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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Molecular and Pheromone Studies of Acrobasis nuxvorella Neunzig (Lepidoptera: Pyralidae) to Improve Pecan IPM

Project Directors (PDs): Raul Francisco Medina [1] Marvin Harris [2]

Lead State: TX Lead Organization: Texas A&M University

Research Funding: $81,107

Start Date: Apr-01-2007 End Date: Mar-31-2009

Pests Involved: Pecan Nut Casebearer

Site/Commodity: Pecans

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. A putative cryptic strain of A. nuxvorella (recently discovered using a new pheromone construct) poses a major threat to pecan. Preliminary data indicate that the two known A. nuxvorella strains are sympatric and have similar phenologies and damage characteristics. Monitoring of A. nuxvorella in the US uses a pheromone that is recognized only by one of the strains. The existence of a strain nonresponsive 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 AFLP markers and a newly synthesized pheromone to: 1) assess the relative ratio of the two strains across the US Southern Region; 2) correlate A. nuxvorella trapped by the two kinds of pheromones with pecan damage; 3) establish if the two strains are reproductively isolated and; 4) assess the population structure of each of the strains. Completion of the proposed work will provide pecan producers with improved methods to monitor A. nuxvorella populations minimizing insecticide use for this pest. Objectives: Objective 1. To determine the relative occurrences of the Mexican strain and the US strain of A. nuxvorella in the Southern Region of the US and to investigate the correlation of trapped moth density with nutlet damage. Impact: Preliminary field studies in Texas, Georgia, and Oklahoma have indicated the presence of the Mexican A. nuxvorella strain in these states. Current pheromone monitoring only employs the US pheromone and thus underestimates densities where both strains coexist. Knowing the relative abundances of each of the strains (i.e. US and Mexican) in pecan growing regions will allow the development of more accurate monitoring/management strategies (i.e., potential for establishing moth density/larval damage economic thresholds; provide a basis for developing direct management strategies, etc.) using pheromone technology in the Southern Region. Objective 2. To establish if A. nuxvorella pheromone strains are reproductively isolated. Impact: Morphologically identical A. nuxvorella have been found to be differentially attracted to two pheromone blends (i.e. US and Mexican pheromone). This suggests the presence of two distinct A. nuxvorella strains. Molecular markers will confirm the existence of these strains and determine if these strains are reproductively isolated. The presence of two reproductively isolated A. nuxvorella strains will explain the differential attraction to the US and Mexican pheromone blends and it will justify the inclusion of the Mexican pheromone for pecan IPM in the US. The existence of other reproductively isolated strains will be assessed by genetically characterizing A. nuxvorella collected as larvae. The existence of additional cryptic strains may indicate the existence of undiscovered pheromones blends. Objective 3. To assess population structure of A. nuxvorella strains across their geographic distribution. Impact: This objective will assess the genetic variability within each of the pheromone strains studied and it will determine if there is population structure across the geographic range of each of the pheromone strains studied. The presence or absence of population structure will provide an estimate of the level of gene flow present in each of the strains.

Final Report:

Results From report submitted by the PI to USDA CRIS report system PROGRESS: 2007/06 TO 2010/06 OUTPUTS: AFLPs have been developed. Samples have been analyzed to establish the existence of pheromone strains. The results suggested that there were geographical strains but not pheromone strains. Field data on the relative abundance of trap catches using the two different pheromone blends have been gathered and analyzed. My graduate student involved with this project was invited to present our results at a symposium entitled: Ecosystem factors and IPM: concepts and implications. Organized by Chow, A., and Ramirez, R at the Southwestern Branch Entomological Society of America Meeting in 2009. Results from this research have also been presented at the Entomological Society of America meeting in 2008 and 2009 and the Texas Pecan Growers Association annual conference in 2008. PARTICIPANTS: The present project was carried out in collaboration with several colleagues: Dr. Ted Cotrell and Dr. Jim Dutcher from Georgia; Dr. Phil Mulder from Oklahoma; Dr. Bill Reid from Kansas; Dr. Joe Ellington from New Mexico; Dr. Mike Hall from Louisiana and Dr. Russ Mizell from Florida. Within Texas, 25 producer cooperators have contributed by sending us samples. The present project has funded in part a Master student, Emilie Hartfield. TARGET AUDIENCES: Our target audience include population geneticists and ecologists as well as pecan growers that will benefit from knowing if they are dealing with pecan nut casebearer strains with differential affinities for distinct pheromone blends. This information will aid IPM practitioners in the design of more effective pheromone based control practices than the ones being currently used. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period. IMPACT: 2007/06 TO 2010/06 We have found that there are two distinct populations of the pecan nut casebearer. One occurs in Mexico and is attracted to the Mexican pheromone only while the other population occurs in the US and it is composed by individuals able to respond to both pheromone types. The results of this study have allowed us to secure additional funding to explore if in the US pecan nut casebearer individuals have the ability to respond to both pheromone types (i.e., standard and Mexican pheromones) or if instead US pecan nut casebearer populations are composed by two kinds of phenotypes: one able to respond to the standard and a different pheromone able to respond to the mexican pheromone. PUBLICATIONS (not previously reported): 2007/06 TO 2010/06 1. Hartfield, E., Harris, M., Medina, R.F. 2010. Searching for Pheromone Strains in the Pecan Nut Casebeare. Entomologia Experimentalis et Applicata. In Press. 2. Hartfield, E., Harris, M., Medina, R.F. 2010. Population structure of Acrobasis nuxvorella. Heredity. Submitted.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system We have found that there are two distinct populations of the pecan nut casebearer. One occurs in Mexico and is attracted to the Mexican pheromone only while the other population occurs in the US and it is composed by individuals able to respond to both pheromone types. The results of this study have allowed us to secure additional funding to explore if in the US pecan nut casebearer individuals have the ability to respond to both pheromone types (i.e., standard and Mexican pheromones) or if instead US pecan nut casebearer populations are composed by two kinds of phenotypes: one able to respond to the standard and a different pheromone able to respond to the mexican pheromone.

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