Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC, USA.
Department of Entomology, Michigan State University, East Lansing, MI, USA.
Environ Entomol. 2022 Dec 16;51(6):1094-1105. doi: 10.1093/ee/nvac081.
Scale insects are frequently abundant on urban trees. Although scales can worsen tree condition, some tree species tolerate moderate scale densities. Scales are prey for many natural enemies. Therefore, scale-infested trees may conserve natural enemies in their canopies and in nearby plants. We examined if scale-infested oaks-Quercus phellos L.-hosted more natural enemies than scale-uninfested oaks-Q. acutissima Carruth. and Q. lyrata Walter in Raleigh, NC. USA. We also tested if natural enemies were more abundant in holly shrubs (Ilex spp.) planted below scale-infested compared to scale-uninfested oaks. We collected natural enemies from the canopies of both tree types and from holly shrubs planted below these trees. To determine if tree type affected the abundance of natural enemies that passively dispersed to shrubs, we created hanging cup traps to collect arthropods as they fell from trees. To determine if natural enemies became more abundant on shrubs below scale-infested compared to scale-uninfested trees over short time scales, we collected natural enemies from holly shrubs below each tree type at three to six-day intervals. Scale-infested trees hosted more natural enemies than scale-uninfested trees and shrubs below scale-infested trees hosted more natural enemies than shrubs under scale-uninfested trees. Natural enemy abundance in hanging cup traps did not differ by tree type; however, shrubs underneath scale-infested trees accumulated more natural enemies than shrubs under scale-uninfested trees in six to nine days. Tolerating moderate pest densities in urban trees may support natural enemy communities, and thus biological control services, in shrubs below them.
介壳虫在城市树木上经常大量存在。虽然介壳虫会使树木状况恶化，但有些树种可以容忍适度的介壳虫密度。介壳虫是许多天敌的猎物。因此，受介壳虫侵害的树木可能在树冠和附近植物中保留天敌。我们在美国北卡罗来纳州罗利市研究了受介壳虫侵害的橡树（Quercus phellos L.）是否比未受介壳虫侵害的橡树（Q. acutissima Carruth. 和 Q. lyrata Walter）拥有更多的天敌。我们还测试了受介壳虫侵害的橡树下方种植的冬青灌木（Ilex spp.）是否比未受介壳虫侵害的橡树下方拥有更多的天敌。我们从这两种类型的树木树冠以及种植在这些树木下方的冬青灌木中收集了天敌。为了确定树的类型是否会影响被动传播到灌木的天敌的丰度，我们创建了悬挂杯诱捕器来收集从树上掉落的节肢动物。为了确定在短时间内受介壳虫侵害的树木下方的天敌是否比未受介壳虫侵害的树木下方的天敌更丰富，我们每隔三到六天从每棵树下方的冬青灌木中收集天敌。受介壳虫侵害的树木比未受介壳虫侵害的树木拥有更多的天敌，而受介壳虫侵害的树木下方的灌木比未受介壳虫侵害的树木下方的灌木拥有更多的天敌。悬挂杯诱捕器中的天敌丰度与树的类型没有差异；然而，在六到九天内，受介壳虫侵害的树木下方的灌木比未受介壳虫侵害的树木下方的灌木积累了更多的天敌。在城市树木中容忍适度的害虫密度可能会支持其下方灌木中的天敌群落，从而支持生物防治服务。
