Biological Control of Diamondback Moth—Increased Efficacy with Mixtures of Beauveria Fungi

Abstract

Diamondback moth (DBM) is an important horticultural pest worldwide as the larvae of these moths feed on the leaves of cruciferous vegetables. As DBM has developed resistance to more than 100 classes of synthetic insecticides, new biological control options are urgently required. Beauveria species are entomopathogenic fungi recognized as the most important fungal genus for controlling a wide range of agricultural, forestry, and veterinary arthropod pests. Previous research, aimed at developing new Beauveria-based biopesticides for DBM, has focused on screening single isolates of Beauveria bassiana. However, these fungal isolates have individual requirements, which may limit their effectiveness in some environments. This current study separately assessed 14 Beauveria isolates, from a range of habitats and aligned to four different species (Beauveria bassiana, B. caledonica, B. malawiensis, and B. pseudobassiana), to determine the most effective isolate for the control of DBM. Further assays then assessed whether selected combinations of these fungal isolates could increase the overall efficacy against DBM. Six Beauveria isolates (three B. bassiana and three B. pseudobassiana) achieved high DBM mortality at a low application rate with the first documented report of B. pseudobassiana able to kill 100% of DBM larvae. Further research determined that applications of low-virulent Beauveria isolates improved the control of DBM compared to mixtures containing high-virulent isolates. This novel approach increased the DBM pest mortality and shortened the time to kill.

You are what you eat: fungal metabolites and host plant affect the susceptibility of diamondback moth to entomopathogenic fungi

“…Two New Zealand-derived fungal isolates, B. pseudobassiana I12 Damo and B. bassiana CTL20, previously identified with high virulence towards DBM larvae ( Soth et al, 2022 ), were selected for this study. The isolates were sourced from the culture collection held at the Bio-Protection Research Centre (BPRC), Lincoln University, New Zealand.…”

“…The isolates were maintained as axenic cultures on PDA (Thermo Fisher Scientific, Waltham, MA, USA; Oxoid Ltd., Basingstoke, UK) at 22 °C until required. The harvest and preparation methods for Beauveria conidia were previously described in Soth et al (2022) .…”

“…Bioassay procedures including Petri dish preparation, spraying methods, incubation conditions, larval mortality assessment, and mycosed cadaver assessment were previously described in Soth et al (2022) . Additionally, for the supernatant assay, the spray program was from half to full strength, and the incubation trays did not require covering with plastic bags to prevent moisture loss.…”

“…The current study therefore investigated the toxicity of culture filtrates produced from three genetically diverse strains of Beauveria previously identified as highly bioactive towards Plutella xylostella (diamondback moth; DBM) larvae ( Soth et al, 2022 ). The aim was to identify a Beauveria strain that could produce high concentrations of several insect toxins with the rationale that this strain would kill DBM more quickly than less bioactive fungal strains.…”

Exposure of honey bees to mixtures of microbial biopesticides and their effects on bee survival under laboratory conditions

“…Some studies reported synergistic or antagonistic effects on target pests after combining microbial biopesticides (Garbutt et al 2011 ; Hodgson et al 2004 ; Li et al 2021 ; Raymond et al 2008 ). Soth et al ( 2022 ) suggested that combining several genetically distinct isolates might lead to synergistic interactions or overcome environmental constraints. Studies using combinations of the two most applied entomopathogens, Bacillus thuringiensis and Beauveria bassiana , on target pests showed various interactions with different effects, including synergistic (Wraight and Ramos 2005 ; Kryukov et al 2009 ; Xue et al 2018 ), additive (Mwamburi et al 2009 ), or antagonistic (Ma et al 2008 ) depending on the pest and doses (Gao et al 2012 ; Mantzoukas et al 2013 ; Sayed and Behle 2017 ; Wraight and Ramos 2017 ).…”