Microbial Biocontrol Strategies for Ambrosia Beetles and Their Associated Phytopathogenic Fungi

Abstract

Ambrosia beetles and their symbiotic fungi are causing severe damage in natural and agro-ecosystems worldwide, threatening the productivity of several important tree crops such as avocado. Strategies aiming at mitigating their impact include the application of broad-spectrum agrochemicals and the incineration of diseased trees, but the increasing demand for environment-friendly strategies call for exploring biological control for the management of ambrosia beetles and their phytopathogenic fungal symbionts. The aim of this review is to examine the existing knowledge on biocontrol approaches using beneficial microorganisms and microbial natural products with entomopathogenic and antifungal activity against ambrosia beetles and fungi. We show that biocontrol has been mainly focused on the insect, using entomopathogenic fungi (EPF) such as Beauveria spp. or Metarhizium spp. However, recent studies have been integrating EPF with mycoparasitic fungi such as Trichoderma spp. to simultaneously challenge the vector and its fungal symbionts. Novel approaches also include the use of microbial natural products as insect lures or antifungal agents. Contrastingly, the potential of bacteria, including actinobacteria (actinomycetes), as biocontrol agents of ambrosia fungi has been little investigated. We thus suggest that future research should further examine the antifungal activity of bacterial strains, with an emphasis on harsh environments. We also suggest pursuing the isolation of more effective microbial strains with dual biocontrol effect, i.e., exhibiting fungicidal/insecticidal activities. Moreover, additional efforts should aim at determining the best application methods of biocontrol agents in the field to ensure that the positive effects detected in vitro are sustained. Finally, we propose the integration of microbiome studies in pest and disease management strategies as they could provide us with tools to steer the beneficial host plant microbiome and to manipulate the beetle microbiome in order to reduce insect fitness.

Isolation and Identification of Pennogenin Tetraglycoside from Cestrum nocturnum (Solanaceae) and Its Antifungal Activity against Fusarium kuroshium, Causal Agent of Fusarium Dieback

“…Because the hydrogen signal of carbon 16 was in the glycosidic region, a selective irradiation TOCSY one dimensional experiment to the β proton of carbon 15 was carried out, which allowed to assign the protons and carbons of positions C-14 and C-16. Chemical shifts for 1 H and 13 C are expressed in ppm using the residual signal of Py-d 5 as reference. The coupling constants (J) for proton are expressed in Hertz (Hz).…”

“…Figure 5 summarizes all correlations determined by ROESY (red double-headed arrows), HMBC (black singleheaded arrows) and COSY (black lines). Chemical shifts for 1 H and 13 C expressed in ppm and with reference to residual signal of Py-d5, as well as the coupling constants (J) for proton expressed in Hertz (Hz).…”

“…The ECn-F4-25 (10 mg) fraction identified as the pure compound pennogenin tetraglycosed was dissolved in 0.5 mL of pyridine-d 5 and transferred to a 5 mm borosilicate tube. All NMR experiments were recorded on a Bruker Avance III HD equipment (Billerica, MA, USA) at 500 MHz for 1 H and 125 MHz for 13 C equipped with a broadband observe (BBO) probe at 50 • C. The hard 90 • H pulse was calibrated before the spectra acquisition with a value of 10.63 µs. The 1 H experiment was recorded using water suppression (O1P = 4.99 ppm) under the ZGCPPR pulse sequence, both 1 H and 13 C were referenced using the residual signal of pyridine-d 5 at 7.22 ppm ( 1 H) and 123.5 ppm ( 13 C).…”

“…Research efforts have considered biological control as an option to mitigate the negative impact of fungal diseases [ 13 ]. In this context, a good strategy is the study of natural products of botanical origin that have historically been considered effective for pest control as well as safer for human health and the environment, because of their short lifetime in the environment.…”

Identification of Antifungal Compounds from Avocado Rhizobacteria (Bacillus spp.) against Fusarium spp., by a Bioassay‐Guided Fractionation Approach

“…Species from the Bacillus subtilis complex have received special attention as they dedicate almost 4–5 % of their genome to antimicrobial compounds biosynthesis, [38] such as polyketides, terpenes, siderophores, and ribosomally and non‐ribosomally synthesized peptides [39] . Nevertheless, CLPs are considered as one of the most relevant antimicrobial compound groups due to their strong antifungal activity [40,41] and represent a promising biocontrol alternative of phytopathogenic fungi of agricultural importance [16,41] …”