Assessment of the diversity and roles of bacterial symbionts in fruit fly development and response to biological control

Abstract

Tephritid fruit flies are among the most destructive pest species of fruits and vegetables in many regions of the world. Apart from high losses in yield, tephritid fruit fly pests pose great socioeconomic and ecological challenges as well as demand effective measures to curb infestation which can be costly. Among currently used management options are the use of chemical insecticides, behavioral, genetic, cultural and biological approaches. However, no single method or combination of control strategies as used in integrated pest management programmes may be infallible to various constraints. It is therefore necessary to broaden the scope of plausible methods of addressing integrated pest management of tephritid fruit flies. This study examined the bacteria associated with the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) particularly in the African region where this invasive pest has established, with a view of identifying the roles of these bacteria in regards to development of the fly and its biological control. Specimens of this pest were collected from various locations in Africa and screened for the endosymbiotic bacteria, Wolbachia. More specimens from Kenya were screened using a high throughput sequencing approach to explicate the gut microbiome associated with this fly. A technique to remove all bacteria from the flies and reintroduce single bacterial isolates back was used to study the roles of individual bacterial isolates during early developmental stages of the fly, and later on to test effects of such bacteria when the flies are exposed to the entomopathogenic fungus, Metarhizium anisopliae ICIPE 69, that has been commercialized in Kenya as a biological control agent for this pest. A low prevalence of Wolbachia that did not strictly associate with maternal haplotypes of B. dorsalis was detected in the African populations. A diverse composition of gut bacterial communities mostly in the phyla Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes was observed in B. dorsalis specimens from Kenya. The recorded compositions suggested a strong effect of diet and environment on the microbiome structure of this fruit fly. A potential entomopathogen, Serratia, was identified among the bacterial communities of this host. In addition, it was observed that the absence of bacteria in this host negatively impacted development of the embryo and larval stages. A strain of Lactococcus lactis was also observed to diminish survival of this pest, when challenged with the entomopathogenic fungus, M. anisopliae ICIPE 69. These findings present useful insights in the biology of this fly as mediated by associated bacteria which may inform pest management options such as selection of probiotics in mass rearing strategies, as well as potential candidates for exploration as bacterial entomopathogens.