A Rapid Sampling Plan for Scirtothrips dorsalis (Thysanoptera: Thripidae) on Container Shrub Rose (Rosa 'Radrazz')

The development of simple and reliable pest sampling programs is needed for growers to adopt economic or aesthetic injury levels. We developed a sampling plan for monitoring chilli thrips Scirtothrips dorsalis Hood populations on KnockOut shrub roses under simulated nursery conditions. The distribution of S. dorsalis among different plant structures revealed that most adults and larvae are found on foliar terminals, when compared with buds and flowers. Based on thrips distribution, the third leaf of actively growing terminals was used to determine a sequential sampling model. Thrips had an aggregated distribution, based on Taylor's power law and Iwao's mean crowding index, with both models showing a good fit (i.e., R-2 of similar to 0.8 and similar to 0.9, respectively). Based on these model parameters, the number of samples required to estimate populations with a 10% precision was similar to 30 leaves according to Green's and Kuno's enumerative sequential sampling plans. A binomial model also estimated the proportion of infested leaf terminals as a function of insect density with an R-2 value of 0.85. An additional study demonstrated that correlation between visual damage to the third leaf terminal and initial thrips populations was modeled by simple power functions. This finding suggests that a more rapid visual sampling of plant damage can be used to indirectly estimate S. dorsalis populations. Our sampling plan provides a tool to monitor S. dorsalis populations that could be used to help make management decisions for this pest in commercial nurseries.