Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2000
Publication Date: 3/20/2001
Citation: Unruh, T.R., Lacey, L.A. 2001. Control of codling moth, Cydia pomonella (Lepidoptera: Tortricidae) with Steinernema carpocapsae: effects of supplemental wetting and pupation site on infection rate. Biological Control. 20:48-56. Interpretive Summary: Mating disruption with synthetic pheromones is rapidly replacing organophosphate use for control of codling moth in apple and pear orchards. Unfortunately, mating disruption is not effective in all situations and sometime must be supplemented with insecticides. We investigated the possibility of using insect-parasitic nematodes in place of insecticides to supplement mating disruption and too continue the reduction of insecticide use in apple and pear. Nematodes are semi-aquatic, typically soil dwelling organisms, while codling moth occurs in tree bark and other hidden sites during the cocoon stage which is most susceptible to infection by nematodes. Methods of making orchard environments more hospitable to nematode activity was explored by wetting before or after nematode treatments. Both pre-treatment and post-treatment wetting of orchard substrates was shown to enhance nematode activity. When temperatures were above 25 C and when both pre- and post-wetting was used, codling moth control approached 100%, showing that this approach may be a highly effective alternative to insecticides for supplementing mating disruption.
Technical Abstract: Parasitism of cocooned codling moth (Cydia pomonella) larvae by the insect-parasitic nematode, Steinernema carpocapsae, was studied in three field experiments. Conventional air-blast sprayer applications of 0.5-5.0 million infective juveniles (IJs)/tree in fall resulted in ca. 30% mortality of larvae in cardboard trap bands while hand-gun application (2 million IJs/tree) produced mortality of ca. 70%. Morning and evening applications caused equivalent larval mortality when a post wetting treatment was included. In a trial conducted in mid-summer, supplemental wetting, either before or after handgun application of 1 million IJs/tree, enhanced nematode-produced mortality. When both pre- and post-wetting was used mortality approached 100%. Larvae in exposed cocoons on apple wood were infected at a higher rate (86%) than those on wood in less exposed positions (73%) or in non-perforated cardboard (72%). Mortality rates for larvae in perforated cardboard were intermediate (77%). Results show that insect-parasitic nematodes are a promising alternative to insecticides that may be very useful in supplementing control provided by mating disruption with synthetic pheromones.