Phenology of phytoseiid populations in an insecticide-free apple orchard
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Rebecca A. Schmidt-Jeffris and Elizabeth H. Beers Department of Entomology WSU-Tree Fruit Research & Extension Center, Wenatchee, WA Email:
[email protected] Amblydromella caudiglans
Background Phytoseiids are important biological control agents of spider mites in a variety of cropping systems, including apple. Although past research has examined the phenology of mite communities in apple orchards, most of this work is several decades old (Hoyt 1967; Oatman 1973; Readshaw 1975; Oatman 1976; Woolhouse and Harmsen 1984). More recent studies are needed, especially those that examine the whole community structure in unsprayed apple orchards. In examining the entire mite community structure, potential drivers of population change can be more easily identified. Additionally, by studying unsprayed orchards, we can more easily identify population dynamics that are strictly due to seasonal changes as opposed to agricultural inputs (which vary highly though time and between orchards). As pesticide use and other integrated pest management practices become more selective, the “typical” orchard may have more in common with an unsprayed system than conventional orchards of the past.
Materials & Methods All samples were collected from an unsprayed 42 year-old research block of ‘Delicious’ apples in Wenatchee, WA. This block has not received routine sprays of insecticides or fungicides; single trees received sprays during the life of the orchard, but none were applied during two years of the study.
Z. mali Phytoseiids
Zetzellia mali was typically found in higher abundances than phytoseiids (Fig 6). Phytoseiid eggs can make up a large portion of Z. mali prey when apple rust mites are scarce (Clements and Harmsen 1990). As in this study, the populations of Z. mali have been noted to relate to those of A. schlechtendali (Hoyt 1967).
Ovipositor
Fig. 3. A. caudiglans abundance over two years
A. caudiglans was also common in the orchard (Fig 3). Like G. flumenis, A. caudiglans prefers to feed on eriophyids over tetranychids (Clements and Harmsen 1993, Blackwood et al. 2004). However, this predator is known to be more generalized than G. flumenis (Blackwood et al. 2004), because it can maintain reproduction on pollen-only diets (Putman 1962). While it has also been characterized as predominately existing in unsprayed habitats (Downing and Moilliet 1972, Prischmann et al. 2005), it is also known to exist in abundance in some commercial orchards (R.A.S-J., unpublished).
Spider mite populations remained very low throughout the season (
