Relationships of yellow sugarcane aphid (Homoptera: Aphididae) density to sorghum damage

Yield reductions, maturity delays, and stunting due to injury to seedling sorghum by yellow sugarcane aphid (YSCA), Sipha flava (Forbes), were investigated in field trials in Central Texas in 1983 and 1984. Regression analysis indicated that yield reductions were significantly related to both YSCA density and plant discoloration symptom ratings. Per panicle yield reduction of plants infested when they averaged 4-6 cm tall was 1.1 g or 2.5% per aphid and 6 g or 15% per unit increase in discoloration rating. Plant height was reduced 2.7% per aphid or 6% per unit increase in discoloration rating. Maturity was delayed 0.5 days per aphid and 1.5 days per unit increase in discoloration rating. Seedling sorghum plants 3.5, 4.5, and 5.5 cm tall infested with an average of six aphids per plant had mean yield losses of 67, 30, and 7% respectively.