Pathogenicity of multiple Providencia species (Enterobacteriales: Morganellaceae) to the mass-reared Mexican fruit fly (Diptera: Tephritidae).

Mexican fruit fly (Anastrepha ludens (Loew)) (Diptera: Tephritidae) represents a major threat to fruit production in the Western Hemisphere. Sterile insect technique is used to suppress and eradicate wild populations. Success of this control method necessitates weekly production of hundreds of millions of flies, their sterilization by irradiation, and their aerial release. Diet needed to produce large fly numbers are conducive to the spread of bacteria. Pathogenic bacteria were isolated from 3 rearing facilities and from multiple sources: eggs, larvae, pupae and spent diet, and were found to include some isolates identified to the genus Providencia (Enterobacteriales: Morganellaceae). We identified 41 Providencia isolates and tested their pathogenicity to A. ludens. Based on 16s rRNA sequences, 3 groups were clustered into several species of Providencia with varying capacities to affect the Mexican fruit fly production. Isolates putatively identified as P. alcalifaciens/P. rustigianii were all pathogenic causing larval and pupal yield reduction of 46-64% and 37-57%, respectively. Among them, Providencia isolate 3006 was the most pathogenic reducing larval and pupae yield by 73 and 81%, respectively. Isolates identified as P. sneebia were not pathogenic. The final cluster, P. rettgeri/P. vermicola, were variable in pathogenicity with 3 isolates yielding like the control and the rest causing larval and pupal yield reduction of 26-53% and 23-51%, respectively. Isolates putatively identified as P. alcalifaciens/P. rustigianii were more virulent than P. rettgeri/P. vermicola. Accurate identification of species is needed to diagnose and monitor pathogenic versus nonpathogenic Providencia strains.

Pathogenicity of Zygosaccharomyces bailii and Other Yeast Species to Mexican Fruit Fly (Diptera: Tephritidae) and Mass Rearing Implications.

Yeasts from all immature life stages of Mexican fruit fly Anastrepha ludens (Loew) (Diptera: Tephritidae) from diet, insectary air, and rearing materials were isolated, identified and evaluated for pathogenicity. Fifteen species of yeasts with one to genus level were identified from 72 yeast cultures obtained. Zygosaccharomyces bailii was the only yeast found to be highly pathogenic to Mexican fruit fly. Seventy-two hours post inoculation, the diet in bioassay cups with Z. bailii consistently showed signs of fermentation with gas bubbling causing the migration of larvae to the walls and lids of bioassay cups. The spent diet from Z. balii-infested cups was crusty, cracked and had a pasty layer. Many larvae were small, moribund, and discolored, appearing caramel or blackish. Insect yield loss with Z. bailii in comparison to that of control ranged from 10 to 44% for larvae and 14 to 47% for pupae. Additionally, Z. bailii caused a reduction in mean pupal weight. The weakly pathogenic yeasts produced significantly less yield of larvae and pupae than the nonpathogenic ones included Trichosporon montevideense, Clavispora lucitaniae, Candida sp., C. rugosa, and Rhodotorula mucilaginosa. Yield loss of larvae caused by this group ranged from 12 (C. lusitaniae) to 18% (R. mucilaginosa). Yield losses for pupa were similar to that of larvae. The mean pupa weight for these species was above the minimum acceptable (16.50 mg) for the SIT program. The nonpathogenic yeast produced yields of larvae and pupae similar to the control included Cryptococcus diffluens, Pichia kudriavzevii, Meyerozyma guilliermondii, Wickerhamomyces anomalus, Trichosporon asahii, Debaryomyces hansenii, Candida tropicalis, Cryptococcus sp., Candida parapsilosis, and Hanseniaspora opuntiae. In conclusion, the identification and management of insect pathogenic yeasts, such as Z. balii in mass rearing systems of Mexican fruit fly must be considered to avoid their potential negative effects.