Effect of Natural and Simulated Rainfall and Wind on Melanaphis sacchari1 on Sorghum

Abstract

The impact of natural and simulated rainfall and wind on sugarcane aphid, Melanaphis sacchari (Zehntner), on sorghum, Sorghum bicolor (L.) Moench, was studied near Rio Bravo, Tamaulipas, northeastern Mexico. In 11 events, natural rainfall intensity ranged from 15 to 51 mm per hour; average winds from 5 to 37 km per hour; and maximum wind (gusts) from 10 to 107 km per hour. Natural rain caused an average reduction of 32% adults, 13% nymphs, and 14% total (adults + nymphs) after 30 minutes; however, 5 days later, aphid abundance increased an average of 14% (range -55 to +93%). Natural rain caused only an average of 0.6% loss of parasitoid mummies of braconid Lysiphlebus testaceipes (Cresson). A rain simulator was designed to test the effects of artificial rainfall (40 mm per 15 minutes), constant wind (20 km per hour), and wind gusts (70 km per hour, 20 seconds every 2 minutes) during 15, 30, 45, and 60 minutes. After 60 minutes in the rain simulator, 77% of M. sacchari survived with rain alone, 44% with rain + constant wind, 34% with rain + wind gusts, and only 22% with rain + constant wind + wind gusts. Combination of rain and wind was more important than rainfall itself, particularly because M. sacchari feeds underneath the leaves, and disturbance produced by wind greatly reduced aphid survival. Multiple regression models well explained (R2 > 0.95) the association of M. sacchari survival (y) with rain and wind independent variables (xn) for natural, simulated, and combined (natural + simulated) conditions.