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Ecology and Management of Canyon Flies (Fannia benjamini complex) in California


Host seeking "canyon flies" (Fannia benjamini complex) (Diptera: Muscidae) cause significant nuisance to humans and animals. To determine if a barrier trapping system using attractive traps would reduce the number of canyon flies reaching a human host within a protected area, a barrier of CO2-baited CDC-type suction traps (without light) was evaluated during the peak fly activity season at a location known for high F. conspicua Malloch activity in southern California. To select a suitable radius for the barrier, the effect of an operating CO2-baited trap on the fly capture rate of a nearby human was evaluated with traps placed at 10, 20, 30 and 40m away from the human collector. The number of flies captured by the human collector was very significantly reduced by traps placed 10m away, only slightly by traps 20m away, and unaffected by traps > 30m away. Because of site characteristics and the rapidly decreasing human-trap interaction between 10-20 m, a 15m radius circular trap barrier was erected, comprised of 8 CO2 traps. This barrier reduced F. conspicua capture by the human collector by 51 %. Reducing the barrier radius to 5m resulted in a 39 % reduction. The diel activity of F. benjamini Malloch and the "trail gnat", Amiota picta Coquillett, in the Carmel Valley, California was determined by hourly sweep net collections in September. Both species had a high activity period during early morning (0830-0930) with a second high activity period in the late afternoon and early evening (1630-1830). A. picta activity almost ceased during the inter-peak period, while F. benjamini remained active, though at reduced numbers, throughout the day. Capture rates of F. benjamini was higher at shaded locations than at sun-exposed locations. Neither the specific human collector nor the clothing color of a human collector had a significant effect on the rate of capture of F. benjamini. Substantially fewer F. benjamini were captured in a CO2 trap relative to the number captured by a human collector, even when traps were baited with the host odors ammonia and 1-octen-3-ol in addition to the CO2. The implications of these studies for management of canyon flies are discussed.

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