Insect pollinivores of sorghum bicolor and plant traits that influence visitation

Authors: Harris-Shultz, Karen; Armstrong, John; Knoll, Joseph - Joe; Sapkota, Suraj; CLEM, CARL - University Of Georgia

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pollinators are experiencing a global decline and recommendations to increase bee populations suggest utilizing nectar-rich plants but rarely recommend plants that provide only pollen. Grasses provide only pollen and at least 51 grass genera have been documented as a pollen source for bees and hover flies. In this study, insects that utilize sorghum pollen were documented and a myriad of sorghum traits were measured to determine the traits that impact insect visitation. The most numerous insect observed collecting/consuming sorghum pollen was the the maize calligrapher followed by honey bees, lined earwigs, lovebugs, southern carpenter bees, common eastern bumble bees, exotic stripetails, margined soldier beetles, a signal fly, and a dusky-winged hover fly. Additionally, our results show that inflorescence (flower) abundance, plant height, and plant disease impact bee visitation in sorghum. Furthermore, field-captured bumble bees successfully fertilized sorghum in a greenhouse study, suggesting that bumblebees can pollinate sorghum flowers in field conditions. These data show that sorghum is serving as a pollinator food source and that bumblebees have the ability to pollinate the crop.

Technical Abstract: Grasses such as sorghum, (Sorghum bicolor (L.) Moench, are rarely considered as an important food resource for pollinators. Here, we report insects collecting or consuming pollen of sorghum over the 8-week flowering period of a mapping population in Tifton, GA. We also examine the response of insects to plant morphological traits and disease damage, and the ability of bumble bees to cross-pollinate sorghum. The most numerous insect observed collecting/consuming sorghum pollen was the hover fly Toxomerus politus Say (i.e. the maize calligrapher) followed by honey bees (Apis mellifera L.), lined earwigs (Doru taeniatum Dorhn), lovebugs (Plecia nearctica Hardy), southern carpenter bees (Xylocopa micans Lepeletier), common eastern bumble bees (Bombus impatiens Cresson), exotic stripetails (Allograpta exotica Wiedemann), margined soldier beetles (Chauliognathus marginatus Fabr.), a signal fly (Rivellia sp. Robineau-Desvoidy), and a dusky-winged hover fly (Ocyptamus fuscipennis Say). Maximum flowering occurred at week 3 which coincided with the maximum number of maize calligraphers, bumble bees, and honey bees observed. A positive linear relationship was seen between the number of flowering plots and the number of maize calligraphers and honey bees. The probability of observing a bee on a panicle increased as plant height increased, whereas the probability of observing a bee or hover fly decreased as plant disease percentage increased. These results suggest that inflorescence abundance, plant height, and plant disease impact bee visitation in sorghum. Furthermore, field-captured bumble bees successfully fertilized sorghum in a greenhouse study, suggesting that bumblebees can pollinate sorghum flowers in field conditions.