Abstract: The effects of different nitrogen fertilization regimes on female development of thevine mealybug, Planococcus ficus (Signoret), and the citrus mealybug, Planococcus citri (Risso)(Hemiptera: Pseudococcidae), were investigated on Vitis vinifera L., cv Vermentino. Theexperiment was carried out under indoor conditions using 50 potted plants, separated in 5 groupsand supplied weekly with 1.5l of water with different rates of ammonium nitrate fertilizer:0, 0.25, 0.5, 1 and 2g/l of nitrogen (N). Five grapevines of each treatment were infested withapprox. 200 first-instar mealybugs (24 hours old) of either P. ficus or P. citri. The female lifehistory parameters recorded included survival, development time from first instar to ovipositingfemale, body length of ovipositing females and number of eggs produced. The concentration ofnitrogen on leaves, indirectly measured throughout the experiment by determining thechlorophyll content by a Spad meter, was significantly lower in unfertilized plants than in thosesupplied with 0.5, 1 and 2g/l of nitrogen. No difference was found between grapevines fertilizedwith 0.25g/l of N and the remaining treatments. The survival of P. ficus in unfertilized plants waslower than in those supplied with nitrogen. The survival of the citrus mealybug did not showdifferences among treatments, but it was by far lower than that of the vine mealybug. Thedevelopment time of P. ficus on unfertilized grapevines was significantly longer than in all othertreatments, while no differences were found on plants infested with P. citri. The developmenttime of the citrus mealybug was significantly longer than that of P. ficus in all treatments. Vinemealybug females reared on vines supplied with 1 g/l of nitrogen were significantly larger in sizethan those of other treatments, while the body size of P. citri females did not differ significantlyamong groups. However, citrus mealybugs were always significantly smaller than P. ficusfemales. The fecundity of the two mealybug species was not significantly affected by increasingnitrogen rates, although P. ficus females produced more eggs than P. citri. The nitrogenfertilization significantly affected development time, size and fecundity of P. ficus, while nodifferences were found on the survival and sex ratio. In contrast, biological parameters of P. citridid not seem to be influenced by different nitrogen regimes, although results might have beenaffected by the high mortality of immatures. V. vinifera showed to be a more suitable host for thedevelopment and reproduction of P. ficus than of P. citri.