INFLUENCE OF MAIZE ROW SPACING ON INFESTATION AND DAMAGE OF INTERCROPPED BEANS BY THE BEAN APHID (APHIS-FABAE SCOP) .1. INCIDENCE OF APHIDS

Investigations were carried out in the field and in the glasshouse to assess the influence of row spacing of intercrop maize on the incidence of the bean aphid, Aphis fabae Scop. (Homoptera: Aphididae), on common beans, Phaseolus vulgaris L., and on aphid dispersal within the intercrops. Maize was planted in the field twice at a 3-week interval, at row spacings of 0.5, 1.0, 1.5 and 2.0 m, while sole and intercropped beans were planted simultaneously with the second maize, at a row spacing of 0.5 m. Aphis fabae incidence was lower on beans intercropped with densely planted maize, with strong interaction effects of spacing and maize growth. In trapping studies in the field, more alate aphids were caught above maize canopies than above the bean crop level. Glasshouse test with A. fabae alates showed that, when maize plants were densely planted, few aphids penetrated the maize canopy to reach and colonize bean plants; fewer plants were therefore infested by the aphid. The results show that maize spacing and size are vital factors influencing A. fabae infestation on beans in bean/maize intercrops.