Tropic interactions of Melanaphis sorghi, an invasive aphid on cultivated sorghum, with co-occurring aphid, predator, and parasitoid

Melanaphis sorghi (Theobald) is a major economic pest of cultivated sorghum around the world. A rich and abundant natural enemy complex has been found responding to this pest on grain sorghum in the Southern United States. Johnsongrass (Sorghum halepense L.), an uncultivated host of M. sorghi, may play a role in supporting natural enemies and enhance conservation biological control of M. sorghi in cultivated sorghum. The corn leaf aphid (Rhopalosiphum maidis Fitch) is an occasional pest with overlapping hosts, distribution, and natural enemy complex to M. sorghi. It is currently unknown how competition with R. maidis effects M. sorghi population growth. Additionally, we investigated the effects of R. maidis as an alternative prey source on natural enemy suppression of M. sorghi. In order to test these objectives, we conducted a laboratory choice and no choice cage study on Johnsongrass, using M sorghi, R. maidis, a lady beetle predator, and an endoparasitoid wasp. Results showed significant effects of natural enemy and aphid diversity treatments on M. sorghi population growth rates. However, important differences between predator and parasitoid treatments were found. These results suggest the presence of corn leaf aphids on Johnsongrass can alter M. sorghi regulation by supporting natural enemy populations. These findings can enhance sorghum pest management by increasing our understanding of pest and natural enemy dynamics on a common non-crop host found throughout sorghum producing regions.