Integration of host plant resistance and biological control: Effects of resistant sorghum cultivars on Melanaphis sorghi (Hemiptera: Aphididae) development and Coccinella septempunctata (Coleoptera:Coccinellidae) predation

The sorghum aphid Melanaphis sorghi is one of the most economically significant pests affecting sorghum production in the western hemisphere. The adoption of resistant sorghum cultivars is an important tool in aphid management. Additionally, biological control with natural enemies, including the ladybug Coccinella septempunctata commonly found in sorghum fields, potentially reduces pest status. In this work, we evaluated the development and reproduction of M. sorghi in three different sorghum varieties (susceptible TX7000 and KS585, resistant TX2783), and the feeding capacity of C. septempunctata adults on M. sorghi reared on these varieties. Life tables of M. sorghi were calculated through daily observations, using 1-day old nymphs individually reared on the sorghum varieties, with 10 replications per variety (one nymph per replication). Aphids reared on TX2783 had a significant increase in pre-reproductive period and a reduction in reproductive lifespan and fertility, which reflected in about 50% reduction in their intrinsic rate of increase (rm), compared to aphids reared on TX7000 and KS585. Additionally, we tested the feeding capacity of adult C. septempunctata on M. sorghi reared on TX2783 and TX7000. We observed no significant differences between the predators consumption rates, indicating that ladybugs in the field might have the same feeding capacity whether the prey was reared on a susceptible (TX7000) or a resistant (TX2783) cultivar. Thus, the use of resistant sorghum varieties can be integrated harmoniously with natural biological control, as the resistance traits in TX2783 significantly reduced aphid population growth potential without compromising predation by C. septempunctata.