Introduction Fungal entomopathogens are important control agents for a range of herbivorous insects. By 2009, half of all reported classical introductions of pathogens were species of fungi (Hajek and Jr, 2010). Seven hundred and fifty species of pathogenic fungi have been discovered but only 1.5% have been further investigated for use as microbial control agents (Lacey et al, 2001). Further research into fungal entomopathogens is therefore vital in order to fully benefit from this untapped valuable resource. The genera commonly used for pest control include Beauveria, Metarhizium, Paecilomyces and Lecanicillium because they can be grown on relatively cheap artificial media and have a fairly long shelf life (Ehlers, 2011). Collectively they target a broad range of insects but individual fungal species are highly specific. Most species invade the insect through the cuticle (exoskeleton) via spore contact so do not have to be eaten. They are therefore the only effective pathogen of sucking sap feeders such as aphids and whiteflies. Natural Epizootics in the Tropical Rainforest Sexually reproducing fungi in the genera Cordyceps are endoparasites that naturally regulate insect populations in tropical forests. David Attenborough has filmed the action of endoparasitoid Cordyceps in nature- check out this malicious drama on YouTube (Title: Cordyceps: attack of the killer fungi - Planet Earth Attenborough BBC wildlife. Address: http://www.youtube.com/watch?v=XuKjBIBBAL8). Problem Although most fungal entomopathogens are very specific, some have been found to infect non-target insects. Beauveria bassiana for example used to control numerous greenhouse pests (including spider mites, western flower thrips, grasshoppers and crickets) can also infect ladybirds (Harper, 2006). This is a problem because ladybirds are useful biocontrol agents themselves. Examples of Fungal BCAs - Paecilomyces fumosoroseus targets aphids, spider mites, thrips, whiteflies. - Paecilomyces lilacinus targets nematodes. - Entomophaga maimaiga was introduced to North America to give classical control of the gypsy moth (Lymantria dispar), an invasive pest of deciduous trees. - The pathogenic fungus Lecanicillium longisporum (previously called Verticillium lecanni) is a commercial biopesticide available to UK growers. It is used in glasshouses to kill sap feeders such as thrips, whiteflies and aphids. The photo shows infection of the aphid Metopolophium dirhodum. Lagenidium giganteum Lagenidium giganteum is widely used to control mosquitoes (Harper, 2006). When a spore detects the insect’s body, specific chemical cues stimulate germination and it penetrates the cuticle, spreading throughout the body. The insect becomes starved and dies within several days. The fungus then produces a new generation of spores on the dead body, which spread and infect new hosts. If no host is available, two spores will join to form a stable, long-lasting, desiccation resistant spore, until a host is present. Transmission is therefore horizontal. Metarhizium anisopliae Metarhizium anisopliae has been the most commonly used species in classical biological control, with 16 introductions reported since 1914 (Hajek and Jr, 2010). The species is used to control locusts, grasshoppers, cockroaches and termites, major pests in both developed and developing countries including America, Australia and Africa. The agent is easy to mass produce as it can be grown on rice grains. Using oil, the green spores are easily spread to parts of the insect which have a high relative humidity (i.e. where the cuticle is thin like the back of the neck or under the wing) where the fungus can germinate and grow. The fungus is highly efficacious, for instance it can kill 90% of locusts within 7-21 days of application, depending on the number of infecting spores. Photo shows a cabbage root fly infected by the fungus Metarhizium anisopliae. Application Method Spraying is not a very cost-effective method of application because it does not reach all areas of the plant inhabited by the pest. Delivery method can however be improved using semiochemicals. Semiochemicals can attract adults to an area where they become contaminated with fungal spores. Contaminated adults then fly off to larval habitats causing the disease to spread. Future Prospects Future use of entomopathogenic fungi will expand if scientists can develop resting spores and competent mycelia. Research into the genetic manipulation to enhance virulence of fungi is increasing but is not as widely investigated as bacteria and viruses. Better understanding of the abiotic and biotic interactions with entomopathogenic fungi is necessary to determine the optimal dose and timing of application. Application timing must consider the susceptible host stage, environmental conditions and agricultural practises (e.g. avoid fungicides). Aphids Neozygites fresenii Neozygites fresenii causes natural epizootics specifically infecting the cotton aphid, Aphis gossypii in South America. The fungus can reduce a population by 80% in 4 days (University of Warwick, accessed online 2011). N. fresenii cannot be produced in vitro and is expensive to produce in vivo. Steinkraus and Boys (2005) however developed a method to harvest and store large quantities of N. fresenii during a natural outbreak for future use in conservation control. As well, cotton farmers can predict 10 days in advance if a natural outbreak will occur and therefore make informed decisions about whether to use expensive pesticides (University of Warwick, accessed online 2011).