Flowers of Black-Seeded and Yellow-Seeded Oilseed Pennycress (Thlaspi arvense): Abundance, Timing, and Potential Insect Visitors

Pennycress is being developed in the Midwestern USA as a new oilseed crop that provides numerous ecosystem services. These services include being an early spring source of pollen and nectar for flower-visiting insects. Most past research on pennycress flower visitors used wild genotypes of pennycress. All wild genotypes have seed coats that are black, which occurs because of high levels of proanthocyanadins (PACs). Concentrations of PACs are minimal in newly developed genotypes with yellow-colored seed coats. However, little is known regarding flower abundance and timing nor insect visitation preferences for black-seeded genotypes (BSG) or yellow-seeded genotypes (YSG) of pennycress. Flower densities were recorded and pan traps were deployed weekly during pennycress flowering at nine site-years in Illinois and Minnesota to examine anthesis and insect preferences for BSG vs. YSG pennycress. BSG and YSG flowered simultaneously, responded similarly to post-sowing growing degree days (peaking at 700 GDD4°C), and produced comparable numbers of open flowers (up to 10,000 m-2) on any given day, although BSG produced significantly greater numbers of cumulative flowers over the course of anthesis in three of nine site-years. Overall, the percentages of all trapped insects comprised of differing taxonomic orders were as follows: Diptera (flies) 33-37%, Thysanoptera (thrips) 27-30%, Hymenoptera (bees and wasps) 13-20%, Hemiptera (true bugs) 7-8%, Coleoptera (beetles) 5-6%, and Lepidoptera (butterflies and moths) 1-3%. Generally, there were no significant differences in the relative abundance of insects found in YSG versus BSG pennycress across site-years. Occasionally, however, pan traps in BSG pennycress contained more insects, which mainly was due to high Dipteran populations. These results suggest that genetic selections for yellow seed coats (with low PACs) will have little impact on flower abundance and attractiveness to most insect visitors.