MSc

The research programme, entitled “Bioefficacy of Aloe vera (L.) in managing pests
of brinjal, Solanum melongena L.” was undertaken at the Department of Agricultural
Entomology, College of Agriculture, Vellayani during the period 2020 to 2022. The
objective of the study was to evaluate the biopesticidal efficacy of A. vera in managing
pests of brinjal.
Laboratory screenings were conducted to find out the repellent, antifeedant,
insecticidal and the effect on fecundity and egg hatchability of aloe leaf extracts viz., crude
aloe gel solution, aloe leaf peel aqueous extract and aloe leaf peel powder aqueous extract
at three different concentrations (2.50 %, 5.00% and 10.00%) against second instar grubs
and adults of Henosepilachna vignitioctopunctata (F.).
The highest per cent repellence recorded was 73.33 and 83.33 in aloe leaf peel
powder aqueous extract 10 % at 8 h after treatment against the second instar grubs and
adults, respectively. Crude aloe gel solution 10 % recorded a per cent repellence of 53.33
against both grubs and adults whereas, aloe leaf peel aqueous extract 10 % recorded 53.33,
30.00 per cent repellence against second instar grubs and adults, respectively.
Aloe leaf peel powder aqueous extract 10 % recorded a potential Antifeedant Index
(AI), of 99.47 per cent and 100 per cent against the grubs and adults, respectively. Crude
aloe gel solution 10 % recorded AI of 88.49 per cent and 99.95 per cent against grubs and
adults, respectively whereas, aloe leaf peel aqueous extract 10 % exhibited AI of 70.93 per
cent and 90.33 per cent against grubs and adults, respectively.
The fecundity of the beetles which were fed on leaves treated with aqueous extract
of 10 % leaf peel powder of aloe was reduced to 57.00 per cent and the percentage
emergence of grubs was only 82.52. Crude aloe gel solution 10 % recorded a reduction of
45.16 per cent in fecundity and the per cent emergence of grubs was 92.17. Aloe leaf peel
aqueous extract 10 % reported only 29.03 per cent reduction in fecundity and 100 per cent
emergence of grubs. None of the treatments recorded any mortality on grubs and adults
even after eight days of treatment.
Based on the results under in vitro experiments, field efficacy of crude aloe gel
solution, aloe leaf peel aqueous extract and aloe leaf peel powder aqueous extract at 10.00
% concentrations were evaluated at the Instructional Farm, College of Agriculture,
Vellayani in managing the population of Aphis gossypii, Amrasca bigutulla bigutulla,
Coccidohystrix insolita, H. vigintioctopunctata and fruit damage caused byLeucinoides
orbonalis.
At 14 days after treatment, aloe leaf peel powder aqueous extract 10 % recorded a
reduction of 56.29, 84.74, 65.18 and 73.50 per cent reduction in the population of aphids,
leafhoppers, mealybug and epilachna beetles, respectively. Two weeks after the treatment,
aloe leaf peel powder aqueous extract 10 per cent was statistically on par with talc-based
formulation of B. bassiana NBAIR Bb5 @ 20 g L-1
in reducing the population of, both
aphids and leafhoppers. And it was on par with neem garlic soap formulation-KAU Raksha
@ 10 g L-1
in reducing the population of aphids, mealybugs and epilachna beetles.
Fifteen days after the treatment, the plots treated with aloe leaf peel powder aqueous
extract 10 % recorded a reduction of 39.13 per cent in fruit damage caused by
L. orbonalis. At 30 days after treatment, all aloe extract treated plots were on par with talcbased formulation of B. bassiana NBAIR Bb5 @ 20 g L
-1
and neem garlic soap
formulation-KAU Raksha @ 10 g L
-1
in reducing the fruit damage caused by the shoot and
fruit borer.
All the aloe extracts were found safe to natural enemies, in comparison with the
chemical check. Fruit yield from aloe leaf peel powder aqueous extract 10 %, aloe leaf peel
aqueous extract 10 % and crude aloe gel solution 10 % treated plots were 0.77, 0.54 and
0.49 kg plant -1
.
From the present study, it was clear that the aloe extracts viz., crude aloe gel
solution, aloe leaf peel aqueous extract and aloe leaf peel powder aqueous extract at
different concentrations exhibited repellent and antifeedant activity in addition to its effect
on fecundity and egg hatchability of epilachna beetles. Aloe leaf peel powder aqueous
extract 10 % was found more effective compared to 10 % concentrations of crude aloe gel
solution and aloe leaf peel aqueous extract in field conditions.
Further research to isolate and elucidate the chemical constituents responsible for
the effectiveness of aloe leaf peel powder aqueous extract, can pave way for the
development of a novel biopesticide.