Comparison of injuries caused by sucking pests and ozone on clones of white clover (Trifolium repens 'Regal')

Abstract

Insects and mites can cause injuries similar to those caused by troposferic ozone (O₃) on the indicator plant white clover (Trifolium repens 'Regal'). We set up an experiment where injuries of 6 species of sucking insects and mites on white clover were accurately described and photographed. Leaf injuries caused by animals, were compared with the injuries of high ozone concentrations on white clover. Leaf injuries in form of necrosis on resistant and sensitive clones of white clover were closely observed at the Laboratory Field of Biotechnical Faculty in Ljubljana from May to September 1998. In the laboratory of the Institute of Phytomedicine at the Biotechnical Faculty in Ljubljana, insects and mites were reared and injuries caused by the sucking animals were observed from August 2001 till the end of October 2001. In the experiment two-spotted spider mite (Tetranychus urticae Koch), onion thrips (Thrips tabaci Lindeman), clover aphid (Nearctaphis bakeri Cowen), two bug species Halticus apterus Linnaeus and rice leafbug (Trigonotylus coelestialium Kirkaldy) and green leafhopper (Cicadella viridis Linnaeus) were observed. The photographs of progression of injuries and the accurate descriptions of the injuries were compared to each other to allow us to distinguish the real agents for the injuries on leaves of white clover (T. repens 'Regal'). All plants were carefully monitored and photographed during the progression of injuries on the plant leaves. Injuries, the white spots caused by the bug Halticus apterus Linnaeus, were the biggest among the injuries caused by the observed pests. They were similar to the injuries by high concentrations of ozon. All other pests caused different tipes of injuries.