Sugar and pollen supply enhances aphid control by hoverflies in strawberry

Larvae of many hoverfly species (Diptera: Syrphidae) are efficient aphid predators, while the adults feed on pollen and nectar. Strawberry crops can be infested by several aphid species, such as the strawberry aphid Chaetosiphon fragaefolii (Cockerell) and the potato aphid Macrosiphum euphorbiae (Thomas), both of which can cause economic damage. Protected cultivation of strawberry seems to be ideal for introducing biological control agents that depend on flower resources, but the nectar and pollen provided by the crop may not be the most suitable for all flower-dependent insects. In this study, we evaluated the biocontrol potential of hoverflies released preventively or curatively against the potato aphid in strawberry in two separate greenhouse experiments and the effect of adding sugars and pollen on their control efficacy. In the curative experiment, Eupeodes corollae (Fabricius) and Sphaerophoria rueppellii (Wiedemann) was released and supported with flowering plants of Fagopyrum esculentum Moench (buckwheat). Both species reduced the aphid numbers significantly compared to the control treatment. In the preventive experiment, we tested three syrphid species, Episyrphus balteatus (De Geer), S. rueppellii, and E. corollae, in the presence and absence of additional food sources (sugar solution and pollen). All three syrphid species reduced the aphid population to a similar extent, but only in the presence of additional food sources. This study shows that hoverflies perform better in strawberry crops when the adults have access to different supplementary food sources.许多食蚜蝇（双翅目：食蚜蝇科 Syrphidae）物种的幼虫为高效蚜虫捕食者，而成虫则以花粉和花蜜为食。草莓作物可被多种蚜虫侵染，例如草莓蚜（Chaetosiphon fragaefolii (Cockerell)）与马铃薯蚜（Macrosiphum euphorbiae (Thomas)），二者均会造成经济损失。草莓保护地栽培似乎十分适合引入依赖花资源的生防天敌，但作物本身提供的花蜜与花粉或许并非适配所有依赖花食性昆虫的最优选择。本研究通过两组独立温室试验，评估了预防性或治疗性释放食蚜蝇对草莓田中马铃薯蚜的生防潜力，并探究了添加糖类与花粉对其控蚜效果的影响。在治疗性试验中，研究人员释放了短翅细腹食蚜蝇（Eupeodes corollae (Fabricius)）与吕贝食蚜蝇（Sphaerophoria rueppellii (Wiedemann)），并辅以普通荞麦（Fagopyrum esculentum Moench, 荞麦）的开花植株。相较于对照组，这两种食蚜蝇均显著降低了蚜虫种群数量。在预防性试验中，我们测试了三种食蚜蝇物种：黑带食蚜蝇（Episyrphus balteatus (De Geer)）、吕贝食蚜蝇与短翅细腹食蚜蝇，设置了添加补充食物源（糖溶液与花粉）和不添加补充食物源两组处理。三种食蚜蝇均能将蚜虫种群降至相近水平，但该效果仅在补充食物源存在的条件下得以实现。本研究表明，当成虫能够获取多样化的补充食物源时，食蚜蝇在草莓作物中的控害表现更佳。