Effect of intercropping common bean with poor hosts and nonhosts on numbers of immature whiteflies (Homoptera: Aleyrodidae) in the Salamá Valley, Guatemala

Abstract

Intercropping with poor and nonhosts was tested as means to reduce densities of whitefly eggs and nymphs on common bean (Phaseolus vulgaris L.) in central Guatemala during dry and rainy seasons. Row and mixed intercrop field designs were used, with pesticides evaluated on a subplot level in the row-intercrop test. Tomato (Lycopersicon esculentum Mill.) was also evaluated in the mixed-intercrop test. Intercropping failed to reduce whitefly densities, although interpretation of data was difficult because of high variability among samples and reduced crop quality in some intercrop and pesticide treatments. Imidacloprid effectively reduced whitefly densities, but imidacloprid combined with intercropping offered no advantage over imidacloprid in monoculture. Laundry detergent and vegetable oil were tested as less-toxic inexpensive alternatives to pesticides under monocropped and intercropped conditions during the dry season, but failed to provide protection against whiteflies or other sucking insects. Trialeurodes vaporariorum Westwood was the predominant whitefly species in the area. Bemisia tabaci (Gennadius) on bean comprised ≈10% of the total whitefly population at the end of the dry season, 46% in the middle of the rainy season, when overall populations were lowest, and 1.15% toward the end of the rainy season. Encarsia pergandiella Howard was the predominant whitefly parasitoid throughout the study, and the only parasitoid reared from whitefly nymphs on bean in the dry season. Members of the Encarsia meritoria species complex and Amitus fuscipennis MacGown & Nebeker were recovered from tomato during the rainy season. Parasitoid diversity increased in the rainy season on tomato intercropped with roselle (Hibiscus sabdariffa L.) and corn (Zea mays L.) compared with tomato grown in monoculture. Intercropping with poor and nonhosts did not reduce whitefly densities on bean in an economically significant manner under high, intermediate, or low whitefly populations levels in either the dry or rainy season.