Recruitment of aphidophagous arthropods to sorghum plants infested with Melanaphis sacchari and Schizaphis graminum (Hemiptera: Aphididae)

A significant question in biological control is the extent to which indigenous natural enemies might be pre-adapted to exploit invasive species that constitute novel prey. We observed the recruitment of natural enemies to aphid microcosms – pots containing four sorghum plants infested with either Melanaphis sacchari (Zehntner), a newly invasive aphid, or Schizaphis graminum (Rondani), an established pest. The first cohort was monitored in open habitat along a tree line near riparian parkland and urban plantings, and the second, within a sorghum monoculture. Both aphid species were eliminated by natural enemies within 13 days in the first cohort, but in the second, M. sacchari reached higher numbers than S. graminum and survived a week longer. Biological control was successful in both cases; neither aphid produced a generation of alates, nor did plants sustain significant damage. Syrphid larvae, primarily Allograpta obliqua (Say), caused most aphid mortality in the first cohort, whereas adult Coccinellidae, primarily Hippodamia convergens Guerin-Meneville, caused most mortality in the second. Eggs and larvae of Chrysoperla carnea Stephens were present in both cohorts, but appeared to suffer more intraguild predation in the first. Flower flies and velvet mites were present only in the first cohort, and flower bugs, only in the second. Aphelinus sp. successfully parasitized both aphids, but Lysiphlebus testaceipes Cresson did not develop in M. sacchari due to their infection with the secondary endosymbiont Hamiltonella defensa (confirmed by DNA analysis). Thus, sorghum infested with M. sacchari attracted the same guild of natural enemies as S. graminum and had similar biological control outcomes. The findings suggest that the capacity of indigenous aphidophagous guilds to respond to, and ultimately control, invasive aphid species may be underestimated.