Diapause, climate, or generation gap: determining the causes of the summer disappearance of adult olive fruit flies (Bactrocera oleae) in California populations

Olive fruit fly (Bactrocera oleae) is a major pest of olives grown in many parts of the world.  It was first detected in California in 1998 and is now an established pest. In Mediterranean climates, a cessation of adult activity and lack of ovarian maturation occurs mid-summer. The purpose of this study is to elucidate the underlying causes of this summer inactivity in the Central Valley of California. We investigated three potential causes: (1) temperature and humidity, (2) generational cycles, and (3) physiological diapause. We monitored adult activity June-October 2015 using baited McPhail Traps placed in an ornamental olive planting on the University of California: Davis campus (Yolo Co., CA). We used HOBO DataLoggers to record fluctuations in temperature and relative humidity. Live flies were also collected three times a week, along with infested olives from July-October, and reared in an incubator at 25 º C with a 12:12 light:dark cycle. We measured the duration of the remainder of wild-caught and laboratory-raised adults’ lifespans to determine population age structure.