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United States Department of Agriculture

Agricultural Research Service

Research Project: Developing Ambient Almond Orchard Volatile Mixtures for NOW Bioassay Analyses

Location: Foodborne Toxin Detection and Prevention

2012 Annual Report


1a.Objectives (from AD-416):
1. Obtain three duplicate samplings of ambient almond grove volatiles via Tenax absorption. The three samplings will correlate to flight times of NOW (mid April, late June, mid September). 2. Determine the identity and relative concentrations of the major VOCs in the ambient grove bouquet via GC-MS analyses. The VOCs will be grouped as average of all three runs as well as according to flight of NOW. 3. Develop a minimum number of volatiles necessary for a corresponding synthetic blend. This blend will be utilized in these research laboratories during puff or EAG studies of NOW. 4. Make available via publication the successful volatile mixture for other researchers to utilize for NOW studies.


1b.Approach (from AD-416):
The navel orangeworm (NOW) continues to be one of the most important insect pests of almonds. In 2002, one of the twelve top research priorities in the almond industry included “develop…more refined monitoring systems for NOW” and “study methods to improve pheromone mating disruption techniques and cost effectiveness for NOW…” Additionally, one of the top educational priorities for the almond industry as “new pest management tools as they become available”.1 Statements and plans such as these underscore the need to address the problems associated with NOW for almonds. Research on attractants for NOW monitoring and lure and trap purposes has not yet yielded a commercially viable and dependable product.2 In the laboratory setting, NOW puff (a volatile sample passed across the insect) or electroantennogram (EAG) studies typically utilize laboratory ambient air as the background volatile. This presents the problem that ambient laboratory air is not providing an appropriate bouquet of VOCs that would normally be perceived by the NOW in an almond grove environment. Consequently, any potential VOC puff the NOW receives from researchers may not elicit an appropriate response due to the absence of typical “grove” volatiles, thus researchers may be missing key signals from the NOW. Although the non-quantified VOC make-up of almond groves has been reported,3 and the VOC composition of removed almonds has been investigated,4 the specific, quantified, ambient almond grove VOC composition has not been investigated. This proposed research will provide current and future NOW bioassay investigations with a quantified analysis of ambient almond grove volatiles, thus offering a realistic VOC composition as the background effluent to test potential NOW attractants. Formerly 5325-42000-036-06T (May, 2011).


3.Progress Report:

This project had three objectives: to collect and identify ambient volatile emissions (odors) of almond orchards over the course of a growing season; to develop a synthetic blend that mimics the primary orchard odor components for laboratory-based bioassays; and, to develop an agricultural adjuvant, or additive, that could be used to enhance existing navel orangeworm trapping and mating disruption. This project is contributing to the overarching goal of the parent project.

The navel orangeworm (NOW) is an insect pest of California tree nuts. Its feeding damage lowers nut kernel quality resulting in extensive monetary loss to growers, producers, and shippers. Moreover, NOW feeding damage directly contributes to aflatoxin contamination. Aflatoxins are mycotoxins produced by Aspergillus flavus and A. parasiticus, ubiquitous fungi in tree nut orchards, and represent a grave food safety problem due to their carcinogenic and teratogenic attributes. There are numerous reports in the literature on both volatile and non-volatile composition of various parts of some almond cultivars. Until recently, the volatile emission of almond and pistachio orchards has not been studied over the course of an entire growing season. This aspect is particularly relevant to research concerning NOW and the identification of any associated and relevant semiochemicals.

The discovery of an efficacious attractant for NOW monitoring/trapping has remained elusive despite breakthroughs with the pheromone, the pheromone blend, long-chain fatty acids, use of almond meal, or caged virgin female NOW. The ability of an insect to locate the desired host plant is in part dependent upon its ability to detect a specific volatile semiochemical (kairomone). As with the complex blend of NOW pheromone noted by Leal et al., a complex mixture of ubiquitous plant volatiles may be necessary to elicit an appropriate response from the insect to the host-plant. Recent investigations of in situ ambient almond emission and corresponding NOW electroantennographic (EAG) bioassays suggested possible kairomonal-type behaviour from several of the collected volatiles. To further explore the presence and role of these ambient volatiles from tree nut orchards, an optimized large-scale ambient orchard volatile collection system was implemented in the 2010 growing season and at varying phenological stages of almond growth. The results from the exploratory 2008 and subsequent 2009 study have been reported. The third year of this project focused on the completion of data analysis of the 2010 volatile collections, their quantification, and associated EAG studies. The fourth and final year of this project entailed evaluation of the blend via EAG and collaborative field trapping studies and comparison to almond meal, the current NOW monitoring standard. Formulations of host plant volatiles from varying almond sources provided a blend (denoted host plant volatile blend) for the season-long field trapping study. The full report of the blend composition and results from the EAG field trapping studies will be provided in an upcoming peer-reviewed journal article. The overall number of NOW captures are the average of five two-week trapping intervals performed in Kern County and are comprised of both male and female adult moths. The host plant volatile blend was able to attract significantly more female NOW moths than the current standard, almond meal. Additionally, the ability of the host plant volatile blend to attract male NOW may have positive implications for monitoring of NOW populations during mating disruption treatments. The volatiles in the host plant volatile blend currently undergoing optimization were comprised of almond hull split and damage volatiles. However, the collection system devised, optimized, and used for the ambient almond orchard volatile project played a significant role in the collection of the volatiles for the host plant volatile blend. Additionally, ambient volatile components are still undergoing investigations for use as a background blend that can be used in conjunction with other NOW attractants. A comprehensive EAG overview of all almond volatiles collected by these laboratories is being conducted and will be reported in the coming months. The progress made in this research will lead to improved NOW control and, thus, lessen the threat of aflatoxin contamination.


Last Modified: 7/28/2014
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