1a. Objectives (from AD-416):
Determine the associations of navel orangeworm (NOW) (flight, oviposition, wounding of nuts by larvae and adult moths) with aflatoxigenic fungi Aspergillus flavus and A. parasiticus. Also determine the ability of NOW to vector propagules of A. flavus/A. parasiticus, when nuts become susceptible to infestation by NOW, and compare the vectored fungi with those producing aflatoxins in nuts.
1b. Approach (from AD-416):
Larvae and pupae from nut mummies from the trees and the ground and NOW moths will be collected periodically from commercial pistachio and almond orchards and the insects plated on specific media to determine the levels of contamination. Strains of A. flavus/A. parasiticus isolated from NOW will be compared with those isolated from infected nuts. Pea size and crinkled pistachio (NOW-damaged and non-damaged, stained, and not stained) will be plated periodically to determine their infection by Aspergillus spp. To determine when nuts become susceptible to NOW, we will periodically bag pistachio clusters and almonds with NOW. All the isolates of S, L, and M strains of A. flavus and A. parasiticus will be identified based on previously published research.
3. Progress Report:
This Specific Cooperative Agreement was established to support Objective 1A of the in-house project and is related to the management of navel orangeworm in tree nut crops. Navel orangeworm is a destructive pest of almonds and pistachios and creates damage not only by directly feeding on the nuts, but by facilitating contamination of almonds and pistachios by the fungi Aspergillus flavus and Aspergillus parasticus, which produce aflatoxins. These studies demonstrated the capability of navel orangeworm to transmit these fungi to nuts as well as transport the fungus into the tree canopy. A University of California Davis scientist in collaboration with an ARS scientist at Parlier collected navel orangeworm male moths from virgin female baited traps and plated these adults on specific media to determine the levels of contamination by Aspergillus flavus and Aspergillus parasiticus, producers of aflatoxins. The prevalence of Aspergillus species varied over time, and was highest in adults emerging from mummy nuts and lowest in adults collected in late June and early July. Companion studies in the laboratory confirmed that the navel orangeworm could serve as a vector for these fungi when larvae tunneled into tree nuts. Additional studies were conducted to demonstrate that culturing navel orangeworm male moths for Aspergillus fungi was a viable method to estimate its prevalence. This information was used to support registration of a new product to suppress the Aspergillus species that produce aflatoxins. This new product, AF36, was applied to more than 75,000 acres this past Spring.