Using entomopathogenic fungi for biological control is an effective method for controlling certain crop pests, with the perspective of reducing the use of chemical pesticides. Yet, the efficiency of pathogenic fungi is dependent upon many factors that need to be evaluated to improve biological control potential in the fields (Lacey, 2001). The article by Chailleux et al. (2024) presents an exciting contribution to the field of biological pest control, specifically focusing on using entomopathogenic fungi to manage the oriental fruit fly, Bactrocera dorsalis. This fly, a member of the Tephritidae family, is a major threat to orchards in Asia, the Pacific and Africa, as it attacks fruit and causes considerable damage, in addition to having a relatively rapid biological invasion dynamic (Clarke et al. 2005). 

The objective of the Chailleux et al. (2024) study was to evaluate the virulence of Metarhizium anisopliae spores (strain Met69) on B. dorsalis adult flies according to various conditions: the inoculation dose and spore load, the formulation (adjuvant) and temperature conditions. The focus on host specificity and on-target applications was conducted to ensure minimal impact on non-target organisms, which is crucial for sustainable agriculture. The main challenge in this system was to achieve high strain virulence to kill wild individuals with a low number of spores—therefore limiting impact on non-target species such as natural enemies—but with a sufficient incubation period to allow transmission from mass-reared insects to wild conspecifics (Leite et al. 2022). A comparison of different inoculation methods is also provided and is interesting from a methodological point of view for future studies or even large-scale applications.

Using a well-designed experimental setup, the authors show that high pathogenicity (measured by LD50) is achievable even at low spore doses and independently of the fly's sex. Lethal action speed was, however, dependent on the dose. Regarding temperature, the authors demonstrated that mycelium growth was affected by the mean temperature but, most importantly, by daily fluctuation regimes; night and day temperature alternation allowed faster growth than constant temperature. These notions of thermal fluctuations are still under-researched in terms of their modulating role in biological control yet seem central to understanding them, as the authors demonstrate here. The correlation between increased virulence and specific abiotic factors, such as temperature, offers valuable additional insights into the bioecology of the insect host and the fungal pathogen. Chailleux et al. finally point out the need for careful selection of adjuvants in formulations and pay attention to interactions with the abiotic environment to avoid compromising the effectiveness of biological control agents. Indeed, the survival rate of inoculated flies increased in the presence of the corn starch adjuvant, but this effect decreased with temperature. As corn starch unexpectedly delayed mortality, the authors suggest a potential for enhancing conspecific transmission

From a broader perspective, the study emphasizes the importance of standardizing virulence evaluation to optimize biological control strategies like auto-dissemination or vectoring with sterile males, particularly in field conditions. The study contributions are timely and essential for advancing sustainable pest management strategies and improving inoculation methods. The findings underscore the need for field trials to refine these strategies, particularly in Africa, where climatic factors may affect pathogen efficacy and fly behavior. I recommend publishing this article in a referenced journal like the Peer Community Journal. 

References

Chailleux, A. Coulibaly, ON, Diouf B, Diop S, Sohel A, Brevault T (2023) Dose, temperature and formulation shape Metarhizium anisopliae virulence against the oriental fruit fly: lessons for improving on-target control strategies. bioRxiv, ver.2 peer-reviewed and recommended by PCI Zoology https://doi.org/10.1101/2023.12.14.571642

Clarke, A. R. et al. (2005). Invasive phytophagous pests arising through a recent tropical evolutionary radiation: the Bactrocera dorsalis complex of fruit flies. Annu. Rev. Entomol., 50, 293-319. https://doi.org/10.1146/annurev.ento.50.071803.130428

Lacey, L. A. (2001). Formulation of microbial biopesticides: beneficial microorganisms, nematodes and seed treatments. J Invertebr Pathol, 77, 147. https://doi.org/10.1006/jipa.2000.5005

Leite, M. O. et al. (2022). Laboratory risk assessment of three entomopathogenic fungi used for pest control toward social bee pollinators. Microorganisms, 10, 1800. https://doi.org/10.3390/microorganisms10091800

Wildlife is increasingly threatened by drops in number of individuals and populations, and eventually by extinction. Besides loss of habitat, persecution, pet trade,… a decrease in individual health status is an important factor to consider. In this article, Ballouard et al (2021)  perform a thorough analysis on the prevalence of two pathogens (herpes virus and mycoplasma) in (mainly) Western Hermann’s tortoises in south-east France. This endangered species was suspected to suffer from infections obtained through released/escaped pet tortoises. By incorporating samples of captive as well as wild tortoises, they convincingly confirm this and identify some possible ‘pet’ vectors. 

In February this year, a review paper on health assessments in wildlife was published (Kophamel et al 2021). Amongst others, it shows reptilia/chelonia are relatively well-represented among publications. It also contains a useful conceptual framework, in order to improve the quality of the assessments to better facilitate conservation planning. The recommended manuscript (Ballouard et al 2021) adheres to many aspects of this framework (e.g. minimum sample size, risk status, …) while others might need more (future) attention. For example, climate/environmental changes are likely to increase stress levels, which could lead to more disease symptoms. So, follow-up studies should consider conducting endocrinological investigations to estimate/monitor stress levels. Kophamel et al (2021) also stress the importance of strategic international collaboration, which may allow more testing of Eastern Hermann’s Tortoise, as these were shown to be infected by mycoplasma.

The genetic health of individuals/populations shouldn’t be forgotten in health/stress assessments. As noted by Ballouard et al (2021), threatened species often have low genetic diversity which makes them more vulnerable to diseases. So, it would be interesting to link the infection data with (individual) genetic characteristics. In future research, the samples collected for this paper could fit that purpose.

Finally, it is expected that this paper will contribute to the conservation management strategy of the Hermann’s tortoises. As such,  it will be interesting to see how the results of the current paper will be implemented in the ‘field’. As the infections are likely caused by releases/escaped pets and as treating the wild animals is difficult, preventing them from getting infected through pets seems a priority.  Awareness building among pet holders and monitoring/treating pets should be highly effective.

References

Ballouard J-M, Bonnet X, Jourdan J, Martinez-Silvestre A, Gagno S, Fertard B, Caron S (2021) First detection of herpesvirus and mycoplasma in free-ranging Hermann’s tortoises (Testudo hermanni), and in potential pet vectors. bioRxiv, 2021.01.22.427726, ver. 4 peer-reviewed and recommended by Peer Community in Zoology. https://doi.org/10.1101/2021.01.22.427726

Kophamel S, Illing B, Ariel E, Difalco M, Skerratt LF, Hamann M, Ward LC, Méndez D, Munns SL (2021), Importance of health assessments for conservation in noncaptive wildlife. Conservation Biology. https://doi.org/10.1111/cobi.13724

Redistribution of domesticated and non domesticated species by humans profoundly affected earth biogeography and in return human activities. This process accelerated exponentially since human expansion out of Africa, leading to the modern global, highly connected and homogenized, agriculture and trade system (Mack et al. 2000, Jaksic and Castro 2021), that threatens biological diversity and genetic resources. To accompany quarantine and control effort, the reconstruction of invasion routes provides valuable information that help identifying critical nodes and edges in the global networks (Estoup and Guillemaud 2010, Cristescu 2015). Historical records and genetic markers are the two major sources of information of this corpus of knowledge on Anthropocene historical phylogeography. With the advances of molecular genetics tools, the genealogy of these introductions events could be revisited and empowered. Due to their idiosyncrasy and intimate association with the contingency of human trades and activities, understanding the invasion and domestication routes require particular statistical tools (Fraimout et al. 2017).

Because it encompasses all these theoretical, ecological and economical implications, I am pleased to recommend the readers of PCI Zoology this article by Mallez et al. (2021) on pine wood nematode invasion route inference from genetic markers using Approximate Bayesian Computation (ABC) methods.

Economically and ecologically, this pest, is responsible for killing millions of pines worldwide each year. The results show these damages and the global genetic patterns are due to few events of successful introductions. The authors consider that this low probability of introductions success reinforces the idea that quarantine measures are efficient. This is illustrated in Europe where the pine-worm has been quarantined successfully in the Iberian Peninsula since 1999. Another relevant conclusion is that hybridization between invasive populations have not been observed and implied in the invasion process. Finally the present study reinforced the role of Asiatic bridgehead populations in invasion process including in Europe.

Methodologically, for the first time, ABC was applied to this species. A total of 310 individual sequences were added to the Mallez et al. (2015) microsatellite dataset. Fraimoult et al. (2017) showed the interest to apply random forest to improve scenario selection in ABC framework. This method, implemented in the DiYABC software (Collin et al. 2020) for invasion route scenario selection allows to handle more complex scenario alternatives and was used in this study. In this article by Mallez et al. (2021), you will also find a clear illustration of the step-by-step approach to select scenario using ABC techniques (Lombaert et al. 2014). The rationale is to reduce number of scenario to be tested by assuming that most recent invasions cannot be the source of the most ancient invasions and to use posterior results on most ancient routes as prior hypothesis to distinguish following invasions. The other simplification is to perform classical population genetic analysis to characterize genetic units and representative populations prior to invasion routes scenarios selection by ABC.

Yet, even when using the most advanced Bayesian inference methods, it is recognized by the authors that the method can be pushed to its statistical power limits. The method is appropriate when population show strong inter-population genetic structure. But the high number of differentiated populations in native area can be problematic since it is generally associated to incomplete sampling scheme. The hypothesis of ghost populations source allowed to bypass this difficulty, but the authors consider simulation studies are needed to assess the joint effect of genetic diversity and number of genetic markers on the inference results in such situation. Also the need to use a stepwise approach to reduce the number of scenario to test has to be considered with caution. Scenarios that are not selected but have non negligible posterior, cannot be ruled out in the constitution of next step scenarios hypotheses.

Due to its interest to understand this major facet of Anthropocene, reconstruction of invasion routes should be more considered as a guide to damper biological homogenization process.

References

Collin, F.-D., Durif, G., Raynal, L., Lombaert, E., Gautier, M., Vitalis, R., Marin, J.-M. and Estoup, A. (2020) Extending Approximate Bayesian Computation with Supervised Machine Learning to infer demographic history from genetic polymorphisms using DIYABC Random Forest. Authorea. doi: https://doi.org/10.22541/au.159480722.26357192

Cristescu, M.E. (2015) Genetic reconstructions of invasion history. Molecular Ecology, 24, 2212–2225. doi: https://doi.org/10.1111/mec.13117

Estoup, A. and Guillemaud, T., (2010) Reconstructing routes of invasion using genetic data: Why, how and so what? Molecular Ecology, 9, 4113-4130. doi: https://doi.org/10.1111/j.1365-294X.2010.04773.x

Fraimout, A., Debat, V., Fellous, S., Hufbauer, R.A., Foucaud, J., Pudlo, P., Marin, J.M., Price, D.K., Cattel, J., Chen, X., Deprá, M., Duyck, P.F., Guedot, C., Kenis, M., Kimura, M.T., Loeb, G., Loiseau, A., Martinez-Sañudo, I., Pascual, M., Richmond, M.P., Shearer, P., Singh, N., Tamura, K., Xuéreb, A., Zhang, J., Estoup, A. and Nielsen, R. (2017) Deciphering the routes of invasion of Drosophila suzukii by Means of ABC Random Forest. Molecular Biology and Evolution, 34, 980-996. doi: https://doi.org/10.1093/molbev/msx050

Jaksic, F.M. and Castro, S.A. (2021). Biological Invasions in the Anthropocene, in: Jaksic, F.M., Castro, S.A. (Eds.), Biological Invasions in the South American Anthropocene: Global Causes and Local Impacts. Springer International Publishing, Cham, pp. 19-47. doi: https://doi.org/10.1007/978-3-030-56379-0_2

Lombaert, E., Guillemaud, T., Lundgren, J., Koch, R., Facon, B., Grez, A., Loomans, A., Malausa, T., Nedved, O., Rhule, E., Staverlokk, A., Steenberg, T. and Estoup, A. (2014) Complementarity of statistical treatments to reconstruct worldwide routes of invasion: The case of the Asian ladybird Harmonia axyridis. Molecular Ecology, 23, 5979-5997. doi: https://doi.org/10.1111/mec.12989

Mack, R.N., Simberloff, D., Lonsdale, M.W., Evans, H., Clout, M., Bazzaz, F.A. (2000) Biotic Invasions : Causes , Epidemiology , Global Consequences , and Control. Ecological Applications, 10, 689-710. doi: https://doi.org/10.1890/1051-0761(2000)010[0689:BICEGC]2.0.CO;2

Mallez, S., Castagnone, C., Lombaert, E., Castagnone-Sereno, P. and Guillemaud, T. (2021) Inference of the worldwide invasion routes of the pinewood nematode Bursaphelenchus xylophilus using approximate Bayesian computation analysis. bioRxiv, 452326, ver. 6 peer-reviewed and recommended by Peer community in Zoology. doi: https://doi.org/10.1101/452326

The sorting of organisms along a fast-slow continuum through correlations between life history traits is a long-standing framework (Stearns 1983) and corresponds to the pace-of-life axis. This axis represents the variation in a continuum of life-history strategies, from fast-reproducing short-lived species to slow-reproducing long-lived species. The pace-of-life axis has been the focus of much research largely in mammals, birds, reptiles and plants but less so in invertebrates (Salguero-Gómez et al. 2016; Araya-Ajoy et al. 2018; Healy et al. 2019; Bakewell et al. 2020). Outcomes from this research have highlighted variation across taxa on this axis and mixed support for, and against, patterns expected of the pace-of-life continuum. Given this, a greater understanding of the variation of the pace-of-life across-, and within, taxa are needed. Indeed, Guicharnard et al. (2023) highlight several points regarding our broader understanding of pace-of-life. In general, invertebrates are poorly represented, the variation of pace-of-life across taxonomic scales is less well understood and the relationship between pace-of-life and dispersal, a key life history, requires more attention. Here, Guicharnard et al. (2023) provide a first attempt at addressing the relationship between dispersal and pace-of-life at different scales.

The authors, under controlled conditions, investigated how life-history traits and effective dispersal covary for 28 lines from five species of endoparasitoid wasps from the genus Trichogramma. At the species level negative correlations were found between development time and fecundity, matching pace-of-life axis predictions. Although this correlation was not found to be significant among lines, within species, a similar pattern of a negative correlation was observed. This outcome matches previous findings that consistent pace-of-life axes become more difficult to find at lower taxonomic levels. Unlike the other life-history traits measured, effective dispersal showed no evidence of differences between species or between lines. The authors also found no correlation between effective dispersal and other-life history traits which suggests no dispersal/life-history syndromes in the species investigated. One aspect that was not assessed was the impact of density dependence on pace-of-life and effective dispersal, largely as this was a first step in assessing relationship of dispersal with pace-of-life at different scales. However, the authors do acknowledge the importance of future studies incorporating density dependence and that such studies could potentially lead to more generalizable understanding of pace-of-life and dispersal within Trichogramma.

A pleasant addition was the link to potential implications for biocontrol. This addition showed an awareness by the authors of how insights into pace-of-life can have an applied component. The results of the study highlighted that selecting for specific lines of a species, to maximise a trait of interest at the cost of another, may not be as effective as selecting different species when implementing biocontrol. This is especially important as often single, established species used in biocontrol are favoured without consideration of the potential of other species which can lead to more efficient biocontrol.    

REFERENCES

Araya-Ajoy, Y.G., Bolstad, G.H., Brommer, J., Careau, V., Dingemanse, N.J. & Wright, J. (2018). Demographic measures of an individual's "pace of life": fecundity rate, lifespan, generation time, or a composite variable? Behavioral Ecology and Sociobiology, 72, 75.
https://doi.org/10.1007/s00265-018-2477-7
 
Bakewell, A.T., Davis, K.E., Freckleton, R.P., Isaac, N.J.B. & Mayhew, P.J. (2020). Comparing Life Histories across Taxonomic Groups in Multiple Dimensions: How Mammal-Like Are Insects? The American Naturalist, 195, 70-81.
https://doi.org/10.1086/706195
 
Guicharnaud, C., Groussier, G., Beranger, E., Lamy, L., Vercken, E. & Dahirel, M. (2023). Life-history traits, pace of life and dispersal among and within five species of Trichogramma wasps: a comparative analysis. bioRxiv, 2023.01.24.525360, ver. 3 peer-reviewed and recommended by Peer Community in Zoology.
https://doi.org/10.1101/2023.01.24.525360
 
Healy, K., Ezard, T.H.G., Jones, O.R., Salguero-Gómez, R. & Buckley, Y.M. (2019). Animal life history is shaped by the pace of life and the distribution of age-specific mortality and reproduction. Nature Ecology & Evolution, 3, 1217-1224.
https://doi.org/10.1038/s41559-019-0938-7
 
Salguero-Gómez, R., Jones, O.R., Jongejans, E., Blomberg, S.P., Hodgson, D.J., Mbeau-Ache, C., et al. (2016). Fast-slow continuum and reproductive strategies structure plant life-history variation worldwide. Proceedings of the National Academy of Sciences, 113, 230-235.
https://doi.org/10.1073/pnas.1506215112
 
Stearns, S.C. (1983). The Influence of Size and Phylogeny on Patterns of Covariation among Life-History Traits in the Mammals. Oikos, 41, 173-187.
https://doi.org/10.2307/3544261

Some of the biodiversity of our planet now exists only in museums, due to continuing habitat destruction and climate change. With more than 380 million entomological specimens already preserved in museums (Johnson and Owens 2023), there is much work left to document what we already have. Fortunately, new advances in DNA sequencing have given us the opportunity to get enormous amounts of information from dried specimens on pins.
 
One such advance is HyRAD-X, which uses RAD-derived probes originally developed using RNA extracted from a selection of specimens with high RNA-integrity (Schmid et al. 2017). These exome-limited probes can then be used to capture low-integrity DNA extracted from a single leg from museum specimens, followed by Illumina sequencing of the enriched libraries.
 
Ground beetles allow an excellent demonstration of this approach, as their diversity, large size, and charismatic appearance has led to them being well represented in museums. Using a HyRAD-X probe set previously developed for a higher phylogeny within the subfamily Carabinae (Toussaint et al. 2021), the authors have now applied the same probe set to produce a comprehensive phylogeny for Arcifera, a clade of four subgenera and ten species within the genus Carabus (Pauli et al. 2024).
 
Of the 96 specimens that they started out with, 90% were from natural history collections and 40% dropped out immediately due to poor DNA extraction yield. After filtering the resulting sequence reads for minimum coverage and minimum number of samples per locus, they ended up with 35 museum specimens with an average of 793 loci. Phylogenetic analysis of this data supported the current classification of these beetles.
 
Pauli et al’s. (2024) study has effectively shown the power of HyRAD-X methods for applications at the species level. In-house production of probes makes the method accessible, expanding the opportunity to use museum specimens for population genetic research.

References

Johnson KR, Owens, (IFP. 2023) A global approach for natural history museum collections. Science 379,1192-1194(2023). https://doi.org/10.1126/science.adf6434

Pauli MT, Gauthier J, Labédan M, Blanc M, Bilat J, Toussaint EFA (2024) Museomics of Carabus giant ground beetles shows an Oligocene origin and in situ alpine diversification. bioRxiv, ver. 5 peer-reviewed and recommended by Peer Community in Zoology. https://doi.org/10.1101/2024.03.21.586057

Schmid, S., Genevest, R., Gobet, E., Suchan, T., Sperisen, C., Tinner, W. and Alvarez, N. (2017), HyRAD-X, a versatile method combining exome capture and RAD sequencing to extract genomic information from ancient DNA. Methods Ecol Evol, 8: 1374-1388. https://doi.org/10.1111/2041-210X.12785

Toussaint EFA, Gauthier J, Bilat J, Gillett CPDT, Gough HM, Lundkvist H, Blanc M, Muñoz-Ramírez CP, Alvarez N (2021) HyRAD-X Exome Capture Museomics Unravels Giant Ground Beetle Evolution, Genome Biology and Evolution, Volume 13, Issue 7, evab112, https://doi.org/10.1093/gbe/evab112