Dynamics of Melanaphis sorghi1 1 and its Natural Enemies in Johnsongrass and Grain Sorghum with Variable Levels of Host Plant Resistance

Melanaphis sorghi Theobald (Hemiptera: Aphididae) is an economic pest of cultivated sorghum ( Sorghum bicolor Moench) and utilizes the common weed Johnsongrass ( Sorghum halepense Pers.) as a non-crop host across North America. Effective management strategies for this aphid include host plant resistance and the conservation of natural enemies. However, the effectiveness of both strategies has been found to vary regionally, with the majority of research conducted in areas with heavy sorghum production. A study was conducted to monitor M. sorghi and its natural enemies over time in Johnsongrass and grain sorghum with varying levels of aphid resistance in Mississippi. The aphid density in susceptible sorghum averaged 67 aphids per leaf, while the aphid densities in the resistant sorghum and Johnsongrass were significantly lower. Trends observed in the densities of seven families of natural enemies among the host plants were similar to those observed with M. sorghi. . The numerical responses of the natural enemies varied considerably less between sorghum varieties than their density alone. The densities of insects and the numerical responses of natural enemies did not vary significant over time during the reproductive growth phase of sorghum or Johnsongrass. This research demonstrates that 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 that there was no antagonism between the host plant resistance and natural enemies, which should enable both to function within sorghum integrated pest management.