Plant sex effects on insect herbivores and biological control in a Short Rotation Coppice willow

Kim K Moritz,Christer Björkman,Amy L Parachnowitsch,Johan A Stenberg

doi:10.1016/j.biocontrol.2017.09.006

Kim K Moritz, Christer Björkman + Show 2 more

Open Access

https://doi.org/10.1016/j.biocontrol.2017.09.006

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Abstract

In the wild, plant sex can affect plant-herbivore interactions and higher trophic levels, including natural enemies of the herbivores. However, the possibility of manipulating plant sex to improve biological control and reduce herbivory in domesticated dioecious crops remains unexplored. The dioecious bioenergy crop, Salix viminalis, is often planted in monoclonal, and thus monosexual, fields. We investigated whether using plant clones of either sex, or mixing plants of both sexes, reduced the performance and abundance of the herbivorous pest insect Phratora vulgatissima and its main natural enemy, Anthocoris nemorum, and whether predation was affected. The herbivore laid more eggs, and the predator survived longer, on female plants in the lab. However, these effects did not translate into differences in predation rates in laboratory experiments or differential insect abundances on plants of either sex or plantation sex composition in the field. Plant genotype did have a significant effect on insect abundances, but this was due to plant traits other than sex. The results indicate that manipulating plant sex will not lead to improved biological control or reduced insect herbivory in S. viminalis energy forestry, but suggest that a focus on plant genotypic differences offers promise for improving management practices.

Highlights

There is strong evidence that wild plant traits can influence insect predators and parasitoids directly (Wäckers et al (2013)) and indirectly (Fortuna et al, 2014), studies on the effects of domesticated crop traits on these agents of biological control are scarce, especially in large-scale field experiments
We investigated whether manipulating plant sex in S. viminalis plantations can reduce herbivore damage by P. vulgatissima and improve the biological control exerted by A. nemorum
We investigated how traits of commercial S. viminalis may influence natural herbivore resistance and biological control by evaluating the effects of plant sex on the field abundances and abundances, behavior, performance, and fitness of an insect pest species and an omnivorous insect predator

Summary

Introduction

There is strong evidence that wild plant traits can influence insect predators and parasitoids directly (Wäckers et al (2013)) and indirectly (Fortuna et al, 2014), studies on the effects of domesticated crop traits on these agents of biological control are scarce, especially in large-scale field experiments. It is important to identify appropriate plant genetically based traits that can directly reduce herbivory or improve the biological control of herbivorous pests. Exceptions to male-biased herbivory in dioecious plants are common (reviewed by Cornelissen & Stiling 2005) and for dioecious species little work has been done on the natural enemies of herbivores that can play an important role in IPM, suggesting that research is needed and sex differences cannot be assumed. Important food resources for both herbivores and their natural enemies, including both predators and parasitoids, often vary in nutritional value among plants and could influence biological control as well as herbivory, offering opportunities for crop breeding (Stenberg et al, 2015)

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