Symbiosis in the service of biological control
Insect-symbiont interactions play an important role in a wide variety of their host’s life history traits and have positive effects on the insect general health and fitness. These positive effects can contribute to the improvement of the olive fruit fly mass production, which is of great importance for both the fly and the parasitoid toward the implementation of AW-IPM programs with a SIT component.
ESR update - Several recent trials to improve artificial rearing of the olive fruit fly indicated that laboratory domestication of the insect can induce dramatic reduction of the original population in the initial generations during colonization. Natural differentiation in gut microbiota is a potential reason for these population drops and often colony collapses in many laboratories. However, the exact causes have not been fully addressed yet. We, therefore, performed Next Generation Sequencing (NGS) of 16S rRNA gene in samples of two wild olive fruit fly populations to characterize the gut microbiota composition of the early developmental stages that were not exposed to any artificial diet and compare it with that of later developmental stages after their introduction to laboratory conditions. NGS results of both the olive fruit fly and its parasitoid wasps have already identified several gut bacteria helping us to unravel the knot of the insect-symbiont interactions. Our data confirmed the predominance of Erwinia dacicola in the olive fruit fly gut as it was reported in previous studies and revealed the presence of a broad gut microbial diversity that is affected not only by the origin of the population but, also, by other parameters, such as the developmental stage of the fruit fly. A diverse number of genera belonging to the Enterobacteriaceae family such as Erwinia, Providencia, Enterobacter and Klebsiella were detected, as well as members of the Bacilli class and the Deinococcus-Thermus and Actinobacteria phyla.
At the same time, utilization of cultivable approaches allowed the isolation of a wide number of bacterial species from the olive fruit fly gut. The subsequent step of our research that is currently in progress includes the use of these gut bacteria as supplements in the insect larval diet. Several isolated bacterial cultures have been added to the fruit fly larval diet and are tested for their ability to improve insect and parasitoid productivity under small-scale rearing conditions. A variety of life history traits related to the efficiency of mass production for both the fruit fly and its parasitoid wasps, such as pupal and adult recovery, pupal weight and adult survival under stress conditions of the fruit fly and the parasitism rate of the parasitoid wasps are currently assessed under the exposure of seven different bacterial isolates.