Population abundance and movement of Frankliniella species and Orius insidiosus in field pepper

1 A recent study revealed the capacity of the Orius insidiosus to suppress populations of Frankliniella spp. in field pepper during the spring when thrips are rapidly colonizing and reproducing. In this study, population abundance in pepper during spring, summer, and autumn was determined to understand better predator/prey dynamics under local conditions. Local movement between pepper flowers also was quantified to examine how population attributes of the predator allow suppression of rapidly moving populations of prey. 2 Randomized complete block experiments established in the autumn of 1998 and the spring of 1999 included treatments of biological and synthetic insecticides, which altered the population densities of predator and prey. Numbers of O. insidiosus in relation to prey were sufficient in 1998 to prevent build-up of thrips populations. In 1999, populations of thrips were unable to recover from near extinction owing to persistence of the predator. The predator rapidly recolonized plots treated with insecticide. 3 Greenhouse plants of the same age as field plants were used to monitor movement by predators and prey. Movement by F. occidentalis was limited, whereas F. tritici and F. bispinosa moved rapidly to the greenhouse plants. The males of each thrips species moved more rapidly than the females. There was evidence that rapid movement assisted F. tritici and F. bispinosa in avoiding predation, but O. insidiosus also moved very rapidly to the greenhouse plants. This attribute explains the predator's ability to suppress thrips rapidly even when populations are rapidly colonizing and reproducing in the flowers.