High summer temperatures affect the survival and reproduction of olive fruit fly (Diptera: Tephritidae)

The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is an invasive pest in California. Identifying environmental constraints that affect the geographic distribution and abundance of any invasive insect pest is fundamental to its effective management. California's Central Valley, where most commercial olives are grown, is extremely hot during the summer, with maximum daily temperatures consistently >35.0 degrees C. This study examined the effects of two diurnal temperature regimens (low 18.3 degrees C, high 35.0 or 37.8 degrees C) reflecting summer conditions in the valley, and one control temperature regimen (low 18.3 degrees C, high 23.9 degrees C) on the fly's survival and reproductive success in the laboratory. The temperature regimen of 18.3-35.0 degrees C resulted in delayed egg maturation and reduced production of mature eggs compared with the control temperature regimen. Egg maturation was possible at the higher temperature regimen when females were provided with water and food, and egg-laying occurred during the cold phase of the temperature cycle. Access to olive fruit and oviposition itself further promoted egg maturation. Under exposure to the 18.3-35.0 degrees C temperature regimen, approximately 50% of eggs died, and the remainder that hatched died as first instars. No egg hatch occurred at the temperature treatment of 18.3-37.8 degrees C. We confirmed these laboratory results through field cage studies with adult B. oleae, conducted in the summer of 2007 and 2008. Under ambient summer temperatures, adult B. oleae survived for 1-2 wk, and females readily laid eggs when provided water and food. No offspring developed in midsummer of 2007, and <2% of the offspring developed to adults in summer 2008 trials. These results suggest that high summer temperatures limit the fly's abundance in California's Central Valley.