Orius insidiosus as biological control agent of Thrips in greenhouse chrysanthemums in the tropics

Abstract

The possibility to use native Orius insidiosus (Say) (Rhynchota Anthocoridae) for control of thrips (Thysanoptera) on chrysanthemums in tropical Brazilian greenhouses was tested. First, thrips infested potted chrysanthemums in cages, cultivars ”White Reagan” (WR) and “Yellow Snowdon” (YS), were exposed to the predator O. insidiosus. The number of thrips/plant increased from 2.0 to 7.0 thrips after six weeks on control plants in the absence of O. insidiosus, while thrips numbers decreased from 2.0 to 0.2 thrips/plant in the presence of the predator on YS. Similar results were obtained for the chrysanthemum cultivar WR. Next, an experiment was carried out in a commercial chrysanthemum greenhouse with the same two cultivars and with a natural infestation of thrips. The predator was introduced five times at rates of 1.5 or 2.0 Orius/m 2 (in total 9.5 Orius/m 2 ). Thrips sampling was done by tapping two plants per flower bed per week, and by then counting thrips and predators. The average number of thrips decreased from 4.7 to 2.5 thrips/plant on YS and from 2.8 for 1.1 thrips/plant on WR after the first release. O. insidiosus reached a population peak in the sixth week after planting, with 0.5 Orius/plant on YS and 0.7 Orius/plant on WR, respectively. Thrips numbers decreased to 0.3 thrips/plant on YS and to 0.4 thrips/plant on WR seven weeks after planting. At this time no injury of thrips was found on chrysanthemum. Nine weeks after planting (chrysanthemum flowering period) the insecticide delthamethrin was sprayed for general pest control, and predatory bugs were eliminated from the greenhouse, resulting in a strong population increase of thrips. We conclude that thrips can be controlled effectively in tropical Brazilian chrysanthemum greenhouses with the native predator O. insidiosus, but that the selection of insecticides for control of other pests needs to be done carefully. Only those pesticides that are compatible with the use of the predator should be used to make commercial thrips biological control in greenhouses possible.