We studied relationships between leaf trichome and silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring, densities on abaxial leaf surface of nine upland cotton, Gossypium hirsutum L., cultivars. The hairy leaf cultivar Stoneville 474 had the highest and the smooth leaf cultivar E1028 had the lowest numbers of SLW eggs, nymphs and adults. Among the eight smooth leaf cultivars, the four okra leaf cultivars as a group had fewer SLW eggs, nymphs and adults compared with the four normal leaf cultivars. The top young leaves on main stem terminals had fewer numbers of SLW eggs, nymphs and adults, but had higher numbers of trichomes compared with older leaves.

and Sparks (1997) that hairy leaf cotton cultivars were more susceptible to silverleaf whitefly colonization compared with smooth leaf cultivars. Stonville 474 also had higher numbers of SLW eggs and nymphs compared to the other cultivars and the highest number of trichomes per cm ² of leaf disk.

In contrast, leaves on leaf node #1 had the highest number of trichomes but the lowest numbers of eggs, nymphs and adults compared with five other older leaves (Table 1).

It has been well documented that hairy leaf cotton cultivars have higher Bemisia densities compared with smooth leaf cultivars (Chu et al. 1997, Norman and Sparks 1997). Results of this study comparing whiteflies on leaf position on the main stem nodes appears to reveal a complex of trichome-whitefly density relationships. Leaves on node #1 have not been exposed to adult oviposition as long as older leaves which confounds the differences observed in the numbers of adults, eggs and nymphs. However, our results of recent studies in greenhouses with short time exposures to whitefly ovipositions showed that the top young leaves below main stem terminals had fewer SLW compared with older leaves (unpublished data).

In addition to higher trichome density, the top young cotton leaves also had thinner leaf laminae and were a yellowish green leaf color that appears more attractive to adults and resulting in higher eggs and nymphs (Chu et al. 2000a and 2000b.) Therefore, the whitefly-trichome relationships are more complex than previously thought.