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Funded Project
Funding Program: Enhancement Grants - Special Projects
Project Title: Pheromone Preferences of Distinct Pecan Nut Casebearer Populations in North America
Project Directors (PDs):
Raul Francisco Medina [1]
Marvin Harris [2]
Lead State: TX

Lead Organization: Texas Agrilife Research
Cooperating State(s): Wyoming
Funding: $24,899
Start Date: May-01-2009

End Date: Apr-30-2010
Pests Involved: Pecan nut casebearer
Site/Commodity: Pecan
Area of Emphasis: Pest pheromones
Summary: Acrobasis nuxvorella is the most damaging pest of pecan. Early season management of this key pest prevents losses of ca. $30 million/yr. 33-56% of the insecticides used in the Southern Region of the US target this pest. Pheromone monitoring and sequential sampling are currently used to assess insecticide treatment needs. Reducing insecticide use is essential for conserving natural enemies of foliar pecan pests and for reducing environmental pollution. Allopatric populations of A. nuxvorella have been recently discovered by our laboratory using neutral molecular markers and synthetic pheromone blends. One of these populations has a Mexican distribution while two other distinct populations are distributed in the southern US. The presence of distinct A. nuxvorella populations poses a potential threat to pecan management. Our molecular data suggests that the Mexican A. nuxvorella is attracted to one pheromone blend only while the US A. nuxvorella is attracted to both of the blends currently used. The existence of populations non-responsive to current pheromone monitoring and presumably oblivious to direct pheromone management strategies jeopardizes existing pecan IPM programs and complicates implementation of pheromone based technologies to manage A. nuxvorella. The proposed work will use olfactometric tests and two synthetic A. nuxvorella pheromones to assess pheromone preferences of A. nuxvorella in the US and in Mexico. Completion of the proposed work will provide pecan producers with knowledge to improve A. nuxvorella monitoring methods minimizing insecticide use for this pest.

Objectives: Objective 1:
To assess the consistency of pheromone preferences of male Acrobasis nuxvorella in the US and in Mexico.

This objective will increase our understanding of the response of A. nuxvorella to each of the synthetic pheromone blends available by allowing male A. nuxvorella to choose multiple times between the two available pheromone blends. What we currently know about the response of A. nuxvorella to the two pheromone blends is based on pheromone trapping which only tells us that the male is responsive to the pheromone with which it was trapped. It is known that A. nuxvorella will mate multiple times. Testing a male multiple times in an olfactometer will allow us to determine how A. nuxvorella will behave when given multiple opportunities to choose a pheromone blend as is the case in their natural setting. Preliminary data gathered in our laboratory suggests that adult males from Mexican populations are attracted to the Mexican pheromone only while in the US catches are obtained using the Mexican as well as the standard pheromone. Objective 1 will allow us to test if Mexican A. nuxvorella are attracted to the Mexican pheromone only (as suggested by preliminary molecular data) and to determine if the US population is composed of A. nuxvorella males that differ in their preference for one pheromone over the other, or if each individual in the population is equally attracted to both pheromone blends. Learning more about male responses to pheromone blends will lead to more efficient A. nuxvorella monitoring and to the successful implementation of mating disruption or other pheromone-based control programs for A. nuxvorella.

Objective 2:
To determine if there are more than two pheromone blends produced by Acrobasis nuxvorella.

This objective will utilize AFLP markers to assess the possibility of the presence of more than two pheromone blends produced by A. nuxvorella. By extracting the DNA from males that are used for olfactometric testing, and developing AFLP markers we will be able to compare the genotypes of individuals that do not show a response to either the Mexican or standard pheromone blends with those that do show a response. If genetic differences correlate with distinct male behaviors in the olfactometer, further investigation will be needed to determine if there are in fact more pheromone blends produced. The possibility of more than two pheromone blends needs to be addressed in order to implement successful pheromone based control methods. If more than two pheromone blends exist, only a fraction of the A. nuxvorella population would be managed using the currently available pheromones and extensive damage to pecan nuts could still occur.

Final Report:

Our results indicate that in the laboratory, pecan nut case bearer do not show any preference for the standard or Mexican pheromone. No differences in behavior were observed between the US and the Mexican PNC strain. In both groups no preference for any of the blends was observed in the laboratory. My undergraduate student involved with this project, Erin Spence, presented our results in a poster at the Entomological Society of America Annual Meeting in Indianapolis in 2009.
We found that the two characterized geographic populations of the pecan nut case bearer (i.e., the Mexican and the US population) show no differences in attraction to any of the two pheromone blends we used (i.e., standard and Mexican pheromone) in the laboratory. Hypothesis to explain why no differences in attraction are observed in the laboratory while strong differences in attraction are observed in the field have been generated.
Potential Impacts
This project will contribute to improve the IPM of pecan nut case bearer through a better understanding of the population genetics and behavior of the pecan nut case bearer. Knowledge on behavioral differences associated with pheromones, between field and laboratory populations will aid in the future implementation of control measurements using pheromones in pecan nut case bearer IPM
Leveraged Funds
Funds from a previous USDA Southern Region IP grant were used to establish the existence of geographically distinct populations of pecan nut case bearer.
Report Appendices

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