Biocontrol potential of the entomopathogenic nematodesHeterorhabditis bacteriophoraandSteinernema carpocapsaeon cucurbit fly,Dacus ciliatus(Diptera: Tephritidae)

AbstractEntomopathogenic nematodes (EPNs) from the families Steinernematidae and Hererorhabditidae are considered excellent biological control agents against many insects that damage the roots of crops. In a regional survey, native EPNs were isolated, and laboratory and greenhouse experiments were conducted to determine the infectivity of EPNs against the cucurbit fly, Dacus ciliatus Loew (Diptera: Tephritidae). Preliminary experiments showed high virulence by a native strain of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and a commercial strain of Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae). These two strains were employed for further analysis while another native species, Steinernema feltiae, was excluded due to low virulence. In laboratory experiments, larvae and adult flies were susceptible to nematode infection, but both nematode species induced low mortality on pupae. S. carpocapsae had a significantly lower LC50 value against larvae than H. bacteriophora in filter paper assays. Both species of EPNs were effective against adult flies but S. carpocapsae caused higher adult mortality. When EPN species were applied to naturally infested fruit (150 and 300 IJs/cm2), the mortality rates of D. ciliatus larvae were 28% for S. carpocapsae and 12% for H. bacteriophora. Both EPN strains successfully reproduced and emerged from larvae of D. ciliates. In a greenhouse experiment, H. bacteriophora and S. carpocapsae had similar effects on fly larvae. Higher rates of larval mortality were observed in sandy loam and sand soils than in clay loam. The efficacy of S. carpocapsae and H. bacteriophora was higher at 25 and 30°C than at 19°C. The results indicated that S. carpocapsae had the best potential as a biocontrol agent of D. ciliatus, based on its higher virulence and better ability to locate the fly larvae within infected fruits.Keywords: Steinernema carpocapsaeHeterorhabditis bacteriophoracucurbit fruit flybiocontrolinsect pathology AcknowledgementsThe authors appreciate staff members of Biocontrol and Insect Pathology Laboratory: R. Darsouei, M. Hassani-Kakhki, Sh. Heidari and Z. Rahatkhah for assistance. We thank Koppert B. V. (Berkel en Rodenrijs, The Netherlands) and Giyah Bazr Alvand CO. for providing the commercial product of EPN.FundingThis study was funded by research deputy of Ferdowsi University of Mashhad [project no. 21201/10 March 2011] and Natural Science Postdoctoral Fellowship from the Ramón Areces Foundation (Spain) to R. Campos-Herrera.Additional informationFunding Funding: This study was funded by research deputy of Ferdowsi University of Mashhad [project no. 21201/10 March 2011] and Natural Science Postdoctoral Fellowship from the Ramón Areces Foundation (Spain) to R. Campos-Herrera.