Dynamics of Melanaphis sorghi and Its Natural Enemies in Johnsongrass and Grain Sorghum with Variable Levels of Host Plant Resistance

Authors: Elkins, Blake; Little, Nathan; Johnson, Christopher - Chris; Allen, Clint

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2024
Publication Date: 5/9/2024
Citation: Elkins, B.H., Little, N., Johnson, C.P., Allen, K.C. 2024. Dynamics of Melanaphis sorghi1 and Its Natural Enemies in Johnsongrass and Grain Sorghum with Variable Levels of Host Plant Resistance. Southwestern Entomologist. 49(2):1-19. https://doi.org/10.3958/059.049.0209.
DOI: https://doi.org/10.3958/059.049.0209

Interpretive Summary: Melanaphis sorghi is an important aphid pest of sorghum in the United States. Without intervention, this aphid can damage sorghum plants, resulting in decreased and less profitable sorghum production. Management strategies for this aphid include host plant resistance and aphid suppression from insect natural enemies. Research has shown the effectiveness of these management strategies can vary regionally based on the level of sorghum production. A study was conducted in Mississippi to evaluate the density of M. sorghi and the response of its natural enemies in two commercial sorghum varieties that differ in their level of host plant resistance and the non-crop host Johnsongrass. The results indicated the effectiveness of host plant resistance in sorghum in suppressing aphids without negatively impacting predatory or parasitoid natural enemies. This research was important because it demonstrated the impact of host plant resistance and host species on aphids and their natural enemies in a region characterized by low amounts of sorghum production. This research also indicated that host plant resistance and natural enemies could function together to reduce aphid levels in sorghum.

Technical Abstract: Melanaphis sorghi Theobald (Hemiptera: Aphididae) is an economic pest of cultivated sorghum (Sorghum bicolor Moench) and utilizes the common weed Johnsongrass (Sorghum halepense Pers.) across North America. Effective management strategies for this aphid include host plant resistance and the conservation of natural enemies. However, the effectiveness of host plant resistance and the level of suppression from natural enemies has been found to vary regionally, with the majority of research being conducted in areas with heavy sorghum production. A study was undertaken to monitor aphids and natural enemy populations over time in Johnsongrass and grain sorghum with varying levels of aphid resistance in Mississippi. Aphid densities were significantly different between host plants, with the highest aphids per leaf in susceptible sorghum and the lowest density in Johnsongrass. Natural enemy densities followed similar trends with aphids. The numerical responses of predators and parasitoids showed considerably less variability between sorghum varieties than natural enemy density. Insect densities and numerical responses did not display any significant variability overtime during the reproductive growth phase of sorghum or Johnsongrass. This research demonstrates host plant resistance and natural enemies in the mid-southern United States, where there is limited sorghum acreage, function similarly to other regions characterized by widespread sorghum production. It also indicated no antagonism between host plant resistance and natural enemies, which should allow both to function within sorghum-integrated pest management.