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Resistance to crop protection products is a concept that rightfully strikes fear in the core of every crop farmer. Without effective protection, current yields will certainly be impacted but also those in years to come. The arrival of various biopesticide options on the market in recent years has meant that farmers could sleep a little more soundly, but it was inevitable. Resistance is now emerging for these products, as it has for conventional insecticides.
Indeed, an international team of scientists has concluded that insects that attack crops have “extraordinary powers” to develop biopesticide resistance. Their recent study was funded by a joint Newton Fund international partnership between the Biotechnology and Biological Sciences Research Council in the UK, the São Paulo Research Foundation in Brazil and the Swedish Research Council.
The team analyzed existing biopesticide research and concludes “that resistance evolution is already occurring and is likely to become widespread as biopesticide use continues to increase.”
Professor Matthew Tinsley and post-doctoral researcher Dr. Rosie Mangan at the Universityof Stirling in the UK published these and other conclusions in a new paper entitled ‘Increasing ecological heterogeneity can constrain biopesticide resistance evolution’ with Dr. Luc Bussière of the University of Gothenburg andDr. Ricardo Polanczyk of São Paulo State University.
Tinsley has noted that in general, people tend to think that resistance will less easily develop in insect populations exposed to biopesticides because they’re derived from natural sources,but “we still need to be worried about pest resistance to thesenew agents.”
Application and product natureAs a team of French scientists noted a few years ago, the stage becomes set for biopesticide resistance when a product has a narrow range of insect targets and is used in a systematic and repeated manner.
“This is more striking when the bio-insecticide is a purified product, for example a single molecule such as a specific Bt toxin,” they explain. “Under these conditions, there is no fundamental difference between a synthetic molecule and a bioinsecticide. However, when the full complexity of the agent is retained, as when using complete Bt spores and crystals, crude neem extracts or genotypically-diverse virus populations, no resistance development has been observed.”
Those conclusions were published in 2015. Does the same apply now? We approached Dr. Michael Brownbridge, biological program manager (disease control) at Bioworks, a biological crop protection product firm based in Victor, NY, for his views.
Dr. Michael Brownbridge
Brownbridge confirms these statements still hold relatively true. In the example of Bt, he notes “there is a very specific mode of action (MOA) and site of action. Several mechanisms of resistance have been proposed, but it seems that the receptors on the insect mid-gut are primarily involved in this evolution. Insects survive where binding with the Bt toxin does not occur, and so resistance is propagated.”
However, Brownbridge explains that when you consider the ‘whole’ Bt organism, various other bacterial components play a role in killing the insect, and resistance does not develop as quickly. “While the primary MOA is the same, survival is not so straightforward because of the other components in the bacterial preparation,” he says. “Similarly, for bioinsecticides based on fungi, the infection process is complex and it’s unlikely that insects will develop resistance to them.”
Resistance to Bt products is an important issue in his view, especially with pests that have rapid life cycles and several generations within a specific cropping cycle. (But while it seems intuitive that warmer regions of the globe may be most challenged by resistance, with many pests surviving year-round with multiple generations, Brownbridge says resistance can occur in any region if the same products are used repeatedly.) As an example of a pest with a rapid life cycle and several generations within that cycle, he points to the diamondback moth. However, he adds that “several
lepidopteran species are good candidates, particularly when Bt-transgenics are deployed or repeated sprays of the same Bt product are made.”
Mangan names the codling moth as the most serious case of pest resistance for microbial biopesticides. This serious orchard pest had been controlled very effectively using a granulovirus biopesticide through to the 2000s, she says, but resistance emerged and required the development of new products containing different viral strains.
Dr. Rosie Mangan
“If we think more broadly,” she adds, “some of the most notorious global crop pests such as fall armyworm, cotton bollworm, diamondback moth, Colorado potato beetle and silverleaf whitefly have repeatedly shown ability to evolve resistance against synthetic products and Bt-plants. It is these pests for which biopesticides may be the most valuable weapons for farmers to use for crop protection, and we need to ensure that microbial biopesticides remain effective against them in the long term.”
Fighting resistanceDiscussing solutions, Mangan first notes there has been a massive global increase in the number of biopesticide products on the market, accompanied by escalating use by farmers. “This is a really good thing, as it gives farmers the tools they need for more environmentally-sustainable pest control, but it does mean that now is the time to proactively consider new resistance management approaches,” she says. “Farmers already have a lot of knowledge about how to use pest control products sustainably and how to manage resistance for synthetics and transgenic crops. However, yes, we believe ‘awareness-raising’ is needed for resistance risks to microbial products.”
She and her colleagues have concluded that to avoid the same treadmill of invention and loss of efficacy that’s happened with synthetic crop protection products, farmers should use more biopesticides and plant a wider diversity of crops. Nothing particularly new in those ideas, but the team advocates novel, collaborative approaches that encourage unprecedented adoption.
“We’ve developed experimental games to test incentives presented to farmers and record their farm management decisions,” Mangan reports. “These games have clarified how power dynamics, economic incentives and social networks affect both behavioural change and
the adoption of new resistance management strategies.”
The team is also interested in identifying the barriers to the uptake of new resistance management approaches, and working closely with agribusiness and extension officers to ensure they’re feasible for adoption.
Tinsley explains that “the key thing here is that the agricultural industry is very used to managing resistance by switching between different chemical pesticide products. It’s easy to imagine that this will also be effective for biopesticides; however, there is little research on the precise mode of action of different biopesticides and the extent that these modes of action overlap between products.”
Professor Matthew Tinsley
As for the other main suggestion, to reduce resistance risk by planting more diverse crop species or crops with different characteristics, Tinsley fully acknowledges it’s more radical. “We have an experimental paper coming out on this topic soon,” he says. “However, more research will be needed to determine how generally effective crop diversification is in combatting resistance across a range of different biopesticides and pest species.”
The team also asks whether, in farming systems where crops cannot be diversified or for monophagous pests that only feed on one crop species, other approaches could play a role in preventing resistance. These include the use of crop variety diversity, biostimulants and endophytic microbes.
Concerning the latter, Brownbridge is cautious. He notes that while all plants contain multiple endophytes, it would be a significant achievement to have an organism gain access to and live within a plant for its entire life at levels that would have a biologically-significant and lasting effect on pests or diseases.
“Very few organisms can do this,” he notes. “Several microbes can colonize and survive on plant roots, where they derive nutrients from root exudates, some Bacillus and Trichoderma species, for example, and some Bacillus species are already used. Even living biopesticides need to re-applied periodically, though, and non-living ones more regularly.”
Cost, mandates and moreBrownbridge agrees that farmer knowledge level about how resistance develops and how to avoid it is critical, but another factor may trump all that. Farming is a
business, he says, and input costs are always a consideration.
He notes that older chemistries tend to be much less expensive than new synthetics and biologicals. And while biologicals can improve pest defense efficacy and reduce the environmental impact of crop protection without lowering yield or crop quality, cost per acre may not be feasible.
“Would mandating use of rotations/biopesticide help?” Brownbridge asks. “It would certainly force the issue, but I genuinely believe most farmers would go the ‘bio’ route once convinced the products work and can do so in a manner that is cost-effective for them, so I would not push for a legal resolution.”
For their part, Mangan’s team has not considered legal mandates. “We’re really interested in studying the best ways to communicate with farmers,” she says, “and the best ways to incentivise adoption of resistance management approaches for microbial biopesticides.”
Looking forward, she and her colleagues observe that it’s likely fewer conventional chemical pesticides will be marketed in future because of stricter regulation, making protection of biopesticide efficacy all the more critical.
They add that “from the industry perspective, it would be beneficial to create incentives for the development of novel products in parallel (rather than launching new products only once legislation or resistance has rendered previous products obsolete) and to alter licensing frameworks to make the registration of new biopesticides more straightforward. Such actions will require care, especially in light of the highly variable and uncertain global pesticides market.”
And while their ideas for using multiple products and widening crop rotation requires further research and also presents adoption challenges, they are convinced these ideas are worth working on. They believe farming systems can exist that do not sacrifice livelihoods, environment or food quality, and in their “embrace of diversity” they can result in “more resilient and evolutionarily-sustainable food production.” ●
Several mechanisms of resistance have been proposed, but it seems that the receptors on the insect mid-gut are primarily involved in this evolution.
A new academic paper presents a Data Decision tree and risk-based flow chart to help identify potential risk when using natural substances in plant protection.
New AG International found out more from the authors.
Recently published in the open access journal Biocontrol Science and Technology, the paper opens with a brief overview of the current regulatory environment. Biocontrol substances used in plant protection, including the use of natural substances, tend to be regulated using the same regulatory system as for conventional chemical pesticides.
“This approach can pose an unnecessarily high and inappropriate regulatory burden because many data requirements and evaluation criteria are not relevant, appropriate or technically feasible for natural substances,” Lara Ramaekers told New AG International. Lara is business development director, biopesticides, for Biobest Group and Chair of the Natural Substances Professional Group at IBMA Global. She is the corresponding author for the paper.
The paper argues that the registration of natural substances, which are biocontrol products from natural origin, should focus on relevant potential risk areas. The paper presents a tiered approach to assessing the risk of a natural substance, resulting in a Data Decision tree that aims to assist all stakeholders when assessing potential risk areas. The Data Decision tree is also presented in a flow chart format. The paper was published in the journal Biocontrol Science and Technology, published by Taylor & Francis, part of Informa Group to which New AG International belongs.
Lara said the work started in June 2019 as a participative project open to all members of the International Biocontrol Manufacturers’ Association (IBMA) who are involved in the Natural Substances Professional Group,
which has more than 100 companies.
“From start to finish, well over 40 regulatory experts have worked together in workshops and meetings to brainstorm, develop, write and comment this work in a time span of four years. This publication lays together many decades of experience each of these experts carry and is therefore an incredible and unique piece of work.”
Why the academic route?The authors of the paper (see Notes) represent different sectors of the industry – association (IBMA), consultancy, and commercial enterprise.
“At the very beginning of the development of this Data Decision tree, we took the conscious decision to produce a paper that would be peer-reviewed and published with open access,” notes Lara. “This way, it is valued as an objective and science-based guidance and can be used by applicants, and referred to by regulators who target registration for plant protection purposes.”
We took the conscious decision to produce a paper that would be peer-reviewed and published with open access. This way, it is valued as an objective and science-based guidance and can be used by applicants, and referred to by regulators who target registration of natural substances for plant protection purposes
Intended audienceThe intended audience for the paper is regulators from authorities, as well as all those making applications to use natural substances for plant protection purposes.
“We aim at helping them to get to market and offer their innovative solutions to the farmer with a clearer pathway and less legal and time uncertainties which are critical especially for SMEs with limited resources,” says Lara.
The paper should also provide value to CROs and research institutions that do trials and develop methods to test natural substances.
Ultimately and hopefully, this paper can be used to develop tailored guidance and data requirements for regulation of natural substances for plant protection in different geographies such as EU or other countries who today are using the same regulatory system for both conventional pesticides and natural substances, expands Lara.
Role reversalThe purpose of the paper could be seen in terms of role reversal.
“Today, we see that the evaluation mindset is still based on synthetic chemical substances which are relatively simple and totally defined (typically, there is only one synthetized chemical molecule with a high purity). Natural substances are often complex mixtures of few to many components, which are impossible to fully characterize and define,” explains Lara.
“In this paper, we motivate why it makes sense to evaluate the mixture as a whole first and only trigger further testing if issues with this mixture are identified. Only then, there is a need to drill down in the mixture to understand which part of the mixture is causing the issue. So the burden of proof is reversed, and not considered guilty by default.”
Often there is already known and published information on these natural substances because of their use in other sectors such as food or pharma. This paper prioritizes the use of published literature, public databases and omics tools as a first approach to evaluate the risk.
Lara adds that typically natural substances are more readily biodegradable which reduces the environmental risk. She notes that this justifies maximum residue level (MRL) exemptions for these natural substances, or may focus the need to establish an MRL for only the lead component.
“If this more pragmatic, need-to-know approach was followed for the regulation of natural substances for plant protection, then this will make the whole registration dossier and process more relevant and efficient, improve the time to registration and decrease the level of uncertainty on timelines/chances on obtaining the registration of natural substances,” explains Lara.
If this more pragmatic, need to know approach would be followed for the regulation of natural substances for plant protection, then this will make the whole registration dossier and process more relevant and efficient, improve the time to registration and decrease the level of uncertainty on timelines/chances on obtaining the registration of natural substances
Defining categoriesThe paper classifies natural substances into three categories.
Group 1 is for natural substances that are, with current knowledge, known to have no established effects on humans, animals and the
environment with recognized specifications e.g., food/feed use.
Group 2 is for natural substances with an established specification and for which the current knowledge indicates that the natural substance may contain known or suspected critical components for humans, animals and/or the environment.
Group 3 is for natural substances that are not based on an established specification.
This set of group definitions was adapted from guidance documents submitted by the FAO and the World Health Organisation (WHO), by the Organisation for Economic Co-operation and Development (OECD) and by the EU (EU, 2014; FAO/WHO, 2017; OECD, 2017).
Lara says there is a lot of data already known and published on natural substances because of their historical use in agriculture in some countries or because of their use in other sectors such as food or pharma. These natural substances are classified in group 1 or 2 in the beginning of the Data Decision tree approach.
“However, sometimes, a fully unknown natural substance pops up which has no or very little background information or prior known use experience. For this group of natural substances, the Data Decision tree will indicate the need for more studies and in-depth risk assessments to define the risk for use of this group 3 natural substances for plant protection.”
Branching outFor each area which is evaluated during registration, specific “branches” of the Data Decision tree have been developed.
Identification, characterization, and analysis (Branch 1) addresses the risk areas and determines the categorization of the natural substance into groups 1, 2 or 3.
The 1,2 and 3 group categories are used for the subsequent branches of the Data Decision tree: effects on human health (branch 2), residues (branch 3) and environmental fate and behaviour (branch 4) but they are not used for effects on non-target organisms (branch 5).
Background informationFor many natural substances, residues will not be relevant as in general they will be used at background levels, degrade in the environment, or decline to background level, says the paper.
For branch 3, the objective of this branch is to assess natural substances exposure by identifying only toxicologically relevant residues that cannot be excluded so, if residues are likely to be present.
“Natural substances are occurring in nature, sometimes even in food or feed. In these cases, reduced risk assessment is required. We however do not compromise on safety. Thus, in the Data Decision tree, if no or only limited information is available, we refer back to the usual risk assessment as is stipulated in the relevant (EFSA) guidance documents so to allow a conclusion on a safe use to protect operators but also other non-consumer and consumer exposure,” expands Lara.
“However, it is important to mention that when natural substances are used at background levels or degrade to background levels it does not make sense to set MRLs, since it would not be possible to differentiate between background and plant protection natural substance, so it is not possible to set up an MRL that cannot be enforced.”
Initial feedbackThe final question was to ask about the initial feedback that the team has received so far on the paper. Lara said: “The publication of the paper took a long time (four years from start to finish). During this time, the IBMA natural substances professional group got many requests from many parties to know when the paper would be published which testifies the great interest and need that stakeholders had to start using the Data Decision tree.
“When the paper was finished and before submission (September 2022), we organized a workshop for IBMA members to use and evaluate the tree using three real-life case studies,” adds Lara. “The conclusion of that workshop was that indeed, the tree was fully fit for purpose for natural substances and helped to identify focus and the right points for discussion for pre-submission meetings with authorities.
“We have also presented this paper at the EU Biopesticides Working Group and received positive feedback. We are working with other associations on the use and evaluation of this data decision tree approach.”
Ramaekers signs off by saying that the IBMA natural substances professional group believes it will take more time and actual use by all stakeholders to really gather in depth feedback and also map any potential for improvement of this data decision tree. ●
Lara Ramaekers, Chair of the Natural Substances Professional Group at IBMA Global
IBMA – International Biocontrol Manufacturers’ Association
Data Decision tree for identifying potential risks for natural substances when used in plant protection
Marloes Busschers, Roma Gwynn, Lara Ramaekers, Jennifer Lewis & Francesco Greco
Biocontrol Science and Technology, 33:7, 597-629, DOI:
10.1080/09583157.2023.2210268
Taylor & Francis Group
The Samurai wasp (Trissolcus mitsukurii) is being touted as a potential future biocontrol superhero against brown marmorated stink bug (BMSB), an insect pest threatening Australia.
The Samurai wasp was first recorded in Australia in 1914, but it hasn’t been seen there since 1998. Australia’s national science agency, CSIRO, recently undertook an egg sentinel survey for the Samurai wasp across Queensland, NSW, Victoria and South Australia.
The Samurai wasp was introduced in a biocontrol program in 1962 to help control the green vegetable bug (GVB), Nezara viridula. Subsequently, it was found in the Australian Capital Territory (ACT), NSW, Queensland, Victoria, Western Australia (WA) and South Australia. But it hasn’t been recorded since 1998, when the last specimens were found in ACT and WA. A biological control program would involve breeding the wasp up in large numbers and releasing it to target BMSB wherever it is found in any future incursion.
But first scientists need to find out more about which hosts T. mitsukurii uses in Australia. The country has a high number of endemic stink bug species (94 genera and 330 species) so it probably uses some of these as hosts. This large number of native stink bug species would also make it tricky to import new host specific exotic biological control agents.
The Australian National Insect Collection (ANIC) recently used CSIRO’s identified stink bugs species from Australia and overseas to train artificial intelligence (AI) to distinguish BMSB from similar looking native species. The result is a smart phone app now being trialed at ports and airports by biosecurity officers.
In addition, CSIRO entomologist Dr. Valerie Caron and her team used egg sentinel surveys to hunt for the tiny Samurai wasp at organic farms and gardens. They established a laboratory colony of GVB to produce eggs to use in the survey, then placed these eggs at organic farms across Queensland, NSW, ACT, Victoria and South Australia during 2021 and 2022. At each field site, the team deployed 10 egg rafts, either glued on a wooden stick or on a bandage and fastened to a marker. After a week, the team brought these back to the laboratory to monitor for parasitoid emergence.
The project team double-checked existing specimens previously found to make sure they really were the Samurai wasp. World leading Trissolcus taxonomist Dr. Elijah Talamas reviewed previous taxonomic work and confirmed a match between previous specimens and T. mitsukurii from Asia. The team also built Australia’s first molecular library of all Trissolcus specimens from Australia and New Zealand. Specialist staff from ANIC used next generation sequencing to extract degraded DNA from old specimens. This new library will allow easy identification of these species.
Unfortunately, the researchers didn’t find any T. mitsukurii Samurai wasps using the egg sentinel survey. But they improved their knowledge of the species in Australia using taxonomic methods and molecular sampling of old specimens. The door remains open for future survey work, which could use broader techniques such as insect traps. These require less input at the field work stage, but more sorting of the samples, because they catch a broader range of insects. One option would be insect traps with chemical lures (pheromone traps). These could be easily manufactured with 3D printers and used across a wider range. ●
The Samurai wasp Trissolcus mitsukurii.
© Dr. Elijah Talamas
CABI has joined forces with FA Bio and Crop Health and Protection (CHAP) as part of a two-year feasibility study investigating the power of native fungi to provide protection against pests and diseases blighting British cereal crops.
The project, which is being led by FA Bio, is funded by Defra through the Farming Innovation Programme (FIP) and delivered via Innovate UK, aims to develop a biopesticide solution.
UK production of wheat is significantly hampered by insect pests and fungal diseases, including cereal aphids such as the cherry-oat and viral agents – notably barley yellow dwarf virus and cereal yellow virus. Through glasshouse trials, the performance of selected fungal isolates against two cereal aphid species will be assessed, while subsequent field trials will focus on determining efficacy against both insect and fungal pests. By leveraging existing data from FA Bio’s prior research and data, this project is set to accelerate the lengthy process of biopesticide commercialization in the UK.
The UK’s first catalogue of UK crop-related microorganisms has now been launched by CHAP, in partnership with CABI Fera. The CHAP National Reference Collection (NRC), which brings together the collections of CABI and Fera, is the first of its type for plant pathogenic fungi and bacteria in the UK. Accessible to all through a single searchable database, this unique catalogue of authenticated UK crop biotic threats can help identify crop pathogens and enable the screening of potential new biopesticides. ●
The power of native fungiwill be harnessed to develop a cutting-edge biopesticide that could revolutionize the British cereal farming industry.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) Spotted Lanternfly Strategic Planning Working Group released the spotted lanternfly five-year strategy for fiscal years 2024-2028.
APHIS brought together the working group in August 2022 with representatives from APHIS, the National Association of State Departments of Agriculture (NASDA) and the National Plant Board (NPB). The working group developed a unified approach to reduce the spotted lanternfly’s spread and impacts through the effective use of available state and federal resources.
“Over the next five years, federal and state partners will work to limit the spotted lanternfly’s advancement as we further scientific research that will help us develop better pest management tools and options,” said Jenny Lester Moffitt, USDA marketing and regulatory programs under secretary.
The five-year strategy prioritizes these goals: effectively limit the advancement of spotted lanternfly and efficiently respond to its introduction within federal and state authority and resource availability; support continued scientific research towards practical management and risk mitigation; and establish a consistent national and state-level outreach message and educational campaign for the public and industries at risk for spreading spotted lanternfly (SLF).
SLF has spread to 13 additional states since it was first detected in Pennsylvania in 2014. Spotted lanternflies prefer to feed on the invasive tree of heaven, but they also feed on a wide range of crops and plants, including grapes, apples, hops, walnuts and hardwood trees.
To reduce the spread, APHIS and states will create a framework to prevent human-assisted movement, promote public reporting and early detection, and leverage the latest research and management tools available. The new strategy builds the capacity to combat SLF in areas at high risk of introduction and stresses that SLF management plans be based on the latest risk-assessment modeling data which helps predict where SLF populations may emerge. Federal and state partners will also unite their research resources and share knowledge about SLF to limit its movement and distribution. While leveraging best practices in the field, state and federal partners will prioritize more research on climate and host-plant suitability, biocontrol agents,as well as other effective management tools. ●
