SURVIVAL AND INFECTIVITY OF ENTOMOPATHOGENIC NEMATODES UNDER ENVIRONMENTAL-STRESS

At two experiments, infective stage juveniles of three heterorhabditid nematode isolates and Steinernema riobravis were placed in sterilized sandy soil in sealed containers buried in corn field during summer. C ontainers were removed daily for 10 consequent days and surviving juve niles were recovered from the soil by Baermann funnel method, then the remainder of soil was subjected to Spodoptera littoralis-baiting tech nique. Apparently, the low level of soil moisture (3%) and ceiling tem perature levels (up to 42 degrees C) as well as faint electric conduct ivity (0.48 mmhos/cm) of the soil containing the nematodes resulted in a rapid decline in the number of nematodes recoverable from the soil over time by Baermann method, The percentage of recovery for the nemat ode isolates EAM8, EIS7 and EAS59 by the Baermann funnel was 35.6%, 43 .9% and 20.5% for the total nematodes recovered in the first trial, re spectively. The nematode numbers increased when the recovery time exte nded from 24 to 48 h at 23 degrees C. Insignificant differences were f ound between nematode numbers recovered daily in both trials. The aver age number of the recovered S. riobravis was more (P less than or equa l to 0.05) than that of any other nematode isolate, Nematodes which we re not recoverable by Baermann technique were infective when bioassaye d over the period of the two experiments, The infective juveniles whic h survived the stressed conditions are recommended to be subcultured t hrough selection regime in order to obtain an improved nematode strain .