Infection of Drosophila suzukii with the obligate insect-pathogenic fungus Entomophthora muscae

First record of Stigmatomyces (Ascomycota: Laboulbeniales) on Drosophilidae from Japan

Three Stigmatomyces species were detected on five drosophilid species from Japan. We report Stigmatomyces majewskii on Drosophila rufa and Drosophila suzukii, Stigmatomyces scaptodrosophilae on Scaptodrosophila coracina and Scaptodrosophila subtilis, and Stigmatomyces sacaptomyzae on Scaptomyza graminum. Except for Scaptomyza graminum, each of these species is a newly identified Stigmatomyces host. Our discovery that D. suzukii is a host of S. majewskii may provide new pest management approaches for this global agricultural pest insect.

The microbial RNA metagenome of Aedes albopictus (Diptera: Culicidae) from Germany

Aedes albopictus is a highly invasive mosquito species that has become widespread across the globe. In addition, it is an efficient vector of numerous pathogens of medical and veterinary importance, including dengue, chikungunya and Zika viruses. Among others, the vector potential of mosquitoes is influenced by their microbiome. However, this influence is very dynamic and can vary between individuals and life stages. To obtain a rough overview on the microbiome of Ae. albopictus populations in Germany, pooled female and pooled male individuals from seven German locations were investigated by total RNA sequencing. The mosquito specimens had been collected as larvae in the field and processed immediately after adult emergence, i.e. without females having fed on blood. RNA fragments with high degrees of identity to a large number of viruses and microorganisms were identified, including, for example, Wolbachia pipientis and Acinetobacter baumannii, with differences between male and female mosquitoes. Knowledge about the natural occurrence of microorganisms in mosquitoes may be translated into new approaches to vector control, for example W. pipientis can be exploited to manipulate mosquito reproduction and vector competence. The study results show how diverse the microbiome of Ae. albopictus can be, and the more so needs to be adequately analysed and interpreted.

Co-option of an extracellular protease for transcriptional control of nutrient degradation in the fungus Aspergillus nidulans

Nutrient acquisition is essential for all organisms. Fungi regulate their metabolism according to environmental nutrient availability through elaborate transcription regulatory programs. In filamentous fungi, a highly conserved GATA transcription factor AreA and its co-repressor NmrA govern expression of genes involved in extracellular breakdown, uptake, and metabolism of nitrogen nutrients. Here, we show that the Aspergillus nidulans PnmB protease is a moonlighting protein with extracellular and intracellular functions for nitrogen acquisition and metabolism. PnmB serves not only as a secreted protease to degrade extracellular nutrients, but also as an intracellular protease to control the turnover of the co-repressor NmrA, accelerating AreA transcriptional activation upon nitrogen starvation. PnmB expression is controlled by AreA, which activates a positive feedback regulatory loop. Hence, we uncover a regulatory mechanism in the well-established controls determining the response to nitrogen starvation, revealing functional evolution of a protease gene for transcriptional regulation and extracellular nutrient breakdown.

Susceptibility of Drosophila suzukii larvae to the combined administration of the entomopathogens Bacillus thuringiensis and Steinernema carpocapsae

Non-native pests are often responsible for serious crop damage. Since Drosophila suzukii has invaded North America and Europe, the global production of soft, thin-skinned fruits has suffered severe losses. The control of this dipteran by pesticides, although commonly used, is not recommended because of the negative impact on the environment and human health. A possible alternative is the use of bio-insecticides, including Bacillus thuringiensis and entomopathogenic nematodes, such as Steinernema carpocapsae. These biological control agents have a fair effectiveness when used individually on D. suzukii, but both have limits related to different environmental, methodological, and physiological factors. In this work, we tested various concentrations of B. thuringiensis and S. carpocapsae to evaluate their efficacy on D. suzukii larvae, when administered individually or in combination by using agar traps. In the combined trials, we added the nematodes after 16 h or concurrently to the bacteria, and assessed larvae lethality from 16 to 48 h. The assays demonstrated a higher efficacy of the combined administration, both time-shifted and concurrent; the obtained data also showed a relevant decrease of the time needed to kill the larvae. Particularly, the maximum mortality rate, corresponding to 79% already at 16 h, was observed with the highest concentrations (0.564 µg/mL of B. thuringiensis and 8 × 10² IJs of S. carpocapsae) in the concurrent trials. This study, conducted by laboratory tests under controlled conditions, is a good starting point to develop a further application step through field studies for the control of D. suzukii.

Fungal artillery of zombie flies: infectious spore dispersal using a soft water cannon

Dead sporulating female fly cadavers infected by the house fly-pathogenic fungus Entomophthora muscae are attractive to healthy male flies, which by their physical inspection may mechanically trigger spore release and by their movement create whirlwind airflows that covers them in infectious conidia. The fungal artillery of E. muscae protrudes outward from the fly cadaver, and consists of a plethora of micrometric stalks that each uses a liquid-based turgor pressure build-up to eject a jet of protoplasm and the initially attached spore. The biophysical processes that regulate the release and range of spores, however, are unknown. To study the physics of ejection, we design a biomimetic 'soft cannon' that consists of a millimetric elastomeric barrel filled with fluid and plugged with a projectile. We precisely control the maximum pressure leading up to the ejection, and study the cannon efficiency as a function of its geometry and wall elasticity. In particular, we predict that ejection velocity decreases with spore size. The calculated flight trajectories under aerodynamic drag predict that the minimum spore size required to traverse a quiescent layer of a few millimetres around the fly cadaver is approximately 10 µm. This corroborates with the natural size of E. muscae conidia (approx. 27 µm) being large enough to traverse the boundary layer but small enough (less than 40 µm) to be lifted by air currents. Based on this understanding, we show how the fungal spores are able to reach a new host.

Mitovirus and Mitochondrial Coding Sequences from Basal Fungus Entomophthora muscae

Fungi constituting the Entomophthora muscae species complex (members of subphylum Entomophthoromycotina, phylum Zoopagamycota) commonly kill their insect hosts and manipulate host behaviors in the process. In this study, we made use of public transcriptome data to identify and characterize eight new species of mitoviruses associated with several different E. muscae isolates. Mitoviruses are simple RNA viruses that replicate in host mitochondria and are frequently found in more phylogenetically apical fungi (members of subphylum Glomeromyoctina, phylum Mucoromycota, phylum Basidiomycota and phylum Ascomycota) as well as in plants. E. muscae is the first fungus from phylum Zoopagomycota, and thereby the most phylogenetically basal fungus, found to harbor mitoviruses to date. Multiple UGA (Trp) codons are found not only in each of the new mitovirus sequences from E. muscae but also in mitochondrial core-gene coding sequences newly assembled from E. muscae transcriptome data, suggesting that UGA (Trp) is not a rarely used codon in the mitochondria of this fungus. The presence of mitoviruses in these basal fungi has possible implications for the evolution of these viruses.

Advances in the Chemical Ecology of the Spotted Wing Drosophila (Drosophila suzukii) and its Applications

Significant progress has been made in understanding the cues involved in the host and mate seeking behaviors of spotted wing drosophila, Drosophila suzukii (Matsumura). This insect pest has been discovered in many fruit growing regions around the world since 2008. Unlike closely related Drosophila species, D. suzukii attacks fresh fruit and has become a severe pest of soft fruits including strawberry, cherry, blackberry, blueberry, raspberry, and may pose a threat to grapes. Prior to 2008, little was known about the courtship and host-seeking behaviors or chemical ecology of this pest. Since then, researchers have gained a better understanding of D. suzukii attraction to specific odors from fermentation, yeast, fruit, and leaf sources, and the visual cues that elicit long-range attraction. Several compounds have also been identified that elicit aversive behaviors in adult D. suzukii flies. Progress has been made in identifying the constituent compounds from these odor sources that elicit D. suzukii antennal responses in electrophysiological assays. Commercial lures based on food volatiles have been developed to attract D. suzukii using these components and efforts have been made to improve trap designs for monitoring this pest under field conditions. However, current food-based lures and trap technologies are not expected to be specific to D. suzukii and thus capture large numbers of non-target drosophilids. Attractive and aversive compounds are being evaluated for monitoring, mass trapping, and for the development of attract-and-kill and push-pull techniques to manage D. suzukii populations. This review outlines presently available research on the chemical ecology of D. suzukii and discusses areas for future research.

Robust manipulation of the behavior of Drosophila melanogaster by a fungal pathogen in the laboratory

Many microbes induce striking behavioral changes in their animal hosts, but how they achieve this is poorly understood, especially at the molecular level. Mechanistic understanding has been largely constrained by the lack of an experimental system amenable to molecular manipulation. We recently discovered a strain of the behavior-manipulating fungal pathogen Entomophthora muscae infecting wild Drosophila, and established methods to infect D. melanogaster in the lab. Lab-infected flies manifest the moribund behaviors characteristic of E. muscae infection: hours before death, they climb upward, extend their proboscides, affixing in place, then raise their wings, clearing a path for infectious spores to launch from their abdomens. We found that E. muscae invades the nervous system, suggesting a direct means by which the fungus could induce behavioral changes. Given the vast molecular toolkit available for D. melanogaster, we believe this new system will enable rapid progress in understanding how E. muscae manipulates host behavior.