Yellow traps reloaded: what is the benefit for decision making in practice?

Sticky traps are a standard tool for monitoring alate arthropod pests in greenhouses. However, in practice, evaluation of traps over the whole growing season is rarely done. For decision making by growers, sticky traps are often only used for detection of pest presence. The reason behind is that although many studies show that pest population densities can be estimated using sticky traps under experimental conditions, validation under growing conditions and monitoring of beneficials are often lacking. In the current study, we evaluated whether trap densities recommended for practice are sufficient to estimate pest population densities of Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) and its natural enemy Encarsia formosa (Hymenoptera: Aphelinidae) in protected tomato cultures throughout the growing season. Our results show that trap catches provide reliable information about pest densities, in which correlations differed for specific developmental stages, i.e. adults\nymphs\nymphs (previous week). A single yellow sticky trap provided reliable information on nymphal density in the tomato crop on an area of at least 170 m2. A rapid increase of parasitoid trap catches indicated high parasitism. In our experiments, a total trap catch of C6 parasitoids/trap was a suitable threshold for sufficient natural enemy activity in the tomato crop. The implementation of these results in practice and the transferability to other cropping systems are discussed.