Host preference and performance of Bemisia argentifolii (Homoptera : Aleyrodidae) on weeds in central Italy

Several herbaceous weed species of the Mediterranean nora found around cult ivated greenhouses of central Italy were used in a comparative study of the developmental rate of Bemisia argentifolii (Bellows & Perring). The relati ve importance of various weed hosts in local population dynamics of the whi tefly was investigated using a choice test and the construction of age spec ific Life tables. Among the 18 weed species studied, 11 were readily accept ed in the choice test. After 72 h, the whiteflies clearly showed a preferen ce for 2 species-Sonchus oleraceous L. and Solanum nigrum L. -on which near ly 53% of the released whiteflies were found. Approximately 90% of the rema ining population preferred Conyza canadensis L. (Cronq.), Euphorbia eliosco pia L, E. peplus L., and spontaneous clover trifolium repens L. Only a very low number of insects (similar to 4.5% of the total) were recorded on the remaining weeds-Ricinus communis L., Euphorbia characias L., Euphorbia macu lata L., Euphorbia dendroides L. Ranking of host plant quality determined b y the life table statistics coincided with the ranking of host preference a ssessed by the choice test. The intrinsic growth rate for whiteflies varied from 0.11 on S. oleraceous to 0.004 of Euphorbia dendroides. These experim ents demonstrated that in the absence of cultivated host plants such as tom ato, squash, or the ornamental plant poinsettia, the whitefly B, argentifol ii may find suitable hosts where it can complete its development.