Fitness trade‐offs associated with oviposition strategy in the winter cherry bug, Acanthocoris sordidus

In phytophagous insects, oviposition strategy is determined by complex trade‐offs among many factors. The winter cherry bug, Acanthocoris sordidus Thunberg (Heteroptera: Coreidae), deposits its eggs not only on host plants, but also on non‐host plants. Oviposition on non‐host plants may cause higher nymph mortality, as nymphs may be unable to find their host plants during the second instar when the first feeding occurs. Therefore, we hypothesised that this uncommon oviposition strategy would be maintained by a trade‐off between egg and nymphal mortality risks. To test this hypothesis, we conducted field surveys to compare egg mortality due to biotic (predation and parasitism) and abiotic factors on host plants vs. non‐host plants. We also conducted a semi‐field experiment to quantify the risk of nymphal mortality caused by oviposition on non‐hosts during the second instar. In terms of mortality risk during the egg stage, a 2‐year field survey revealed that oviposition on non‐host plants resulted in higher survival of eggs than on host plants; this strategy was also particularly effective for avoiding attacks by ground‐living arthropod predators. In terms of mortality risk during the nymphal stage, the semi‐field experiment demonstrated that nymphs placed off host plants do risk being unable to reach host plants. However, the presence of conspecific adults on host plants increased the probability that nymphs reached host plants. Therefore, second instars may have evolved the ability to utilise chemical cues emitted by adults on host plants or by host plants fed by adults to reduce their risk of not reaching host plants. We concluded that oviposition on non‐host plants by A. sordidus females could be maintained by the balance between the benefit of lower egg mortality and the cost of higher nymph mortality compared to oviposition on host plants.