Variation in Sorghum Aphid (Melanaphis sorghi)¹ Populations Translates into Life History Traits on Sorghum-Sudangrass (Sorghum ´ drummondii).

Sorghum aphid (Melanaphis sorghi; SA) (Theobald) is a new invasive pest of sorghum first reported in the USA in 2013. Since then, the use of synthetic pesticides and resistant cultivars have increased, which has caused levels of differences in the populations of SAs and led to the potential emergence of new biotype(s) of SA. However, most research has concentrated on comparing SA fed on sorghum, sugarcane, and other hosts, which may have obscured any population differences that may exist within sorghum. To understand this, we collected three populations of SA that fed on sorghum from three different locations around the Rio Grande Valley, Texas. We examined possible variations in their life history traits, feeding behavior through an electrical penetration graph (EPG) and host plant defenses post-infestation of SA by growing them on sorghum-sudangrass. The results from the life history traits showed significant differences in the net reproductive rate and intrinsic rate of increase among the three populations of SA tested. However, no significant difference in feeding behavior was observed from the EPG. We also found that the epicuticular wax varied significantly on sorghum-sudangrass when fed on by the three SA populations, while the total activity of polyphenol oxidase did not. Altogether, we show that the population level differences of SA translated into variation in specific traits, but further research is merited to fully understand the presence of SA biotype(s). [ABSTRACT FROM AUTHOR]