MSc

A study on “Insecticide resistance in cowpea aphid, Aphis craccivora (Koch)
and its management” was conducted in College of Agriculture, Vellayani and
farmer’s field at Vallamcode, Thiruvananthapuram district during 2016-2018. The
main objectives were to assess the insecticide resistance in field population of cowpea
aphid, A. craccivora and to evaluate the efficacy of new generation insecticides
against resistant population of A. craccivora.
A preliminary survey was carried out among major cowpea farmers in
Kalliyoor area of Thiruvananthapuram district during 2017-18 revealed the continous
use of single insecticide viz., fenvalerate, lambda cyhalothrin, imidacloprid and
quinalphos and the occurrence of control failures in the field populations of
A.craccivora.
Bioassay was carried out in CRD to assess the insecticide resistance in field
population of A. craccivora collected from three different locations based on the
intensity of insecticide application. A series of concentrations of three insecticides
viz. fenvalerate, imidacloprid and quinalphos were prepared in aqueous solution and
bio assay was done using F2 generations of aphid populations collected from three
locations. Results revealed that population collected from Location-I (Vilavoorkal)
was found to be susceptible to insecticides with resistance ratio-1. Population
collected from Location- II (Instructional farm, College of Agriculture, Vellayani)
was found to be moderately resistant with resistant ratios of 1.67, 2.97 and 2.81 and
aphid population collected from Location- III, (Vallamcode) showed more resistance
with resistant ratios of 1.71, 19.46 and 7.94 for quinalphos, fenvalerate and
imidacloprid respectively.
Laboratory experiments were conducted to evaluate the efficacy of new
generation insecticides viz. acetamiprid 15 g a.i.ha-1, thiamethoxam 25 g a.i.ha-1,
thiacloprid 24 g a.i.ha-1, dinotefuran 25 g a.i.ha-1, thiamethoxam + lambda cyhalothrin
27.5 g a.i.ha-1
and dimethoate (as check ) 200 g a.i.ha-1 against the resistant
population of A. craccivora. The result revealed that, significantly higher mortality
was observed in A. craccivora treated with thiamethoxam + lambda cyhalothrin 27.5
g a.i.ha-1(100 %) followed by thiacloprid 24 g a.i.ha-1 (91.67 %) and thiamethoxam 25
g a.i.ha-1(90.00 %) which were on par with each other after 3 hours of treatment.
Field experiment was laid out in RBD at Vallamcode from where resistant
population was collected with four treatments selected from laboratory experiment of
aphids. The percent reduction recorded were 97.63, 93.97 and 91.50 respectively in
thiamethoxam + lambda cyhalothrin 27.5 g a.i.ha-1, thiamethoxam 25 g a.i.ha-1 and
thiacloprid 24 g a.i.ha-1 treated plots at one day after spraying. Dissipation of residues
of these effective insecticides was studied by analysing the pods collected at 0, 1, 3,
5, 7 and 10 days after application of insecticides at recommended dose and the result
showed that insecticides were dissipated within five days with half-lives of 0.37,
1.73, 1.21 and 4.37 days respectively.
The present study revealed the development of insecticide resistance in the
field populations of A. craccivora against fenvalerate and imidacloprid. By
considering the less mammalian toxicity, good aphicidal activity, consumer safety
and high dissipation rate, thiamethoxam 25 g a.i.ha-1 followed by thiamethoxam +
lambda cyhalothrin 27.5 g a.i.ha-1 and thiacloprid 24 g a.i.ha-1 could be recommended
against A. craccivora in cowpea. Further studies have to be taken up to develop and
popularize Insecticide Resistance Management strategies against A. craccivora by
giving emphasis on efficient use of insecticides and to conserve the ecosystem for
sustainable pest management.