Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2011
Publication Date: October 22, 2011
Citation: Woods, J., James, D., Lee, J.C., Gent, D.H. 2011. Evaluation of airborne methyl salicylate for improved conservation biological control of two-spotted spider mites and hop aphid in Oregon hop yards. Experimental and Applied Acarology. 55:401-416. Interpretive Summary: When plants are attacked by pests, plants release volatile odors for defensive and signalling purposes. Methyl salicylate (MeSA) is a common volatile released that is also attractive to natural enemies. When synthetic MeSA is applied to crops, it has been demonstrated to increase natural enemies in vineyards and hop yards. In this study, we investigated the outcomes of applying MeSA to hop plants in the Mid-Willamette Valley. Paired control and MeSA-treated plots about 0.5 ha in size were compared on three farms in 2008 and 2009. Generally, mean numbers of two-spotted spider mite appeared reduced in five of the six MeSA-baited plots. Stethorus spp., a ladybug that is a key spider mite predator, tended to be more numerous in MeSA-baited plots compared to control plots on a given farm. However, mean seasonal densities of hop aphid and other natural enemies (e.g., minute pirate bug, and whirligig mites, etc.) were similar between MeSA-treated and control plots.
Technical Abstract: The use of synthetic herbivore-induced plant volatiles (HIPV) to attract natural enemies has received interest as a tool to enhance conservation biological control (CBC). Methyl salicylate (MeSA) is a HIPV that is attractive to several key predators of two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Homoptera: Aphididae). A two-year study was conducted to evaluate the use of MeSA in hop yards in Oregon. Slow-release MeSA dispensers were stapled to supporting poles in 0.5 ha plots and these plots were compared to a paired non-treated plot on each of three farms in 2008 and 2009. Across both years, there was a trend for reduced (40 to 91%) mean seasonal numbers of T. urticae in five of the six MeSA-baited plots. Stethorus spp., key spider mite predators, tended to be more numerous in MeSA-baited plots compared to control plots on a given farm. However, mean seasonal densities of hop aphid and other natural enemies (e.g., Orius spp., Anystis spp., etc.) were similar between MeSA-treated and control plots. Variability among farms in suppression of two-spotted spider mites and attraction of Stethorus spp. suggests that the use of MeSA to enhance CBC of spider mites in commercial hop yards may be influenced by site-specific factors related to the agroecology of individual farms or seasonal effects. The current study also suggests that CBC of hop aphid with MeSA in this environment may be unsatisfactory.