MSc

The study entitled ‘Novel bioformulations of entomopathogenic fungi and
their efficacy against banana weevils’ was carried out at Dept. of Agrl.
Entomology, College of Agriculture, Vellayani during 2016-2018, with the
objective
to
develop
novel
formulations
of
entomopathogenic
fungi,
Metarhizium anisopliae (Metch.) Sorokin, Beauveria bassiana (Bals.) Vuillemin
and to evaluate their efficacy in managing banana weevils. It was intended to
develop capsule and gel formulations.
Experiment to standardize a coating material for developing capsules revealed
that Hard Gelatin Transparent (HGT), Hard Gelatin Coloured (HGC) and
Hydroxy Propyl Methyl Cellulose (HPMC), were equally stable under ambient
conditions of storage (26 -33°C and RH 60-80%). On testing their ability to
disintegrate under field conditions, it was noted that chitosan filled HGT capsules
easily disintegrated at 20% soil moisture after 36 h and after 24 h at 30 % soil
moisture. It took 144 h for all capsules to disintegrate in sheath or leaf axil and 24
h in bore holes. Talc and chitosan were superior, in maintaining storage stability
as well as degradability.
A trial conducted to determine the moisture content of capsules, revealed that
10 % was the ideal moisture level content of the ingredient, to maintain storage
stability as well as viability of the formulation. Viability noticed after three months
was 2.29 × 107 cfu mL-1 and 2.27 × 107 cfu mL-1 in chitosan based capsules of
M. anisopliae and B. bassiana and 2.10 × 107 cfu mL-1 and 0.76 × 107 cfu mL-1 in
talc based capsules. Therefore, capsules were developed with HGT coating, with
chitosan / talc as carrier at 10 % moisture content.
Shelf life studies revealed that chitosan was the best carrier material
compared to talc in retaining viability of Metarhizium capsules, with a mean cfu
of 2.51 × 107 mL-1 and 1.77× 107 mL-1. During a period of three months of
storage, there was no decline in the number of viable colonies, cfu ranging from
1.72 × 107 mL-1 to 2.79 × 107 mL-1. . Storage under refrigeration had better
retention of viability (2.63 × 107 cfu mL-1) than at room temperature (1.64× 107
cfu
mL-1). In Beauveria capsules, the viability did not differ in both chitosan
and talc based capsules. Here also, the number of viable colonies did not decline
statistically, till three months of storage, with mean cfu values ranging from 1.85
× 107 mL-1 to 2.36 × 107 mL-1. In general, shelf life of capsules could be extended
by two months when chitosan was used as the carrier material. Low temperature
storage could also improve the shelf life by two months.
Shelf life studies of gel formulations indicated that both Metarhizium and
Beauveria gels exhibited high viability in chitosan at room temperature and under
refrigeration. The mean number of viable colonies observed was 2.39 × 106 cfu
mL-1 in chitosan based gels of Metarhizium and 2.17 × 106 cfu mL-1 in Beauveria
gels. The number of viable colonies of Metarhizium and Beauveria observed
throughout the experimental period did not vary significantly over three months of
storage. The mean number of cfu being 2.26 × 107 mL-1 on the 15th day and 1.41 x
106 mL-1 on the 90th day . It was also inferred that chitosan when used for
formulating gels could extend the shelf life of both organisms by one month.
Pathogenicity test disclosed the affinity of M. anisopliae to rhizome
weevil and B. bassiana to pseudostem weevil. Pot culture studies to evaluate
chitosan and talc based capsules of B. bassiana revealed that both the capsules of
Beauveria were effective as chlorpyriphos 20 EC 0.05% for pseudostem weevil, in
prophylactic and curative methods. The damage index (DI) was one each and
reduction in pest population was 91.67 % in prophylactic control and 91.67-100 %
in curative control. Metarhizium capsules reduced the damage caused by rhizome
significantly, but the reduction in pest population was only to the tune of 47-55 %
in prophylactic and 50- 58 % in curative control. Chitosan based gel of
Metarhizium tested against rhizome weevil, reduced the damage significantly
(DI 46.67 and 30, in prophylactic and curative methods). The pest population was
reduced by 61.11 % in prophylactic and 36.11 % in curative methods.
The study could standardize the protocol for capsule and gel formulations
of entomopathogenic fungi, retaining the viability and infectivity upto three
months of storage. It is concluded that placement of Beauveria capsules in leaf
axils prophylactically and curatively can effectively control pseudostem weevil and
Metarhizium capsules and gels placed in the rhizosphere could manage the rhizome
weevil moderately.