Evaluation of Metarhizium rileyi Farlow (Samson) impregnated with azadirachtin and indoxacarb against Helicoverpa armigera (Hubner)

Abstract

Background Entomopathogenic fungi are the most versatile having a wide host range, capable of infecting insects at different developmental stages. In the present study, Metarhizium rileyi, at the concentrations of 102, 103, 104, 105, 106, 107 and 108 conidia/ml and sub-lethal concentrations of azadirachtin (1.02 and 1.53 ppm) and indoxacarb (0.72 ppm) were evaluated against the 1st, 2nd, 3rd, 4th and 5th larval instars of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) under laboratory conditions. Results M. rileyi applied at 106 conidia/ml caused a maximum mortality of 83.33 and 80.00% of 1st and 2nd larval instars of H. armigera, respectively. The maximum mortality of 3rd, 4th and 5th larval instars of H. armigera with 108 conidia/ml of M. rileyi was 83.33, 76.67 and 53.33%, respectively. When M. rileyi blended with azadirachtin at 1.02 ppm, the highest mortality rate of 86.21% at 106 conidia/ml against 2nd instar larvae was resulted. Similarly, M. rileyi applied at 108 conidia /ml mixed with azadirachtin (1.53 ppm) showed 89.66% mortality of 3rd instar larvae. The 2nd instar larvae treated with M. rileyi at 106 conidia/ml, mixed with indoxacarb (0.72 ppm), the corrected mortality rate was 82.14%. Concentration mortality response of 3rd instar larvae to M. rileyi blended with indoxacarb (0.72 ppm) was 85.71% at 108 conidia/ml. The median lethal concentration (LC50) values were 5.51 × 103, 1.86 × 104, 2.81 × 105 and 5.55 × 105 conidia/ml for 1st, 2nd, 3rd and 4th larval instars, respectively, after 7 days of treatment. M. rileyi when mixed with sub-lethal concentrations of azadirachtin (1.02 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 1.09 × 104 conidia/ml and 1.37 × 104 conidia/ml against 2nd instar larvae, respectively, after 24 hours. Similarly, M. rileyi mixed with sub-lethal concentrations of azadirachtin (1.53 ppm) and indoxacarb (0.72 ppm) resulted LC50 values of 3.12 × 108 and 3.06 × 105 conidia/ml against 3rd instar larvae, respectively, after 24 hours. The study revealed that the susceptibility of larvae decreased in case of large larval instars. Conclusions M. rileyi can be utilized as one of the component of Integrated Pest Management Program for the eco-friendly management of H. armigera. As the application of M. rileyi @ 107 conidia/ml alone or in combination with azadirachtin (1.02 and 1.53 ppm) or indoxacarb (0.72 ppm) resulted to the highest mortality.

Compatibility of Entomopathogenic Fungus <i>Metarhizium rileyi</i> with Biorationals

“…However, beyond such concentrations, spore viability or colony growth is delayed and suppressed, indicating that neem oil can cause loss of potency or inhibition of entomopathogenic agents (Togbé et al, 2014). Dev et al (2021) evaluated M. rileyi Farlow (Samson) impregnated with azadirachtin against Helicoverpa armigera (Hubner) and reported M. rileyi blended with azadirachtin @ 10 6 conidia/ ml and @ 10 8 conidia/ ml caused the highest mortality of 86.21% and 89.66% of 2 nd and 3 rd instar larvae of H. armigera, respectively. Sahayaraj et al (2011) used liquid and dual plate bioassays to investigate the compatibility of commercial botanicals (Biospark, Exodos, and Phytophrate) with Isaria fumosorosea, Beauveria bassiana and Lecanicillium lecanii in vitro.…”

Natural Prevalence, Molecular Characteristics, and Biological Activity of Metarhizium rileyi (Farlow) Isolated from Spodoptera frugiperda (J. E. Smith) Larvae in Mexico

“…Metarhizium rileyi (Farlow) Kepler, SA Rehner, and Humber (formerly Nomurea rileyi ) (Hypocreales: Clavicipitaceae) is a cosmopolitan pathogen that infects many species of Lepidoptera [ 10 , 17 , 18 ]. Natural epizootics of this fungus have been reported in several noctuid pests [ 19 , 20 , 21 , 22 , 23 ], including S. frugiperda [ 24 , 25 , 26 , 27 , 28 ]. Although M. rileyi has been recognized as an effective control agent to complement integrated pest management strategies [ 10 ], its efficacy in causing mortality is isolate-specific [ 5 ].…”