Survival and efficacy ofsteinernema carpocapsaein an exposed environment

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Abstract
Factors affecting the persistence and activity of the infective juveniles (IJs) of the nematode Steinernema carpocapsae ’Mexican’ strain on the foliage of bean plants were determined at 45, 60 and 80% relative humidity (RH). The rate of nematode mortality was related to the RH. A gradual reduction in nematode survival was recorded during a 6 h exposure period at 80% and 60% RH, whereas at 45% RH high mortality was observed within 2 h. Addition of the antidesiccant ‘Folicote’ (6% w/w) to the nematode suspension was most effective in ensuring IJ survival at 60% RH, resulting in 38–60% increase in viability during 6 h of exposure. At 80% RH ‘Folicote’ treatment resulted in only 10–20% increase in IJs viability, as compared with non‐treated IJs. At 45% RH, ‘Folicote’ treatment did not significantly increase IJ survival (P>0.05). Survival of the IJs on tomato and soybean leaves was 30–35% higher than of those recovered from leaves of cotton, pepper and bean as well as from filter paper. At 60% RH, IJ movement ceased within 45–60 min of exposure and the nematode body shrank. However, nematode pathogenicity remained almost unaltered up to 4 h of exposure, resulting in 75% mortality of larvae of the Egyptian cotton worm Spodoptera littoralis. A drastic reduction in the nematodes’ efficacy was recorded when the insects were introduced 6 and 8 h after nematode application.