Evaluation of certain Egyptian Heterorhabditids Isolates as Molluscicidal Nematodes for the Control of Deroceras reticulatum and D. leave Slugs under Laboratory Conditions

Deroceras laeve Müller and D. reticulatum Müller are serious slugs of field crops in Egypt. Chemical control using metaldehyde baits is still the main control tactic. In 2018, a survey of terrestrial slugs at Belbies district, Sharkia Governorate, Egypt failed to find the molluscicidal nematode, Phasmarhabditis hermaphrodita. Dead slugs produced only free-living or non pathogenic nematodes belong to Family Rhabditidae. Two imported EPNs species; Steinernema carpocapsae (All strain) and Heterorhabditis bacteriophora (HP88 strain) were screened for molluscicidal activity against D. laeve and D. reticulatum compared with three Egyptian Heterorhabditis isolates, Ht strain, Ar-4 strain and Serag1 strain. S. carpocapsae (All strain) and H. bacteriophora (HP88 strain), showed promising results by killing territorial slugs. S. carpocapsae (All strain) resulted in the greatest percentage mortalities 100% in D. laeve and D.reticulatum after 14 days at a concentration of 2000IJs/cm whereas, the application of H. bacteriophora (HP88 strain) induced percentages mortality 50 and 66.67% with D. laeve and D. reticulatum, respectively. The Egyptian strain H. bacteriophora showed less molluscicidal activity against the two tested slugs. After 14 days, D. reticulatum mortalities were 36.67, 40.00 and 46.33 % by the application of H. bacteriophora (Serag1 strain), H. bacteriophora (Ht strain) and H. bacteriophora (Ar-4 strain), respectively. Whereas, the percentage mortalities were 20.00, 23.33 and 26.67 %; 10.00, 13.33 and 13.33% in D. leave at low concentrations (1000 IJs/cm2 & 500 IJs/cm2), respectively. Egyptian isolates showed less encourage usage as a specific biological control agent against D. laeve and D. reticulatum compared to S. carpocapsae (All strain) and H. bacteriophora (HP88 strain). Finally, results of this study indicate the need to an extensive survey in all Egypt to detect and isolate the slug parasitic nematode, P. hermaphrodita as it was recorded in Dakahlia governorate infesting different snails and slug species and research should proceed to find virulent isolates from EPNs to control terrestrial slugs.