ECOLOGY AND POPULATION BIOLOGY Daily and Seasonal Activity Patterns of Rhagoletis indifferens (Diptera: Tephritidae) in Washington State

The diurnal and seasonal activity patterns of the western cherry fruit ßy, Rhagoletis indifferensCurran,weredeterminedon three sweet cherry trees,Prunus avium (L.), from0700 to 1900 hours during June and July 2001 in Yakima County, WA. There were signiÞcant effects of time of day and season on numbers of ßies seen on fruit relative to leaves, indicating that presence on or attraction to these substrates for feeding, mating, or oviposition, whether caused by visual or chemical cues, was greatly modiÞed by temperature. When temperatures were 15Ð16 C at 0700 hours in early June, ßies of both sexes were seen mostly on leaves, but when the temperature reached 20 C, more ßies of both sexesmovedonto fruit. Peakßy sightings occurred at 25Ð35 C,usually after 1000hours.At 35 C,most ßies vanished from view, and those seenwere less active. Over the entire season,maleswere seen four timesmore often than females and spentmore time on fruit than on leaves. Femaleswere seen equally on and spent equal time on fruit and leaves when temperatures were 20Ð35 C. Mating was initiated on fruit but was completed on fruit and leaves. Overall ßy sightings and daily temperatures were positively correlated early in the season when it was cooler, uncorrelated in the middle of the season, and negatively correlated in late season when it was warmest. The results show that R. indifferens presence and times spent on fruit and leaves are greatly altered by daily and seasonal changes in temperature, but they also suggest that at 20Ð35 C substrate-seeking behaviors of each sex do not change with time of day or season.