Pollen loads of insects caught in cultivated fields of oilseed pennycress

Authors: FORCELLA, FRANK - Retired ARS Employee; SHEIK, ELLINOR - Vassar College; ZAVADA, MICHAEL - University Of Minnesota; Bernards, Mark

Submitted to: Great Lakes Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pennycress (Thlaspi arvense) is being domesticated from a weed to be used as an oilseed crop. It is anticipated that it will be planted in the fall, after corn or wheat, forming a rosette that will cover the soil over the winter. In the early spring pennycress begins growing rapidly and flowers near the time when many pollinators begin foraging for pollen and nectar. Understanding what insects use pennycress resources and how they interact with the other insects present among the flowers is important for developing appropriate management recommendations for pennycress and crops that will follow pennycress. We showed that there are many different insects that forage for pollen and nectar in pennycress flowers including bees, flies, bugs, and moths. Bee species carried more pennycress pollen on their bodies than flies, but flies were present in much greater numbers. Both bees and flies will play an important role in moving pollen. In addition, some of the flies, bugs, and moths carrying pennycress pollen on their bodies are potential pests of pennycress and crops likely to follow pennycress, e.g., soybean, dry bean, sunflower. However, there were also bees and flies that are predators of some of the potential pests organisms, suggesting a rich ecological interaction among insect species within a pennycress crop canopy. This data will be used by agronomists and farmers to develop appropriate integrated pest management recommendations for pennycress and the crops that follow it in a rotation.

Technical Abstract: During early spring of 2024, insects associated with floral canopies of oilseed pennycress (Thlaspi arvense L.) in Illinois and Minnesota were captured in sweep nets, frozen, sorted by species, and sonicated to remove pollen. Pollen was counted, and pollen loads per individual insect calculated. Although Diptera, Hemiptera, and Hymenoptera accounted for 66%, 16%, and 14% of the 850 insects examined, these same taxonomic orders were responsible for 18%, 3%, and 78%, respectively, of the total pollen load of nearly a quarter million pollen grains. Insects carrying > 1000 pollen grains per adult included the hymenopterans Apis mellifera (Apidae), Halictus confusus, H. rubicundus, Lasioglossum pruinosum (all Halictidae), and Andrena sp. (Andrenidae); as well as the dipterans Dolichopus sp. (Dolichopidae), Eristalis tenax, and Eupeodes americanus (both Syrphidae). Additionally, several insect species carried moderate pollen loads. Included in this group of possible pollinators were several parasitoids (e.g., Diadegma insulare, Hymenoptera: Ishneumonidae), predators (e.g., Toxomerus marginatus, Diptera: Syrphidae), as well as crop pests (e.g., Delia platura, Diptera: Anthomyiidae), which suggests that the flowering canopy of pennycress is a complex floral ecosystem with a wide variety of potential pollinators and associated ecological interactions.