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Final report
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Polyethylene plastic films used in greenhouse construction contain various ultraviolet (UV) light-absorbing components that result in transmission of different amounts of ultraviolet (UV) light into the greenhouse. It was previously known that UV light can affect insect flight behavior. In this project we used small, completely enclosed tunnels to compare the flight response of insect pests (whiteflies and thrips) under greenhouse plastics with different levels of UV light transmission. When given a choice between entering a tunnel constructed of a standard greenhouse plastic or a high UV-absorbing greenhouse plastic, released whiteflies and thrips overwhelmingly (85 to 98%) entered tunnels constructed of standard plastics. This indicated a distinct preference of both whiteflies and thrips to enter tunnels that transmitted more UV light, and suggested that greenhouse plastics could have significant influence on the initial attraction of insects into greenhouses. In California, growers frequently use greenhouses that are open on the sides to allow natural ventilation. It was not known if the UV-absorbing materials would still be effective if used in structures with open sides that allow unfiltered light to enter. Thus, we conducted field trials on flowering crops grown in large open-sided greenhouses covered with either a high UV-absorbing or standard UV-absorbing greenhouse plastic. In these field trials, there were fewer aphids and thrips captured on traps and counted on plants under the high UV-blocking plastic compared to the standard plastic. The difference in the numbers of insects was not as dramatic, as observed, in the small, completely closed tunnels we first tested, perhaps because unfiltered sunlight was entering through the open sides of the greenhouses. In contrast to finding in small tunnels, there was no difference in the numbers of whiteflies present under different plastic types in our field trials. These results suggest that the high UV-absorbing greenhouse plastics can be useful in developing IPM programs for insect management. Both the design of the greenhouse, and the targeted insect pests must be considered.
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