Multivariate Approach to Identifying Patterns of Bemisia argentifolii (Homoptera: Aleyrodidae) Infesting Cotton
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The influence of agronomic factors on the abundance and distribution of Bemisia argentifolii Bellows & Perring infesting cotton was described using principal component and multiple regression analyses. Densities of immature whitefly from leaf samples and 10 measures of cultural and management practices, which included insecticide use, cropping patterns, planting date, field size, and natural enemy abundance, were quantified for 56 and 30 cotton fields located throughout the Imperial Valley, California, in the summers of 1993 and 1994, respectively. Whitefly densities declined with increasing insecticide use and field size. Large (>32 ha), frequently sprayed fields exhibited lower whitefly densities than small fields receiving <5 insecticide applications. Whitefly densities were significantly and negatively related to the proximity and acreage of spring melons to the 56 cotton field sampled in 1993, suggesting spring melon fields as a source of whitefly infesting cotton. A similar relationship was also observed early in the 1994 season. In addition, densities of adult natural enemy numbers were positively correlated with immature B argentifolii, suggesting that the existing natural enemy complex did not regulate whitefly populations in the cotton fields sampled in 1994. Consistent positive relationships among planting dates and whitefly densities on all sample dates and for both years suggest that cotton fields planted earlier in the season will be host to fewer whiteflies relative to those fields planted later in the season. Within the constraints presented by cotton production with the Imperial Valley, results from this study suggest that cotton should be planted early in the season and far from melons to reduce whitefly pressure within cotton.
