Comparison of indigenous and exotic entomopathogenic nematode strains for control of the cedar web-spinning sawfly, Cephalcia tannourinensis in vitro

Abstract

Cedars of Lebanon Cedrus libani have been attacked since 1990s by a hymenopteran sawfly, Cephalcia tannourinensis (Chevin), causing considerable damage to the foliar buds. A biological control programme using entomopathogenic nematodes (EPNs) was conducted in vitro against C. tannourinensis prenymphs. Two EPNs strains belonging to the same species Heterorhabditis bacteriophora were used; one indigenous to the country (LIB04) and the other a commercial strain (HbCom). Four EPNs concentration rates (40, 100, 250, 480 infective juveniles) were tested against C. tannourinensis prenymphs. Higher mortality was noted for the indigenous strain, LIB04, independently from all concentrations (100%). Emergence of EPNs was observed following 12–17 days from the first contact between EPNs and C. tannourinensis prenymphs. This parameter indicated that EPNs succeeded to complete all their reproductive cycle inside the C. tannourinensis cadavers before emerging. Bioassays were realised in jars containing soil extracted from the forest in order to validate the scenario suggested for application in situ. Most C. tannourinensis prenymphs were attacked by the EPNs on the surface.