MULTIVARIATE APPROACH TO IDENTIFYING PATTERNS OF BEMISIA-ARGENTIFOLII(HOMOPTERA, ALEYRODIDAE) INFESTING COTTON

The influence of agronomic factors on the abundance and distribution o f Bemisia argentifolii Bellows & Perring infesting cotton was describe d using principal component and multiple regression analyses. Densitie s of immature whitefly from leaf samples and 10 measures of cultural a nd management practices, which included insecticide use, cropping patt erns, planting date, field size, and natural enemy abundance, were qua ntified for 56 and 30 cotton fields located throughout the Imperial Va lley, California, in the summers of 1993 and 1994, respectively. White fly densities declined with increasing insecticide use and field size. Large (>32 ha), frequently sprayed fields exhibited lower whitefly de nsities than small fields receiving <5 insecticide applications. White fly densities were significantly and negatively related to the proximi ty and acreage of spring melons to the 56 cotton field sampled in 1993 , suggesting spring melon fields as a source of whitefly infesting cot ton. A similar relationship was also observed early in the 1994 season . In addition, densities of adult natural enemy numbers were positivel y correlated with immature B. argentifolii, suggesting that the existi ng 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 bot h 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 shou ld be planted early in the season and far from melons to reduce whitef ly pressure within cotton.