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Entomopathogenic fungi are widely used for the biological control of different
crop pests. They are commonly derived from a number of sources, including soil,
plants, decaying wood and mycosed cadavers. Isolation, identification, and evaluation
of native entomopathogenic fungi are essential to develop a diverse pool of biocontrol
agents adapted for effective pest management. Fungi from other regions may not
perform well due to varying environmental conditions.
In this background, the native fungal isolates viz., two isolates of Simplicillium
aogashimaense (EPF 2 and EPF 4), one isolate of Lecanicillium psalliotae (EPF 5) and
two isolates of Purpureocillium lilacinum (EPF 3 and EPF 7) maintained at AICRP on
BCCP, College of Agriculture, Vellanikkara were evaluated for their pathogenicity
against different pests. The present study entitled “Bioefficacy of native fungal isolates
against different pests” was carried at Department of Agricultural Entomology during
2022-2024 with the objectives of evaluating the pathogenicity of native fungal isolates
against different pests and standardizing the suitable medium for promising fungal
isolates.
These five fungal isolates were assessed for their pathogenicity against second
instar larvae of tobacco caterpillar Spodoptera litura Fab., adults of red flour beetle
Tribolium castaneum Herbst, adults of cowpea aphid Aphis craccivora Koch and adult
gravid females of red spider mite Tetranychus truncatus Ehara.
The preliminary screening bioassay with the five fungal isolates at 108 spores
ml-1 showed no mortality of S. litura. However, the larvae treated with P. lilacinum
(EPF 7) resulted in malformed pupae (36.67%) and adults (23.33%). No mortality was
recorded for adults of T. castaneum by any of these fungal isolates. The promising
isolates found against A. craccivora were L. psalliotae (EPF 5) and two isolates of P.
lilacinum (EPF 7 and EPF 3), which resulted in more than 75.0 per cent mortality. T.
truncatus showed mortality of 76.67 and 73.33 per cent for isolates of P. lilacinum
(EPF 7 and EPF 3), respectively. These treatments were followed by L. psalliotae (EPF
5), which recorded 56.67 per cent mortality. The isolates of S. aogashimaense (EPF 2
and EPF 4) recorded lower mean mortality against A. craccivora (60.0 and 63.33%) and
T. truncatus (33.33 and 40.0%), respectively.
The three most promising fungal isolates in the preliminary screening bioassay
against A. craccivora and T. truncatus were subjected to dose-response and exposure
time-response bioassay. Spore suspensions of five different concentrations ranging from
105 to 109 spores ml-1 were tested against these pests by contact toxicity method.
Lecanicillium psalliotae (EPF 5) at a concentration of 109 spores ml-1 recorded
the highest mortality of 100.0 per cent against A. craccivora, ten days after treatment.
At the same concentration, P. lilacinum (EPF 7 and EPF 3) registered 86.29 and 79.63
per cent mortality, respectively. L. psalliotae (EPF 5) exhibited the lowest LC50 (1.3
×105 spores ml-1) and LT50 (3.95 days) at 109 spores ml-1.
Purpureocillium lilacinum (EPF 7) recorded the highest mortality of 83.33 and
76.67 per cent at 109 and 108 spores ml-1 followed by P. lilacinum (EPF 3) at 109 spores
ml-1 (73.33%) against adult gravid females of T. truncatus, ten days post treatment. P.
lilacinum (EPF 7) showed the lowest LC50 (1.04×106 spores ml-1) and LT50 (6.40 days)
among the three isolates.
The promising isolates against A. craccivora and T. truncatus were grown in six
different media. For this, Potato Dextrose Agar (PDA), Czapek Dox Agar (CDA),
Sabouraud Maltose Agar (SMA), Sabouraud Maltose Agar with Yeast Extract (SMAY),
Sabouraud Dextrose Agar (SDA) and Sabouraud Dextrose Agar with Yeast Extract
(SDAY) and their broths were used to assess the effect of media on radial growth,
sporulation, viability of spores, production of biomass and virulence against target
pests. The effect of media on the virulence of fungal isolates was assessed by treating
the test pests with spore suspension from each medium at the concentration of 1×108
spores ml-1.
Lecanicillium psalliotae (EPF 5) showed maximum radial growth (58.5 mm),
sporulation (7.87×108 spores ml-1), viable spores (3.5×108 cfu ml-1) and mycelial
biomass (1.93g) in SMAY. The spore suspension from SMY broth recorded the highest
mortality (95.0%) against A. craccivora, which was on par with SDY and PD broths
(92.5%).
Purpureocillium lilacinum (EPF 7) recorded the maximum radial growth (70.75
mm), sporulation (4.25×109 spores ml-1), and viable spores (15×108 cfu ml-1), in SDY
broth while the highest mycelial biomass was obtained in PD broth (5.15g). The spore
suspension from SDY broth recorded the highest mortality (85.0%) against gravid
females of T. truncatus, which was on par with PD broth (82.5%) and SMY broth
(80.0%).
In conclusion, the study highlights the potential of native entomopathogenic
fungi as sustainable biocontrol agents. Among the isolates, L. psalliotae (EPF 5)
demonstrated unparalleled efficacy against A. craccivora. Its optimal growth and
virulence in SMAY make it a prime candidate for large-scale application. Similarly, P.
lilacinum (EPF 7) proved to be the most pathogenic isolate against gravid females of T.
truncatus, demonstrating significant mortality rate when cultured in SDAY. These
findings not only reinforce the significance of selecting native fungal isolates but also
emphasize the critical role of optimized growth media in enhancing biocontrol
efficiency.