The influence of agent density for biological control of young Brazilian peppertree (Schinus terebinthifolia) with the Brazilian peppertree thrips (Pseudophilothrips ichini)

Abstract

ABSTRACT Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae), is an invasive tree in the Southeastern United States, Texas, California, and Hawaii. The Brazilian peppertree thrips, Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae), is a recently approved biological control agent for use within the US. The thrips have since been released in the field and are expected to reduce Brazilian peppertree performance. Pseudophilothrips ichini is likely to impact young trees but the impacts may vary based on thrips population size and tree age. To better understand the factors contributing to agent impact on young trees and P. ichini population growth, we measured the effect of P. ichini density (0, 4, 10, and 20 thrips) and tree age (3-, 4-, and 6-month-old plants), on tree performance and P. ichini productivity in the laboratory. Brazilian peppertree height and the number of growing tips were reduced across all age groups. However, the negative impact was more pronounced on the youngest trees, which had a reduction in the relative change in height of 171% and a 100% reduction in the number of growing tips. Pseudophilothrips ichini production was positively correlated with tree height (r = 0.44) and biomass (r = 0.56), but thrips relative production was similar across tree age. Results indicate that P. ichini have a great capacity for population increase regardless of starting density. Field studies are needed to corroborate these findings and identify barriers to agent success. This work aims to refine expectations of the impacts to Brazilian peppertree caused by P. ichini.