Documenting potential sunn hemp (Crotallaria juncea L.)(Fabaceae) pollinators in Florida

Authors: Meagher, Robert - Rob; WATROUS, KRISTAL - University Of California; FLEISCHER, SHELBY - Pennsylvania State University; Nagoshi, Rodney; Brown, James; Bowers, Kristen; Miller, Neil; Hight, Stephen; Legaspi, Jesusa; Westbrook, John

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2018
Publication Date: 2/10/2019
Citation: Meagher Jr, R.L., Watrous, K., Fleischer, S., Nagoshi, R.N., Brown, J.T., Bowers, K.E., Miller, N.W., Hight, S.D., Legaspi, J.C., Westbrook, J.K. 2019. Documenting potential sunn hemp (Crotallaria juncea L.) (Fabaceae) pollinators in Florida. Environmental Entomology. 48(2):343-350. https://doi.org/10.1093/ee/nvy190.
DOI: https://doi.org/10.1093/ee/nvy190

Interpretive Summary: Vegetable growers in Florida generally plant cover crops on their land either before the main crop is planted or after harvest. Cover crops provide many benefits including adding nitrogen and nutrients to the soil, suppressing weeds, and reducing nematode populations. However, pest insects, such as fall armyworm, can increase their populations on some cover plant species. Researchers with USDA-ARS, Center for Medical Agricultural and Veterinary Entomology, in Gainesville and Tallahassee, Florida and Southern Plains Agricultural Research Center, College Station Texas, and colleagues at the University of California-Riverside and Pennsylvania State University, collaborated to complete a four-year study to assess potential benefits of non-traditional cover crops by comparing insect populations on two alternative cover plants, sunn hemp and cowpeas. One of the research objectives was to determine the number and species of pollinating bees that were attracted to sunn hemp or cowpeas. It was found that sunn hemp produces flowers early in the season, attracted several pollinators in large numbers and provided food and habitat for many species of pollinators for the whole growing season. These finding suggest that the use of sunn hemp as an alternative cover crop would not only provide soil nitrogenation along with weed and nematode suppression but also provide an improved reservoir for pollinators.

Technical Abstract: Sunn hemp, Crotalaria juncea L., is a warm-season legume that is planted before or after a vegetable cash crop to add nutrients and organic matter to the soils, for weed growth prevention, and to suppress nematode populations. Sunn hemp flowers also provide nectar and pollen for pollinators and enhance biological control by furnishing habitat for natural enemies. Experiments were conducted in northern and north-central Florida to compare bee populations within plots of different cover crop plants, including sunn hemp, sorghum-sudangrass (Sorghum bicolor (L.) Moench), and cowpea (Vigna unguiculata (L.) Walpers spp. unguiculata). Over 200 bees in 14 species and over 700 bees in 15 species collected in pan (bee bowls) and blue vane traps, respectively, with equal numbers among cover plant plots, but many species were not visitors to sunn hemp. A sunn hemp cultivar that was developed in the southeastern U.S. flowered from May through November and provided an opportunity to determine which bees were pollinating the flowers. Collections of bees that visited ‘AU Golden’ flowers indicated that Xylocopa virginica (L.), X. micans Lepeletier, Megachile sculpturalis Smith, M. mendica (Cresson), and M. georgica Cresson were present in large numbers in May through July and then again in October. ‘AU Golden’ sunn hemp flowers early in the season to provide food and habitat for pollinators and can produce an abundant seed crop in north and north-central Florida.