Low Efficacy of Isaria fumosorosea against Box Tree Moth Cydalima perspectalis: Are Host Plant Phytochemicals Involved in Herbivore Defence against Fungal Pathogens?

Rostislav Zemek,Zain Ul Abdin,Jana Konopická

doi:10.3390/jof6040342

Abstract

Buxus sp. is an important native and ornamental tree in Europe threatened by a serious invasive pest Cydalima perspectalis. The larvae of this moth are able to defoliate box trees and cause their death. The development of novel biopesticides targeting this pest might help protect Buxus trees grown wildly or in city parks. Laboratory experiments were conducted to assess the efficacy of entomopathogenic fungus Isaria fumosorosea strain CCM 8367 against C. perspectalis. The last-instar larvae of the box tree moth were treated by the suspension of fungus conidia at concentrations ranging from 1 × 104 to 1 × 108 spores per 1 mL. Fungus infection was observed mostly in pupae, but the maximum mortality did not exceed 60%, indicating a very low susceptibility of C. perspectalis to I. fumosorosea. Furthermore, a number of ungerminated fungal conidia were found on larval cuticles using a low-temperature scanning electron microscopy. Our data also reveal that the hydroalcoholic extract from B. sempervirens leaves significantly inhibits both the germination of I. fumosorosea conidia and fungus growth. It can be speculated that the strain CCM 8367 of I. fumosorosea is not a potent biocontrol agent against C. perspectalis and low virulence of the fungus might be due to the accumulation of host plant phytochemicals having antimicrobial activity in larval cuticle of the pest.

Highlights

Box trees, Buxus sp., are important evergreen shrubs occurring in natural Buxus forests [1] or grown as ornamental trees in city parks in Europe
They are endangered by the box tree moth (BTM), Cydalima perspectalis (Walker) (Lepidoptera: Crambidae), which is a serious invasive pest native to Asia that was first detected in Germany in 2007 and has since invaded a large area causing significant damage [2,3]
Last-instar larvae of C. perspectalis were collected from unsprayed Buxus sempervirens trees located in a private garden in Staré Hodějovice (South Bohemia, Czech Republic, 49◦ N) and maintained in net cages at a room temperature with 16L:8D photoperiod for a few days before they were used in bioassays

Summary

Introduction

Buxus sp., are important evergreen shrubs occurring in natural Buxus forests [1] or grown as ornamental trees in city parks in Europe They are endangered by the box tree moth (BTM), Cydalima perspectalis (Walker) (Lepidoptera: Crambidae), which is a serious invasive pest native to Asia that was first detected in Germany in 2007 and has since invaded a large area causing significant damage [2,3]. Fungi 2020, 6, 342 their application in natural habitats is problematic because of their adverse side effects on non-target species Their frequent application possibly leads to the risk of resistance development in the pest. Entomopathogenic fungi (EPFs) represent other promising biocontrol agents Their advantages are that they do need to be ingested as they are able to penetrate the host cuticle and can be relatively produced [12]. In vitro experiments confirmed that the hydroalcoholic extract of Buxus leaves suppressed spore germination and fungus growth

Insects

Entomopathogenic Fungus

Bioassays

Data Analysis

Results and Discussion