Higher plasticity in feeding preference of a generalist than a specialist: experiments with two closely related Helicoverpa species

Yan Wang,Qing-Bo Tang,Xin-Cheng Zhao,Su-Xia Gao,Chen-Zhu Wang,Ying Ma,Dong-Sheng Zhou,Joop J A Van Loon

doi:10.1038/s41598-017-18244-7

Abstract

Herbivorous insects have been categorized as generalists or specialists depending on the taxonomic relatedness of the plants they use as food or oviposition substrates. The plasticity in host plant selection behavior of species belonging to the two categories received little attention. In the present work, fifth instar caterpillars of the generalist herbivore Helicoverpa armigera and its closely related species, the specialist Helicoverpa assulta, were fed on common host plants or artificial diet, after which their feeding preference was assessed individually by using dual - and triple- plant choice assays. Results show both the two Helicoverpa species have a preference hierarchy for host plants. Compared to the fixed preference hierarchy of the specialist H. assulta, the generalist H. armigera exhibited extensive plasticity in feeding preference depending on the host plant experienced during larval development. Whereas the specialist H. assulta exhibited a rigid preference in both dual and triple-plant choice assays, our findings demonstrate that the generalist H. armigera expressed stronger preferences in the dual-plant choice assay than in the triple-plant choice assay. Our results provide additional evidence supporting the neural constraints hypothesis which predicts that generalist herbivores make less accurate decisions than specialists when selecting plants.

Highlights

Phenotypic plasticity can be defined as the ability of organisms to express modifications in morphology, physiology and/or behavior in response to fluctuating environments[1,2]
Fifth instar caterpillars of the generalist H. armigera with different feeding experiences consumed different amounts in leaf choice assays (Fig. 1A)
Caterpillars of H. armigera raised on cotton leaves preferred cotton leaf disks over tobacco leaf disks (PC = 0.7572 ± 0.0350; Preference index for tobacco (PT) = 0.2428 ± 0.0350) (Fig. 1A’, Cotton reared)

Summary

Introduction

Phenotypic plasticity can be defined as the ability of organisms to express modifications in morphology, physiology and/or behavior in response to fluctuating environments[1,2]. Herbivorous insects display a considerable degree of plasticity in host plant selection behaviors and this may have a significant effect on evolutionary change in host use[6,26,27,28,29] It has been well documented for several herbivorous insects that dietary experience with a particular compound[30,31,32,33,34] or plant[27,28,29,35,36,37] can increase the relative acceptability of that compound or plant. Fifth instar caterpillars of H. armigera significantly preferred cotton leaf disks over pepper leaf disks, whereas caterpillars of H. assulta preferred pepper disks over cotton disks, and these contrasting preferences were consistent with the neural coding of the respective leaf saps by maxillary taste sensilla[10,25]

Methods

Results

Discussion

Conclusion