The biology ofCirrospilus coachellae Gates (Hymenoptera: Eulophidae), an ectoparasitoid of the larvae ofMarmara gulosa Guillén & Davis (Lepidoptera: Gracillariidae) was studied in the laboratory. In total, 120.3 ± 21.2 adults were produced per female at 26°C. Females survived an average of 23.5 ± 4.4 d and parasitized an average of 49.8 ± 10.2 hosts over their lifetime.C.coachellae is a facultatively gregarious parasitoid with up to eight parasitoids developing per host with an average of 2.5 ± 0.1 in the laboratory. A female-biased sex ratio of 0.31 (male/total) was exhibited. Development times decreased with increasing temperatures from 23.7 ± 0.2 d at 20°C to 9.2 ± 0.1 at 29°C. Estimated lower and upper development thresholds were 14.1 and 36.7°C, respectively. Maximal development rate occurred at 31.3°C, and 138 degree-days was required to complete the cycle.