Abstract
BackgroundThe symbiosis between the olive fruit fly, Bactrocera oleae, and Candidatus Erwinia dacicola has been demonstrated as essential for the fly’s larval development and adult physiology. The mass rearing of the olive fruit fly has been hindered by several issues, including problems which could be related to the lack of the symbiont, presumably due to preservatives and antibiotics currently used during rearing under laboratory conditions. To better understand the mechanisms underlying symbiont removal or loss during the rearing of lab colonies of the olive fruit fly, we performed experiments that focused on bacterial transfer from wild female flies to their eggs. In this research, eggs laid by wild females were treated with propionic acid solution, which is often used as an antifungal agent, a mixture of sodium hypochlorite and Triton X, or water (as a control). The presence of the bacterial symbiont on eggs was evaluated by real-time PCR and scanning electron microscopy.ResultsDGGE analysis showed a clear band with the same migration behavior present in all DGGE profiles but with a decreasing intensity. Molecular analyses performed by real-time PCR showed a significant reduction in Ca. E. dacicola abundance in eggs treated with propionic acid solution or a mixture of sodium hypochlorite and Triton X compared to those treated with water. In addition, the removal of bacteria from the surfaces of treated eggs was highlighted by scanning electron microscopy.ConclusionsThe results clearly indicate how the first phases of the colony-establishment process are important in maintaining the symbiont load in laboratory populations and suggest that the use of products with antimicrobial activity should be avoided. The results also suggest that alternative rearing procedures for the olive fruit fly should be investigated.
Highlights
The symbiosis between the olive fruit fly, Bactrocera oleae, and Candidatus Erwinia dacicola has been demonstrated as essential for the fly’s larval development and adult physiology
The PCR-Denaturing Gradient Gel Electrophoresis (DGGE) profiles of egg samples washed with water (CE) showed more complex band patterns than did those obtained from egg samples treated with propionic acid (PAE) and the mixture hypochlorite + TritonX (SHTXE) or samples of water control water (CW), PAW and SHTXW (Fig. 1)
In each DGGE profile of eggs treated with water, a clear band was consistently present that showed the same migration behavior as the band formed by the sample of the oesophageal bulb of B. oleae used as marker of Ca
Summary
The symbiosis between the olive fruit fly, Bactrocera oleae, and Candidatus Erwinia dacicola has been demonstrated as essential for the fly’s larval development and adult physiology. To better understand the mechanisms underlying symbiont removal or loss during the rearing of lab colonies of the olive fruit fly, we performed experiments that focused on bacterial transfer from wild female flies to their eggs. Insects display a great variety of symbiotic relationships with microorganisms that allow them to exploit almost every substrate as food source and to colonize any habitat on earth. Such microorganisms comprise viruses as well as bacteria, fungi, protozoa and multicellular symbionts [1]. Research on the symbiotic relationships of fruit flies has often focused on potential pest control applications. Following Lauzon’s review [12], research on this topic was greatly increased by the advent of molecular techniques, improving microorganism identification
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