Data from: Classical biological control and apparent competition: evaluating a waterhyacinth invaded community module

The scope and complexity of interactions within community food webs necessitates their simplification to a community module scale for conducting empirical studies. An outdoor mesocosm study in the USA quantified the strengths of direct and indirect interactions between two herbivore congeners that fed on two aquatic plant species while sharing a parasitoid. Kalopolynema ema (Hymenoptera: Mymaridae) is a stenophagous native egg parasitoid that attacks the hemipteran species in this study, Megamelus davisi (Hemiptera: Delphacidae), a native herbivore that feeds on the native aquatic species Nuphar advena, and the introduced biological control agent Megamelus scutellaris (Hemiptera: Delphacidae) that feeds on the non-native aquatic species waterhyacinth, Pontederia crassipes. The presence of M. scutellaris did not significantly increase parasitism of M. davisi indicating that apparent competition was not a factor in this community module. There was no evidence of any trophic cascades caused by these interactions based on the relative growth rates of biomass and leaf area for both plant species. The relative strengths of interactions varied with herbivore densities suggesting that should negative indirect effects occur they would likely be transient and closely linked to population dynamics as influenced by abiotic factors like temperature. The primary negative interaction was biotic resistance to Megamelus scutellaris from attack by Kalopolynema ema. Despite identifying potential negative interactions using path analysis, we saw no apparent competition following the insertion of a weed biological control agent into a community that contains an ecological analog.

群落食物网内的交互作用范围与复杂度均较高，因此需将其简化至群落模块尺度以开展实证研究。
本研究在美国开展了室外中型实验生态系统（mesocosm）研究，量化了以两种水生植物为食、共享一种寄生蜂的两种同属植食性昆虫之间的直接与间接交互强度。
本次研究中的狭食性本土卵寄生蜂Kalopolynema ema（膜翅目：缨小蜂科）可寄生半翅目昆虫卵；其中一种寄主为本土植食性昆虫Megamelus davisi（半翅目：飞虱科），其取食本土水生植物Nuphar advena；另一种为引进的杂草生防天敌Megamelus scutellaris（半翅目：飞虱科），其寄主为外来水生植物凤眼蓝（Pontederia crassipes）。
Megamelus scutellaris的存在并未显著提升对Megamelus davisi的寄生率，表明表观竞争并非该群落模块中的作用因子。
基于两种植物的生物量与叶面积相对生长速率，未观测到此类交互作用引发营养级联效应的证据。
交互作用的相对强度随植食性昆虫密度发生变化，这提示若出现负面间接效应，其大概率具有瞬时性，且与受温度等非生物因子影响的种群动态紧密相关。
本次研究中最主要的负面交互作用为：Kalopolynema ema的寄生攻击对Megamelus scutellaris形成了生物抗性。
尽管通过路径分析识别出了潜在的负面交互作用，但在将杂草生防天敌引入包含生态类似物的群落后，并未观测到表观竞争现象。