SOYBEAN HOST-PLANT RESISTANCE MECHANISMS THAT ALTER ABUNDANCE OF WHITEFLIES (HOMOPTERA, ALEYRODIDAE)

Trichome density and erectness, plant height, plant canopy closure, an d epicuticular lipid composition were measured from 14 soybean genotyp es at 2 locations in Tift County, Georgia, for, potential whitefly res istance mechanisms. Differences were noted in the number of trichomes per 300-mm(2) leaf area, plant heights, and canopy closure indices for the 14 soybean entries, but these differences showed no correlation t o 1993 and 1994 infestation levels of Bemisia argentifolii Bellows & P erring and Trialeurodes abutilonea (Haldeman). However, differences in trichome erectness ratings corresponded to differences in whitefly po pulations during both seasons, particularly in 1994 when overall popul ation densities were higher 'N88-91', 'Cook', and 'Perrin' had lower s easonal mean densities of whiteflies in 1993 and 1994 than several of the other entries. These entries also had higher erectness ratings (tr ichomes flat on leaf surface) than the entries with higher whitefly po pulations. 'N89-1' had lower erectness ratings (trichomes erect) and h igher whitefly populations than most other entries in both 1993 and 19 94. Analysis of the epicuticular lipid composition of 10 soybean genot ypes detected differences among the entries of levels for n-hentriacon tane, alpha-amyrin, beta-amyrin, and lupeol (triterpenol). These diffe rences were not correlated to whitefly population densities for any of the chemical constituents. However, entries with low levels of lupeol (below 5 mu g/cm(2)) tended to have higher whitefly populations. B. a rgentifolii was the predominant whitefly species observed at this test site. Over 85% of the immatures observed on the leaf surface and over 90% of the adult whiteflies captured on yellow sticky cards were B. a rgentifolii, whereas low numbers of T. abutilonea were observed.