Several species of aggressive bark beetle in the genus Dendroctonus (Coleoptera: Curculionidae) undergo large fluctuations in population density with distinct outbreak and non‐outbreak phases. We investigated attributes we hypothesized as subject to density‐dependent variation (in particular, those likely to express phenotypic plasticity) in the southern pine beetle (SPB), Dendroctonus frontalis, as possible indicators of population fluctuations. These traits were morphology (body size and hindwing shape) and the sex ratio of trap‐captured, dispersing SPB populations. We compared attributes of beetles from locations that ranged from having zero to high numbers (>1500) of SPB infestations (spots) at the county level for two summers. Southern pine beetle were obtained from six states in the southeastern USA and had been collected during a springtime, region‐wide trapping survey used for forecasting outbreaks annually. Although we detected an expected but weak sexual dimorphism in both size and shape‐related traits, no morphological differences were found between SPB collected from traps in counties with low or high densities of spots (≤10 or >10 per county, respectively). We found no relationship between numbers of SPB spots per county and trapped sex ratios in 2016, but we observed a strong trend in 2017, with about three times higher proportions of females trapped in counties with low compared with high numbers of spots. This implies that one or more known or possible factors influencing trapped sex ratios (e.g., disparities between the sexes in their responses to semiochemicals or in their propensity to disperse) can be density‐dependent. Including trap‐captured sex ratios in prediction models may improve current forecasting of SPB outbreaks in the southeastern USA, informing more timely and effective management of one of the most economically and ecologically important beetle species of this region.

中文翻译：

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爆发性树皮甲虫的密度依赖性变异及其在爆发预测中的价值

Dendroctonus（Coleoptera：Curculionidae）属中的几种侵略性树皮甲虫的种群密度出现较大的波动，具有明显的爆发和非爆发阶段。我们调查了我们假设的属性，这些属性在南部松树甲虫（SPB），齿end龙虾中受到密度依赖的变异（特别是那些可能表现表型可塑性的变异）的影响，作为人口波动的指标。这些特征是形态（身体大小和后wing形状）和捕获的，分散的SPB种群的性别比。我们比较了两个夏季在县级从零到高数量（> 1500）SPB感染（点）的地点的甲虫的属性。南方松甲虫是从美国东南部的六个州获得的，是在春季，区域范围的诱捕调查中收集的，该调查每年用于预测暴发。尽管我们在大小和形状相关性状上都检测到了预期的但较弱的性二态性，但在斑点密度低或高的县（分别为每个县≤10或> 10）中，从诱捕器收集的SPB之间未发现形态学差异。我们发现，2016年每个县的SPB斑点数量与被困性别比率之间没有关系，但我们在2017年观察到了强劲的趋势，被发现的低比例县中，女性被困地区的比例高出三倍。这意味着一个或多个已知或可能的因素会影响被困的性别比率（例如，性别之间对化学信息素的反应或他们的分散倾向之间的差异）可能是密度依赖性的。在预测模型中包括捕获陷阱的性别比率可能会改善当前对美国东南部SPB暴发的预测，从而为该地区最经济和生态上最重要的甲虫物种之一提供更及时，有效的管理。被困在县中的女性比例大约是高点的三倍。这意味着一个或多个已知或可能的因素会影响被困的性别比率（例如，性别之间对化学信息素的反应或他们的分散倾向之间的差异）可能是密度依赖性的。在预测模型中包括捕获陷阱的性别比率可能会改善当前对美国东南部SPB暴发的预测，从而为该地区最经济和生态上最重要的甲虫物种之一提供更及时，有效的管理。被困在县中的女性比例大约是高点的三倍。这意味着一个或多个已知或可能的因素会影响被困的性别比率（例如，性别之间对化学信息素的反应或他们的分散倾向之间的差异）可能是密度依赖性的。在预测模型中包括捕获陷阱的性别比率可能会改善当前对美国东南部SPB暴发的预测，从而为该地区最经济和生态上最重要的甲虫物种之一提供更及时，有效的管理。性别对化学信息素的反应或分散倾向之间的差异可能取决于密度。在预测模型中包括捕获陷阱的性别比率可能会改善当前对美国东南部SPB暴发的预测，从而为该地区最经济和生态上最重要的甲虫物种之一提供更及时，有效的管理。性别对化学信息素的反应或分散倾向之间的差异可能取决于密度。在预测模型中包括捕获陷阱的性别比率可能会改善当前对美国东南部SPB暴发的预测，从而为该地区最经济和生态上最重要的甲虫物种之一提供更及时，有效的管理。