Fall application of Metarhizium brunneum microsclerotia as soil applied granules to reduce summer emergence of walnut husk maggot adults

Rhagoletis fruit flies damage many fruit and nut crops, and the Sauvis group in this genus includes pests of walnuts in the Americas.  The walnut husk maggot, Rhagoletis sauvis (Loew) (Diptera:  Tephritidae) causes damage to walnuts when the maggots feed inside the husk around developing nuts.  The adult stage is most susceptible to chemical control by applications of insecticides during summer months before oviposition in the walnut husk.  To evaluate a biological control strategy, granules laced with microsclerotia of the entomopathogenic fungi Metarhizium brunneum F52 were applied to the soil during September to target mature larvae as they leave the fallen nut to pupate in the soil.  The treatment was evaluated for pest control based on adult emergence during the following summer.  September applications generally reduced the number of flies emerging from treated plots by 35% when compared with untreated plots in each of two years.  Thus, this biological control strategy may contribute to integrated control of this pest and potentially to related pests with similar life cycles.