Assessing the impact of pest monitoring traps on Bombus griseocollis (Hymenoptera: Apidae) colony growth and development

Study Extent

This study was conducted in corn (Zea mays Linnaeus) fields in Cache and Box Elder counties in northern Utah in 2020 and 2021. Corn fields were selected following U.S. Department of Agricultural, Animal and Plant Health Inspection Service (USDA APHIS) approved methods for H. armigera pest surveillance (CAPS 2022). The four treatments occurred with five randomized replicates in 2020 (n = 20) and four in 2021 (n = 16) (N = 36). For treatments i-iii, two multi-colored bucket traps (International Pheromone Systems, Cheshire, United Kingdom) were placed in each field 5 m and 100 m away from the Bombus colony and 1.5 m above the ground. A single pheromone lure for H. armigera was placed within the lure basket of the trap canopy for treatments ii and iii. An insecticide strip (Hercon Vaportape II: 10% dimethyl 2,2-dichlorovinyl phosphate, Hercon Environmental Corportation, Emigsville, PA) and a small, cellulose sponge were placed inside each bucket to kill the captured insects and absorb rainwater, respectively. Insecticide strips and H. armigera pheromone lures were changed every 28 days throughout the collection period following USDA APHIS approved methods for pest surveillance (CAPS 2022). Trap contents were collected biweekly (treatments i–iii), and colony-only fields (treatment iv) were net surveyed (36-cm diameter insect net, Bioquip, Compton, CA) over a ten-minute time period both 5 and 100 m away from the colony to survey the resident Bombus community and identify B. griseocollis collected from the released colony while foraging.

Sampling

Colonies were monitored weekly from the time of deployment until September each year. Each week, the nest was weighed to the nearest gram and the number of workers entering and exiting the nest was recorded over a 10-minute time interval. Data collections occurred between 9:00 a.m. and 6:00 p.m. to comply with land and homeowner restrictions. This resulted in the concern that colony weights may be underestimated since workers forage during this time. Therefore, colonies were also weighed in the evening (between 7:00 and 9:00 pm) in 2020, and we found no significant difference in daytime vs. nighttime weights. All collected specimens were stored in a freezer (-18˚C) until they were pin-mounted, labeled, and identified to species. All captured female B. griseocollis were then subjected to DNA extraction and microsatellite PCR amplification.

Method steps

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1. Apidae
   rank: family
2. Hymenoptera
   rank: order
3. Bombus
   rank: genus