Faculty of Agriculture, Laboratory of Systems Ecology, Saga University, Saga, Japan.
The United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima, Japan.
PLoS One. 2021 May 26;16(5):e0252239. doi: 10.1371/journal.pone.0252239. eCollection 2021.
Oviposition site selection by herbivores can depend not only on the quality of host resources, but also on the risk of predation, parasitism and interference. Females of the lycaenid butterfly Arhopala bazalus (Lepidoptera) lay eggs primarily on old host foliage away from fresh growth, where larval offspring live and feed. Resource availability of young host leaves seems not to affect the oviposition site preference by the females. To clarify the adaptive significance of A. bazalus oviposition behavior on old foliage, we tested three hypotheses: eggs on fresh foliage are (1) easily dropped during rapid leaf expansion (bottom-up hypothesis), (2) more likely to be attacked by egg parasitoids (top-down hypothesis), and (3) frequently displaced or injured by other herbivores (interference hypothesis). In field surveys, rates of egg dropping and parasitism by egg parasitoids were not significantly different between fresh and old host parts. However, the portions of fresh leaves on which A. bazalus eggs had been laid were cut from shoots on which conspecific larvae fed. Laboratory experiments demonstrated that eggs on young leaves were displaced in the presence of conspecific larvae and we observed that fifth instar larvae actively displaced conspecific eggs by feeding on the surrounding leaf tissue. These findings indicate that eggs laid on fresh leaves are at risk of being displaced by conspecific larvae, and support the interference hypothesis. Larval behavior is a likely evolutionary force for A. bazalus to lay eggs apart from larval feeding sites on the host plant.
植食性动物的产卵地点选择不仅取决于宿主资源的质量，还取决于被捕食、寄生和干扰的风险。灰蝶科蝴蝶 A. bazalus 的雌性主要在远离新生长的旧宿主叶片上产卵，幼虫在那里生活和进食。嫩叶的资源供应似乎不会影响雌性的产卵地点偏好。为了阐明 A. bazalus 在旧叶片上产卵行为的适应意义，我们检验了三个假说：在快速叶片扩张过程中，（1）新鲜叶片上的卵更容易掉落（自下而上假说），（2）更容易受到卵寄生蜂的攻击（自上而下假说），以及（3）经常被其他食草动物取代或伤害（干扰假说）。在野外调查中，新鲜和旧宿主部分的卵掉落率和卵寄生蜂的寄生率没有显著差异。然而，在 A. bazalus 卵已产下的新鲜叶片部分是从同种幼虫取食的枝条上剪下的。实验室实验表明，在有同种幼虫存在的情况下，年轻叶片上的卵会被取代，我们观察到第五龄幼虫通过取食周围的叶片组织积极取代同种卵。这些发现表明，新鲜叶片上的卵有被同种幼虫取代的风险，支持干扰假说。幼虫行为可能是 A. bazalus 将卵产在远离宿主植物上幼虫取食部位的一个进化力量。
