ABSTRACT
Studies were conducted in tropical greenhouses to elucidate the role of UV light (UV) for the orientation and flight behavior of the thrips Ceratothripoides claratris (Shumsher) (Thysanoptera: Thripidae), an important pest on tomato (Lycopersicum spp.), in the hot and humid tropics of South-East Asia. Four greenhouse types characterized by different combinations of UV-absorbing or -transmitting plastic films and nets on the roof and sidewalls, respectively, were used in these studies. In choice experiments C. claratris always preferred the environment with higher UV intensity. Furthermore, natural thrips populations around the greenhouses were captured during the majority of control dates in lower numbers on sticky traps on the outer sidewalls of greenhouses clad with UV-absorbing materials compared with UV-transmitting materials. The immigration of thrips into the UV-absorbing greenhouses also was impeded, as measured by sticky traps on the inner side walls. UV-absorbing plastic roofs showed the most pronounced deterrent effect for thrips movement toward greenhouses, and the UV-absorbing net effectively reduced thrips numbers crossing the net barrier into the greenhouse. A simple extension of UV-absorbing plastic roof around conventional greenhouses clad with UV-transmitting plastic and net reduced thrips capture rates inside the greenhouse up to 77% when thrips was released at 1 m distance from the net walls. These results are discussed in the context of wavelength dependent insect vision and the dilemma of tropical greenhouse constructions, i.e., physical pest exclusion versus appropriate ventilation to ensure a conducive microclimate for plant growth.
