Field Guide for Integrated Pest Management in Hops

68At-A-GlanceSpiders◆◆Spiderpresence in hopsis a good signof low pesticideinput.◆◆Spiders oftenserve as buffersthat limit initialexponentialgrowth of preypopulations.◆◆Spiders mayhelp regulateaphids andcaterpillars.◆◆Use insecticidesand miticides safeto spiders.SpidersDescriptionSpiders are common residents inmost low-chemical-input hop yards andcan reach high densities on the groundfloor and in the hop canopy. Some of thecommon spiders found in hop yards includejumping spiders (Figs. 139 and 140), crabspiders (Fig. 141), sheet web weavers, andsac spiders. Spiders are one of the mostabundant predators in hop yards.Biology and Life HistorySpiders often serve as buffers thatlimit the initial exponential growth ofprey populations. However, the specificrole of spiders as effective predators hasreceived little attention and is difficultto demonstrate. There is evidence inmany ecosystems that spiders reduce preypopulations. They are generalists that acceptmost arthropods as prey in their webs orin their paths. They eat the eggs and larvaeof all the insects and mites that infesthops. Spiders disperse easily to new areasin hop yards and colonize rapidly by aerialballooning and walking between bines.They are also blown around with the windand debris. The abundance and diversityof spiders in hop yards is linked to thelarge-scale landscape complexity (hop yardmargins, overwintering habitat, weediness)and local management practices (pesticideuse, tillage practices).Figure 140. A jumping spider. (D. G. James)Figure 141. A crab spider feeding on a wasp.(D. G. James)Figure 139. A jumping spider (Phidippia sp.)feeding on a beetle larva. (D. G. James)SpidersMonitoring, Importancein IPM and Compatibilitywith PesticidesSpiders can be monitored byshaking bines over a tray. The valueof spiders to biocontrol is thoughtto be considerable, but has yet tobe evaluated. Most pesticides harmspiders, but populations tend torecover rapidly.