PHOSPHORUS-NUTRITION AND LEAF AGE EFFECTS ON SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE) HOST SELECTION

The sweetpotato whitefly, Bemisia tabaci (Gennadius), is a major agric ultural pest, causing over $200 million damage to cotton alone in the United States in 1992. To understand sweetpotato whitefly feeding beha vior, we examined the effects of phosphorus nutrition and leaf age on sweetpotato whitefly host selection. Cotton (Gossypium hirsutum L.) se edlings grown either hydroponically in growth chambers or in sand cult ure in the greenhouse were exposed to sweetpotato whitefly adults when two fully expanded true leaves were present. Phosphorus deficiency re duced oviposition on true leaves by 40% in the growth chamber, and by 38% on the youngest expanded leaf in the greenhouse, but had no effect on oviposition on cotyledons in either environment. When individual l eaves from the greenhouse were analyzed, host acceptance was significa ntly correlated with low leaf sucrose concentration, but appeared to b e unrelated to amino acid concentration or amino acid:sucrose ratio. T his suggests that host selection was based on minimizing osmotic stres s to the insect rather than on maximizing amino acid ingestion.