The Mitosporic Fungi - Essay Example

FUNGI IN SCIENCE RESEARCH INTRODUCTION: Fungi which are entomopathogenic in nature: (causing disease to insects), are successfully used for pest control, killing insects in fields, greenhouses and gardens around the world. Thus, entomopathogenic fungi are used as classical biological control agents. Classical biological control has been defined as “the intentional introduction of a biological control agent for permanent establishment and long-term pest control” (Eilenberg, et al, 2001, quoted in Hajek, et al, Hokkanen (Ed.). 2003: p.15). The Mitosporic fungi belonging to the class Hyphomycetes have been developed as biological control agents, state Esser; Lemke (2002: p.111) Strains of two fungi, according to Enserink (2005:p.1531), called Beauveria bassiana and Metarhizium anisopliae, have been found to kill mosquitoes. Several different strains of each fungus exist, and there is one to kill almost any insect species, says Christiaan Kooyman, who studies locust control using fungi, at Benin (as quoted in Enserink, 2005: p.1531). Kooyman adds that since mosquitoes are increasingly becoming resistant to chemical pesticides, new control tools such as biopesticides are necessary. DISCUSSION: Among the major groups of microbes, fungi and viruses are well known for causing dramatic epizootics (epidemic animal disease) resulting in rapid decline of insect populations (Hokkanen (Ed.). 2003: p.15). These agents, used for classical biological control, are expected to establish themselves in the environment, persist to survive and grow, and increase in density in response to increases in host population density. Dynamic interactions between the pathogen, insect host and environment influence the epizootics, and the efficacy of mycoinsecticides (Esser; Lemke, 2001: p.111). Fungi cause infection by contact and penetration. Therefore ingestion: by oral consumption, is not required as in infection caused by other entomopathogens such as bacteria, protozoa and viruses (Mukerji, et al, 2001: p.39). According to Kinghorn; Turner (1992: p.178), entomopathogenic fungi invade their hosts by direct penetration of the insect cuticle, a process that is likely to involve both mechanical pressure and enzymic hydrolysis. Another desired attribute is host-specificity (Eilenberg, et al, 2001, quoted in Hajek, et al, Hokkanen (Ed.). 2003: p.16). Whether organisms other than the target hosts remain unaffected by the fungal infection continues to be under research. Fungi infect a broader rangeof insects than do other microorganisms. The host ranges of some of the fungi, like Beauveria bassiana and Metarhizium anisopliae are very broad, and encompass most of the insect groups. In the classical biological control approach, the intent is that a fungus not endemic to that area becomes established, self-perpetuating for long-term control (Goettel, et al, 2001: quoted in Hokkanen (Ed.) 2003: p.16). Both the species are relatively easy to produce, as they produce vast amounts of asexual conidia in culture as well as on insects. They have low mammalian toxicity and few nontarget impacts (Arora, et al 2004: p.81). Vurro (2001:pp.217-218) states that B. bassiana and M. anisopliae are globally distributed, they have already been used commercially in many countries as biological control agents, but their slow speed of kill as compared to chemical insecticides is leading to attempts to engineer pathogen performance. Before new research on mosquito eradication, other insect pests like locusts have been successfully eliminated by Beauveria bassiana and Metarhizium anisopliae. According to Upadhyay (2003:p.158), a new sustainable control strategy for the tsetse fly which causes sleeping sickness in certain ecological and social conditions, with the help of Metarhizium anisopliae as an environmetally friendly biopesticide, was being developed successfully. Larone (2002: p.277) had observed that Beauveria Bassiana which is commonly considered as a contaminant, is known to be pathogenic in insects, especially silkworms. Early studies conducted by Al-Aidroos K. and Roberts, D.W. in 1978 and by Clark et al in 1968 were pioneering works in the discovery of M. anisopliae and B. bassiana respectively as entomopathogenic fungi that can be used against Anopheles mosquitoes: the vectors of malaria parasites. Dhaliwal; Koul (2002: p.240) are of the opinion that the use of these fungi from both temperate and tropical regions confirm the pivotal role of Beauveria bassiana in pest management practices. Earlier research on the biological control of mosquitoes by these fungi, showed that the pathogens infect the larval stages, rapidly gaining access to the haemocoel, with extensive intramatrical growth resulting in death followed by extramatrical sporogenesis (Howard, 2003: p.50). Recent studies by Bart Knols and team in the Netherlands, and by Andrew Read and Matt Thomas in London (Enserink, 2005: p.1531) on these entomopathogenic fungi have shown that their fungal spores applied as sprays, just like chemical pesticides can infect and kill adult Anopheles mosquitoes, the vectors of malarial parasites. Knols’ team showed that Anopheles gambiae could be infected by direct application of the fungal spores to the insects’ bodies. They suspended cloths of three square metre dimensions impregnated with the fungus M. anisopliae, from the ceilings of traditional houses in a rural Tanzanian village, collected mosquitoes in the homes for three weeks, and kept the insects alive on glucose. Some 23% of female Anopheles gambiae became infected, shortening average life span by four to six days, compared to controls from untreated homes. The team demonstrated how such results could alter malaria transmission in a village if the cloths were applied year-round. The number of infective bites for the average villager would fall from 262 to 64 annually. In order to drastically reduce the malaria cases and deaths, the dose has to be increased, and the entire walls of all the houses should be sprayed. Andrew Read and team report that the true effect of a fungus, in their case: B. bassiana on malarial transmission may be even more pronounced than Knols’ data suggest. In laboratory studies using Plasmodium chabaudi, a rodent malaria parasite, and a mosquito species called Anopheles stephensi, the group found that even in surviving mosquitoes, the fungus severely hampered the parasites’ ability to develop (Enserink, 2005: p.1533). The research teams are working on the sprays’ formulations to improve infection rates, since the one drawback is that the spores start losing their infectiousness in a matter of weeks. Simon Blanford et al (2005: p.1640) have conducted further studies, to reduce malaria transmission by reducing adult mosquito survival and altering Plasmodium survival or maturation in the mosquitoes. They identified a range of isolates causing around 90% mortality within 12 to 15 days. Further, mosquitoes cannot transmit sporozoites until about two weeks after an infectious blood feed, and rapid killing of the mosquito is not necessary for reducing malaria transmission. According to Scholte et al (2005: p.1641), significantly shorter life spans were observed in fungus-infected Anopheles gambiae, compared with non-infected mosquitoes. Relatively simple modifications such as higher dosage and improved efficacy of conidial formulation, larger sheets and coverage of more area for application would increase the overall effectiveness of the intervention with fungi. CONCLUSION: Innovative biotechnology including transformation systems and recombinant DNA techniques are now being used to study the mechanisms of pathogenicity and virulence at the molecular level. This knowledge will enhance the ability to manipulate the genetics of entomopathogenic fungi (Berenbaum, 2000 p.165) to enhance their use as biological pesticides against insect pests such as mosquitoes. Only an integrated approach to vector management will bring about the needed results. REFERENCES Arora, Dilip K; Bridge, Paul D; Bhatnagar, Deepak. Fungal Biotechnology in Agricultural, Food and Environmental Applications. New York: Marcel Dekker, 2004. Al-Aidroos, K; Roberts, D.W. “Mutants of Metarhizium anisopliae With Increased Virulence Towards Mosquito Larvae”. Journal: Canadian Journal of Genetic Cytology, Vol.20 (1978), pp.211-219. Berenbaum, May R, National Research Council. The Future Role of Pesticides in U.S. Agriculture. Washington, D.C: National Academy Press, 2000. Blanford, et al. “Fungal Pathogen Reduces Potential for Malaria Transmission”. Journal: Science, Vol.308, No.1638 (2005), pp.1638-1640. Clark, T.B; Kellen, W.R; Fukuda, T; Lindegren, J.E; “Field and Laboratory Studies of the Pathogenicity of the Fungus Beauveria bassiana to Three Genera of Mosquitoes”. Journal: Journal of Invertebrate Pathology, Vol.11 (1968), pp.1-7 Dhaliwal, Gurmail S; Koul, Opender. Microbial Biopesticides. Taylor and Francis, 2002. Enserink, Martin. “Mosquito-Killing Fungi May Join the Battle Against Malaria”. Journal: Science, Vol.308, 10June (2005): pp.1531-1533. Esser; Lemke. The Mycota: A Comprehensive Treatise on Fungi as Experimental Systems for Basic and Applied Research. Springer, 2002. Hajek, Anne E; Hokkanen, Heikki M.T (Ed.). Environmental Impacts of Microbial Insecticides: Need and Methods for Risk Assessment. Publisher: Springer, 2003. Howard, Dexter H. Pathogenic Fungi in Humans and Animals. New York: Marcel Dekker, 2003. Kinghorn, James R; Turner, Geoffrey. Applied Molecular Genetics of Filamentous Fungi. Springer, 1992. Larone, Davise Honig. Medically Important Fungi: A Guide to Identification, Fourth Edition. Washington, D.C., A.S.M. Press, 2002. Mukerji, K.G; Chamola, B.P; Upadhyay, R.K. Biocontrol Potential and Its Exploitation in Sustainable Agriculture. Springer, 2001. Scholte, Ernst-Jan; Ng’habi, Kija; Kihonda, Japheth; Takken; Willem; Paaijmans, Krijn; Abdulla, Salim; Killeen, Gerry F; Knols, Bart G.J. “An Entomopathogenic Fungus for Control of Adult African Malarial Mosquitoes”. Journal: Science, Vol.308, 10 June, 2005, pp.1640-1642. Upadhyay, Rajeev K. Advances in Microbial Control of Insect Pests. New York, London: Springer, 2003. Vurro, Maurizio (Ed.). Enhancing Biocontrol Agents and Handling Risks. Washington, DC: IOS Press, 2001. Read More