Antibiosis Effect of Sorghum on the Convergent Lady Beetle (Coleoptera: Coccinellidae), a Third-Trophic Level Predator of the Greenbug (Homoptera: Aphididae)

Abstract

The effects of a tri-trophic level (grain sorghum-greenbug-coccinellid) interaction were examined in the laboratory using greenhouse-grown plants. Two resistant sorghum, Sorghum bicolor (L.) Moench, hybrids, Dekalb DK-41 Y and DK-59E, which exhibit antibiosis to green bugs, Schizaphis graminum (Rondani), were tested along with a greenbug-susceptible hybrid, Horizon 101G. Single egg clusters from Hippodamia convergens Guerin females were randomly separated at hatching into two groups. Each group was fed greenbugs from either a resistant or susceptible grain sorghum hybrid. Plant antibiosis reduced larvalpupal survival and increased the amount of time from egg eclosion to pupation in coccinellids that fed on greenbugs from both of the resistant hybrids compared with the susceptible hybrid. Survival to adulthood was 82.9% in the 101G-susceptible treatment and 62.1% for larvae fed greenbugs from resistant DK-41 Y. Survival was 91.6% in the susceptible 101G treatment and 86.5% in the resistant DK-59E treatment. Resistant sorghum hybrid DK-59E had a significant treatment-by-sex interaction effect on coccinellid adult weights, with females that consumed greenbugs from the resistant hybrid weighing less, whereas males weighed more when compared with the respective sexes feeding on greenbugs from the susceptible sorghum hybrid.