مجال
التميز
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تميز دراسي و بحثي
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البحوث المنشورة
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البحث (1):
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عنوان البحث:
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Toxicity testing of Metarhizium conidia and
toxins against aquatic invertebrates
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تاريخ النشر:
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23/10/2015
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موجز عن البحث:
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Entomopathogenic fungi offer
much potential for the control of arthropod pests. Very little is known about
the impact of inoculum drift and runoff on aquatic non-target invertebrates.
In general, there are no clear guidelines on risk assessment of these
biological control agents and their secreted compounds. In the current study,
Metarhizium brunneum conidia and crude metabolite extracts were tested
against the larvae of three mosquito species (Anopheles stephensi, Culex
quinquefasciatus, and Aedes aegypti) and the aquatic, non-target arthropods
Artemia salina and Daphnia pulex. Both A. salina and D. pulex are recognised
ecotoxicology indicator species. Extracts were prepared from filtrates of
three M. brunneum strains, grown in three different culture media, using
conventional solvent and new nanofiltration technologies. Metarhizium conidia
and extracts affected the survival of all the aquatic invertebrates with An.
stephensi also exhibiting abnormal development 96 h after exposure to the
extracts. Ingestion of M. brunneum conidia induced apoptosis in aquatic
non-targets as reflected by elevated caspase activity. Mortality appeared to
be due to a combination of stress and secreted fungal metabolites independent
of culture media. Due to their extreme sensitivity, An. stephensi and D.
pulex are highly recommended as ecotox indicator species when conducting risk
assessment of inoculum and metabolites of entomopathogenic fungi in aquatic
environments.
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البحث (2):
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عنوان البحث:
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Metarhizium brunneum Blastospore Pathogenesis in Aedes aegypti Larvae:
Attack on Several Fronts Accelerates Mortality
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تاريخ النشر:
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07/07/2016
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موجز عن البحث:
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Aedes aegypti is
the vector of a wide range of diseases (e.g. yellow fever, dengue,
Chikungunya and Zika) which impact on over half the world’s population.
Entomopathogenic fungi such as Metarhizium anisopliae and Beauveria
bassiana have been found to be highly efficacious in killing
mosquito larvae but only now are the underlying mechanisms for pathogenesis
being elucidated. Recently it was shown that conidia of M. anisopliae caused
stress induced mortality in Ae. aegypti larvae,
a different mode of pathogenicity to that normally seen in terrestrial hosts.
Blastospores constitute a different form of inoculum produced by this fungus
when cultured in liquid media and although blastospores are generally
considered to be more virulent than conidia no evidence has been presented to
explain why. In our study, using a range of biochemical, molecular and
microscopy methods, the infection process of Metarhizium brunneum (formerly M. anisopliae)
ARSEF 4556 blastospores was investigated. It appears that the blastospores,
unlike conidia, readily adhere to and penetrate mosquito larval cuticle. The
blastospores are readily ingested by the larvae but unlike the conidia are
able infect the insect through the gut and rapidly invade the haemocoel. The
fact that pathogenicity related genes were upregulated in blastospores
exposed to larvae prior to invasion, suggests the fungus was detecting host
derived cues. Similarly, immune and defence genes were upregulated in the
host prior to infection suggesting mosquitoes were also able to detect pathogen-derived
cues. The hydrophilic blastospores produce copious mucilage, which probably
facilitates adhesion to the host but do not appear to depend on production of
Pr1, a cuticle degrading subtilisin protease, for penetration since protease
inhibitors did not significantly alter blastospore virulence. The fact the
blastospores have multiple routes of entry (cuticle and gut) may explain why
this form of the inoculum killed Ae. aegypti larvae
in a relatively short time (12-24hrs), significantly quicker than when larvae
were exposed to conidia. This study shows that selecting the appropriate form
of inoculum is important for efficacious control of disease vectors such
as Ae. aegypti.
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البحث (3):
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عنوان البحث:
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Differential Pathogenicity of Metarhizium Blastospores and Conidia
Against Larvae of Three Mosquito Species
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تاريخ النشر:
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28/11/2016
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موجز عن البحث:
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Biorational
insecticides are being increasingly used in integrated pest management
programs. In laboratory bioassays, the pathogenicity of blastospores and
conidia of the entomopathogenic fungus Metarhizium brunneum ARSEF 4556 was
evaluated against larvae of three mosquito species. Three propagule
concentrations (1 × 106, 1 × 107, and 1 × 108 spores ml − 1) were used in the
bioassays. Results showed that Aedes aegypti had lower survival rates when
exposed to blastospores than when exposed to conidia, whereas the converse
was true for Culex quinquefasciatus larvae. Anopheles stephensi larvae
survival rates were similar when exposed to blastospores and conidia, except
at the higher doses, where blastospores were more virulent. Several assays
showed little difference in mortalities when using either 1 × 107 or 1 × 108
spores ml − 1, suggesting a threshold above which no higher control levels or
economic benefit would be achieved. When tested at the lowest dose, the LT50
of Cx. quinquefasciatus using blastospores, wet conidia, and dry conidia was
3.2, 1.9, and 4.4 d, respectively. The LT50 of Ae. aegypti using
blastospores, wet conidia, and dry conidia was 1.3, 3.3, and 6.2 d,
respectively. The LT50 of An. stephensi using blastospores, wet conidia, and
dry conidia was 2.0, 1.9, and 2.1 d, respectively. These observations suggest
that for optimized control, two different formulations of the fungus may be
needed when treating areas where there are mixed populations of Aedes,
Anopheles, and Culex.
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البحث (4): |
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عنوان البحث: |
Combined use of the
entomopathogenic fungus, Metarhizium brunneum, and the mosquito predator,
Toxorhynchites brevipalpis, for control of mosquito larvae: Is this a risky
biocontrol strategy? |
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تاريخ النشر:
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06/02/2018
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موجز عن البحث:
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Mosquitoes transmit several
diseases, which are of global significance (malaria, dengue, yellow fever, Zika).
The geographic range of mosquitoes is increasing due to climate change, tourism
and trade. Both conidial and blastospore formulations of the entomopathogenic
fungus, Metarhizium brunneum ARSEF 4556, are being investigated as mosquito
larvicides. However, concerns have been raised over possible non-target impacts
to arthropod mosquito predators such as larvae of Toxorhynchites brevipalpis
which feed on larvae of mosquito vector species. Laboratory-based, small
container bioassays showed, that T. bevipalpis larvae are susceptible to
relatively high concentrations (i.e. ≥107 spores ml−1) of inoculum with
blastospores being significantly more virulent than conidia. At lower
concentrations (e.g. <107 spores ml−1), it appears that M. brunneum
complements T. brevipalpis resulting in higher control than if either agent was
used alone. At a concentration of 105 spores ml−1, the LT50 of for conidia and
blastospores alone was 5.64 days (95% CI: 4.79–6.49 days) and 3.89 days (95%
CI: 3.53–4.25 days), respectively. In combination with T. brevipalpis, this was
reduced to 3.15 days (95% CI: 2.82–3.48 days) and 2.82 days (95% CI:
2.55–3.08 days). Here, combined treatment with the fungus and predator was
beneficial but weaker than additive. At 107 and 108 blastospores ml−1, mosquito
larval mortality was mostly due to the fungal pathogen when the predator was
combined with blastospores. However, with conidia, the effects of combined
treatment were additive/synergistic at these high concentrations. Optimisation
of fungal concentration and formulation will reduce: (1) risk to the predator
and (2) application rates and costs of M. brunneum for control of mosquito
larvae.
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