Abstract
Intercropping can be used to reduce pest insects within agricultural systems, e.g., through deterring pests directly or by increasing habitat for their natural enemies. For example, plant produced volatile organic compounds (VOCs) can deter or confuse host-finding by insects through olfactory disruption. Drosophila suzukii is an invasive fruit fly of agricultural concern as it can lay its eggs in both ripening and fresh fruits and, uses olfactory cues to identify its wide range of host plants. Peppermint plants (Mentha × piperita) produce high levels of VOCs while growing and may, therefore, be suitable as an intercrop to reduce D. suzukii infestations in the field, as peppermint essential oil VOCs have previously been shown to deter D. suzukii in olfactory trials. We conducted a field intercropping experiment to evaluate the effectiveness of peppermint plants compared to traditional ryegrass/clover mixes in reducing D. suzukii oviposition in the field, and the effect of peppermint intercrops on other invertebrates. In the field, we monitored sentinel fruit baits weekly for D. suzukii infestation. Additionally, we monitored intercropping effects on the invertebrate community through weekly pitfall trap collection and through a pollinator point survey. We monitored for local, farm level presence of D. suzukii through apple cider vinegar traps within crop fields and along hedgerows and found high abundance of D. suzukii (>3,000 individuals trapped). Peppermint intercrops had fewer D. suzukii emerge from fruit baits and supported greater beneficial insect abundance (predators and pollinators) compared to ryegrass/clover. However, levels of D. suzukii were low across both intercrop types. Overall, we found that peppermint intercrops could be a potential aromatic intercrop used to reduce D. suzukii adult emergence from fruit compared to conventional ryegrass/clover mixes, however this trial should be replicated over multiple growing seasons, geographic locations, and host fruits. Furthermore, further study should determine the effects of the intercrop on the focal crop of interest.
Highlights
Increased plant diversity on farms can improve ecosystem services such as nutrient cycling, soil conservation, pollination, and pest control (Isbell et al, 2017)
Through a series of field assays at the University of British Columbia (UBC) Farm, we evaluated whether a peppermint intercrop could (1) reduce D. suzukii infestations in ripe fruit, (2) increase the number of beneficial ground dwelling invertebrates, and (3) increase pollinators compared to the common alley groundcover of ryegrass and white clover
From April 19 to August 16, 2018, we captured more D. suzukii in hedgerows compared to blueberry and strawberry production fields [trap location: X2(2,280) = 48.10, p < 0.0001], and captures depended upon sample date [X2(1,280) = 102.47, p < 0.0001], and the interaction between trap location and sample date [X2(2,280) = 7.93, p = 0.02]
Summary
Increased plant diversity on farms can improve ecosystem services such as nutrient cycling, soil conservation, pollination, and pest control (Isbell et al, 2017). Within a cropping system, including two or more crops (e.g., polyculture, intercropping, etc.), or utilizing companion plants (e.g., insectary plants Brennan, 2013, 2016) can support pest control goals in a multitude of ways. In which other control options have limited utility (e.g., due to the development of insecticide resistance or the inaccessibility of the pest to pesticide application) or are otherwise restricted (e.g., to maintain organic certification and/or to avoid negative interactions with pollinators), intercropping may present a more sustainable option for growers (Brennan, 2013, 2016; Pickett et al, 2014). Finding more effective and sustainable means of control for D. suzukii is of utmost importance due to the substantial losses experienced in berry and small fruit industries (Asplen et al, 2015; Haye et al, 2016) and the intensive management required to maintain marketable fruit
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