Abstract
The Mediterranean fruit fly (medfly) Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is often referred to as the most severe agricultural pest. Its biological control is mainly through the Sterile Insect Technique (SIT). Colonization, mass-rearing conditions and the irradiation process impact the competitiveness of sterile males and disrupt symbiotic associations by favoring some bacterial species and suppressing others. Levels of Providencia species have been shown to fluctuate considerably in the gut of the medfly laboratory strain Vienna 8 under irradiation, increasing by up to 22%. This study aimed to determine the pathogenicity of Providencia rettgeri isolated from the gut of laboratory Vienna 8 medfly strains by examining the effects of 1) two different treatment doses on egg-hatching and development and 2) two infection methodologies (ingestion and injection) of male and female adults according to their mating status. Treatment of eggs with P. rettgeri (2%) significantly decreased the mean egg to pupae recovery rate. Our data showed significant high mortality in flies with both injection and ingestion after 24 hours without any effect of sex. Microbial counts demonstrated that the bacteria could proliferate and replicate in adult flies. There was a significant sex-dependent effect after infection, with mortality decreasing significantly for males more than females. Providencia rettgeri can be considered as a potential pathogen of C. capitata. Mating protected males and females against infection by P. rettgeri by triggering an immune response leading to double the levels of Cecropin being secreted compared to infected virgin adults, thus reducing the virulence of the bacteria.
Highlights
The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is often referred to as the most sever agricultural pest [1,2] with a host range that exceeds 300 plant species
We examined the pathogenicity of P. rettgeri according to two methods of infection of male and female adults, 1) comparing the male and female adult mortality according to the infection method, 2) followed by the monitoring proliferation of bacteria and their ability to replicate in male and female adults
The 16SrDNA gene sequence of 1485 bp showed 99% sequence identity with P. rettgeri, NR-115880.1 in GeneBank database under the accession number of MG752971 (S1 Table). This isolate is a representative of the three clades of P. rettgeri group according to rpoB clustering [50]. These results suggest that this isolate could be a new variant related to C. capitata
Summary
The Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is often referred to as the most sever agricultural pest [1,2] with a host range that exceeds 300 plant species. Biological control of medfly has mainly involved the Sterile Insect Technique (SIT). SIT is a biological environmentally friendly method of pest suppression or elimination which fits very well to the area wide approach of integrated pest management (AW-IPM) [3]. Since the seventies, this technique has become widely applied against C. capitata populations. SIT is a species-specific technique that is based on mass production of the target species, its sterilization and release in the field. SIT success is mainly related to male fitness and competitiveness [5] These males have undergone different stresses such as colonization, mass rearing and irradiation
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