Date of Award:

5-1-1989

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology (Entomology)

Committee Chair(s)

Donald W. Davis

Committee

Donald W. Davis

Abstract

The navel orangeworm, Amyelois transitella (Walker), completed development in sunburned walnuts late in the growing season, but moths did not emerge until post-harvest. Only sunburned walnuts with undamaged kernels were suitable for larval development. Navel orangeworm infestation levels up to 38% were recorded in sunburned walnut samples from the San Joaquin Valley of California. Sunburned and green, undamaged walnut kernel temperatures averaged 4.1°C and 1.8°C higher, respectively, than orchard shade air temperature. Premature hullsplit occurred in sunburned walnuts of early and later maturity varieties. Development of U.S.D.A. culture navel orangeworm moths in mummy Payne walnuts required a mean of 621 degree-days (DD) (males) and 646 DD (females). Feral moths required a mean of 608 DD (males) and 62 6 DD (females). Fifty percent moth emergence occurred after a mean of 640 DD and 602 DD for U.S.D.A. and feral moths, respectively. A phenology model based on a biofix of first egg and mean DD to 3% feral moth emergence of 520 DD was fit to navel orangeworm egg trap data from commercial walnut orchards in the San Joaquin Valley. This model predicted the onset of second and third generation navel orangeworrn oviposition in orchards where distinct generations occurred. Where ovipositional activity was erratic, the model did not accurately predict the onset of major ovipositional periods. Both U.S.D.A. and feral navel orangeworm neonate larvae successfully infested pre-hullsplit walnut husk fly (Rhagoletis completa Cresson) damaged walnuts. Navel orangeworm larval development occurred in hull and kernel tissue in these nuts. Moth development was completed in walnut husk fly damaged walnuts of several commercial varieties in both coastal and San Joaquin Valley walnut orchards.

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