Insect Herbivore Populations and Plant Damage Increase at Higher Elevations.

Sulav Paudel,Edwin G Rajotte,Dependra Bhatta,Vinod Pandit,Gary W Felton,Pragya Kandel

doi:10.3390/insects12121129

Abstract

Simple SummaryIt is vitally important to understand the effects of climate change on insect pest populations and crop losses. Using elevation as a proxy for climate change, a field study was conducted in farmer’s fields in Nepal at various elevations in the Himalayan Mountains. At higher elevations, natural herbivore populations and plant damage from herbivory were significantly higher compared to their low-elevation counterparts. Temperature varied with elevation in the field and significantly affected both insect populations and plant damage. A geographical shift of insect pests towards higher elevations is predicated, so it is important to better understand how biotic and abiotic ecological factors and evolutionary processes will act together to affect ecosystem dynamics to reliably predict future pest problems.Elevation gradients are used as a proxy to simulate climate change effects. A field study was conducted along an elevational gradient in Nepal to understand the effects of abiotic conditions on agriculturally important insect herbivore populations (tobacco caterpillar: Spodoptera litura, tomato fruit worm: Helicoverpa armigera, and South American leaf miner, Tuta absoluta) and herbivory damage on tomatoes. Elevation ranged from 100 m to 1400 m above sea level, representing different climatic zones where tomatoes are grown. Contrary to our hypothesis, natural herbivore populations and herbivory damage significantly increased at higher elevations. Individual insect species responses were variable. Populations of S. litura and T. absoluta increased at higher elevations, whereas the H. armigera population was highest at the mid-elevational range. Temperature variations with elevation also affected insect catch numbers and the level of plant damage from herbivory. In the context of climate warming, our results demonstrate that the interactive effects of elevation and climatic factors (e.g., temperature) will play an important role in determining the changes in insect pest populations and the extent of crop losses.

Highlights

IntroductionElevational gradients are characterized by large variations in environmental conditions over relatively short distances [1]
The present study evaluates the changes in natural herbivore populations and herbivory damage in tomatoes (Solanum lycopersicum) along an elevation gradient in Western Nepal
The present study suggests that natural herbivore populations and plant damage increase at higher elevations and are influenced by abiotic factors

Summary

Introduction

Elevational gradients are characterized by large variations in environmental conditions over relatively short distances [1]. They are used in experiments to simulate changes expected under climate change scenarios [2]. The level of plant secondary compounds (e.g., phenolics, glucosinolates, volatile organic compounds) and leaf morphological characteristics (e.g., leaf toughness and trichome density) can vary with changing abiotic conditions affecting plant resistance to herbivores along elevation gradients [3,8,9]. A combination of herbivore pressure and plant defense responses can presage the level of plant damage and crop losses in the context of a warming climate [10]

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