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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research » Research » Publications at this Location » Publication #378940

Research Project: Management of Diseases, Pests, and Pollinators of Horticultural Crops

Location: Southern Horticultural Research

Title: Floral Visitors to Helianthus verticillatus, a Rare Sunflower Species in the Southern United States

item STRANGE, NICOLAS - University Of Tennessee
item MOULTON, JOHN - University Of Tennessee
item BERNARD, ERNEST - University Of Tennessee
item KLINGEMAN, WILLIAM - University Of Tennessee
item Sampson, Blair
item TRIGIANO, ROBERT - University Of Tennessee

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2020
Publication Date: 11/2/2020
Citation: Strange, N.C., Moulton, J.K., Bernard, E.C., Klingeman, W.E., Sampson, B.J., Trigiano, R.N. 2020. Floral Visitors to Helianthus verticillatus, a Rare Sunflower Species in the Southern United States. HortScience. 55(12):1980–1986.

Interpretive Summary: The whorled sunflower is a visually attractive but endangered plant found only in the southeastern United States. Insects are believed to be critical for this plant’s pollination and survival. However, surveys are needed to identify the most important pollinating insects of the whorled sunflower. During this study, surveys of wild sunflower habitat and molecular techniques identified 36 species of visitors including 25 species of bees and wasps, 7 species of flies, a butterfly, and a moth. Pollinator counts, as well as pollen counts on their bodies, coupled with subsequent pollen DNA analysis confirmed that the most effective pollinators of the whorled sunflower were abundant bumble bees, small carpenter bees and sweat bees.

Technical Abstract: Helianthus verticillatus Small (whorled sunflower) is a federally endangered plant species found only in the southeastern United States. This species has potential horticultural value. Evidence suggests that H. verticillatus is self-incompatible and reliant on insect pollination for seed production. However, the identity of probable pollinators is unknown. Floral visitors were collected and identified during September of 2017 and 2018. Thirty-six species of visitors, including 25 hymenopterans, 7 dipterans, 2 lepidopterans, and 2 other insect species were captured during seven collection days at a site in Georgia (1 day) and two locations in Tennessee (6 days). Within a collection day (7:45 to 18:15), there were either 5 or 6 discrete half-hour collection periods when insects were captured. Insect visitor activity peaked during the 11:45-12:15 and 13:45-14:15 periods and was least during the 7:45-8:45 and 9:45-10:15 periods at all three locations. Visitors were identified to genus and/or species with morphological keys and sequences of the COX-1 mitochondrial gene. The most frequent visitors at all sites were Bombus spp. (bumblebees); Ceratina calcarata (a small carpenter bee species) and members of the halictid bee tribe Augochlorini were the second and third most common visitors at the two Tennessee locations. Helianthus pollen on visitors was identified by microscopic observations and via direct PCR of DNA using Helianthus-specific microsatellites primers. Pollen grains were collected from the ten most frequent visitors and Apis mellifera (honeybee) and counted using a hemocytometer. Based on the frequency of the insects collected across the three sites, and the mean number of pollen grains carried on the body of the insects, Bombus spp., Halictus ligatus (a sweat bee), Agapostemon spp. and Dialictus spp. are collectively the most probable primary pollinators of H. verticillatus.