Mediterranean fruit flies (Ceratitis capitata Wiedemann, Dipt.: Tephritidae) harbour a diverse community of bacteria in their digestive system. This microbiota may have important functions impacting on the fly’s fitness. Recently, we described the effect of eliminating intestinal bacteria on the reproductive success of C. capitata males and females. Here, we expand the view on the nature of fly–bacteria interactions by examining the effect of bacteria on male and female longevity. Antibiotics were used to suppress the gut bacterial community and mortality rates were compared between antibiotic‐treated and non‐treated flies when either nutritionally stressed (maintained on sugar) or provided with a full diet. These tests revealed that eliminating the gut bacterial population prolonged longevity, but only when flies were nutritionally stressed, indicating that the effect of bacteria on lifespan was diet dependent. Considering these results in light of other known effects of bacteria on fitness components of the fly demonstrates a cost‐benefit relationship between C. capitata and its gut microbiota.

Fruit flies (Diptera: Tephritidae) maintain diverse yet stable communities of Enterobacteriaceae that reside in their digestive system. Focusing on one species of this family, Ceratitis capitata, the Mediterranean fruit fly (medfly), we applied the PCR-DGGE approach to study the influence of temporal and spatial variations on the composition and diversity of the enterobacterial community associated with the medfly. Our results revealed that the Enterobacteriaceae constituted not only dominant, but also constant and stable populations in the medfly's gut. Nevertheless, changes in both time and space had an impact on the structure and diversity of these bacterial populations, and while some populations (e.g., Klebsiella spp.) were stable, others fluctuated. Whether the bacterial population fluctuated according to the ecological needs of the insect during different environmental conditions, or reflected opportunistic colonization abilities of some bacterial strains, remains to be determined.

The effect of soil solarization and Trichoderma harzianum on induced resistance to grey mould (Botrytis cinerea) and powdery mildew (Podosphaera xanthii) was studied. Plants were grown in soils pretreated by solarization, T. harzianum T39 amendment or both, and then their leaves were inoculated with the pathogens. There was a significant reduction in grey mould in cucumber, strawberry, bean and tomato, and of powdery mildew in cucumber, with a stronger reduction when treatments were combined. Bacillus, pseudomonad and actinobacterial communities in the strawberry rhizosphere were affected by the treatments, as revealed by denaturing gradient gel electrophoresis fingerprinting. In tomato, treatments affected the expression of salicylic acid (SA)‐, ethylene (ET)‐ and jasmonic acid (JA)‐responsive genes. With both soil treatments, genes related to SA and ET – PR1a, GluB, CHI9 and Erf1 – were downregulated whereas the JA marker PI2 was upregulated. Following soil treatments and B. cinerea infection, SA‐, ET‐, and JA‐related genes were globally upregulated, except for the LOX genes which were downregulated. Upregulation of the PR genes PR1a, GluB and CHI9 in plants grown in solarized soil revealed a priming effect of this treatment on these genes' expression. The present study demonstrates the capacity of solarization and T. harzianum to systemically induce resistance to foliar diseases in various plants. This may be due to either a direct effect on the plant or an indirect one, via stimulation of beneficial microorganisms in the rhizosphere.

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