Addition of nectar sources affects a parasitoid community without improving pest suppression

Jacob H Miall,Peter G Mason,Andrew M R Bennett,Naomi Cappuccino,Gary A P Gibson,Paul K Abram,José L Fernández-Triana

doi:10.1007/s10340-020-01274-y

Abstract

A life-table approach was used to test the effect of adding flowering buckwheat to leek plots on mortality and estimated population growth of the invasive leek moth, Acrolepiopsis assectella. This approach was used to estimate the benefits of nectar provisioning on multiple members of the leek moth’s parasitoid complex, and the impact of parasitism on the pest’s predicted population growth rate. Addition of buckwheat to leek plots shifted the relative abundance of different larval and pupal parasitoid species but did not increase or decrease parasitism levels or their population-level impact on the leek moth. The life-table analysis demonstrated that parasitoids reduced the estimated population growth rate of the leek moth by up to 72%, which far exceeds similar estimates from its native range. Parasitoids found to contribute to leek moth mortality were Itoplectis conquisitor, Conura albifrons and the biological control agent Diadromus pulchellus. In addition, Gambrus ultimus, Scambus calobatus, and Habrobracon sp. are reported here developing on A. assectella for the first time. This study reinforces the hypothesis that the addition of nectar resources to agricultural systems may not have straightforward positive effects and can favour some natural enemies over others, but may not have any overall impact on pest suppression.

Highlights

Increased plant diversity often increases the species richness and abundance of beneficial insects, including natural enemies, in the field (Poveda et al 2008; Langellotto and Denno 2004; Berndt et al 2006; Letourneau et al 2011)
The effect of floral treatment depended on cage treatment (χ2 = 4.09, df = 1, P = 0.043): in the uncaged treatment, neonate mortality tended to be lower in plots with buckwheat (χ2 = 23.88, df = 1, P < 0.0001), whereas there was no effect of buckwheat on neonate mortality in the caged treatment (χ2 = 0.31, df = 1, P = 0.58) (Fig. 1)
Comparison of caged versus uncaged plants across treatments in our experiments suggests that predation is likely an important contributor to leek moth mortality

Summary

Introduction

Increased plant diversity often increases the species richness and abundance of beneficial insects, including natural enemies, in the field (Poveda et al 2008; Langellotto and Denno 2004; Berndt et al 2006; Letourneau et al 2011). Conservation biological control strategies, including the addition of nectar resources to agricultural systems, can provide refuges and supplementary sugar sources for natural enemies, sometimes leading to improved pest suppression and reduced crop damage (Wratten et al 2000; Poveda et al 2008; Tscharntke et al 2016; Zemenick et al 2019). Addition of floral resources may improve biological control by specific agents through niche separation, by providing potential competitors with a variety of habitats and food sources within an agricultural system (Pedersen and Mills 2004) It can cause shifts in the composition of the natural enemy complex (Baggen and Gurr 1998; Tscharntke et al 2007). It is important to consider the full range of consequences before implementing a conservation biological control strategy, as added effort to support functionally redundant or counterproductive natural enemies may cause these strategies to reduce overall crop yield where arable land is used for intercropping or companion planting in place of crop production (Tscharntke et al 2005; Letourneau et al 2011)

Methods

Results

Discussion

Conclusion