Effect of repeatedin vitrosub-culturing on the virulence ofMetarhizium anisopliaeagainstHelicoverpa armigera(Lepidoptera: Noctuidae)

An Improved Bioassay Method for Entomopathogenic Fungi of Sugarcane Pests and Its Evaluation in Studies of Virulence in Subcultures

“…In view of the relationship with the extent of conidiation and virulence, hydrophobin (Kamp and Bidochka 2002) and Pr1 (Shah et al 2007) could serve as markers for the extent of pleomorphic degradation and quality changes in virulence, respectively. The contradictory observations that up to 30 subcultures did not attenuate several fungi whereas M. anisopliae enhanced LC 50 or LT 50 against third instar larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) in 40 subcultures (Nahar et al 2008) notwithstanding, significantly reduced mortality in 15th subculture of M. anisopliae in the present study indicated possible onset of degeneration and the need to pass the fungus through natural host after 10 subcultures. Overall, the similar pattern of results obtained in virulence tests with diet-reared and field-collected larvae validated the suitability of the modified bioassay method for such tests.…”

“…in media and virulence against the whiteflies Bemisia argentifolii and Trialeurodes vaporariorum (Meekes et al 2002), and the non-significant correlations spore output displayed with LC 50 or mortality percentage and LT 50 in our studies suggested that virulence is influenced by factors other than spore production. This is because alterations in conidiation and virulence in repeated subcultures are associated with changes in physical and chemical properties such as hydrophobin concentration (Kamp and Bidochka 2002), hydrophobicity, spore-bound Pr1, adhesion to surfaces (Shah et al 2007), appressorium formation, cuticledegrading enzyme production and genetic composition (Nahar et al 2008). A strong correlation between conidial output and mortality parameters, however, would enable the use of the former as a simple marker for virulence of experimental or commercial fungal cultures.…”

“…On the other hand, repeated in vitro transfers (10-30 times) of M. anisopliae and different EPF did not always lead to loss of virulence against their hosts (reviewed in Nahar et al 2008). These contrasting observations, viewed in the light of the variations in spore production we experienced with B. brongniartii, B. bassiana and M. anisopliae in laboratory cultures and the strain-related degeneration reported earlier (Kamp and Bidochka 2002), emphasized the need to examine degeneration in our strains of EPF.…”

Molecular, morphological and pathogenic characterization of six strains of Metarhizium spp. (Deuteromycotina: Hyphomycetes) for the control of Aegorhinus superciliosus (Coleoptera: Curculionidae)

“…Moreover, successive cultures of entomopathogenic fungi in these media have the disadvantage of negatively affecting virulence, increasing the lethal time and dose (Nahar et al, 2008), and decreasing the adhesion of the conidia to the cuticle of the insect (Shah et al, 2007), decreasing conidia production and their ability to tolerate UV radiation (Santoro et al, 2014).…”

Comparison ofMetarhiziumisolates for biocontrol ofHelicoverpa armigera(Lepidoptera: Noctuidae) in chickpea

“…Recently, Metarhizium anisopliae M34412 has been identified as a potential commercial strain for control of Helicoverpa armigera infestation on pulses (Nahar et al 2003(Nahar et al , 2004b. Repeated in vitro sub-culturing on artificial media reduced the virulence of M34412 towards H. armigera (Nahar et al 2008). Although the virulence of M. anisopliae was restored by four to five passages through H. armigera larvae, it was not always feasible to maintain and revive cultures from the insect host.…”