Biological performance of Melanaphis sorghi (Theobald, 1904) (Hemiptera: Aphididae) on different host plants

The sorghum aphid, Melanaphis sorghi (Theobald, 1904) (Hemiptera: Aphididae), is a significant pest. This study classified the host suitability of seven Poaceae genotypes: commercial and wild sorghum (S. bicolor, S. sudanense, S. bicolor verticilliflorum), pearl millet (Pennisetum glaucum), and maize (Zea mays). Aphid biological performance was assessed via leaf-disc bioassays under controlled conditions (24 ± 2 °C, 60 ± 10% RH). Infestation progression and plant injury were evaluated in greenhouse trials. Plant cell wall composition was analyzed using NIRS spectroscopy. Results established a clear host suitability gradient. All Sorghum genotypes were suitable hosts, supporting positive population growth. The commercial hybrid AG1090 exhibited the highest net reproductive rate (R₀ = 16.17). Pearl millet and maize were non-hosts, with reproduction virtually absent (R₀ ≤ 0.08). Greenhouse data confirmed this pattern, with sorghum genotypes (e.g., S. sudanense, S. bicolor verticilliflorum) reaching infestation levels above 84%, while pearl millet and maize remained below 24% with no visible injury. Statistical analysis revealed that plant susceptibility was positively correlated with leaf hemicellulose content. Principal Component Analysis (PCA) segregated susceptible sorghum genotypes from the non-host species based on this biochemical factor. It is concluded that pearl millet and maize are not hosts for M. sorghi. The cell wall composition, specifically hemicellulose content, is a key factor influencing aphid infestation levels. These findings provide a basis for developing sorghum cultivars with reduced susceptibility.