Effect of photoperiod on fitness of greenbug, Schizaphis graminum, biotypes on sorghum

Understanding the fitness of greenbug, Schizaphis graminum (Rondani), biotypes 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. These aphids kill seedlings and reduce yields of older plants of sorghum and small grains. Effect of three photoperiods, 14:10 (summer), 12:12 (fall/spring), and 10:14 (winter) 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. Greenbug fitness differed more by photoperiod than biotype. Pre-reproductive periods for biotypes E and I were 1.5 times longer at 10:14 light:dark hours (14.0 days) than at 14:10 (9.5 and 9.6 days, respectively) and 1.2 and 1.1 times longer than at 12:12 light:dark hours (11.8 and 12.7 days, respectively). Each biotype E greenbug produced 17.8 nymphs at 10:14 light:dark hours, but produced 3.3 times more nymphs (58.8 per greenbug) at 14:10. Biotype I greenbugs produced 3.8 times more nymphs at 14:10 light:dark hours (62.9 per greenbug) than at 10:14 (16.7 nymphs). The reproductive periods for biotypes E and I were 1.5 and 1.3 times longer at 10:14 than at 14:10 light:dark hours. Longevity of biotypes E and I at 14:10 light:dark hours were 1.7 and 1.6 times longer (46.2 and 47.3 days, respectively) than at 10:14 (26.7 and 30.2 days, respectively). Photoperiod significantly affects the fitness of greenbugs and should be considered when evaluating sorghum for resistance.