The entomopathogenic fungus Akanthomyces muscarius is commonly used in agriculture to manage insect pests. Besides its use as a commercially important biological control agent, it also presents a potential model for studying host–pathogen interactions and the evolution of virulence in a laboratory setting. Here, we describe the first high-quality genome sequence for A. muscarius. We used long- and short-read sequencing to assemble a sequence of 36.1 Mb with an N50 of 4.9 Mb. Genome annotation predicted 12347 genes, with 96.6 % completeness based on the core Hypocrealen gene set. The high-quality assembly and annotation of A. muscarius presented in this study provides an essential tool for future research on this commercially important species.

The entomopathogenic fungus Akanthomyces muscarius is used as a biological control agent for the management of insect pests in agriculture. It also presents a potential model for studying host-pathogen interactions and the evolution of virulence in a laboratory setting. Here, we present the first high-quality genome sequence for A. muscarius. We used long- and short-read sequencing to assemble a sequence of 36.1 Mb with an N50 of 4.9 Mb. Genome annotation predicts 12,347 genes, with 96.6 % completeness based on the core Hypocrealen gene set (Benchmarking Universal Single-Copy Orthologs). The first high-quality assembly and annotation of A. muscarius presented in this study provide a powerful tool for further research on this commercially important species.

The entomopathogenic fungus Akanthomyces muscarius is commonly used in agriculture to manage insect pests. Besides its use as a commercially important biological control agent, it also presents a potential model for studying host-pathogen interactions and virulence evolution in a laboratory setting. Here, we describe the first high-quality genome sequence for A. muscarius. We used long- and short-read sequencing to assemble a sequence of 36.1 Mb with an N50 of 4.9 Mb. Genome annotation predicts 12,347 genes, with 96.6 % completeness based on the core Hypocrealen gene set (Benchmarking Universal Single-Copy Orthologs). The high-quality assembly and annotation of A. muscarius presented in this study provide an essential tool for future research on this commercially important species.

AbstractChanges in parasite virulence are commonly expected to lead to trade-offs in other life history traits that can affect fitness. Understanding these trade-offs is particularly important if we want to manipulate the virulence of microbial biological control agents. Theoretically, selection across different spatial scales, i.e. between- and within-hosts, shapes these trade- offs. However, trade-offs are also dependent on parasite biology. Despite their applied importance the evolution of virulence in fungal parasites is poorly understood: virulence can be unstable in culture and commonly fails to increase in simple passage experiments. We hypothesized that manipulating selection intensity at different scales would reveal virulence trade-offs in a fungal pathogen of aphids,Akanthomyces muscarius. Starting with a genetically diverse stock we selected for infectivity, parasite yield or speed of kill by manipulating competition within and between hosts and between groups of hosts over 7 rounds of infection. We characterized ancestral and evolved lineages by whole genome sequencing and by measuring virulence, growth rate, sporulation and fitness. While several lineages showed increases in virulence, we saw none of the trade-offs commonly found in obligately-killing parasites. Phenotypically similar lineages within treatments often shared multiple single-nucleotide variants, indicating strong convergent evolution. The most dramatic phenotypic changes were in timing of sporulation and spore productionin vitro.We found that early sporulation led to reduced competitive fitness but could increase yield of spores on media, a trade-off characteristic of social conflict. Notably, the selection regime with strongest between-group competition and lowest genetic diversity produced the most consistent shift to early sporulation, as predicted by social evolution theory. Mutli-level selection therefore revealed social interactions novel to fungi and showed that these biocontrol agents have the genomic flexibility to improve multiple traits -virulence and spore production - that are often in conflict in other parasites.Author summaryUnderstanding the ecological forces that shape virulence is a key challenge in evolutionary biology. Here we investigated how competition at different levels of selection (within-hosts, between-hosts, between populations) could alter investment in virulence in a fungal entomopathogen. We predicted that cooperative investment in virulence would increase at higher scales of competition and aimed to further our understanding of potential trade-offs shaping life-history of a fungal insect pathogens. We found moderate increases in virulence in different selection regimes but importantly, none of the commonly expected trade-offs, such as that between spore production and virulence or a relationship between virulence and growth rate, which is consistent with cooperation. However, we found convergent genetic changes and significant differences in timing and production of spores, dependent how we manipulated scales of selection. Our data suggests that this is driven by social conflict regarding the timing of sporulation. This carries fundamental importance for understanding how varying selection pressure at different scales shape pathogen life history. In addition, these results also have applied importance for understanding how to improve and select for beneficial traits in biocontrol agents.

Understanding the ecological and genetic factors that determine the evolution of virulence has broad value for invertebrate pathology. In addition to helping us understand the fundamental biology of our study organisms this body of theory has important applications in microbial biocontrol. Experimental tests of virulence theory are often carried out in invertebrate models and yet theory rarely informs applied passage experiments that aim to increase or maintain virulence. This review summarizes recent progress in this field with a focus on work most relevant to biological control: the virulence of invertebrate pathogens that are 'obligate killers' and which require cadavers for the production of infectious propagules. We discuss recent theory and fundamental and applied experimental evolution with bacteria, fungi, baculoviruses and nematodes. While passage experiments using baculoviruses have a long history of producing isolates with increased virulence, studies with other pathogens have not been so successful. Recent passage experiments that have applied evolution of virulence frameworks based on cooperation (kin selection) have produced novel methods and promising mutants with increased killing power. Evolution of virulence theory can provide plausible explanations for the varied results of passage experiments as well as a predictive framework for improving artificial selection.

The entomopathogenic fungus (EPF) Akanthomyces muscarius has been used as a biocontrol agent for the management of insect pests in agriculture. Nevertheless, the licensing and commercial success of aphid biocontrol agents has been a challenge. This project had three main aims: test if this fungus could be used as a management tool for the control of insecticide resistant aphids (Myzus persicae); to test whether we could apply evolutionary theory to improve the properties of this species as biocontrol agents and finally to produce a high quality genome of this fungus as a resource for future use.
While we expected that pesticide resistant insects might have a fitness cost that would increase susceptibility to fungus, this proved not to be the case. In contrast, some susceptible clones, particularly those subject to decades of laboratory rearing, showed enhanced susceptibility to a fungal pathogen, but not reduced reproductive fitness, an observation consistent with down-regulation of costly immune functions in culture. Nevertheless, changes in susceptibility were small and overall, fungal pathogen control is compatible with insecticides and should not increase the selection pressure for resistance of M. persicae to chemical insecticides.
Experimental passage has been used to successfully increase virulence of insect pathogens. Passage experiments with EPF are relatively unexplored. Here we adopted a theory based approach and selected for speed of kill, pathogen yield and infectivity at different scales of competition in M. persicae. The selection experiment resulted in small but significant increases in virulence when compared to the ancestor, which also resulted in increased virulence against another aphid host, Brevicoryne brassicae. In addition, we also observed
increases in spore production on solid media and changes in timing of sporulation in some treatments. Changes in sporulation were unrelated to virulence showing that it is possible to produce more virulent mutants with improved sporulation characteristics.
We also present a new population genomic resource for A. muscarius comprising a high-quality genome assembly together with resequenced genomes of 13 experimentally selected lineages of this fungi.
The work presented here benefits industrial partners and stakeholders by providing novel methodologies for strain improvement of EPF and efficacy data of EPF on aphid genotypes resistant to synthetic insecticides. Increased use of biopesticides containing EPF can lead to a reduction in the use of chemical pesticides, increased biodiversity and reduced impacts on pollinators and other beneficial insects and could facilitate integrated biocontrol of difficult to manage aphid pests.

BACKGROUND: Biological control is a cornerstone of integrated pest management and could also play a key role in managing the evolution of insecticide resistance. Ecological theory predicts that the fitness cost of insecticide resistance can be increased under exposure to invertebrate natural enemies or pathogens, and can therefore increase the value of integrating biological control into pest management. In this study of the peach potato aphid, Myzus persicae, we aimed to identify whether insecticide resistance affected fitness and vulnerability of different aphid clones to the entomopathogenic fungus Akanthomyces muscarius. RESULTS: Insecticide resistant clones were found to be slightly less susceptible to the pathogen than susceptible clones. However, this pattern could also be explained by the influence of length of laboratory culture, which was longer in susceptible clones and was positively correlated with susceptibility to fungi. Furthermore, resistance status did not affect aphid development time or intrinsic rate of increase of aphids. Finally, in a cage trial the application of fungus did not increase the competitive fitness of insecticide resistant clone 'O'. CONCLUSION: We found no fitness cost in reproductive rate or pathogen susceptibility associated with chemical resistance in M. persicae. In contrast, some susceptible clones, particularly those subject to decades of laboratory rearing, showed enhanced susceptibility to a fungal pathogen, but not reduced reproductive fitness, an observation consistent with down-regulation of costly immune functions in culture. Overall, fungal pathogen control is compatible with insecticides and should not increase the selection pressure for resistance of M. persicae to chemical insecticides.

AbstractThe lack of commercially available low-cost laboratory spraying equipment for testing microbial control agents can hinder advancement in the field of biocontrol. This study presents an inexpensive, portable sprayer that is calibrated utilizing laboratory consumables. The computer aided design files are made available so that it is freely modifiable and can be used for machine routing or 3D printing. Bioassay data was obtained by spraying Myzus persicae with spores of entomopathogenic fungi. Observed variation in droplet deposition within tested pressure and volume settings, and spore deposition within sprayed concentrations were low. Bioassay results show reproducible mortality for the tested doses.