The activity of phenoloxidase in haemolymph plasma is not a predictor of Lymantria dispar resistance to its baculovirus.

Nikita S Kasianov,Stanislav A Bakhvalov,Irina A Belousova,John D Podgwaite,Ivan M Dubovskiy,Vyacheslav V Martemyanov,Sergey V Pavlushin

doi:10.1371/journal.pone.0183940

Nikita S Kasianov, Stanislav A Bakhvalov + Show 5 more

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https://doi.org/10.1371/journal.pone.0183940

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Abstract

Host innate immunity is one of the factors that determines the resistance of insects to their entomopathogens. In the research reported here we studied whether or not phenoloxidase (PO), a key enzyme in the melanogenesis component of humoral immunity of insects, plays a role in the protection of Lymantria dispar larvae from infection by L. dispar multiple nucleopolyhedrovirus. We studied two types of viral infection: overt and covert. The following lines of investigation were tested: i) the intravital individual estimation of baseline PO activity in haemolymph plasma followed by virus challenging; ii) the specific inhibition of PO activity in vivo by peroral treatment of infected larvae with phenylthiourea (PTU), a competitive inhibitor of PO; iii) the evaluation of PO activity in the haemolymph plasma after larval starvation. Starvation is a stress that activates the covert infection to an overt form. All of these experiments did not show a relationship between PO activity in haemolymph plasma of L. dispar larvae and larval susceptibility to baculovirus. Moreover, starvation-induced activation of covert viral infection to an overt form occurred in 70 percent of virus-carrying larvae against the background of a dramatic increase of PO activity in haemolymph plasma in the insects studied. Our conclusion is that in L. dispar larvae PO activity is not a predictor of host resistance to baculovirus.

Highlights

Gypsy moth Lymantria dispar L. (Lepidoptera: Eribidae) is a typical eruptive insect species that may cause defoliation over large areas
The total mortality rate for the group of larvae challenged by strain Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV)-27/0 was 80.8% while the mortality rate of insects challenged by strain LdMNPV-NY was higher—86,9% (χ2 = -2.23, p = 0.026)
The same result was shown for the infection by American LdMNPV-NY strain (Fig 1A), except when PO activity was normalized on the μl of haemolymph plasma

Summary

Introduction

Gypsy moth Lymantria dispar L. (Lepidoptera: Eribidae) is a typical eruptive insect species that may cause defoliation over large areas. (Lepidoptera: Eribidae) is a typical eruptive insect species that may cause defoliation over large areas. The range of L. dispar includes a large part of Eurasia (Western and Eastern Europe, Russia, and the Baltic states), countries of the Middle East and central Asia, northern China, Korea, North America (USA, Canada), as well as Japan and North Africa [1]. Phenoloxidase activity is not a predictor of Lymantria dispar resistance to its baculovirus. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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