Pollen Loads of Insects Caught in Cultivated Fields of Oilseed Pennycress

Although many insects are known to be associated with the floral canopies of oilseed pennycress (Thlaspi arvense L., Brassicaceae), those that carry the crop’s pollen are unknown. During early spring of 2024 insects associated with pennycress flowers in Illinois and Minnesota were captured in sweep nets, frozen, sorted by species, and sonicated to remove pollen. Pollen grains were counted, and pollen loads per individual insect were calculated. Members of the orders Diptera, Hemiptera, and Hymenoptera accounted for 66%, 16%, and 14% of the 850 insects examined, but these same orders were responsible, respectively, for 18%, 3%, and 78% of the total pollen load of nearly a quarter of a million pollen grains. Insects carrying > 1000 pollen grains per adult included the bees (Hymenoptera) Apis mellifera (Apidae), Andrena cressonii (Andrenidae), Halictus confusus, H. rubicundus, and Lasioglossum pruinosum (Halictidae); as well as the flies Dolichopus sp. (Dolichopodidae), Eristalis tenax and Eupeodes americanus (Syrphidae). Additionally, several insect species carried modest pollen loads (50–500 grains per individual), including parasitoids (e.g., Diadegma insulare, Hymenoptera: Ichneumonidae), predators (e.g., Toxomerus marginatus, Diptera: Syrphidae), as well as crop pests (e.g., Delia platura, Diptera: Anthomyiidae). This suggests that the flowering canopy of pennycress is a diverse floral ecosystem with many potential insect pollinators and an array of associated ecological interactions.