The navel orange worm, Paramyelois transitella (walker), which was first found in California in 1942 has developed into It serious pest of walnuts, The insect is a scavenger, but seriously attacks sound walnuts once the husks crack as maturity, is reached, There are a number of generations each year. The insect has no diapause and passes the winter as a caterpillar. The navel orangeworm carries over from one crop to the other in walnuts on the ground or in the trees. By early summer these breeding sources are all but eliminated. At this period walnuts of the current season's crop infested with the codling moth furnish excellent breeding sites. They fill the developing gap in the food chain. Although less important than the codling moth, walnut blight, Bacterium juglandis Pierce, adds to the problem as do other factors responsible for the production of unsound walnuts. Heat and dryness are unfavorable for optimum development of the navel orange worm. An effective spray program against the pest has not been developed. However, the following practices are useful in holding a potentially destructive population below a serious economic level: Secure excellent control of the codling moth; discourage walnut blight; harvest at the earliest possible date: immediately dry the crop; fumigate crop as soon as dried; keep storage areas dry; practice orchard and plant sanitation.