Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings
Publication Acceptance Date: February 15, 2003
Publication Date: July 1, 2003
Citation: Pfannenstiel, R.S., Unruh, T.R. 2003. Conservation of leafroller parasitoids through provision of alternate hosts in near-orchards habitats. International Symposium on Biological Control of Arthropods. USDA Forst Service Pub. FHTET-03-05. p. 256-262. Interpretive Summary: Biological control of insect pests of orchards may depend on species of non-pest insects that occur both inside and outside of orchards. The use of pheromones to control codling moth, the key pest of apples and pears, has reduced insecticide use in orchards but this has allowed some minor pests to increase in importance. Pandemis pyrusana, one such pest, is generally not controlled by parasites, especially in the spring generation. Parasites of Pandemis require another leafroller host on which to overwinter and this host does not occur in orchards. Where this alternative host, the strawberry leafroller, occurs in abundance on wild roses next to orchards, the parasitism of Pandemis in the adjacent orchards was very high. To see if this relationship could be manipulated we planted roses and strawberry gardens near orchards and infested them with the alternate host. The following spring we found parasitism on leafrollers in the orchards near our gardens at much higher rates than the 2 years prior to the gardens. These results demonstrate a complex interaction that can be simplified and used to increase biological control and further reduce pesticide use.
Technical Abstract: Two endemic leafroller species are important pests of apple and pear in the Northwestern pome fruit production regions. The pest status of these bivoltine leafrollers has become more problematic with the implementation of mating disruption for codling moth control and concomitant reduction of pesticides used for this pest. Pandemis pyrusana, the focus of this work, is attacked by a complex of parasitoids including the eulophid Colpoclypeus florus, and the braconid, Oncophanes americanus, which over winter on alternate hosts outside of orchards. Pandemis is also attacked by the tachinids, Nemorilla pyste and Nilea erecta, and several ichneumonids who over wintering biologies are unknown. Large-scale measurement of parasitism in orchard-landscape mosaics in 1999 and 2000 showed very low parasitism in spring and C. florus was only detected at low rates in orchards near to riparian habitats. In contrasts, parasitism of leafrollers in orchards near rose patches (Rosa woodsii) invested with an alternate host, Ancylis comptana, showed high parasitism of pest leafrollers in nearby orchards in spring at one site and again in summer at the second site. Phenological studies show this is because Ancylis provides both an overwintering host and a bridge between summer generations for C. florus. Gardens of rose and strawberry planted on orchard borders showed strongly elevated parasitismof sentinel Pandemis near the gardens in the spring of 2001. Our provision of gardens demonstrate that parasitism can be enhanced by changing the plant species occurring on the perimeter of orchards and present a possible approach for further reductions in pesticide use in apple and pear orchards.