Metarhizium brunneum and anisopliae

How to Use Metarhizium spp.

Biocontrol category: Augmentative—must be released/applied repeatedly

When to use: Because the spores of Metarhizium fungi can be inhibited by too much exposure to ultraviolet light, it is best to apply this biological control agent in the late afternoon or evening, or on cloudy or rainy days.

Rate: Application rates vary depending on the pest and crop. Always follow the instructions on the label when applying this biopesticide. 

Maximizing effectiveness:To make the application of biopesticides containing Metarhizium spp. most effective, applications should be undertaken when the humidity is high, when the UV light is low (late afternoon or cloudy/rainy days), and at warm temperatures 64° – 85°F (18° - 29°C). Manufacturers sometimes offer additional useful tips for applying their products most effectively.

Pest stage:
Larvae: thrips, ticks, root weevils, aphids, whiteflies

Adults: mites, aphids, ticks, whiteflies

Mode of action: This product works as a parasite of insect pests. The fungi attach to the cuticle (shell/skin) of the insect and breaks it down with enzymes. Once it can enter the hemolymph (the insect blood stream), it rapidly takes over the inside of the host and uses it for nutrients. <a href=”#infection”>More information on the infection process</a>.

Conservation: Although Metarhizium spp. are naturally occurring in the soil, fungicides usually should not be applied at the same time or close to the application of products containing Metarhizium spp. [2, 3]. Always read the label before applying pesticides. 

Compatibility: A summary of the compatibility of biopesticides containing Metarhizium spp. with other types of pesticides.

• Acaricides—sometimes compatible (product dependent)

• Adjuvants—sometimes compatible (product dependent)

• Fungicides—usually not compatible; check label for specific application intervals

• Herbicides—generally compatible

• Insecticides—generally compatible

• Other biopesticides—generally compatible

Risk: The label of a pesticide containing Metarhizium spp. will also have information about potential risks to people and the environment. May cause eye irritation and can be harmful if inhaled, swallowed, or absorbed through the skin. May be toxic to fish – do not discharge rinsate into bodies of water or public waterways or apply this product over standing water or near aquatic habitats. See “Learn More” section for more information on the risks of Metarhizium spp. to non-target organisms.

Commercially available:No—Novozymes Biologicals, Inc., the producer of the commercial products containing Metarhizium anisopliae, stopped the production of all products containing Met52 in 2020. As of April 1, 2022, Lallemand Plant Care, a Canadian company, has registered a product with the U.S. EPA under the new product name “Lalguard® M52 GR”. However, this product was not available for purchase as of early 2023. Additionally, this product has been updated to reflect the new nomenclature of the active ingredient, which is now Metarhizium brunneum. As better tools have become available for distinguishing different species of Metarhizium, we now know that some products that listed M. anisopliae on the label actually contained M. brunneum.

Learn more about Metarhizium spp.

The fungus that we now know as Metarhizium anisopliae was first described by European scientist Elie Metchnikoff (sometimes spelled Metschnikoff) in 1879 as Entomopthora anisopliae after he observed the disease attacking the cereal cockchafer (Coleoptera, Anisoplia austriaca) and related scarab beetles in Russia [1]. In 1883, E. anisopliae was moved to the genus Metarhizium by Sorokīn, where it has stayed ever since. Metarhizium anisopliae is one of the most widely used fungi for the biological control of insects worldwide and has been a subject of interest for pest control since its discovery in 1879 [2]. Like other commonly used entomopathogenic fungi, M. anisopliae is a generalist pathogen with a wide host range, although it is more restricted than that of Beauveria bassiana (see the article on B. bassiana for more information about that insect pathogen) [2]. Veen 1968 [3] reports that M. anisopliae can infect over 200 species of insects, most of which are beetles (order Coleoptera). Similarly to other entomopathogenic fungi (EPF), M. anisopliae can be found in soils and infecting insects worldwide in habitats ranging from arctic to tropical [2].

M. anisopliae Infection process

Like EPF, M. anisopliae follows the same general infection process [2]. Insect infection by EPF starts with contact between the fungal spore and insect cuticle (Figure 1). Then the spore germinates, forms an appressoria, and penetrates the cuticle. During the penetration step, the fungus produces enzymes (e.g., lipases, chitinases, proteases, etc.) to break down the insect cuticle [4]. Once the appressoria enters the body of the insect, the fungus begins to overcome the immune responses of the host insect and then begins to spread throughout the inside of the insect body. After depleting all the nutrients from the now mummified cadaver of the insect, the fungi grow out of the body and begins to produce new spores. A more detailed explanation of the fungal infection process can be found within Aw & Hue [5].

Effects on Non-target Organisms

Beneficial organisms (parasitoids, predators, pollinators, etc.)

Because M. anisopliae is a generalist parasite of insects and has a large host range, the safety of beneficial and non-target organisms is of particular concern when applying any types of pesticides to the environment. Under laboratory conditions, Vestergaard et al. [6] reports that M. anisopliae can infect a wide array of insects, and Veen [3] reports that the fungus can infect over 200 species of insects. However, it should be noted that the physiological host range (e.g., the host range that can be infected in the lab) and the ecological host range (e.g., the hosts that are infected under natural or field conditions), can vary greatly between fungal strains [7]. The table below summarizes some of the laboratory and field studies that investigated the effects of M. anisopliae on non-target organisms (modified from Zimmermann 2007 [2] with author permission). For more information on the specific effects on a particular organism, please see the article cited above.

Soil microorganisms

Because M. anisopliae is already present in most soils worldwide, one might be concerned about the effects of applying a non-native strain to a new environment. Hu & St. Leger [8] released genetically modified M. anisopliae at a University of Maryland research farm and found that there was no evidence of suppression of the local fungal populations. When screened against phoretic mites, Shabel [9] found that the two species evaluated against M. anisopliae were susceptible to fungal infections. This same study found that mites were also able to transfer conidia to new hosts on their own cuticles. Other soil organisms such as collembola have also been screened against M. anisopliae. Dromph [10] found that collembolans can move viable fungal spores and that result in the infection of new host insects. This study also found that the amount of spores that are carried by the collembola is related to their body size, with larger collembola dispersing more viable spores [10]. Finally, this study found that M. anisopliae had low virulence against the three species of collembolans that were tested, and it was suggested that the ingestion of spores by some species of collembola can reduce spore viability.

Aquatic invertebrates

Due to the nature of application of products containing M. anisopliae, there has been some concern about adverse effects of spores in waterways to non-target aquatic invertebrates such as shrimp and aquatic insects. In two laboratory studies completed by Genthner et al. [9, 10], the authors found variable responses of grass shrimp embryos at different spore concentrations, but confirmed dead larvae with visible M. anisopliae fungal growth even at lower spore concentrations. At higher concentrations, they saw significant increases in adverse effects on the larvae. However, these findings could be strain specific (the strain used was not a commercial strain), and likely do not reflect natural conditions of shrimp larval exposure levels. Milner et al. [13] did not observe any adverse effects on mayfly nymphs in Australia, and these authors concluded that the level of spores that enter the water during/after application is very low and is therefore not likely to significantly affect aquatic organisms.

Vertebrates (excluding mammals)

Generally, M. anisopliae is considered safe for use around fish, reptiles, birds, and amphibians. A few studies have reported adverse (but variable) effects of exposure or from feeding M. anisopliae to embryo or juvenile fish (inland silverside fish, Menidia beryllina,  and mosquito fish, Gambusia affinis) [10, 12], but no adverse effects were observed when G. affinis adults species fed on the fungus directly. Milner et al. [13] reported no effects on rainbow fish fry (Melanotaenia duboulayi), and Roberts [15] found that conidia in the water had no effect on Epiplatys bifasciatus mortality. For amphibians there is also little evidence of negative effects on frog development. One study [16] reports no frog mortality or fungal recovery from any leopard frog (Rana pipiens) tissues after frogs were fed spore suspensions of M. anisopliae. Regarding reptiles such as lizards, terrapins, and crocodilians, M. anisopliae has been found in lesions on crocodiles, and it was shown that it was possible to infect other reptiles [17]. Peveling & Demba [18] found that M. anisopliae (var. acridum) posed no risks to fringe-toed lizards when used at field application rates. In this study, the lizards were exposed to high rates of M. anisopliae via three exposure routes: inhalation exposure of dry spores, oral exposure with an oil-miscible flowable concentrate of spores, and feeding exposure with diseased locusts. The exposure and infection risk of birds exposed to M. anisopliae is of particular concern, since birds can be exposed to conidia that are deposited on their food or may even consume infected insects. However, studies on multiple bird species (Japanese quail [19], ring necked pheasants [18, 19]) have found no evidence of mortality, abnormal behavior, or changes in weight or growth rate due to feeding on M. anisopliae.

Mammals (including humans)

When compared to other biopesticides (such as B. bassiana), M. anisopliae has had very few reported instances of allergic reactions after exposure. However, individuals with compromised immune systems or those who work in high exposure environments, such as plants where M. anisopliae products are produced or in the agricultural industry, should take extra measures to protect themselves from exposure to spores by wearing proper personal protective equipment like gloves, protective eyewear, or respirators when necessary.

In small mammals, exposure to M. anisopliae has resulted in variable observations of allergenicity and pathogenicity. A study by El-Kadi et al. [22] showed no allergic reactions from guinea pigs and mice that were exposed to conidia, while Instanes et al. [23] found that M. anisopliae increased allergic responses in mice. In 1998, Muir et al. [24] described a cat that was diagnosed with invasive mycotic rhinitis from M. anisopliae that was treated with an oral antifungal medication.

In humans, there has also been variable allergenic and pathogenic responses from exposure to M. anisopliae. Goettel et al. [25] reported a severe dermal hyperallergic response in humans at one company. Additionally, because of the widespread use of M. anisopliae on sugar cane in Brazil, several agricultural workers presented with asthmatic symptoms due to the fungus [26]. Alternatively, Copping [27] reports that manufacturing staff, researchers, and field staff had no allergic responses from working with various strains of M. anisopliae. There have been several verified cases of pathogenic infection of immunocompetent individuals by M. anisopliae, which has resulted in multiple cases of keratomycosis (fungal infection of the eye) [26, 27] from injuries to the eye, two cases of frontal and ethmoid sinusitis (inflammation of the frontal and ethmoid sinuses) [30], and recurrent skin lesions across the body [31]. In all of these cases, the infections were successfully treated with antifungal medications. More recently, Nourrisson et al. [32] identified eight new cases of human infection from fungi in the genus Metarhizium. Sadly, there is a verified case of a fatal infection from M. anisopliae. In 1998, Burgner et al. [33] reported the death of a 9-year-old immunosuppressed patient with a history of acute leukemia. After testing the susceptibility of the fungus to antifungal treatments, it was found that the specific strain that infected this patient was resistant to itraconazole, fluconazole, ketoconazole and 5-flucytosine.

Products containing M. anisopliae are evaluated by the U.S. Environmental Protection Agency (EPA) for health and safety concerns. View the EPA evaluation for strain F52 (pdf).

Effectiveness

The effectiveness of M. anisopliae can be affected by abiotic factors, such as temperature, humidity, and UV radiation, and by biotic factors like the availability of host insect or specific fungal strain virulence. Metarhizium spp. function between 15°C and 35°C, with an ideal temperature range of 25°C to 30°C, although some strains are viable at lower or higher temperatures [2, and ref. within]. The storage temperature of M. anisopliae can also impact the efficacy of the fungus, where higher storage temperatures usually decreases spore viability (in addition to light exposure during storage) [34]. Humidity is also a very important factor for fungal survival and efficacy since higher humidity (generally as high to 100% relative humidity as possible) is necessary for fungal germination [35]. The next most important environmental factor for spore viability is exposure to UV radiation (UV-A and UV-B). Braga et al. [36] reported that exposure to only 4 hours of direct sunlight completely inactivated the conidia of two M. anisopliae strains.