Effect of Different Light Spectrum in Helicoverpa armigera Larvae during HearNPV Induced Tree-Top Disease.

Mandira Bhattarai,Ji-Nian Feng,Upendra Bhattarai,Dun Wang

doi:10.3390/insects9040183

Abstract

Lepidopteran larvae upon infection by baculovirus show positive photo-tactic movement during tree-top disease. In light of many insects exploiting specific spectral information for the different behavioral decision, each spectral wavelength of light is an individual parsimonious candidate for such behavior stimulation. Here, we investigated the responses of third instar Helicoverpa armigera larvae infected by Helicoverpa armigera nucleopolyhedrovirus (HearNPV) to white (broad-spectrum), blue (450–490 nm), UVA (320–400 nm), and UVB (290–320 nm) lights for the tree-top disease. Our findings suggest that tree-top phenomenon is induced only when the light is applied from above. Blue, white and UVA lights from above induced tree-top disease, causing infected larvae to die in an elevated position compared to those larvae living in the complete dark. In contrast, UVB from above did not induce tree-top disease. Blue light exerted the maximum photo-tactic response, significantly (p < 0.01) higher than white light. The magnitude of the response decreased with decreasing wavelength to UVA, and no response at UVB. Our results suggested that the spectral wavelength of the light has a significant effect on the induction of the tree-top disease in H. armigera third instar larvae infected with HearNPV.

Highlights

Behavior manipulation in the host-parasite interaction has been defined as the phenotypic changes in the host organism [1]
In SeMNPV–S. exigua interaction, egt was involved indirectly in tree-top disease by prolonging the lifespan of infected larvae [18]. These findings suggest that the effect of egt on the tree-top disease is not conserved among all baculoviruses
We investigated the importance of lights of different wavelength categories: White light, blue light (450–490 nm), UVA (320–400 nm), and UVB (290–320 nm) in relation to climbing before death behavior in Helicoverpa armigera nucleopolyhedrovirus (HearNPV) infected H. armigera third instar larvae, and surprisingly found that white light along with blue and UVA applied from above induced tree-top disease, but UVB did not

Summary

Introduction

Behavior manipulation in the host-parasite interaction has been defined as the phenotypic changes in the host organism [1]. It has evolved as one of the primary tools in all major phylogenetic lineages of parasites and been efficiently utilized to perpetuate their genes [2,3,4,5]. Baculoviruses are host specific pathogens associated with arthropods and mainly infect lepidopteran larvae [11]. Induced behaviors in lepidopteron host larvae by their pathogenic baculoviruses have been a field of extensive research since few decades. Two kinds of altered behaviors in the infected larvae have been reported and are governed by different triggering mechanisms in the baculovirus [12]. The enhanced locomotory activity (ELA), where larvae become hyperactive [13,14] and secondly, the tree-top disease (Wipfelkrankheit) where, infected larvae climb high up to the top of the tree before death, resulting in the better dispersal of virus particles with

Methods

Discussion

Conclusion