Evaluation of augmentative releases of Franklinothrips orizabensis for control of Scirtothrips perseae in California avocado orchards

The efficacy of augmentative releases of a predatory thrips, Franklinothrips orizabensis, was assessed for control of avocado thrips, Scirtothrips perseae. F. orizabensis were released weekly at a rate of 50 pupae per tree into replicated experimental blocks in two different ‘Hass’ avocado orchards in southern California, USA. Thrips-days calculated from weekly population counts and yellow sticky card monitoring were used to compare S. perseae and F. orizabensis densities in release and non-release (control) blocks. Augmentative releases of this predator failed to demonstrate an ability to control low densities (<5 S. perseae larvae per leaf) on small avocado trees (<3 m in height) and medium sized trees (4–5 m in height). Average field emergence rates of predators from deployed pupae ranged from 67 to 83% and sex ratio of emerged predators was male biased ranging 53–71%. Significant differences in emergence rates and sex ratio of predators were detected between sites and insectaries. Field longevity of predators was significantly affected by sex and the amount of food available. Male and female predators died quickly (accumulation of 14–23 day-degrees) when food was either absent or present in low quantities. Consequently, pre-emptive releases of mass-reared F. orizabensis to control low densities of S. perseae in avocado orchards in southern California in anticipation of pest outbreaks are not recommended.