The encyrtid parasitoids Coccidoxenoides perminutus Girault and Anagyrus nr. sp. pseudococci (Girault) were compared in the laboratory as parasitoids of the mealybug Planococcus ficus (Signoret). Female C. perminutus preferred second-instar P. ficus for oviposition, and produced more adult offspring (149.3 per female) than A. nr. sp. pseudococci (54.1 per female). The development time, from egg to adult emergence, of C. perminutus decreased with increasing constant temperatures between 18.5 and 30.1°C; at lower (12.0 and 15.0°C) and higher (31.1, 32.7, and 34.2°C) temperatures, the parasitoid did not develop. The lower threshold was calculated by linear methods to be 10.97°C, and the thermal constant was calculated to be 507.98 degree—days. The development times of C. perminutus were longer than those of A. nr. sp. pseudococci, and C. perminutus had narrower temperature tolerances than P. ficus or A. pseudococci. Argentine ants (Linepithema humile (Mayr)) reduced the amount of time C. perminutus foraged on mealybug-infested squash, but did not affect the number of oviposition attempts or offspring produced, whereas Argentine ants reduced A. nr. sp. pseudococci foraging time, oviposition attempts, and number of offspring obtained. Overall, the results suggest that under certain conditions, including optimal conditions of temperature and host-stage availability, C. perminutus outperforms A. nr. sp. pseudococci, and may be an effective augmentative control agent even when ants are tending the hosts. However, temperature limitations and host-stage selection behaviors would reduce C. perminutus performance in the field, and in the absence of ants, other parasitoids may be favored.