Walnut husk fly (Rhagoletis completa): Patterns of emergence in California

There is currently little information for growers on the environmental factors influencing the timing of the Dipteran pest Walnut Husk Fly (WHF). A preliminary phenology model for WHF was created based on 16 years of trap catch and temperature data from Red Bluff, CA and thermal constants from OR. Subsequent lab experiments showed a a correlation between rainfall and first walnut husk fly emergence. This is supported by other data that suggests emergence for some insects is related to total seasonal rainfall.  Additionally, the effects of chill time, timing of simulated rainfall and walnut cultivar on accumulated degree-day requirements for WHF were used to improve the phenology model. The estimated threshold temperatures, thermal requirements of WHF populations and monitoring of rainfall in California, can be used to finalize a model useful for walnut growers in California in order to appropriately adjust management practices and better predict the annual emergence time of walnut husk fly.