UV-absorbing films and nets affect the dispersal of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae)

UV-absorbing films and nets are frequently used as covering materials for netted greenhouses and film tunnels in protected cultivation systems. This study explored the effects of such materials on the dispersal behaviour of western flower thrips (WFT), Frankliniella occidentalis, in flight cages under greenhouse conditions with additional artificial UV-A light sources. The study involved releaserecapture experiments in choice and no-choice layouts. Different trapping methods were compared (blue sticky cards, plants and transparent cards) for recapture of thrips. In choice experiments, insects were released from a black box compartment between two tunnels covered with either UV-transmitting or UV-absorbing materials. A significantly higher proportion of (8298%) WFT was recaptured in UV-transmitting tunnels compared with UV-absorbing tunnels. In no-choice experiments, WFT were found to infiltrate the tunnels at different rates depending on the trap type used and experimental layout. In small-scale dispersal experiments using blue sticky cards and plants as traps, infiltration was not significantly different between UV-absorbing and UV-transmitting tunnels, whereas when using transparent cards, WFT penetrated further into the UV-transmitting plastic film tunnels. In larger-scale dispersal experiments, plants or blue sticky cards were arranged in concentric circles around a source plant at the release point. Dispersal was found to differ depending on the method of release, but WFT tended to exhibit reduced dispersal from source plants under UV-deficient conditions. In conclusion, our data support the hypothesis that manipulation of spectral light properties using UV-absorbing cladding materials for protected crop stands interferes with the orientation and host finding of WFT, resulting in reduced dispersal into and within plant stands in UV-deficient environments.