Comparison of bee composition in sunn hemp and other cover crops

Authors: Meagher, Robert - Rob; WATROUS, KRISTAL - Dominican University Of California; FLEISCHER, SHELBY - Pennsylvania State University; Nagoshi, Rodney; Brown, James; Westbrook, John

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2019
Publication Date: 1/17/2021
Citation: Meagher Jr, R.L., Watrous, K., Fleischer, S., Nagoshi, R.N., Brown, J.T., Westbrook, J.K. 2021. Comparison of bee composition in sunn hemp and other cover crops. Florida Entomologist. 103(4):419-424.

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 at USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, in collaboration with scientists at USDA-ARS, SPARC, College Station, Texas, University of California-Riverside and Pennsylvania State University, completed a two-year study comparing insect populations on two alternative cover plants, sunn hemp and cowpeas. The objective of this report was to determine the species of bees that were attracted to sunn hemp and cowpeas and their population sizes. It was found that bees were collected in all cover crop plots, and that sunn hemp produces flowers that can provide food and habitat for many species of pollinators over a full growing season. The findings suggest that the use of sunn hemp would provide an important alternative cover crop that supports numerous pollinators over a full growing season.

Technical Abstract: Cover crops can be planted in rotation to cash crops to improve soils, assist in weed growth prevention, and help suppress plant pathogenic nematode populations. Experiments were conducted in northern and north-central Florida to evaluate bee populations within cover crop plants, including sunn hemp (Crotalaria juncea L.), sorghum-sudangrass [Sorghum bicolor (L.) Moench x S. bicolor var. sudanense (Piper) Stapf.], and cowpea (Vigna unguiculata (L.) Walp.). Over 200 bees in 14 species and over 700 bees in 15 species were collected in pan (bee bowls) and blue vane traps, respectively. Both sets of traps captured bees from within all cover crop plots, indicating that these bees can persist in disturbed habitats. However, fallow plots yielded significantly more bees than sorghum-sudangrass, cowpea, or sunn hemp plots. The dominant bees collected, Melissodes spp., are ground-nesting solitary bees which may have been utilizing the fallow plots in this research farm as a nesting site. Only a subset of the species composition associated with the cover crops was relevant to the pollination of sunn hemp, which requires large-bodied bees such as species of Xylocopa and Megachile.