Evidence for the Stage Inducing Phenotypic Plasticity in Pupae of the Polyphagous Whiteflies Trialeurodes vaporariorum and Bemisia argentifolii (Homoptera: Aleyrodidae) and the raison d'être

Abstract

The effect of leaf surface topography on the production of homologous dorsal 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 separately at either high or low nymphal densities on a hirsute poinsettia, Euphorbia pulcherrima (Willdenow), most (>95%) pupal exuviae had wax extrusions ( T. vaporariorum ) or setae ( B. argentifolii ). When either species was reared at a low density on a glabrous lettuce, Lactuca sativa L., or on a normally pubescent salvia, Salvia splendens F. Sellow ex Roemer & Schultes, only 30% or fewer of the pupae had dorsal structures. When high nymphal densities of T. vaporariorum developed on both lettuce or salvia, however, a significant increase occurred in the percentage of pupae with dorsal wax extrusions; and a significant, although slight, increase occurred in the dorsal setae of B. argentifolii. Differences in leaf trichome density among 3 isolines of soybean, Glycine max L., regardless of the whitefly density on the leaf, influenced the number of dorsal pupal structures occurring on the 2 whitefly species. More than 90% of the pupal exuviae of both species exhibited dorsal structures when reared on the hirsute isoline. In contrast, cohorts of the 2 species developing on the normal and on the glabrous isolines produced <39% of T. vaporariorum pupae and <10% of B. argentifolii pupae with dorsal structures, an indication that host plant nutrition probably does not quantitatively affect dorsal structures. When cohorts of the 2 species developed on large, fully expanded and on small, partially expanded leaves on the same zinnia plant, Zinnia elegans Jacquin, significantly more pupae with dorsal structures of both species occurred when reared on the partially expanded leaf than when reared on the expanded leaf. Because the number of trichomes on a zinnia leaf does not change during leaf expansion, fewer trichomes/unit area of leaf occur on expanded leaves. This within-host test demonstrated that crawlers emergent on a fully expanded leaf would have had a lower probability of tactile experiences before settling and feeding than crawlers emergent on an unexpanded leaf. Out discussion includes an interpretation of why sensory setae and well-developed antennae may occur only in the crawler, the impact of crawler behavior on polyphenism, the importance of polyphenism to polyphagous whiteflies, the role of adult wax particles, and a recommendation for host plant resistance.