The aphid Uroleucon ambrosiae (Thomas) is one of the principal pests found oil greenhouse lettuce crops, and there is no efficient biological control agent of this pest in Brazil. This work evaluates the aphid U. ambrosiae as a host for the parasitoid Praon volucre (Haliday), aimed at using P. volucre as a potential biological control agent of U ambrosiae on lettuce. As Macrosiphum euphorbiae (Thomas) is a common host of P. volucre in the field, the development of the parasitoid was compared on these two aphid species. Twenty nymphs of the 2nd instar were kept with P. volucre for one hour at 22 [plus or minus] 1[degree]C, 70 [plus or minus] 10% RH and a 12 h photophase. The size of the aphid's tibiae at the moment of oviposition indicated that there was no significant size difference between U. ambrosiae (0.6 [plus or minus] 0.02 mm) and M. euphorbiae (0.7 [plus or minus] 0.03 mm). When mummies were formed, M. euphorbiae had significantly longer tibia (1.5 [plus or minus]! 0.03 mm) than U. ambrosiae (1.4 [plus or minus] 0.02 mm). No significant differences were detected in the percentage emergence (74.9 [plus or minus] 7.92 and 87.5% [plus or minus] 3.31 for U. ambrosiae and M. euphorbiae, respectively), or proportion of female offspring (56.2 [plus or minus] 7.62 and 44.2 [plus or minus] 7.14%). The development time from oviposition to adult and longevity of females and males of P. volucre reared oil the two host species were not different. High parasitism levels were recorded for both lost aphid species, but the percentage parasitism of M. euphorbiae (54.4 [plus or minus] 4.40) was higher than of U. ambrosiae (35.6 [plus or minus] 5.30). Female parasitoids reared on M. euphorbiae had longer tibiae (0.78 [plus or minus] 0.01 mm) than those reared on U. ambrosiae (0.72 [plus or minus] 0.01 mm). Our results demonstrate that the alternative host species U. ambrosiae, compared to the natural host species M. euphorbiae, affects the female's size! , but did not affect parasitoid development time, longevity, emergence or sex ratio. The parasitoid P. volucre seems to be a good candidate for using as a biological control agent of U. ambrosiae oil lettuce in Brazil. none