Thermal tolerance of Liothrips tractabilis, a biological control agent of Campuloclinium macrocephalum recently established in South Africa

Abstract

AbstractThe South American herb Campuloclinium macrocephalum (Less.) DC. (Asteraceae; pompom weed), which invades grasslands, savannas, and wetlands in South Africa, is a recent target for biological control. A foliage‐deforming thrips, Liothrips tractabilis Mound & Pereyra (Thysanoptera: Phlaeothripidae), was released in South Africa in 2013, following confirmation of its host specificity and damage potential in quarantine. However, weed biocontrol agents sometimes fail to establish or have the desired impact because they are poorly suited to the climate of the new range. Thermal tolerance trials, within the range of 15–32.5 °C, were conducted prior to the thrips’ release to determine its developmental threshold and to generate a degree‐day model to highlight areas best suited for its establishment in South Africa. These laboratory data were validated by outdoor trials. The thrips completed development from egg to adulthood at all except the lowest and highest laboratory test temperatures, with developmental duration decreasing with increasing temperature. The lower developmental threshold was estimated at 9.6 °C with 546.9 degree days required to complete development. Within the regions invaded by C. macrocephalum in South Africa, the thrips was predicted to complete 3–9 annual generations. Developmental times in the outdoor trials were largely consistent with those in the laboratory. Liothrips tractabilis is largely compatible with the broader South African climate and seems likely to establish and proliferate on C. macrocephalum populations throughout the country. These predictions have partially been verified in that L. tractabilis has become established at several sites in South Africa, many of these in colder, high‐altitude areas which were predicted to support fewer annual generations.