Mass reared pupae of the native predatory Franklinothrips orizabensis Johansen were released in an avocado orchard in Ventura County, California. The effect of weekly releases on the occurrence of Scirtothrips persea Nakahara, a significant pest in California avocado, was surveyed for 52 weeks. With release rates of 50 F. orizabensis pupae per tree per week, the number of immature S. persea were lower from July through November 2001 in released plots when compared to control plots. Although numbers of adult S. persea in the release plots were also lower during most of summer and fall 2001, this trend was less consistent. Considering the high release rate of F. orizabensis, levels of S. persea control were low. The sex ratio of released F. orizabensis pupae was strongly male-biased. However, there was a consistently greater proportion of females in field collections. Throughout the year, numbers of F. orizabensis larvae observed in both release and control plots remained low and showed no association with release rates. Therefore, it seems that F. orizabensis did not establish in the release plots. More research is needed to determine F. orizabensis can be used as a successful biological control agent for S. persea.