Effect of photoperiod on greenbug (Hemiptera: Aphididae) on sorghum

Understanding the fitness of biotypes of greenbug, Schizaphis graminum (Rondani), in relation to environmental conditions, such as photoperiod, would aid in understanding how biotypes develop and in evaluating sorghum Sorghum bicolor (L.) Moench, for resistance to this major aphid pest of sorghum and small grains. Effects of three photoperiods of 14:10, 12:12, and 10:14 light:dark hours on greenbug biotypes E and I were evaluated on susceptible ‘Tx399 x RTx430’ sorghum at constant daily night (dark) and day (light) temperatures of 10 and 23°C, respectively, in an incubator. Fitness of greenbug biotypes E and I differed significantly by photoperiod but not by biotype. As the number of hours of light increased, the number of days before biotypes E and I combined produced the first nymphs decreased significantly from 14.0 to 12.6 and 9.5 at 10:14, 12:12, and 14:10 light:dark hours, respectively. Reproductive days of greenbug biotypes E and I combined increased from 16.5 to 26.4 at 10:14 and 12:12 light:dark hours, respectively, but were intermediate (23.6 days) at 14:10 light:dark hours. Total fecundity of biotypes E and I combined increased from 24.6 to 51.9 and 61.7 nymphs per greenbug as light increased from 10:14 to 12:12 and 14:10 light:dark hours, respectively. Longevity of greenbug biotypes E and I combined was 38.7 and 60.9 days at 10:14 and 12:12 light:dark hours, but intermediate (52.3) with the greatest number of hours of light. Photoperiod affects the fitness of greenbug biotypes E and I and should be considered when evaluating sorghum for more durable resistance.