The impact of pollen and nectar availability on insect communities of cultivated sunflowers

The availability of floral rewards (i.e., pollen and nectar) influences their consumption by insects in flowering plants such as cultivated sunflowers (Helianthus annuus L.). Wild bees are attracted to sunflowers with greater nectar accessibility and pollen, although how floral rewards affect other insects is understudied. Many insect pests of sunflower heads feed on pollen as larvae and many natural enemies consume pollen and nectar in addition to prey. We established a field experiment using near-isogenic sunflower lines varying in pollen availability and lines differing in floret length (nectar accessibility) to determine how floral rewards affect visitation by pollinators and natural enemies and inhabitation by insect pests. There were four replications of six treatments: male-fertile (pollen present) with short florets, cytoplasmic male sterile (CMS, pollen absent) with short florets, male-fertile with long florets, CMS with long florets, and two control groups, one wild sunflower line and one line with extra-long florets. The insect community was sampled using clear sticky traps for small insect visitors, vial capture for larger insect visitors, destructive sampling of sunflower heads for resident pests, and floral eDNA collection by wash for the overall insect community. We expect that insect visitation and inhabitation will be greatest in the male-fertile lines with short florets. The results from this experiment will elucidate how floral rewards affect different insect functional groups and could be used to enhance pollinator-plant interactions, minimize insect pest damage, and reduce the use of pesticides through the attraction of natural enemies.