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Virulence of MetarhiziumM isolates against the polyphagous defoliator pest, Spilarctia obliqua (Llepidoptera: Aarctiidae)

By N Sapna Bai, TO Sasidharan, OK Remadevi, Priyadarsanan Dharma Rajan and M Balachander

Abstract

Species of the entomopathogenic fungus Metarhizium are some of the most promising biocontrol agents against Lepidopteran pests. Laboratory bioassays were conducted to study the virulence of five isolates of Metarhizium sp. against larvae of the polyphagous pest, Spilarctia obliqua (Lepidoptera: Arctiidae). The Metarhizium isolates used in the study were recovered from soil and various insect hosts belonging to Lepidoptera, Coleoptera and Isoptera. Initially, a preliminary assay was carried out involving 18 Metarhizium isolates at a spore concentration 10<sup>7</sup> conidia ml<sup>-1</sup> and five isolates, MIS 1, MIS 2, MIS 3, MIS 8 and MIS 9, which caused more than 50% mortality were chosen for the detailed bioassay. The assay was carried out with four different spore concentrations of each isolate, ranging from 10<sup>4</sup>-10<sup>7</sup> conidia ml<sup>-1</sup>. The lethal concentration LC<sup>50</sup> of these five isolates ranged from 2.1 × 10<sup>5</sup> to 38.9 × 10<sup>5</sup> conidia ml<sup>-1</sup>. The lethal time LT<sub>50</sub> of the isolates ranged from 7.0-8.1, 6.0-7.7, 5.1-6.7, 4.6-5.4 days at concentrations 1 × 10<sup>4</sup>, 1 × 10<sup>5</sup>, 1 × 10<sup>6</sup>, 1 × 10<sup>7</sup> conidia ml<sup>-1</sup> respectively. The most pathogenic among the five isolates was the MIS 2 isolate with the lowest LC<sub>50</sub> of 2.11 × 10<sup>5 </sup>conidia ml<sup>-1</sup> and LT<sub>50</sub> of 4.6, 5.1, 6.0 and 7.0 days respectively at concentrations 1 × 10<sup>7</sup>, 1 × 10<sup>6</sup>, 1 × 10<sup>5</sup>, 1 × 10<sup>4</sup> conidia ml<sup>-1</sup>. Isolate MIS 3 was second in effectiveness. These two isolates showed promise for use as biocontrol agents against S. obliqua

Topics: G Journal Papers
Publisher: Forest Research Institute Malaysia
Year: 2010
OAI identifier: oai:eprints.atree.org:136
Provided by: ePrints@ATREE
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