MSc

An investigation on “Bioefficacy of neonicotinoid insecticides against insect pests of
okra (Abelmoschus esculentus (L.) Moench)” was undertaken in the Department of
Agricultural Entomology, College of Horticulture, Vellanikkara, Kerala Agricultural
University during 2013- 2014. The study was carried out by conducting two field
experiments at the Instructional Farm, College of Horticulture in two seasons viz., April 2013 to July 2013 and October 2013 to January 2014.
Two neonicotinoid insecticides - thiamethoxam and imidacloprid - were fieldevaluated for their biological efficiency against major insect pests of okra, safety to naturaenemies, influence on plant growth parameters and terminal residues in okra fruits. The twoinsecticides were applied in three methods viz., seed treatment (ST), two foliar treatments (2FT) and a combination of seed treatment followed by a single foliar treatment (ST+FT). Thetreatments comprised of ST thiamethoxam 30FS @ 3 g a.i. kg
-1
(T1) and ST imidacloprid48FS @ 6 g a.i. kg
-1
(T2) before sowing, two foliar sprayings ( 2FT) with thiamethoxam25WG @ 25g ai ha
-1
(T3) and imidacloprid 70WG @ 25 g a.i. ha
-1
(T4) at 15 and 30 daysafter sowing (DAS) and a combination of seed treatment followed by a foliar spraying(ST+FT) with thiamethoxam (T5) and imidacloprid (T6) at 30 DAS. A standard checkinsecticide quinalphos 25EC @ 250 g a.i. ha
-1
as two foliar sprayings (FT) at 15 and 30DAS (T7) along with an untreated control (T8) were also included in the field experiment. Both thiamethoxam and imidacloprid were found to be significantly effective than
quinalphos against Amrasca biguttula biguttula Ishida in okra. All the three methods of
application with thiamethoxam and imidacloprid showed equal effectiveness upto 30 DAS.
However, both the foliar treatment and the combination of seed treatment followed by a
single foliar treatment with thiamethoxam proved to be equally effective throughout the
season to A. biguttula biguttula. Thiamethoxam and imidacloprid by all the three application methods (seed treatment,
foliar treatment and combination of seed treatment followed by foliar treatment) were equally
effective against
Aphis gossypii Glover upto 25 DAS. From 30 to 50 DAS, two foliar
sprayings at 25 g a.i. ha
-1
revealed a highest reduction of 88.49 per cent in the population of
A. gossypii. Two foliar sprayings with imidacloprid 70 WDG @ 25 g a.i. ha-1
at 15 and 30
DAS recorded the lowest population of Bemisia tabaci Gennadius and least leaf damage by Sylepta derogata Fabricius in okra. Thiamethoxam 25WDG with two foliar sprayings (2 FT)
@ 25 g a.i. ha
-1
at 15 and 30 DAS significantly reduced the shoot and fruit damage by Earias vitella
Fabricius.
With regard to the impact of thiamethoxam and imidacloprid on natural enemies, two
foliar sprayings with thiamethoxam at 25 g a.i. ha
-1
showed highest coccinellid population in
the first season. In the second season, seed treatment with thiamethoxam @ 3 g a.i. kg

indicated the highest population of coccinellids. However, imidacloprid was found to be safer
than the standard check quinalphos to coccinellids in both seasons. But the spider population
was observed to be relatively less in all the treatments of thiamethoxam and imidacloprid as
compared to the untreated control. Thiamethoxam and imidacloprid showed no adverse
effect on other predators such as syrphids, chrysoperla and rove beetles in okra field.
Thiamethoxam and imidacloprid indicated phytotonic effects on okra plant for they
exhibited significant effects on plant growth parameters. Two foliar sprayings of
thiamethoxam significantly increased the plant height, number of leaves, flowers per plant,
fruit weight and fruit length. Seed treatment with both thiamethoxam and imidacloprid
reduced the days for flower initiation. Terminal residue in fruits was below detectable limit
at 15 days after spraying in all the treatments with thiamethoxam and imidacloprid.