Identification of Exoenzymes Secreted by Entomopathogenic Fungus Beauveria pseudobassiana RGM 2184 and Their Effect on the Degradation of Cocoons and Pupae of Quarantine Pest Lobesia botrana

Beauveria pseudobassiana RGM 2184 has shown 80% maximum efficacy against the pest Lobesia botrana in the autumn and winter seasons. This suggests that the strain possesses an interesting battery of enzymes that are cold-adapted to penetrate the thick and hydrophobic cocoon of L. botrana. In this study, screening of the proteolytic, lipolytic, and chitinolytic activity of enzyme extracts secreted by the RGM 2184 strain was carried out in various culture media. The enzyme extracts with the highest activity were subjected to zymography and mass spectrometry. These analyses allowed the identification of two proteases, two lipases, and three chitinases. Comparative analysis indicated that the degree of similarity between these enzymes was substantially reduced when the highest degree of taxonomic relatedness between RGM 2184 and the entomopathogenic fungus strain was at the family level. These results suggest that there is a wide variety of exoenzymes in entomopathogenic fungi species belonging to the order Hypocreales. On the other hand, exoenzyme extract exposure of cocoons and pupae of L. botrana provoked damage at 10 °C. Additionally, an analysis of the amino acid composition of the RGM 2184 exoenzyme grouped them close to the cold-adapted protein cluster. These results support the use of this strain to control pests in autumn and winter. Additionally, these antecedents can form a scaffold for the future characterization of these exoenzymes along with the optimization of the strain’s biocontrol ability by overexpressing them.

Identification of Entomopathogenic Fungi as Naturally Occurring Enemies of the Invasive Oak Lace Bug, Corythucha arcuata (Say) (Hemiptera: Tingidae)

Simple Summary

The oak lace bug (OLB), Corythucha arcuata, is a cell sap-sucking insect that is native to North America but has spread rapidly in European countries as an invasive pest. The main hosts are oaks, but it can develop on other forest species as well. Its occurrence is worrying in terms of the cumulative impacts that it could have on forests, as well as the molestation of imago in cities that have been frequently reported. Since the pest is still a new element of a biocoenosis, there is a lack of research on its natural enemies and competitors that could form a potential foundation for biological control strategies. Although there have been reports that lace bugs are quite susceptible to a fungal diseases amid more humid conditions, to date, none of the pathogenic fungi found on OLBs under natural conditions were identified in the literature. In this study, we provide evidence of four entomopathogenic fungi: Beauveria pseudobassiana, Lecanicillium pissodis, Akanthomyces attenuatus and Samsoniella alboaurantium that could present a potential as biological control agents against OLBs.

Abstract

The oak lace bug (OLB), Corythucha arcuata (Hemiptera: Tingidae), was first identified as an invasive pest in Europe in northern Italy in 2000 and since then it has spread rapidly, attacking large forested areas in European countries. The OLB is a cell sap-sucking insect that is native to North America, with Quercus spp. as its main host. Its rapid expansion, successful establishment in invaded countries, and observations of more damage to hosts compared to native areas are most likely due to a lack of natural enemies, pathogens and competitors. In its native area, various natural enemies of OLBs have been identified; however, little is known about the occurrence and impact of OLB pathogens. None of the pathogenic fungi found on OLBs in natural conditions have been identified until now. In this study, we provide evidence of four entomopathogenic fungi that are naturally occurring on invasive OLBs found in infested pedunculate oak forests in eastern Croatia. On the basis of their morphology and multilocus molecular phylogeny, the fungi were identified as Beauveria pseudobassiana, Lecanicillium pissodis, Akanthomyces attenuatus and Samsoniella alboaurantium. The sequences generated for this study are available from GenBank under the accession numbers MT004817-MT004820, MT004833-MT004835, MT027501-MT27510, and MT001936-MT0011943. These pathogenic species could facilitate biological control strategies against OLBs.

Carnauba wax enhances the insecticidal activity of entomopathogenic fungi against the blowfly Lucilia sericata (Diptera: Calliphoridae)

Blowfly, Lucilia sericata (Diptera: Calliphoridae), is a problematic synanthropic insect pest, a vector of microbial pathogens, and the causal agent of secondary myiasis. Fungal biopesticides are considered eco-friendly tools, alternative to synthetic pesticides, for the control of arthropod pests; however, to date, little is known about their bioactivity against blowflies. In this study, we assessed the insecticidal activity of three well-known entomopathogenic fungi, Beauveria bassiana, Beauveria pseudobassiana and Akanthomyces muscarius against L. sericata. In addition, we tested powdered carnauba wax as an electrically charged dust carrier in an attempt to enhance the virulence of fungal spores. Pathogenicity tests on adult flies, by adult immersion in conidial suspension (10⁸ conidia mL^-1), showed that the median lethal time (LT₅₀) was 5.3, 5.9, and 6.2 days for B. bassiana, A. muscarius and B. pseudobassiana, respectively. In topical tests, when 10⁸ dry conidia were mixed with or without carnauba wax, the LT₅₀ was 7.7, 10.2, and 14 days without this carrier and 6.9, 8.6, and 13.8 days with it for B. bassiana, B. pseudobassiana and A. muscarius, respectively. Overall, our findings showed that, among the tested fungi, B. bassiana was the most virulent when formulated as a dry powder with carnauba wax, which greatly improved fungal efficacy against the blowfly. We discuss the utility of carnauba wax for electrostatic formulation powder of fungal spores in the integrated management of blowflies as an environmentally sustainable tool to reduce the over-reliance on chemical insecticides and their risk of resistance.

Potential biological control of the pupal stage of the European grapevine moth Lobesia botrana by the entomopathogenic fungus Beauveria pseudobassiana in the winter season in Chile

OBJECTIVE

Lobesia botrana, the European grapevine moth, affects Vitis vinifera L. and other species of economic importance in a number of countries through damage caused by its larvae in berries and associated secondary diseases such as Botrytis cinerea. Control of the moth in urban areas is difficult due to poor chemical management of infested plants in houses. Additionally, in winter, L. botrana is in its pupal stage covered with a cocoon that prevents the penetration of chemical pesticides. For this reason, the objective of this work was to control the pupal stage with a formulation based on the entomopathogenic fungus Beauveria pseudobassiana in urban areas.

RESULTS

The strain RGM 1747 was identified as B. pseudobassiana by multilocus sequence analysis. The biocontrol activity of this formulated fungus against the infestation of vines with breeding pupae without cocoons showed 100% infection 21 days after inoculation under winter conditions. Finally, the biocontrol activity of the formulated fungus against natural infestations of L. botrana in winter in urban areas reached an efficacy of 51%. This result suggests that the B. pseudobassiana formulation is able to penetrate the cocoon and contributes to the integrated pest management of L. botrana.

Complete mitochondrial genome of the entomopathogenic fungus Beauveria pseudobassiana (Ascomycota, Cordycipitaceae)

The complete mitochondrial genome of the entomopathogenic fungus Beauveria pseudobassiana (Ascomycota, Cordycipitaceae) was determined and found to be 28,006 bp in length. It encodes genes for 14 proteins, 2 ribosomal RNA subunits, 25 transfer RNAs with the synteny identical to those of B. bassiana and B. brongniartii. The overall base composition is 36.7% A, 35.8% T, 15.3% C and 12.2% G with an AT content of 72.5%. Group-І introns were found in large rRNA gene (rnl) and cox2 gene that include rps3 gene and putative GIY-YIG homing endonuclease, respectively. The mitochondrial genome of B. pseudobassiana will contribute to the investigation of the phylogenetic relationship, taxonomic resolution and biogeography of Beauveria.