INFLUENCE OF WIND-SPEED ON RESIDENCE TIME OF UROLEUCON-AMBROSIAE ALATAE (HOMOPTERA, APHIDIDAE) ON BEAN-PLANTS IN BEAN MONOCULTURES AND BEAN MAIZE MIXTURES

The departure of winged aphids from a plant by flying or walking to neighboring plants may, in theory, be affected by wind speed or the density of leaf bridges between plants. This study explored the effects of these two factors on the departure rate of winged Uroleucon ambrosiae (Thomas) from bean plants, Phaseolus vulgaris L., in monocultures and in mixtures with maize, Zea mays L., in Costa Rica. Residence half-time, herein defined as the length of time required for half the winged aphids placed on a plant to depart, was shorter in mixed crops than in bean monocultures and was negatively correlated with wind speed at bean canopy level. Residence half-time had no detectable correlation with the number of interplant leaf bridges. Departure by flight, based on these findings, may have been more common than walking from plant to plant via leaf bridges. Maize in mixed crops formed barriers that reduced wind speed at bean canopy level, leading U. ambrosiae alatae to depart more readily from bean plants in bean-maize mixtures than in bean monocultures.