1a. Objectives (from AD-416):
1) Characterize seasonal abundance of navel orangeworm in southern Central Valley walnuts, and compare these data with codling moth abundance and walnut infestation by these two pests. 2) Estimate the relative contribution of residents and immigrants to navel orangeworm populations in orchards in this region. 3) Examine the impact of mating disruption on reproduction and damage of navel orangeworm in the southern Central Valley.
1b. Approach (from AD-416):
For objectives 1 & 2, female-baited and oviposition traps will be used to compare abundance of navel orangeworm males and eggs, respectively, between the center and edges of walnut orchards with historically high damage, and also to compare these codling moth and navel orangeworm abundance with infestation by these pests in harvest samples. For objective 3, mating disruption for navel orangeworm will be applied to orchard with historically high damage. Impact of mating disruption will be assessed based on the ability of males to locate live females in traps, oviposition by females, and infestation at harvest by navle orangeworm and codling moth.
3. Progress Report:
Progress was made to support objective 2F (Determine abundance and evaluate monitoring methods for navel orangeworm in walnuts) in the parent project. The navel orangeworm is considered the principal insect pest of almonds and pistachios in California, but generally of secondary importance in walnuts. In the former nut crops, however, there is a gradient of navel orangeworm abundance and damage, with less damage in the north and more to the south. Efficacy of mating disruption for navel orangeworm has been demonstrated in almonds, but separate examination of mating disruption in walnuts is important due to a very different canopy structure compared to walnuts. In 2012 abundance of navel orangeworm was examined in walnuts in the southern portion of the California growing area, and the impact of mating disruption on navel orangeworm in this crop was assessed. Traps with unmated females as a pheromone source found cohort structures of male abundance similar to those observed in almonds. Extensive arrays of egg traps contained many eggs during first flight, but few during subsequent flights. Comparison of males in pheromone traps with distance to other tree nut crops, and spatial analysis of egg trap captures in a walnut site adjacent to almonds suggest that year-round navel orangeworm abundance at these sites is not due principally to immigration from other crops. Biological impact of mating disruption was demonstrated; i.e., near-complete suppression of males captured in female-baited traps and significant reduction of eggs in egg traps, demonstrating both disruption of sexual communication and impact on fertility. Insect damage at harvest was >10% in some cases. The impact of mating disruption on this harvest damage was less clear than the biological impact, although this was also true of grower standard insecticide treatments in the absence of mating disruption. Comparison of seasonal abundance of navel orangeworm and codling moth suggests some commonly-used insecticide timings for codling moth can also reduce navel orangeworm populations, while other codling moth insecticide timings are likely to be less effective for navel orangeworm. Similar data are being collected in the 2013 growing season.