Issue link: http://read.dmtmag.com/i/63050
Sustainable Agriculture codling moth! T Watch out, he abundance of spiders in orchards has increased tremendously since grow- ers have been shifting away from using the older, broad-spectrum pesticides, says Dr. Tom Unruh, entomologist with the U.S. Department of Agriculture in Yakima, Washington. Large spider populations are particularly evident in organic orchards but are Spiders will eat also being noticed in conventional orchards where more selective insecticides are used. Spider populations can be so high that people put pipes on the front of their four-wheel vehicles to keep webs out of their faces as they drive through the orchards. The spiders have more than a curiosity value, Unruh believes. Spiders anything they can physically tackle, including codling moth larvae and pupae. by Geraldine Warner are generalist predators that will eat anything that comes their way if it's an appropriate size— meaning it's smaller than them—says entomologist Dr. Gene Miliczky, a colleague of Unruh's. Young spiders have a different menu than older ones. Small spiders might feed on thrips, mites, and small aphids. Bigger ones might eat grasshoppers, wasps, bees, butter- flies, or moths, including codling moth larvae or pupae. In fact, they're not at all picky about their food and will also eat lacewing larvae, lacewing nymphs, and other spiders. But Miliczky said that since pests tend to be more abundant in the orchard than beneficial insects, pests probably make up most of their diet. Unruh and Miliczky are working on a research project to find out how much spiders might be contributing to codling moth control. Unlike parasites that might consume the innards of their host and leave some evidence, spiders eat their prey, making it difficult to tell what they're attacking. So, the scientists are examining the gut contents of spiders to find out if they've recently eaten codling moth larvae or pupae. Miliczky's role in the project is to capture spiders in orchards and identify the species, while Unruh is in charge of analyzing their gut contents. Different species Miliczky has been capturing and identifying spiders since he joined the Agricultural Research Service in Yakima in the mid-1990s. He estimates he has found 35 to 40 different spider species in apple and pear trees and that many or more species on the ground. Some spiders, such as wolf spiders, live on the ground and are rarely seen in canopy. These are captured with sweep nets or pitfall traps, which consist of plastic cups sunk into the ground. Spiders that live in the trees are caught on beating trays or by searching for webs in the trees. The species of spiders vary depending on the location and the insecticides used. When he began collecting spiders, Miliczky might find a total of one or two spiders from 25 to 30 beating tray samples in a typical conventional orchard, compared with up to 100 from the same number of beating tray samples in an organic orchard. Use of insecticides is the number-one factor that determines the abundance of spiders in an orchard, he said. "I think probably regardless of what you do other- wise, if you're still using insecticides heavily, you're going to harm your spider populations and other beneficials as well." Joe Shelton, orchard manager at Broetje Orchards in 16 MAY 1, 2012 GOOD FRUIT GROWER A pair of Neoscona oaxacensis spiders. The smaller spider on the right, which is the male, appears to be courting the female in preparation for mating. He has his pedipalps extended toward her and these will be used to transfer sperm if she is receptive. Cheiracanthium spiders are known as yellow sac spiders. They are usually pale colored and are 1/5 to 3/8 inch long. Gut- content analysis has shown evidence of feeding on codling moth. In central Washington, C. mildei is the species most commonly found. Prescott, Washington, said his company has both conventional and organic orchards. He (continued on page 18) A female Neoscona oaxacensis orb-weaving spider. Joseph Berger, Bugwood.org Joseph Berger, Bugwood.org chris peters chris peters