Abstract
Specialist insect herbivores are constrained by highly specific odor recognition systems to accept suitable host plants. Given that odor recognition leads specialist insects to accept a limited range of plants, we hypothesized that phylogenetically distant plants produce odors that are physicochemically different from host odors and would be less attractive or even repellent to a specialist herbivore. We tested this hypothesis by examining behavioral and ovipositional responses of swede midge (Contarinia nasturtii, Diptera: Cecidomyiidae), a specialist of brassicas, to broccoli sprayed with non-host essential oils. Specifically, we asked: (1) How do essential oils from different plant species influence host-seeking and oviposition behaviors of swede midge? (2) Do odors from non-host plants that are not phylogenetically related or physicochemically similar to host plants affect host-seeking or ovipositional behavior of swede midge? In oviposition assays, we found that non-host odors varied in their ability to modify female midge behavior and that phylogenetic relatedness was negatively correlated with larval density. In y-tube assays, we found that female midges most frequently avoided non-host odors that were more similar to brassica odors. Females were less likely to oviposit on or choose any treated host plants, but particularly avoided garlic, spearmint, thyme, eucalyptus lemon, and cinnamon bark treatments. Overall, we found that plant phylogenetic relatedness and odor similarity are related to repellency. Therefore, altering the diversity of plant odors by explicitly accounting for plant phylogenetic distance and odor similarity, relative to host plants, may be an important, underexploited tactic for sustainably managing challenging pests.
Highlights
The majority of phytophagous insects are specialists[1] that use volatile cues to find and accept their host plants[2,3,4]
Plants treated with essential oils had lower larval densities under no-choice conditions (Fig. 1; F18 = 5.045, P < 0.05) and were chosen less frequently for oviposition during choice tests (Figs 2 and 3), than those treated with water
We found that female midges responded in y-tube behavioral trials
Summary
The majority of phytophagous insects are specialists[1] that use volatile cues to find and accept their host plants[2,3,4]. Females recognize their plant hosts using visual cues[5,6,7] and volatile organic compounds (VOCs)[8,9,10,11,12,13]. Some insect herbivores are clearly repelled by non-host odors[18,19,20], there is still limited understanding on how interspecific variation of plant odors influences host-seeking and acceptance of specialist herbivores. Plant-based compounds that repel herbivores could be a valuable tool for pest management, but there are few guidelines available on how to systematically identify plant species that are repellent to specific insect pests. Non-host odors can mask the recognition of host odors by physically disrupting the reception of host compounds, effectively cancelling www.nature.com/scientificreports/. Testing how insect specialists behaviorally respond to increasingly phylogenetically distant non-host plants could provide a better understanding of how plants with non-preferred chemistry influence host-seeking and subsequent ovipositional behavior of specialist herbivores
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