The willow sawfly, Nematus oligospilus (Förster), is a pest in Salix commercial forests and has been reported worldwide. Female adults must recognize a suitable host plant to oviposit, since her offspring lack the ability to move to another host. We evaluated the effect of conspecific herbivory on the oviposition choices of N. oligospilus females by providing damaged (DP) and undamaged (UP) plants of Salix humboldtiana, a native willow from South America, as oviposition substrates. Local and systemic effects were studied. For the local treatment, a twig from the DP with damaged leaves was contrasted to a twig from a UP in dual choice experiments. For systemic treatment, a twig from the DP with intact leaves was contrasted to a twig from a UP. We estimated the use of olfactory and contact cues by comparing volatile emission of DP and UP, and by analysing the behaviour of the females during host recognition after landing on the leaf surface. In the context of the preference–performance hypothesis (PPH), we also tested if oviposition site selection maximizes offspring fitness by evaluating neonate hatching, larval performance and survival of larvae that were born and bred on either DP or UP. Our results demonstrate that previous conspecific herbivory on S. humboldtiana has a dramatic impact on female oviposition choices and offspring performance of the sawfly N. oligospilus. Females showed a marked preference for laying eggs on UP of S. humboldtiana. This preference was found for both local and systemic treatments. Volatile emission was quantitatively changed after conspecific damage suggesting that it could be related to N. oligospilus avoidance. In the dual choice preference experiments, the analysis of the behaviour of the females once landing on the leaf surface suggested the use of contact cues triggering egg laying on leaves from UP and avoidance of leaves from DP. Furthermore, 48 h of previous conspecific feeding was sufficient to dramatically impair neonate hatching, as well as larval development and survival, suggesting a rapid and effective reaction of the induced resistance mechanisms of the tree. In agreement with the PPH, these results support the idea that decisions made by colonizing females may result in optimal outcomes for their offspring in a barely studied insect model, and also opens the opportunity for studying tree-induced defences in the unexplored South American willow S. humboldtiana.

中文翻译：

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以前的食草动物会提醒同种妊娠锯蝇避免不合适的寄主植物

柳叶蜂，少刺线虫(Förster)，是一种害虫柳属商业森林，并已在世界范围内报道。成年雌性必须识别适合产卵的寄主植物，因为她的后代缺乏转移到另一个寄主的能力。我们评估了同种食草动物对产卵选择的影响N. oligospilus雌性通过提供受损（DP）和未受损（UP）的植物沙柳，来自南美洲的本地柳树，作为产卵基质。研究了局部和全身效应。对于局部处理，在双重选择实验中，将来自 DP 的带有受损叶子的树枝与来自 UP 的树枝进行对比。对于全身处理，将来自 DP 的具有完整叶子的树枝与来自 UP 的树枝进行对比。我们通过比较 DP 和 UP 的挥发性排放，并通过分析雌性在着陆叶表面后识别宿主期间的行为来估计嗅觉和接触线索的使用。在偏好性能假设 (PPH) 的背景下，我们还通过评估在 DP 或 UP 上出生和繁殖的幼虫的孵化、幼虫性能和存活率来测试产卵位点选择是否最大限度地提高了后代的适应性。我们的研究结果表明，以前的同种食草动物在洪堡天竺葵对雌性产卵选择和锯蝇的后代表现有显着影响N. oligospilus。雌性对在 UP 时产卵表现出明显的偏好S.洪堡。这种偏好适用于局部和全身治疗。同种损伤后挥发性排放量发生了定量变化，表明它可能与N. oligospilus回避。在双重选择偏好实验中，对降落在叶子表面的雌性行为的分析表明，使用接触线索触发从 UP 的叶子上产卵和避免从 DP 的叶子。此外，之前 48 小时的同种喂养足以显着损害新生儿孵化以及幼虫的发育和存活，这表明树的诱导抗性机制发生了快速有效的反应。与 PPH 一致，这些结果支持这样一种观点，即在几乎没有研究过的昆虫模型中，通过殖民雌性做出的决定可能会为其后代带来最佳结果，并且也为研究未开发的南美柳树中树木诱导的防御提供了机会S.洪堡。