Insect feeding on sorghum bicolor pollen and Hymenoptera attraction to aphid-produced honeydew

Authors: Harris-Shultz, Karen; Armstrong, John; CABALLERO, MICHAEL - Oklahoma State University; HOBACK, WYATT - Oklahoma State University; Knoll, Joseph - Joe

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2022
Publication Date: 12/14/2022
Citation: Harris-Shultz, K.R., Armstrong, J.S., Caballero, M., Hoback, W., Knoll, J.E. 2022. Insect feeding on sorghum bicolor pollen and Hymenoptera attraction to aphid-produced honeydew. Insects. 13(12). Article 1152. https://doi.org/10.3390/insects13121152.
DOI: https://doi.org/10.3390/insects13121152

Interpretive Summary: Pollinators are experiencing a global decline, potentially reducing both human food supply and plant diversity. To support pollinator populations, planting of nectar-rich plants with different flowering seasons is encouraged while promoting wind-pollinated plants, including grasses, is rarely recommended. However, many bees and other pollinators have been often documented collecting pollen from grasses. Sorghum, a crop primarily used for grain in the U.S., is never listed as a plant recommended to homeowners to feed pollinators despite frequent bee sightings. In an effort to quantify pollinators and beneficial insects of sorghum collecting or consuming sorghum pollen, observation data were recorded. Honeybees, bumblebees, and carpenter bees were recorded collecting sorghum pollen whereas hoverflies and earwigs were documented consuming sorghum pollen. Additionally sorghum susceptible to sugarcane aphids attracts a large number of flies, bees, wasps, and ants that feed on the sugary rich waste product of the aphids. Pan traps and yellow sticky cards were placed in sorghum and Johnsongrass fields in infested and non-infested areas and insects were collected. Nearly 4,000 sawflies, wasps, bees, and ants belonging to 31 families were collected from grain sorghum with 84% associated with aphid infestations. There were almost 4 times and 20 times as many sawflies, wasps, bees, and ants in infested sorghum and Johnsongrass plots compared to uninfested plots, respectively From these two studies, sorghum especially sorghum susceptible to sugarcane aphids is a valuable crop for preserving pollinators and other beneficial insects.

Technical Abstract: Pollinators are experiencing a global decline, potentially reducing both human food supply and plant diversity. To support pollinator populations, planting of nectar-rich plants with different flowering seasons is encouraged while promoting wind-pollinated plants, including grasses, is rarely recommended. However, many bees and other pollinators have been documented collecting pollen from grasses. In addition to pollen, Hymenoptera may collect honeydew from sorghum infested with the sorghum aphid (SA), Melanaphis sorghi. In this study, insects consuming or collecting pollen from a sweet sorghum F4 population were recorded and pan traps and yellow sticky card surveys were placed in grain sorghum and in areas with Johnsongrass to assess Hymenoptera diversity. For the F4 population, Toxomerus politus was the most abundant on sorghum panicles followed by Apis mellifera, Doru taeniatum, Nola sorghiella, and Bombus sp. Xylocopa sp. were also observed collecting pollen on the grain sorghum border plots. Date effects were seen for the probability of observing a bee or insect on a sorghum panicle. Among the F4 lines, there were differences seen for the number of total insects observed on the sorghum panicles but not for total bees (bumblebee and honeybee) or hoverflies. Among the F4 lines, differences for plant height and panicle length varied but had no effect on the number of total insects, total bees, or hoverflies. Nearly 4,000 Hymenoptera belonging to 31 families were collected from grain sorghum with 84% associated with aphid infestations. There were almost 4 times and 20 times as many Hymenoptera in SA infested sorghum and Johnsongrass plots compared to uninfested plots, respectively. The presence of aphids significantly increased the number of ants, halictid bees, scelionid wasps, and sphecid and braconid wasps for infested sorghum plots. These data show that sorghum is serving as a pollen food source for hoverflies, earwigs, and bees and sorghum susceptible to sorghum aphids can provide a food source for Hymenoptera that feed on honeydew. Future research should examine whether planting strips with susceptible sorghum at crop field edges benefits Hymenoptera and other beneficial insects