Walnut Husk Fly (Diptera: Tephritidae): Evaluation of Traps for Timing of Control Measures and for Damage Predictions

Abstract

In 2 yr of field tests in commercial walnut, Juglans regia L., orchards in northern California, an ammonium carbonate-baited fluorescent yellow Pherocon AMrectangle was approximately 10 times more attractive to adult walnut husk flies, Rhagoletis completa Cresson, than the standard Pherocon AMtrap or an unbaited green sphere during most of the season.The green sphere was not attractive in early seasonwhen husk fliesbegan to emerge but increased in attractiveness relative to the other traps as the season progressed. Once the sphere began to catch husk flies, it was as effective as the standard Pherocon AM trap. Adult flies began to respond to ammonium carbonate-baited and standard AM traps long before (42 and 44 d, respectively) females oviposited. Catches on green sphere traps, on the other hand, were closely synchronized with egg laying, becoming attractive shortly before or at the time nuts were attacked. The interval from first oviposition to harvest was the same on early- and late-maturing varieties. Cumulative catch on the ammonium carbonate- baited Pherocon AM trap was a better predictor for the infestation level at harvest than catches on the green sphere. These studies suggest that the green sphere is a better indicator for the timing of chemical treatments, whereas the ammonium carbonate-baited yellow rectangle appears to be more reliable for evaluating the damage potential of a husk fly population.