Field Guide for Integrated Pest Management in Hops

64 17Predatory and Parasitic FliesA number of fly species from at least five families are known as predators or parasitoidsof hop pests in the Pacific Northwest.At-A-GlancePredatory& ParasiticFlies◆◆Identify andmonitor adultand larvalpredatory flies.◆◆Predatory fliesfeed on aphids,spider mites,thrips, and theeggs and adultsof small insects.◆◆Useinsecticides andmiticides safe topredatory flies.◆◆Encourageflowering groundcovers thatprovide nectarfor predatoryflies.Hover FliesThe yellow-and-black-banded adulthover fly resembles a stinging bee or wasp,but only has one pair of wings (Fig. 128).Hover flies lay single white, oblong eggs nearaphid infestations. The adult is not predaceousbut feeds on flower nectar. The larvae areapproximately ¼ to ½ inch long, green to lightbrown, with a wrinkled-looking body that isblunt at the rear and pointed at the mouthend (Fig. 129). The pupae are pear-shaped andgreenish to dark brown (Fig. 130). A numberof species occur in hop yards and may be blackand yellow or black-and-white banded.Hover flies overwinter as pupae inthe soil or above ground in leaves and plantmaterial. The adult flies become active duringspring (April and May), laying eggs on leavesand stems of hop plants harboring aphids.Hover flies are good fliers, disperse widely, andseek out aphid infestations very effectively.Larvae feed on aphids for approximately 7to 10 days and then pupate. The larvae arevoracious feeders: as many as 300 to 400aphids may be consumed by one larva duringdevelopment.Adult hover flies may be monitoredusing yellow sticky traps; the maggot-likelarvae can be found amongst aphid colonies.Hover flies are an important component ofbiologically based hop aphid management. Incombination with lady beetles and predatorybugs, they can provide rapid control of aphidinfestations. Hover flies are generally sensitiveto broad-spectrum pesticides.Figure 128. Adult hover fly. The adult hoverfly resembles a stinging bee or wasp, but onlyhas one pair of wings. (D. G. James)Figure 129. Hover fly larva attacking hop aphid.Larvae are ¼ to ½ inch long. (D. G. JamesFigure 130. Hover fly pupa.(D. G. James)Dance FliesThe adults are small to mediumsized(< ¼ inch), dark-colored flies witha humpbacked thorax, long taperingabdomen, and slender legs. Dance flies arepredators as adults and larvae, consumingsmaller insects like aphids. Adults fly anduse their front legs to grasp small insects onthe wing and pierce them with their sharpsnout. The larvae are pale and cylindricaland live in the soil or decaying vegetation,preying on small insects and mites. Adultsalso visit flowers and swarm for mating.The larvae are generally found on moistterrestrial soil or rotten wood and arepredacious on various arthropods.Adult dance flies may be monitoredusing yellow sticky traps. Their value inhop yards is undetermined but they maycontribute to suppression of hop aphids.