Location: Temperate Tree Fruit and Vegetable Research
Project Number: 2092-22430-003-055-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Mar 1, 2023
End Date: Feb 28, 2025
Objective:
Objective 1: Determine efficacy of existing semiochemicals and trap types for Greater Banded Hornets (GBH). Current GBH survey methods in Guam are utilizing traps baited with orange juice and rice wine, which has been reported to attract other Vespa species. Unfortunately, this generic bait has not been effective for GBH in Guam, and it can attract other insects, resulting in large numbers of unwanted bycatch such as fruit flies or native insects. This one-year project will take advantage of existing research on known vespid attractants and traps and will incorporate semiochemicals identified from hornet food sources to jump start research into effective lures for GBH. This objective will be completed by the end of the project, although additional surveys may be conducted in following years to improve lure and trap efficacy.
Objective 2: Collect, isolate, and identification of putative pheromones. In parallel to the trapping study, an initial study to identify pheromones of GBH will be conducted. There are three categories of pheromones that should be investigated to create species-specific pheromone lures: alarm pheromone (used to recruit workers to assist with attacking/stinging an identified threat), marking pheromone (used to recruit workers for an attack on nests of prey insects), and queen pheromone (used to attract males from other nests to mate). We will conduct “proof of concept” field bioassays with dissected venom glands and swabbed gland samples to demonstrate the attractiveness of queen and alarm pheromones to conspecifics. Preliminary chemical analyses on the pheromone sources will be done to identify structures of the putative pheromones. ARS researchers are currently working on the identifications of the alarm and marking pheromones for NGH, which could help expedite the discovery of GBH pheromones if both species use the same or similar compounds. The information obtained from this objective will also serve as preliminary data to help develop new species-specific lures, thus providing another tool for GBH management.
Approach:
Experimental Design for Field Tests: There will a total of 12 treatments, which includes two trap types and six different lures (2 traps x 6 lures). The six lures are: 1) isobutanol + acetic acid (IBAA); 2) 2-methyl butanol + acetic acid “2MBAA”; 3) heptyl butyrate + acetic acid “HBAA”; 4) “honey bee volatiles”; 5) “vespid volatiles”; and 6) “bacteria volatiles”. The traps that will be used are modified 2 L green plastic bottles and modified Unitraps. Field tests will be conducted at 20 apiaries around the island, and they will be divided evenly based on trap type. Therefore, all sites will test the 6 different lures, but 10 sites will have bottle traps and the other 10 sites will have Unitraps. At each site, traps will be placed 10-15 m apart and will be checked 1x/week during the GBH active season. During the weekly trap checks, the traps will be rotated one position to prevent locational effects and lures will be replaced biweekly for season long studies. Each site will be considered a spatial replicate for each trap type, and each trap check will be considered a temporal replicate. Data will be analyzed using a generalized mixed model by comparing the average number of hornets trapped per treatment replicate using treatment and date (trap checks) as a fixed effect.
Preliminary Pheromone Identification: Queen and worker hornets will be collected in Guam and immediately frozen until needed for field trials or chemical analyses. Insect material, both dissected venom sacs and whole insects, will be shipped to Washington state for chemical analyses.
Chemical Analyses: Solid Phase Microextraction (SPME) will be used to both collect volatiles from venom glands (Cheng et al., 2017; Ono et al., 2003) and to sample compounds from the surface of intersegmental sternal glands, which are known to contain queen sex pheromones (Dong et al., 2022; Wen et al., 2017) and “marking” pheromones from workers (Mattila et al., 2022a; Mattila et al., 2022b; Ono et al., 1995; Ono et al., 2003). All samples collected with SPME fibers will be analyzed using Gas Chromatography – Mass Spectrometry (GC-MS) and compounds will be identified by comparison of their mass spectra with those reported in electronic libraries (NIST) and by checking their mass spectra and retention times against those of authentic standards. Samples from queen and worker hornets will also be examined for chemical differences. We will also conduct “proof of concept” field bioassays with dissected venom glands and swabbed gland samples to demonstrate the attractiveness of queen and alarm pheromones when a nest is located. This will be assessed using time lapse cameras.
