Structural heterogeneity of wildflower strips enhances fructose feeding in parasitoids

Abstract

The use of wildflower strips to provide carbohydrate resource for parasitoids and enhance pest regulation is widely recommended in agriculture. However, how the management of wildflower strips affects resource availability and utilisation by parasitoids has never been studied. Using orange orchards as a model system, three experimental alleyway management treatments were investigated: a control treatment where naturally occurring vegetation in the alleyways between rows of trees was managed under standard farm practice; a standard management wildflower treatment in which sown wildflower strips in alleyways were managed by cutting once a year; and an active management wildflower treatment, in which the wildflower strips in alleyways was managed by cutting three times a year. Wildflower strips under standard management prevented the seasonal decline of nectar, supporting fructose feeding in parasitoids across all three seasons. The abundance of floral and hemipteran honeydew carbohydrate resources in the orchard alleyways and citrus canopy was consistently greater with the standard management treatment than the control or the active management treatments. In turn, this treatment was associated with twice the abundance of primary parasitoids than with the control and active management treatments in both summer and autumn. In addition, in autumn, parasitoids were more likely to have recently fed on carbohydrate in the standard management treatment than in the other two alleyway treatments. Finally, greater carbohydrate feeding in parasitoids was associated with increased structural heterogeneity of vegetation within the orchard alleyways. This study demonstrates that the nutritional status of parasitoids in a perennial cropping system can be improved using wildflower strips, which could enhance pest regulation, and emphasises the importance of studying the management of wildflower strips when targeting specific resource requirements.