Evidence for the stage inducing phenotypic plasticity in pupae of the polyphagous whiteflies Trialeurodes vaporariorum and Bemisia argentifolii (Homoptera : aleyrodidae) and the raison d'etre

The effect of leaf surface topography on the production of homologous dorsa l pupal structures in 2 major pest species, Bemisia argentifolii Bellows & Perring, and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), was determined. When cohorts of the 2 whitefly species developed separatel y at either high or low nymphal densities on a hirsute poinsettia, Euphorbi a pulcherrima (Willdenow), most (>95%) pupal exuviae had wax extrusions (T. vaporariorum) or setae (B, argentifolii). When either species was reared a t a low density on a glabrous lettuce, Lactuca sativa L., or on a normally pubescent salvia, Salvia splendens P. Sellow ex Roemer & Schultes, only 30% or fewer of the pupae had dorsal structures. When high nymphal densities o f T. vaporariorum developed on both lettuce or salvia however, a significan t increase occurred in the percentage of pupae with dorsal wax extrusions; and a significant, although slight, increase occurred in the dorsal setae o f B. argentifolii. Differences in leaf trichome density among 3 isolines of soybean, Glycine mat L., regardless of the whitefly density on the leaf, i nfluenced the number of dorsal pupal structures occurring on the 2 whitefly species. More than 90% of the pupal exuviae of both species exhibited dors al structures when reared on the hirsute isoline. In contrast, cohorts of t he 2 species developing on the normal and on the glabrous isolines produced <39% of T. vaporariorum pupae and <10% of B. argentifolii pupae with dorsa l structures, an indication that host plant nutrition probably does not qua ntitatively affect dorsal structures. When cohorts of the 2 species develop ed on large, fully expanded and on small, partially expanded leaves on the same zinnia plant, Zinnia elegans Jacquin, significantly more pupae with do rsal structures of both species occurred when reared on the partially expan ded leaf than when reared on the expanded leaf Because the number of tricho mes on a zinnia leaf does not change during leaf expansion, fewer trichomes /unit area of leaf occur on expanded leaves. This within-host test demonstr ated that crawlers emergent on a fully expanded leaf would have had a lower probability of tactile experiences before settling and feeding than crawle rs emergent on an unexpended leaf. Out discussion includes an interpretatio n of why sensory setae and well-developed antennae may occur only in the cr awler, the impact of crawler behavior on polyphenism, the importance of pol yphenism to polyphagous whiteflies, the role of adult wax particles, and a recommendation for host plant resistance.