Location: Insect Control and Cotton Disease Research
Project Number: 3091-30400-043-003-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 15, 2026
End Date: Jul 14, 2028
Objective:
The pecan nut casebearer (PNC), Acrobasis nuxvorella, is arguably the most destructive nut-infesting insect pest of pecans in the United States. Although trapping systems and effective insecticides exist to manage this pest, human safety and environmental concerns associated with insecticide applications, along with recent trap detection failures, has prompted the need to develop alternative management strategies and to determine the cause of these trap detection failures. It is generally accepted that two strains of PNC populations exist in North America - one that occurs in most parts of the United States (referred to as the U.S. strain) and the other that is present in Mexico and some southern parts of the United States (referred to as the Mexican strain). The U.S. strain is attracted to a pheromone lure comprised of a single pheromone component [(9E,11Z)-hexadecadienal], whereas a dual component lure [(9E,11Z)-hexadecadienal + (9E,11Z)-hexadecadienyl acetate] is used to attract the Mexican strain. It has been speculated that the recent trap detection failures associated with the single or dual pheromone component lures in Texas are related to the composition or distribution of the two strains. However, both the single and dual component pheromone lures attract PNCs throughout most areas of the United States, raising questions about the distribution and/or existence of two PNC strains. The long-term goals of this project are to improve detection of the PNC and to identify natural enemies that may be used to develop a biological control program. To achieve these goals, the three main objectives of this project are to: 1) identify genomic and pheromone composition differences between the two strains; 2) survey orchards throughout Texas to identify parasitoids of PNCs; and 3) confirm predation of PNC eggs and larvae by predatory hemipterans (e.g., Orius and Deraeocoris spp.).
Approach:
To address Objective 1, whole genome sequences will be obtained and compared among pecan nut casebearers (PNCs) collected from Mexico (Mexican strain) and Georgia (U.S. strain) using a PacBio Sequel II System. Reads will be assembled into a high quality, chromosome-level reference genome for each strain, and genomic differences between strains will be analyzed. Concurrently, pheromone produced by the two sources of PNCs will be analyzed by gas chromatography–mass spectrometry. PNC females from each source will be held in pheromone collection vessels, and pheromone released into the headspace of the vessels will be collected over a 24-h period. Collected pheromone will be analyzed on a Shimadzu GCMS-QP2010Ultra. For Objective 2, both the insidious flower bug (Orius insidiosus) and predatory mirids (Deraeocoris spp.) will be collected weekly between mid-April and mid-May to coincide with the first generation egg lay of PNCs in south central Texas. Hemipteran predators will be collected from four orchards – the USDA orchard in Somerville, TX, and three commercial orchards at Fentress, Comal, and Seguin, TX. Within each orchard, the lower foliage of 10 trees will be sampled with a Stihl® reverse leaf blower for 30 seconds. Captured predators from each tree will be transferred into Ziploc bags and placed in a cooler filled with ice. Upon return to a laboratory, respective predators will be surface sterilized in a 3% bleach solution for 40 minutes and then stored in 100% ethanol at -80C. Insects will be macerated individually to expose the gut contents, and DNA will be extracted using a Qiagen DNAeasy Blood and Tissue Kit followed by cleanup and PCR. DNA primers specific to the PNC will be developed based on results of the first objective, and gut samples will be analyzed for PNC DNA to confirm whether the predators fed on PNC. For Objective 3, various life stages from each generation of PNCs will be collected and observed in the laboratory for parasitoid presence/emergence. The first collection will occur prior to budbreak (February to early March) and will involve collection of at least 100 overwintering hibernacula from each orchard (same orchards used in Objective 2). For the second generation (late April and early May), at least 200 nutlets will be collected from each orchard and returned to a lab where they will be examined for PNC eggs. For the third generation and final collection, at least 100 nuts with PNC entry holes will be collected. Collected materials (hibernacula, and nuts with egg masses or PNC entry holes) will be held individually in 30-ml plastic cups and placed in an environmental chamber at 23.9 C. Materials will be observed at least every other day for parasitoid emergence. For years 1 and 2, all collected parasitoids will be stored in 70% ETOH and sent to the Texas A&M University Insect Collection facility for species identification. During year 2 of the project, efforts will also focus on collecting male and female adults of the most commonly collected parasitoids and developing protocols to rear them under laboratory conditions.