The influence of nitrogen content of poinsettia, Euphorbia pulcherrima, on the sweetpotato whitefly, Bemisia tabaci, and its parasitoid Encarsia formosa

Changes in nitrogen content of Euphorbia pulcherrima (Euphorbiaceae) is an important mechanism influencing its acceptability and suitability to Bemisia tabaci (type B) (Homoptera: Aleyrodidae). More whiteflies were found on fertilized plants, than on non-fertilized plants. Higher oviposition on ammonium nitrate treated plants than on non-fertilized or calcium nitrate treated plants suggests that acceptability of a plant by the whitefly is in response to plant cues. These cues reflect changes in nitrogen content and are perceived during probing of the leaf surface by female whiteflies.;While egg mortality was higher on ammonium nitrate-treated plants than on non-fertilized or calcium nitrate treated plants, larval mortality was higher on non-fertilized plants than on fertilized plants. Thus, significantly more adults were produced from fertilized plants than from non-fertilized plants.;The number of eggs deposited on mature and old leaves was greater than that deposited on young leaves. The latter type of leaf has significantly lower concentration of nitrogen. Thus, it appears that levels of nitrogen also play a role in whitefly oviposition preferences within a plant. Whiteflies may use nitrogen concentration of the leaf tissue to assess indirectly the nitrogen content of the phloem sap since the two were correlated.;Variability in the development, survival and fecundity of the parasitoid Encarsia formosa "Beltsville strain" (Hymenoptera: Aphelinidae) appears to be due to host plant mediated differences in the quality of whiteflies as hosts. Although the nitrogen content of whitefly pupae decreased linearly as the level of nitrogen applied to plants increased, the nitrogen content of parasitoid pupae was not influenced by fertilizer level applied to plants. However, the nitrogen concentration of parasitoid pupae was higher when reared from hosts on calcium nitrate treated plants compared to those reared on ammonium nitrate treated plants. Observation of the behavior of E. formosa on the leaf surface indicates females select host based on assessment by antennation, and by oviposition probing and drilling. These behaviors help assess the nutritional suitability of the host, which influences whether to continue with oviposition, feeding, or leave.