Performance of selected lines of Trichopria drosophilae and of Ganaspis brasiliensis on different fruit

A few generations of laboratory selection can increase the developmental
success of native parasitoids on invasive targets. However, for this
approach to be used more widely for biological control we need to
understand if the improved performance of native species, achieved under
artificial laboratory conditions, translates to improved control in more
natural environments. It is also unknown what the biocontrol potential of
laboratory selected generalist native parasitoids may be compared to
co-evolved specialists that are typically introduced for biological
control of invasive species. To assess how rearing in artificial diet
affected host finding ability in natural hosts we used laboratory selected
(adapted) and non-adapted populations of the generalist native parasitoid
Trichopria drosophilae to parasitize the invasive fly, Drosophila suzukii
in three different fruit types. In a separate experiment, we compared the
effectiveness of adapted and non-adapted populations of T. drosophilae in
raspberries with a co-evolved specialist larval parasitoid Ganaspis
brasiliensis from Asia that was recently approved for release in the USA.
More adult parasitoids emerged in each fruit type of the adapted compared
to the non-adapted population of T. drosophilae. Drosophila
suzukii emergence rates were reduced on average by 85% by the adapted T.
drosophilae population indicating that the artificial rearing conditions
did not significantly impair the ability of parasitoids to locate and
attack hosts in natural hosts. The specialist G. brasiliensis had higher
adult emergence than the adapted population of T. drosophilae, however,
both parasitoid species were able to reduce D. suzukii populations to the
same extent. These results show that despite the lower developmental
success of the laboratory selected T. drosophilae they killed the same
proportion of D. suzukii as G. brasiliensis when host choice was
restricted. In nature, where host choices are available specialist and
generalist parasitoids will be unlikely to exhibit the same biocontrol
potential.