Abstract: The koinobiont endoparasitoid Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae) has been widely used as a biological control agent of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), in citrus orchards and ornamental greenhouses. Previous studies showed that the vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is a suitable host for the parasitoid to complete its development. In the current experiment, the preference of L. dactylopii for the two hosts was investigated in a two-choice test. Newly-emerged parasitoid females, reared on one of the two mealybug species, were mated and exposed to third-instar nymphs and young adult females of both P. ficus and P. citri in an experimental arena. In order to investigate the influence of a previous oviposition experience on the host preference, the experimental wasps were naïve (inexperienced) or had oviposition experience with one of the two hosts before the release in the test arena. The foraging behavior of female wasps was observed for 30 minutes. Leptomastix dactylopii females reared on P. ficus showed a strong preference for vine mealybugs, irrespective of the oviposition experience, while those reared on P. citri did not show a clear preference. The oviposition experience before the two-choice test did not affect the percentage of P. ficus encountered and examined by parasitoids; on the other hand, L. dactylopii females experienced on P. ficus probed and laid eggs preferentially on vine mealybugs. During the test, L. dactylopii females were observed feeding on mealybug fluids exuding from oviposition wounds (host-feeding), although rearing host species and oviposition experience did not affect the wasp behavior. Further experiments on host-parasitoid interactions under field conditions are being developed in order to verify the effectiveness of L. dactylopii in controlling P. ficus infestations in vineyard agroecosystems.