Impact of Larval Food Source on the Stability of the Bactrocera dorsalis Microbiome.

Bacterial symbionts are crucial to the biology of Bactrocera dorsalis. With larval diet (fruit host) being a key factor that determines microbiome composition and with B. dorsalis using more than 400 fruits as hosts, it is unclear if certain bacterial symbionts are preserved and are passed on to B. dorsalis progenies despite changes in larval diet. Here, we conducted a fly rearing experiment to characterize diet-induced changes in the microbiome of female B. dorsalis. In order to explicitly investigate the impacts of larval diet on the microbiome, including potential stable bacterial constituents of B. dorsalis, we performed 16S rRNA sequencing on the gut tissues of teneral female flies reared from four different host fruits (guava, mango, papaya, and rose apple) infested using a single cohort of wild B. dorsalis that emerged from tropical almond (mother flies). Although B. dorsalis-associated microbiota were predominantly shaped by the larval diet, some major bacterial species from the mother flies were retained in progenies raised on different larval diets. With some variation, Klebsiella (ASV 1 and 2), Morganella (ASV 3), and Providencia (ASV 6) were the major bacterial symbionts that were stable and made up 0.1-80% of the gut and ovipositor microbiome of female teneral flies reared on different host fruits. Our results suggest that certain groups of bacteria are stably associated with female B. dorsalis across larval diets. These findings provide a basis for unexplored research on symbiotic bacterial function in B. dorsalis and may aid in the development of novel management techniques against this devastating pest of horticultural importance.

Gut bacterial population and community dynamics following adult emergence in pest tephritid fruit flies.

Gut microbiota are important contributors to insect success. Host-microbe interactions are dynamic and can change as hosts age and/or encounter different environments. A turning point in these relationships the transition from immature to adult life stages, particularly for holometabolous insects where there is radical restructuring of the gut. Improved knowledge of population and community dynamics of gut microbiomes upon adult emergence inform drivers of community assembly and physiological aspects of host-microbe interactions. Here, we evaluated the bacterial communities of the pest tephritid species melon fly (Zeugodacus cucurbitae) and Medditeranean fruit fly (medfly, Ceratitis capitata) associated with the pupae life stage and timepoints immediately following adult eclosion. We used a combination of culturing to determine cultivatable bacterial titers, qPCR to determine 16S-rRNA SSU copy numbers, and 16S V4 sequencing to determine changes in communities. Both culturing and qPCR revealed that fly bacterial populations declined upon adult emergence by 10 to 100-fold followed by recovery within 24 h following eclosion. Titers reached ~ 107 CFUs (~ 108 16S rRNA copies) within a week post-emergence. We also observed concurrent changes in amplicon sequence variance (ASVs), where the ASV composition differed overtime for both melon fly and medfly adults at different timepoints. Medfly, in particular, had different microbiome compositions at each timepoint, indicating greater levels of variation before stabilization. These results demonstrate that tephritid microbiomes experience a period of flux following adult emergence, where both biomass and the makeup of the community undergoes dramatic shifts. The host-microbe dynamics we document suggest plasticity in the community and that there may be specific periods where the tephritid gut microbiome may be pliable to introduce and establish new microbial strains in the host.

Raspberry Ketone Trifluoroacetate Trapping of Zeugodacus cucurbitae (Diptera: Tephritidae)in Hawaii.

Melon fly, Zeugodacus cucurbitae (Coquillett), is a serious pest of tropical horticulture, causing damage to cucurbits, other fruiting vegetables, and certain tree fruits. The deployment of male lures comprises an important component of several detection and control strategies for this pest, with the main male attractant currently in use being cuelure (CL). A novel fluorinated analog of CL, raspberry ketone trifluoroacetate (RKTA), has been developed for the control of Bactrocera tryoni, a related pest; here, we test this compound for attraction to Z. cucurbitae. In outdoor screen cage testing, observations showed both more flies on filter papers, and a higher percentage of flies feeding, on papers treated with RKTA than on those with CL or melolure (ML). Field trapping with both yellow sticky traps and bucket traps found that RKTA captured more flies during the first 6 h of trapping than CL, while trap captures in the subsequent 18 h did not differ between the two lures. When comparing combined 24 h trap captures, yellow sticky traps containing RKTA captured more flies than those with CL, while bucket trap captures did not vary by lure. Analysis of lures weathered on filter paper found that nearly all applied RKTA hydrolyzed to RK within 6 h. Fine-scale melon fly behaviors digitally recorded in the field showed median resting distances from the lure of responding flies were shorter for RKTA than for CL. This study demonstrates the inherent attractiveness of RKTA while also highlighting the instability of this compound due to hydrolysis.