Does summer heat kill olive fruit fly (OLF)?

Laboratory, greenhouse, and field cage studies indicate that high summer temperatures in parts of the Central Valley can kill olive fruit fly eggs, first instar larvae and adults. OLF eggs exposed to temperatures of 100 F and higher for three days or more will not hatch. First instar larvae within fruit exposed to similar high temperatures take about 10 days to die, but some (about 10 percent) may survive the high temperatures.

OLF adults that have plenty of water and food (e.g., honeydew) can withstand long periods of high temperatures (100 F and greater). However, flies that are unable to obtain both food and water can die within five days time if temperatures remain high. Work is underway to understand what proportion of the OLF population is unable to find food and water during hot periods. Control of black scale populations via cultural controls may deprive OLF adults of food (i.e., honeydew) needed to survive the hot periods.

Should GF-120 treatments be halted during hot periods?

Presently, we are unable to accurately predict whether high summer temperatures will kill enough flies to eliminate the need for bait spray treatments during the summer. Based on analysis of climatic maps, it is apparent that periods of high summer heat (e.g., 100 F or greater for three to five days in length) vary dramatically within and between the San Joaquin and Sacramento Valleys. Behavioral observations also show that OLF adult behavior changes at temperatures greater than 95 F.

The absence of captured flies in monitoring traps during hot periods does not necessarily mean that flies have died, but may mean that flies are remaining inactive to survive the heat. Work is continuing to better understand the interaction between OLF and high temperatures. Of significant importance is the necessity of protecting the olive crop when temperatures decline in the latter part of August and early September and beyond. Flies that survive the high temperatures will return to their normal activity when temperatures decrease. This decline will happen at different times within the Central Valley.