Plant-plant interactions affect the susceptibility of plants to oviposition by pests but are disrupted by ozone pollution

Abstract Plant volatiles convey information about the physiological status of a plant to other organisms, including neighboring plants and herbivores searching for a suitable oviposition site. Tropospheric air pollutants, such as ozone, can impair plant–plant interactions, e.g. by degrading volatile signals. In this study, field and laboratory experiments were conducted to assess whether plant–plant interactions between damaged and undamaged cabbage ( Brassica oleracea var. capitata ) plants provide receivers with a competitive advantage by altering their susceptibility to oviposition by the specialist herbivores Pieris brassicae and Plutella xylostella . We tested the phenomenon in oviposition choice tests under ambient and enriched ozone conditions. We also investigated the effect of receiving a signal from a different Brassica oleracea cultivar group, in this study broccoli ( Brassica oleracea var italica ), on the susceptibility to oviposition of cabbage plants. Cabbage plants exposed to damaged cabbage neighbors under ambient ozone were less susceptible to oviposition by P. brassicae in the field, but not in the laboratory. At ambient ozone levels P. xylostella preferred to oviposit on cabbage plants exposed to undamaged conspecifics in both the field and laboratory. At enriched ozone levels in the field, P. xylostella showed no oviposition preference for cabbage exposed to damaged or undamaged cabbage neighbors. In multiple choice tests in the laboratory, P. xylostella preferred to oviposit on cabbage plants exposed to damaged broccoli plants at ambient ozone over plants exposed to undamaged broccoli plants at ambient ozone and damaged and undamaged broccoli plants at enriched ozone. We conclude that plant–plant interactions and ozone interplay when influencing the susceptibility of plants to oviposition by herbivores.