Microbial control of caged population of Zonocerus variegatus using Beauveria bassiana and Metarhizium sp.

Microbial control of caged populations of Zonocerus variegatus was carried out using indigenous fungal entomopathogens isolated from the grasshopper's cadaver. Bioassay response indicated a dose-dependent mortality coupled with drastic reduction in food consumption among spores infected grasshoppers. Lethal time (LT50) of 4.6 days for 103 spores/ml and 3.8 days for 107 spores/ml of oil formulation of Beauveria bassiana were observed. While Metarhizium sp recorded LT50 of 9.0 days and 2.8 days for 103 and 107 spores/ml, respectively. The results obtained were discussed in relation to use of the isolates in the control Z. variegates infestation in forest agro-ecosystem of south west, Nigeria. Key Words: Microbial control, entomopathogenic fungi, Beauveria bassiana, Zonoccrus variegatus, Metarhizium sp. African Journal of Biotechnology Vol.4(1) 2005:113-11

A novel method for standardized application of fungal spore coatings for mosquito exposure bioassays

<p>Abstract</p> <p>Background</p> <p>Interest in the use of fungal entomopathogens against malaria vectors is growing. Fungal spores infect insects via the cuticle and can be applied directly on the insect to evaluate infectivity. For flying insects such as mosquitoes, however, application of fungal suspensions on resting surfaces is more realistic and representative of field settings. For this type of exposure, it is essential to apply specific amounts of fungal spores homogeneously over a surface for testing the effects of fungal dose and exposure time. Contemporary methods such as spraying or brushing spore suspensions onto substrates do not produce the uniformity and consistency that standardized laboratory assays require. Two novel fungus application methods using equipment developed in the paint industry are presented and compared.</p> <p>Methods</p> <p>Wired, stainless steel K-bars were tested and optimized for coating fungal spore suspensions onto paper substrates. Different solvents and substrates were evaluated. Two types of coating techniques were compared, i.e. manual and automated coating. A standardized bioassay set-up was designed for testing coated spores against malaria mosquitoes.</p> <p>Results</p> <p>K-bar coating provided consistent applications of spore layers onto paper substrates. Viscous Ondina oil formulations were not suitable and significantly reduced spore infectivity. Evaporative Shellsol T solvent dried quickly and resulted in high spore infectivity to mosquitoes. Smooth proofing papers were the most effective substrate and showed higher infectivity than cardboard substrates. Manually and mechanically applied spore coatings showed similar and reproducible effects on mosquito survival. The standardized mosquito exposure bioassay was effective and consistent in measuring effects of fungal dose and exposure time.</p> <p>Conclusions</p> <p>K-bar coating is a simple and consistent method for applying fungal spore suspensions onto paper substrates and can produce coating layers with accurate effective spore concentrations. The mosquito bioassay was suitable for evaluating fungal infectivity and virulence, allowing optimizations of spore dose and exposure time. Use of this standardized application method will help achieve reliable results that are exchangeable between different laboratories.</p

Thermal behaviour of Anopheles stephensi in response to infection with malaria and fungal entomopathogens

<p>Abstract</p> <p>Background</p> <p>Temperature is a critical determinant of the development of malaria parasites in mosquitoes, and hence the geographic distribution of malaria risk, but little is known about the thermal preferences of <it>Anopheles</it>. A number of other insects modify their thermal behaviour in response to infection. These alterations can be beneficial for the insect or for the infectious agent. Given current interest in developing fungal biopesticides for control of mosquitoes, <it>Anopheles stephensi </it>were examined to test whether mosquitoes showed thermally-mediated behaviour in response to infection with fungal entomopathogens and the rodent malaria, <it>Plasmodium yoelii</it>.</p> <p>Methods</p> <p>Over two experiments, groups of <it>An. stephensi </it>were infected with one of three entomopathogenic fungi, and/or <it>P. yoelii</it>. Infected and uninfected mosquitoes were released on to a thermal gradient (14 – 38°C) for "snapshot" assessments of thermal preference during the first five days post-infection. Mosquito survival was monitored for eight days and, where appropriate, oocyst prevalence and intensity was assessed.</p> <p>Results and conclusion</p> <p>Both infected and uninfected <it>An. stephensi </it>showed a non-random distribution on the gradient, indicating some capacity to behaviourally thermoregulate. However, chosen resting temperatures were not altered by any of the infections. There is thus no evidence that thermally-mediated behaviours play a role in determining malaria prevalence or that they will influence the performance of fungal biopesticides against adult <it>Anopheles</it>.</p

Genome Sequencing and Comparative Transcriptomics of the Model Entomopathogenic Fungi Metarhizium anisopliae and M. acridum

Metarhizium spp. are being used as environmentally friendly alternatives to chemical insecticides, as model systems for studying insect-fungus interactions, and as a resource of genes for biotechnology. We present a comparative analysis of the genome sequences of the broad-spectrum insect pathogen Metarhizium anisopliae and the acridid-specific M. acridum. Whole-genome analyses indicate that the genome structures of these two species are highly syntenic and suggest that the genus Metarhizium evolved from plant endophytes or pathogens. Both M. anisopliae and M. acridum have a strikingly larger proportion of genes encoding secreted proteins than other fungi, while ∼30% of these have no functionally characterized homologs, suggesting hitherto unsuspected interactions between fungal pathogens and insects. The analysis of transposase genes provided evidence of repeat-induced point mutations occurring in M. acridum but not in M. anisopliae. With the help of pathogen-host interaction gene database, ∼16% of Metarhizium genes were identified that are similar to experimentally verified genes involved in pathogenicity in other fungi, particularly plant pathogens. However, relative to M. acridum, M. anisopliae has evolved with many expanded gene families of proteases, chitinases, cytochrome P450s, polyketide synthases, and nonribosomal peptide synthetases for cuticle-degradation, detoxification, and toxin biosynthesis that may facilitate its ability to adapt to heterogenous environments. Transcriptional analysis of both fungi during early infection processes provided further insights into the genes and pathways involved in infectivity and specificity. Of particular note, M. acridum transcribed distinct G-protein coupled receptors on cuticles from locusts (the natural hosts) and cockroaches, whereas M. anisopliae transcribed the same receptor on both hosts. This study will facilitate the identification of virulence genes and the development of improved biocontrol strains with customized properties

Can fungal biopesticides control malaria?

Recent research has raised the prospect of using insect fungal pathogens for the control of vector-borne diseases such as malaria. In the past, microbial control of insect pests in both medical and agricultural sectors has generally had limited success. We propose that it may now be possible to produce a cheap, safe and green tool for the control of malaria which, in contrast to most chemical insecticides, will not eventually be rendered useless by resistance evolution. Realising this potential will require lateral thinking by biologists, technologists and development agencie

Effet De La Temperature Et De L\'humidite Relative Sur Le Developpement De La Mycose A Entomophaga grylli batko (Zygomycètes, Entomophthorales) chez Zonocerus Variegatus L. (Orthoptera, Pyrgomorphidae)

L\'étude a été conduite au laboratoire à l\'Institut International d\'Agriculture Tropicale (IITA) à Cotonou au Bénin sur la mycose à Entomophaga grylli, un champignon entomopathogène, chez Zonocerus variegatus. L\'influence de la température et de l\'humidité relative (HR) sur la sporulation et la germination des conidies a été évaluée. L\'infection artificielle des criquets par le champignon a été réalisée au laboratoire et l\'effet des facteurs abiotiques précédents étudié. La sporulation intervient entre 6 et 10 h de temps après la mort de l\'insecte et continue au-delà de 24 h à 25 °C et à 100 % d\'humidité relative. Le maximum de spores est libéré entre 10 et 20 h après incubation des insectes dans les conditions précédentes. La germination des conidies primaires nécessite une humidité relative proche de la saturation. La température optimale de germination s\'est située entre 20 et 25 °C. L\'infection artificielle par exposition directe des insectes aux conidies fraîchement projetées des cadavres d\'insectes a permis d\'obtenir 90 % de mortalité en moyenne et plus de 62 % d\'infection à 25 °C. La température affecte significativement les taux de mortalité et d\'infection de même que la période d\'incubation. La température optimale de développement de la maladie est de 25°C avec une durée d\'incubation moyenne de 9 jours.The study was conducted in laboratory at the International Institute of Tropical Agriculture (IITA) at Cotonou in Benin, on the mycosis of Entomophaga grylli, an entomopathogenic fungus, in Zonocerus variegatus. The influence of temperature and relative humidity (RH) on sporulation, conidial germination and the infection steps of the fungus was evaluated. Sporulation of the pathogen, generally, started between 6 and 10 h after death of the host organism and continued beyond 24 hr at 25 °C and 100 % relative humidity. Maximum sporulation occurred between 10 and 20 hr after the death of the host. The optimal temperature for the germination of the primary conidia were between 20 and 25 °C. Conidial germination required a RH near saturation. Artificial infection by exposing grasshoppers to conidial showers from the fungus-killed grasshoppers appeared to be most effective resulting in up to an average of 90 % mortality and more than 62 % infection at 25 °C. Temperature significantly affected mortality and infection rates and so did incubation period. The optimum temperature for the disease development was found to be about 25 °C with a mean incubation period of 9 days. Keywords: Infection artificielle, Entomophaga grylli, Zonocerus variegatus,conidies, Bénin; Artificial infection, Entomophaga grylli, Zonocerus variegatus, conidia, Sporulation, BéninAgronomie Africaine Vol. 16 (2) 2004: pp. 19-3