Anna Spescha

Last Name

Spescha

First Name

Anna

ORCID

0000-0002-9184-2937

Organisational unit

08857 - Maurhofer, Monika (Tit.-Prof.) / Maurhofer, Monika (Tit.-Prof.)

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Publications 1 - 6 of 6

Sequestration of cucurbitacins from cucumber plants by Diabrotica balteata larvae provides little protection against biological control agents
Bruno, Pamela; Arce, Carla C.M.; Machado, Ricardo A.R.; et al. (2023)
Journal of Pest Science
Cucurbitaceae plants produce cucurbitacins, bitter triterpenoids, to protect themselves against various insects and pathogens. Adult banded cucumber beetles (Diabrotica balteata), a common pest of maize and cucurbits, sequester cucurbitacins, presumably as a defensive mechanism against their natural enemies, which might reduce the efficacy of biological control agents. Whether the larvae also sequester and are protected by cucurbitacins is unclear. We profiled cucurbitacin levels in four varieties of cucumber, Cucumis sativus, and in larvae fed on these varieties. Then, we evaluated larval growth and resistance against common biocontrol organisms including insect predators, entomopathogenic nematodes, fungi and bacteria. We found considerable qualitative and quantitative differences in the cucurbitacin levels of the four cucumber varieties. While two varieties were fully impaired in their production, the other two accumulated high levels of cucurbitacins. We also observed that D. balteata larvae sequester and metabolize cucurbitacins, and although the larvae fed extensively on both belowground and aboveground tissues, the sequestered cucurbitacins were mainly derived from belowground tissues. Cucurbitacins had no detrimental effects on larval performance and, surprisingly, did not provide protection against any of the natural enemies evaluated. Our results show that D. balteata larvae can indeed sequester and transform cucurbitacins, but sequestered cucurbitacins do not impact the biocontrol potential of common natural enemies used in biocontrol. Hence, this plant trait should be conserved in plant breeding programs, as it has been demonstrated in previous studies that it can provide protection against plant pathogens and generalist insects.
Entomopathogenic pseudomonads can share an insect host with entomopathogenic nematodes and their mutualistic bacteria
Regaiolo, Alice; Keel, Christoph; Maurhofer, Monika; et al. (2024)
The ISME Journal
A promising strategy to overcome limitations in biological control of insect pests is the combined application of entomopathogenic pseudomonads (EPPs) and nematodes (EPNs) associated with mutualistic bacteria (NABs). Yet, little is known about interspecies interactions such as competition, coexistence, or even cooperation between these entomopathogens when they infect the same insect host. We investigated the dynamics of bacteria–bacteria interactions between the EPP Pseudomonas protegens CHA0 and the NAB Xenorhabdus bovienii SM5 isolated from the EPN Steinernema feltiae RS5. Bacterial populations were assessed over time in experimental systems of increasing complexity. In vitro, SM5 was outcompeted when CHA0 reached a certain cell density, resulting in the collapse of the SM5 population. In contrast, both bacteria were able to coexist upon haemolymph-injection into Galleria mellonella larvae, as found for three further EPP-NAB combinations. Finally, both bacteria were administered by natural infection routes i.e. orally for CHA0 and nematode-vectored for SM5 resulting in the addition of RS5 to the system. This did not alter bacterial coexistence nor did the presence of the EPP affect nematode reproductive success or progeny virulence. CHA0 benefited from RS5, probably by exploiting access routes formed by the nematodes penetrating the larval gut epithelium. Our results indicate that EPPs are able to share an insect host with EPNs and their mutualistic bacteria without major negative effects on the reproduction of any of the three entomopathogens or the fitness of the nematodes. This suggests that their combination is a promising strategy for biological insect pest control.
Exploring the Biocontrol Potential of Insecticidal Fluorescent Pseudomonads Applied Alone and in Combination with Entomopathogenic Nematodes and Fungi
Spescha, Anna (2023)
This thesis focuses on the biocontrol of insect pests using insecticidal Pseudomonas bacteria. Fluorescent pseudomonads are well-known for their abilities to promote plant growth, suppress pathogens and induce systemic resistance. In the last decade, research focused on the mechanisms underlying oral insecticidal activity of P. chlororaphis and P. protegens subgroups as well as their ecological interactions with insects. We aimed at exploiting the insecticidal activity of pseudomonads for controlling below-ground insect pests alone and in combination with entomopathogenic nematodes and fungi. Furthermore, we explored the phyllosphere competence of fluorescent pseu- domonads, a prerequisite to control foliar pests and pathogens. In the first part of this thesis, we investigated the potential of P. chlororaphis and P. pro- tegens strains to control the cabbage maggot Delia radicum, an important pest of Brassicacean crops for which no satisfactory control exists. We then combined the most potent strain, P. chlororaphis PCLRT03, with the entomopathogenic nematode Stein- ernema feltiae RS5 and the entomopathogenic fungus Metarhizium brunneum Bip5 in screening, greenhouse, semi-field experiments and a field trial. The consortium of P. chlororaphis, S. feltiae and M. brunneum could successfully reduce D. radicum damage in the field trial and the individual members had no impact on the survival of each other on roots and in the soil. The biocontrol agents applied alone were also effective, yet the Pseudomonas strain was more efficient than the nematode and the fungus. Under screening and semi-field conditions, combinations of pseudomonads with either nematodes or fungi resulted in synergistic interactions. In a next step, the consortium was applied in laboratory assays against the leaf-feeding large cabbage white Pieris brassicae and the root-feeding banded cucumber beetle Diabrotica balteata and the interaction between the three biocontrol agents inside the larvae was investigated. The triple consortium was the most lethal and fastest killing treatment against both insects. A combination of plating and qPCR approaches allowed us to simultaneously monitor all biocontrol agents including the nematode-associated bacterium Xenorhabdus bovienii in the same insect. After simultaneous application, all three agents as well as the xenorhabds established inside the larvae in the early stages of the infection. P. chlororaphis seems to profit from the other BCA and reached the highest colonisation densities in co-infections in both insects. S. feltiae and M. brunneum, however, seemed to be mutually exclusive in double applications of nematodes and fungi. Interestingly, all four insecticidal organisms could be detected in several individual larvae. These results suggest that P. chlororaphis, S. feltiae and M. brunneum can indeed co-infect the same insect. In the last part of this thesis, fluorescent pseudomonads were isolated from radish leaves and screened for their abilities to kill insects, suppress pathogens and persist in the phyllosphere. Unfortunately, no P. chlororaphis and P. protegens strains were discovered, but strains from the subgroups P. fluorescens, P. koreensis and the group P. putida. Several strains showed insecticidal activity upon injection into Galleria mellonella larvae. Two leaf isolates of the P. fluorescens subgroup showed potent oral insecticidal activity against the diamondback moth Plutella xylostella, comparable to P. chlororaphis PCLRT03 and P. protegens CHA0. Furthermore, the new leaf isolates persisted better in the phyllosphere than the tested P. chlororaphis and P. protegens strains. The results obtained in this thesis suggest that insecticidal pseudomonads from the P. chlororaphis subgroup can be used to control below-ground insect pests. Furthermore, our findings show that insecticidal pseudomonads are compatible and co-operate with entomopathogenic nematodes and fungi. The consortium of P. chlororaphis, S. feltiae and M. brunneum can potentially be used to control a variety of below-ground insect pests. Applying the consortium might improve efficacy or stability of biocontrol. How- ever, further research on performance in the field and efficacy against different insect pests is needed. The approaches used in this thesis can be used to build and evaluate further consortia against other pests. Finally, the insights gained in this thesis are highly valuable for the development of biocontrol strategies based on insecticidal pseudomonads and consortia of biocontrol agents.
When Competitors Join Forces: Consortia of Entomopathogenic Microorganisms Increase Killing Speed and Mortality in Leaf- and Root-Feeding Insect Hosts
Spescha, Anna; Zwyssig, Maria; Hess Hermida, Mathias; et al. (2023)
Microbial Ecology
Combining different biocontrol agents (BCA) is an approach to increase efficacy and reliability of biological control. If several BCA are applied together, they have to be compatible and ideally work together. We studied the interaction of a previously selected BCA consortium of entomopathogenic pseudomonads (Pseudomonas chlororaphis), nematodes (Steinernema feltiae associated with Xenorhabdus bovienii), and fungi (Metarhizium brunneum). We monitored the infection course in a leaf- (Pieris brassicae) and a root-feeding (Diabrotica balteata) pest insect after simultaneous application of the three BCA as well as their interactions inside the larvae in a laboratory setting. The triple combination caused the highest mortality and increased killing speed compared to single applications against both pests. Improved efficacy against P. brassicae was mainly caused by the pseudomonad-nematode combination, whereas the nematode-fungus combination accelerated killing of D. balteata. Co-monitoring of the three BCA and the nematode-associated Xenorhabdus symbionts revealed that the four organisms are able to co-infect the same larva. However, with advancing decay of the cadaver there is increasing competition and cadaver colonization is clearly dominated by the pseudomonads, which are known for their high competitivity in the plant rhizosphere. Altogether, the combination of the three BCA increased killing efficacy against a Coleopteran and a Lepidopteran pest which indicates that this consortium could be applied successfully against a variety of insect pests.
Genetic analysis of resistance to bean leaf crumple virus identifies a candidate LRR-RLK gene
Ariza-Suarez, Daniel; Keller, Beat; Spescha, Anna; et al. (2023)
The Plant Journal
Bean leaf crumple virus (BLCrV) is a novel begomovirus infecting common bean (Phaseolus vulgaris L.), threatening bean production in Latin America. Genetic resistance is required to ensure yield stability and reduce the use of insecticides, yet the available resistance sources are limited. In this study, three common bean populations containing a total of 559 genotypes were evaluated in different yield and BLCrV resistance trials under natural infection in the field. A genome-wide association study identified the locus BLC7.1 on chromosome Pv07 at 3.31 Mbp, explaining between 8.22% to 16.08% of the phenotypic variation for BLCrV resistance. Comparatively, whole-genome regression models explained 51% to 78% of the variation and identified the same region on Pv07 to confer the resistance. The most significantly associated markers were located within the gene model Phvul.007G040400, which encodes a leucine-rich repeat receptor-like kinase subfamily III member and is likely involved in the innate immune response against the virus. The allelic diversity within this gene revealed five different haplotype groups, one of which was significantly associated with BLCrV resistance. As the same genome region was previously reported with resistance against other geminiviruses affecting common bean, our study highlights the role that historical breeding for virus resistance has played in the accumulation of positive alleles against newly emerging viruses. In addition, we provide novel diagnostic SNP markers for marker-assisted selection to exploit BLC7.1 for breeding against geminivirus diseases in one of the most important food security crops worldwide.
Combining entomopathogenic Pseudomonas bacteria, nematodes and fungi for biological control of a below-ground insect pest
Spescha, Anna; Weibel, Joana; Wyser, Lara; et al. (2023)
Agriculture, Ecosystems & Environment
Below-ground insect pests are challenging to control because they are hard to target with control measures. Moreover, broad spectrum insecticides are or will soon be banned due to their negative effects on non-target organisms. In this study, we have developed a biological control method for the cabbage maggot Delia radicum (Diptera: Anthomyiidae), a significant pest of Brassicacean crops, based on a consortium of three biocontrol agents (BCAs). We chose the bacterium Pseudomonas chlororaphis because it can be used in a dual strategy against insect pests and fungal plant diseases, and combined it with the nematode Steinernema feltiae and the fungus Metarhizium brunneum that have a long history of commercial use against different pest insects. Our aim was to combine BCAs with different modes of action in order to achieve a stable and reliable biocontrol effect. We first tested double combinations of the bacterium with either the nematode or the fungus for improved potential to kill D. radicum in laboratory assays. We then evaluated the effect of double and triple combinations on D. radicum development and maggot-induced damage on radish bulbs in a series of pot experiments with artificial cabbage maggot infection performed in the greenhouse and outdoors and finally in a field trial with a natural infestation. Our results show that i) insecticidal pseudomonads are highly efficient in D. radicum control, ii) the three BCAs are compatible and neither inhibit each other's infectiousness nor survival in the soil or on the roots, iii) synergistic effects of Pseudomonas-nematode and Pseudomonas-fungus combinations on maggot killing are possible, and iv) the triple combination reduced both pest survival in greenhouse experiments and maggot-induced damage on radish bulbs in the field by 50% each. The strategy we present here is a promising step forward to a reliable and efficient environmentally friendly biological control method for the cabbage maggot, which can also be adapted to other problematic below-ground pests.

Publications 1 - 6 of 6

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