The grounds for burrowing: The impact of substrate on Heterocampa pulverea (Notodontidae) wandering behavior

Current landscape designs may help explain declines in Lepidopteran diversity and abundance within managed landscapes, particularly regarding ground covers under host trees, as this is frequently the site of pupation. We used modified choice test methods to elucidate the influence of substrate type and soil compaction on the subsurface pupation and wandering behavior using Heterocampa pulverea (Notodontidae) as a model organism to compare turf, mulch, leaves, and bare soil. At the start of the wandering phase, a caterpillar was placed at the center of the mesocosm, and a video recording was started. Up to 2-5 caterpillars entered a single mesocosm at separate times. Caterpillars pupated at different depths across the substrates, with a greater average depth within mulch and leaves compared to turfgrass. Caterpillars also preferred mulch and avoided bare soil. Mulch had the highest rate of immediate pupation, 70%, and it was selected most often by 40% of caterpillars. Bare soil was selected by only 4.8% of caterpillars and the time spent digging was nearly five times that in mulch.  Pupation occurred equally often in turf and leaves and these substrates had comparable rates of pupation success for each dig attempt. Landscapers should prioritize protecting the soil beneath trees with organic substrates and reducing disturbances to promote efficient pupation of H. pulverea, and by inference, many other macro-moth species that are disappearing from urban and suburban spaces.

当前的人工管理景观中，鳞翅目昆虫（Lepidopteran）的多样性与丰度呈下降趋势，现有景观设计或可对此作出解释，其中尤以寄主树木下方的地被覆盖物为关键影响因素——因为该区域往往是鳞翅目幼虫化蛹的主要场所。本研究采用改良选择试验法，以粉柔舟蛾（Heterocampa pulverea，舟蛾科Notodontidae）为模式生物，探究基质类型与土壤压实度对其地下化蛹及漫游行为的影响，实验设置了草坪草皮、覆盖物、落叶与裸土四种基质开展对比。在漫游阶段初期，将1条幼虫放置于中型生态箱（mesocosm）的中心位置，并启动视频录制。单次中型生态箱可先后接入2至5条幼虫。幼虫在不同基质中的化蛹深度存在显著差异：与草坪草皮基质相比，覆盖物与落叶基质中的幼虫平均化蛹深度更大。幼虫同时偏好覆盖物基质，且回避裸土。覆盖物基质的即时化蛹率最高，达70%，且有40%的幼虫优先选择该基质；仅有4.8%的幼虫选择裸土基质，其挖掘耗时近乎为覆盖物基质的5倍。幼虫在草坪草皮与落叶基质中的化蛹频率相当，且两种基质的单次挖掘尝试的化蛹成功率相近。园林绿化从业者应优先采用有机基质保护树木下方的土壤，并减少土壤扰动，以促进粉柔舟蛾的高效化蛹；据此可推断，该结论同样适用于众多正从城市与近郊区域消失的大型蛾类物种。