Symbiotic control of <i>Halyomorpha halys</i> using a microbial biopesticide

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Abstract

Microbial biocontrol agents are promising tools for sustainable crop protection, as many strains showed high potential against various pathogens and pests. A still underexplored field for their use is symbiotic control, i.e. insect pest suppression through targeting obligate bacterial symbionts. Symbiotic control has been proposed against the brown marmorated stink bug Halyomorpha halys, by interrupting acquisition of its symbiont ‘ Candidatus Pantoea carbekii’ by newborns from egg surface. We investigated the success of symbiotic control of H. halys by exposing various developmental stages to spray applications of the commercial formulation Amylo-X ^®, containing the biocontrol agent Bacillus velezensis (previously B. amyloliquefaciens). Along with treating egg masses, 2 ^nd and 4 ^th instar nymphs were submitted also to direct or residual contact exposures to explore the contribution of symbiont- and insect-targeted antagonistic action in short term. We demonstrated significant mortality induced in Amylo-X ^®-treated samples, regardless of the insect stage and type of contact. Quantitative PCR analysis indicated that death of neonates was related to the missed acquisition of P. carbekii, due to symbiont elimination from the egg surface. Nevertheless, nymphal mortality after direct contact with Amylo-X ^® seemed resulting from an unknown antagonistic activity exerted by B. velezensis. Residual contact induced a combination of anti-symbiont and anti-insect activities, depending on the exposed instar. Our results support the use of Amylo-X ^® for symbiotic control of H. halys through field applications targeting egg masses; still B. velezensis deserves further studies to explore its additional functions against insects.

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A Method of Computing the Effectiveness of an Insecticide

W. Abbott (1925)

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Mode of Action of Microbial Biological Control Agents Against Plant Diseases: Relevance Beyond Efficacy

Jürgen Köhl, Rogier Kolnaar, Willem Ravensberg (2019)

Microbial biological control agents (MBCAs) are applied to crops for biological control of plant pathogens where they act via a range of modes of action. Some MBCAs interact with plants by inducing resistance or priming plants without any direct interaction with the targeted pathogen. Other MBCAs act via nutrient competition or other mechanisms modulating the growth conditions for the pathogen. Antagonists acting through hyperparasitism and antibiosis are directly interfering with the pathogen. Such interactions are highly regulated cascades of metabolic events, often combining different modes of action. Compounds involved such as signaling compounds, enzymes and other interfering metabolites are produced in situ at low concentrations during interaction. The potential of microorganisms to produce such a compound in vitro does not necessarily correlate with their in situ antagonism. Understanding the mode of action of MBCAs is essential to achieve optimum disease control. Also understanding the mode of action is important to be able to characterize possible risks for humans or the environment and risks for resistance development against the MBCA. Preferences for certain modes of action for an envisaged application of a MBCA also have impact on the screening methods used to select new microbials. Screening of MBCAs in bioassays on plants or plant tissues has the advantage that MBCAs with multiple modes of action and their combinations potentially can be detected whereas simplified assays on nutrient media strongly bias the selection toward in vitro production of antimicrobial metabolites which may not be responsible for in situ antagonism. Risks assessments for MBCAs are relevant if they contain antimicrobial metabolites at effective concentration in the product. However, in most cases antimicrobial metabolites are produced by antagonists directly on the spot where the targeted organism is harmful. Such ubiquitous metabolites involved in natural, complex, highly regulated interactions between microbial cells and/or plants are not relevant for risk assessments. Currently, risks of microbial metabolites involved in antagonistic modes of action are often assessed similar to assessments of single molecule fungicides. The nature of the mode of action of antagonists requires a rethinking of data requirements for the registration of MBCAs.

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Impact of the Invasive Brown Marmorated Stink Bug in North America and Europe: History, Biology, Ecology, and Management.

Tracy C. Leskey, Anne Nielsen (2018)

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is an invasive pentatomid introduced from Asia into the United States, Canada, multiple European countries, and Chile. In 2010, BMSB populations in the mid-Atlantic United States reached outbreak levels and subsequent feeding severely damaged tree fruit as well as other crops. Significant nuisance issues from adults overwintering inside homes were common. BMSB is a highly polyphagous species with a strong dispersal capacity and high reproductive output, potentially enabling its spread and success in invaded regions. A greater understanding of BMSB biology and ecology and its natural enemies, the identification of the male-produced aggregation pheromone, and the recognition that BMSB disperses into crops from adjacent wooded habitats have led to the development of behavior-based integrated pest management (IPM) tactics. Much is still unknown about BMSB, and continued long-term collaborative studies are necessary to refine crop-specific IPM programs and enhance biological control across invaded landscapes.