Control of codling moth, Cydia pomonella (Lepidoptera : Tortricidae), withSteinernema carpocapsae: Effects of supplemental wetting and pupation siteon infection rate

Infection of cocooned codling moth (cydia pomonella) larvae by the entomopa thogenic nematode Steinernema carpocapsae was studied in three held experim ents. Factors that varied within or between experiments included method of application, type of substrate containing cocooned larvae, time when nemato des were applied, seasonal effects, and supplemental wetting before or afte r nematode application. Conventional air-blast sprayer applications of 0.5- 5.0 million infective juveniles (IJs)/tree in fall resulted in ca. 30% mort ality of larvae in cardboard trap bands, whereas hand-gun application (2 mi llion IJs/tree) produced mortality of ca. 70%. Application in the evening c aused higher larval mortality than application in the morning when no suppl emental wetting was used after treatments. Morning and evening applications caused equivalent larval mortality when a postwetting treatment was includ ed. In a trial conducted in midsummer, supplemental wetting, either before or after hand-gun application of 1 million IJs/tree, enhanced nematode-prod uced mortality. Mortality approached 100% if both pre- and postwetting was used. Larvae in exposed cocoons on apple wood were infected at a higher rat e (86%) than those on wood in less exposed positions (73%) or in nonperfora ted cardboard (72%). Mortality rates for larvae in perforated cardboard wer e intermediate (77%). Application volumes used to deliver nematodes slightl y enhanced infection rate of larvae in some substrates but not others. In o ne trial, parasitism of codling moth by the wasp Mastrus ridibundus (Ichneu monidae) was negatively correlated with nematode infection of codling moth larvae. Dissections showed that ca. 10% of larvae infected by nematodes had been attacked by the wasp. (C) 2000 Academic Press.