Virulence and Reproduction of Entomopathogenic Nematodes Isolated from a Single Mexican Locality1

Entomopathogenic nematodes (EPNs) are important biological control agents of insect pests. Strains or isolates obtained in specific regions and utilized in situ might contribute to the success of EPNs, since they are adapted to local abiotic conditions. We isolated and identified three isolates each of Heterorhabditis bacteriophora Poinar and Steinernema carpocapsae (Weiser) from soils at Saltillo, Coahuila State, Mexico. These six isolates were bioassayed against larvae of Tenebrio molitor L., using six concentrations of infective juveniles (IJs) per larva (0, 10, 25, 50, 100, 200). EPN-induced mortality of the isolates ranged from 15.2% to 100%. The designated M5 isolate of S. carpocapsae caused 100% mortality after 72 h at concentrations ≥25 IJs/larva with a median lethal concentration of 4.99 IJs/larva. Comparison of mortality levels induced at the same concentration of the six EPN isolates indicated that the Steinernema isolates, in general, induced higher mortality levels than the Heterorhabditis isolates. IJ production in T. molitor larvae also was greatest with the M5 isolate of S. carpocapsae following exposure of larvae to a concentration of 100 IJs/larva with a mean of 17,320 IJs/larva. Based on induced mortality and IJ production, the S. carpocapsae M5 isolate appears to be a viable candidate for further study and possible development for use in insect pest management programs. This study indicates that naturally coexisting local nematode isolates possess different attributes critical for their use as biocontrol agents.