypothesised that the intraspecific variability in encapsulation ability is related to these different morphotypes. Four major morphotypes have been evaluated for the ability to encapsulate D. longicaudata eggs. The total and differential haemocyte counts and number of encapsulated and non"=encapsulated parasitoid eggs for the parasitized fly larvae were recorded at different time intervals after parasitisation, for each morphotype. The haemocyte counts were compared with that of unparasitized larvae of the same age as that of the parasitized ones. Additionally, the impact of parasitoid adaptation to the host has been investigated by recording the number of encapsulated and non"=encapsulated eggs of consecutive generations of D. longicaudata reared on B. invadens. The potential use of this parasitoid species in classical biological control of B. invadens will be discussed.

Keywords: Bactrocera invadens, Diachasmimorpha longicaudata, immuno-suppression


Contact Address: Katharina Merkel, University of Bremen, Population Ecology LabBremen, Germany, e-mail: kmerkel@icipe.org
Andreas Deininger, November 2008