UA ENTO 446 - Autodissemination of the entomopathogenic fungus Metarhizium anisopliae

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AbstractBackgroundMethodsResultsConclusionIntroductionMaterials and MethodsBioassaysMosquitoesFungusExperimental proceduresBioassay 1Bioassay 2Bioassay 3Bioassay 4Data analysisResultsDiscussionConclusionAuthors' contributionAcknowledgementsReferencesBioMed CentralPage 1 of 6(page number not for citation purposes)Malaria JournalOpen AccessResearchAutodissemination of the entomopathogenic fungus Metarhizium anisopliae amongst adults of the malaria vector Anopheles gambiae s.s.Ernst-Jan Scholte*1, Bart GJ Knols1,2 and Willem Takken1Address: 1Laboratory of Entomology, Wageningen University Research Centre, Binnenhaven 7, P.O. Box 8031, Wageningen, the Netherlands and 2Entomology Unit, Agency's laboratories Seibersdorf, International Atomic Energy Agency, A-2444 Seibersdorf, AustriaEmail: Ernst-Jan Scholte* - [email protected]; Bart GJ Knols - [email protected]; Willem Takken - [email protected]* Corresponding author AbstractBackground: The entomopathogenic fungus Metarhizium anisopliae is being considered as abiocontrol agent for adult African malaria vectors. In the laboratory, work was carried out to assesswhether horizontal transmission of the pathogen can take place during copulation, as this wouldenhance the impact of the fungus on target populations when compared with insecticides.Methods: Virgin female Anopheles gambiae sensu stricto were exposed to conidia whilst resting onfungus-impregnated paper. These females were then placed together for one hour withuncontaminated males in proportions of either 1:1 or 1:10 shortly before the onset of matingactivity.Results: Males that had acquired fungal infection after mating indicate that passive transfer of thepathogen from infected females does occur, with mean male infection rates between 10.7 ± 3.2%and 33.3 ± 3.8%. The infections caused by horizontal transmission did not result in overalldifferences in survival between males from test and control groups, but in one of the threeexperiments the infected males had significantly shorter life spans than uninfected males (P < 0.05).Conclusion: This study shows that autodissemination of fungal inoculum between An. gambiae s.s.mosquitoes during mating activity is possible under laboratory conditions. Field studies arerequired next, to assess the extent to which this phenomenon may augment the primarycontamination pathway (i.e. direct contact with fungus-impregnated targets) of vector populationsin the field.IntroductionControl of the main African malaria vector Anopheles gam-biae (Diptera: Culicidae) continues to rely heavily onapplication of residual insecticides, either for indoorresidual house spraying [1] or bednet impregnation [2].These approaches have been highly effective in reducingmalaria morbidity and mortality [2], but associated prob-lems regarding environmental pollution [3,4], acceptabil-ity and cost [5,6] and the now widespread and continuingdevelopment of resistance [7-10] underscore the need foralternative strategies, such as vector control with biologi-cal agents [1,11,12].Published: 28 November 2004Malaria Journal 2004, 3:45 doi:10.1186/1475-2875-3-45Received: 25 August 2004Accepted: 28 November 2004This article is available from: http://www.malariajournal.com/content/3/1/45© 2004 Scholte et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Malaria Journal 2004, 3:45 http://www.malariajournal.com/content/3/1/45Page 2 of 6(page number not for citation purposes)Entomopathogenic fungi are among the biological con-trol agents used against insect pests. Interest in using thehyphomycete Metarhizium anisopliae against adult Africanmalaria vectors has recently increased [13]. The fungushas proven to be highly virulent for this vector, both in thelaboratory [14] as well as in the field (Scholte et al., inpreparation). The principal method of contamination ofthe target insect population with the fungus is throughapplication of conidia on indoor resting targets. However,in order to achieve the highest possible impact on the tar-get population, it is desirable that contamination path-ways other than the primary mode of contamination areutilised, for instance horizontal transmission. Horizontaltransmission of pathogens within the same host/targetspecies is called autodissemination, and this phenome-non has been suggested for biocontrol of several insectpests [15,16]. Successful transmission of M. anisopliae byhoneybees for infection of the pollen beetle Meligethesaeneus [17], of Beauveria bassiana between adult flies ofDelia radicum [18] and of M. anisopliae and B. bassianabetween adult tsetse flies, Glossina morsitans morsitans [19]confirms the capability of insects to transmit fungi hori-zontally. Autodissemination of insecticidal biocontrolagents, such as insect-pathogenic fungi, provides an addi-tional advantage over pesticides, as the impact on pestpopulations increases beyond direct contact. In severalcases, autodissemination of entomopathogenic fungiwithin populations of insect pests, using attractant trapsas the initial source of infection, has succeeded [18,20-22]. The strategy envisaged for the use of M. anisopliaeagainst adult An. gambiae is that host-seeking females, andoccasionally also males that rest indoors, will receive pri-mary infections while resting indoors on fungus-impreg-nated resting targets. Under optimal circumstances, priorto death, this infection may be transmitted to conspecificsupon contact (e.g. during mating). These mosquitoes are,therefore, not infected through direct contact with fungus-impregnated materials, but indirectly, upon physical con-tact with infected counterparts. It is estimated that approx-imately half of newly hatched, virgin females take a bloodmeal before mating [23,24]. A female, with contaminatedlegs and mouthparts following the blood-feeding visit toa house containing fungus-impregnated resting targets,may contaminate male counterparts when she mates thefollowing dusk period, thereby spreading the fungusthrough the population.The objective of this study was to investigate whetheradult An. gambiae infected with M. anisopliae can transmitthe fungus to uncontaminated mosquitoes of the oppo-site sex through physical contact during the matingprocess.Materials and


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UA ENTO 446 - Autodissemination of the entomopathogenic fungus Metarhizium anisopliae

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