PEST-FREE PERIOD FOR WALNUT HUSK FLY (DIPTERA, TEPHRITIDAE) AND HOST STATUS OF STONE FRUITS FOR EXPORT TO NEW-ZEALAND

The pest-free period for walnut husk fly, Rhagoletis completa Cresson, that occurs from the beginning of stone fruit harvest in spring throu gh 1 July was verified by trapping for adults in walnut orchards and r oadside trees at eight locations in Merced, Madera, Fresno, Tulare, an d Kern counties in the San joaquin Valley of California. Peaches, Prun us persica (L.) Batsch; nectarines, P. persica (L.) Batsch var. nucipe rsica; Japanese plums, P. salicina Lindl.; and walnuts, Juglans regia, were evaluated for acceptability for walnut husk fly oviposition and immature development. Field choice tests resulted in the following mea n number of ovipositional sites per fruit and mean number of pupae tha t developed per ovipostional site in each fruit species: peaches and n ectarines, <1 site, <1 pupa; plums, 0 sites, 0 pupae; and walnuts, <1 site, 4.5 pupae. One- or 3-d laboratory choice tests showed that peach es and nectarines were more acceptable and plums were less acceptable than walnuts for oviposition, but survival to the pupal stage was sign ificantly lower in the three stone fruit species (<1 mean pupa per ovi positional site) than in walnuts (seven mean pupae per ovipositional s ite). Laboratory no-choice tests showed that walnut husk fly will ovip osit in the three stone fruit species and walnuts, but the mean number of pupae that developed per ovipositional site was <1 in peaches and nectarines, 0 in plums, and eight in walnuts. Our results demonstrate that peaches and nectarines are poor hosts for walnut husk fly develop ment, plums are not an acceptable host, and walnuts are the natural ho st.