Abundance of Entomopathogenic Fungi in Leaf Litter and Soil Layers in Forested Habitats in Poland

Abstract

This study aims to determine the species composition and density of colony-forming units (CFU) of entomopathogenic fungi (EPF) in leaf litter at different depths of the top layer of forest soils depending on the type of forest (coniferous, deciduous and mixed forest), and the date of sampling (spring, autumn). In each type of forest, leaf litter and soil were collected using a soil stick from four depths of soil: 0–5, 5–10, 10–15 and 15–20 cm. Entomopathogenic fungi were isolated by a soil or litter dilution plating method on a selective medium. Four fungal genera were found: Beauveria spp., Cordyceps spp., Metarhizium spp., and Lecanicillium spp. The density of EPF was usually higher in leaf litter than in the layers of soil below, and the most frequently isolated species from both environments were Beauveria spp. among soil samples from all forest types; Beauveria spp. were most abundant in the top layer (0–5 cm), and their density of CFUs gradually decreased deeper into the soil profile.

First Report of Entomopathogenic Fungi Occurrence in Forest Soils in Croatia

“…Although the highest average number (density) of colonies belonged to the genus Metarhizium, those fungi were found in three of the five localities, in comparison with genus Beauveria that was found to be naturally present in forest soils in most of the investigated localities (i.e., four of the five) and at the highest number of sampling points (16 of the 25). The dominance of B. bassiana in soils collected from various types of forests is also confirmed by studies conducted in Denmark [50], Finland [51], Poland [12,52,53], Japan [54], Italy [55], Spain [56,57], Austria [58], Mexico [59], Brazil [60], and Portugal [61]. In other research, Metarhizium was also the most abundant fungal genus detected [e.g., 31,35,58,62,63], with variable proportions of other species.…”

“…Fungi from the genus Lecanicillium W. Gams & Zare occur on a diverse range of insect species, and have been isolated from forest soils around the world [12,49,64,73,74] and utilized for the control of different pests [75,76]. This genus was found at three studied locations, with a 12% share at Location 1, but in the total share of the identified entomopathogenic fungal species at all locations, it represented only 3%.…”

“…Species composition, frequency, and the number of colonies depends on different factors such as geographical location, type of habitat, microclimatic conditions (temperature and humidity), and time of year (which determines the activity of insects in the soil environment and the transfer of spores and other forms of fungal propagation) [11,12,51,63,64], as well as the use of chemical pesticides, especially fungicides that can change the occurrence, infectivity, and population dynamics of EPF in the soil [68,[88][89][90]. In general, EPF are more abundant in soils that have less disturbance [1,34,91].…”

“…Among these fungi, Beauveria spp., Metarhizium spp., Isaria (=Cordyceps) spp., and Lecanicillium spp. are common genera found in agricultural and forest soils and have the greatest potential for biological control [9][10][11][12].…”

“…Many hypocrealean EPF are adapted to the soil, where they spend most of their life cycles, a feature that allows them to infect and utilize not only typical soil-inhabiting pests but also a large group of insect pests that use soil as a site for hibernation, pupation, or periodic diapause [12][13][14][15]. It is estimated that soil plays habitat to more than 90% of all insect pests at some point in their development cycle [16].…”