Ambily Paul

Synergist induced susceptibility of tobacco caterpillar, Spodoptera litura (Fabricius) from Kerala, India exposed to conventional insecticides

The present study was undertaken to assess the insecticide resistance developed in various field collected population of S. litura and to induce susceptibility by using the synergists. Third-instar larvae collected from three different locations of Kerala viz., Thiruvananthapuram (TVM), Pathanamthitta (PTA) and Alappuzha (ALP) were exposed to conventional insecticides like chlorpyriphos, quinalphos, lambda-cyhalothrin and cypermethrin by leaf dip bioassay and resistance ratios were calculated by using the baseline data generated for respective insecticides using susceptible strain. Resistance ratios recorded were 1965, 840 and 320 against chlorpyriphos, 605, 255 and 59 against quinalphos, 926, 250 and 108 against lambda-cyahlothrin and 2566, 534 and 396 against cypermethrin respectively for TVM, PTA and ALP populations. The effect of selected synergists viz., piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP) was studied in combination with respective test insecticides against the highly resistant population of S.litura collected from TVM of Kerala. The population was tested with insecticide in combination of the above synergists at different ratios. When PBO, TPP and DEM at ratio of 1:4 were used the synergistic ratio was 8.47, 7.26 and 3.98 for chlorpyriphos, 6.09, 5.26 and 3.05 for quinalphos, 13.37, 4.53 and 7.39 for lambda cyhalothrin and 4.77, 3.36 and 3.40 for cypermethrin respectively. PBO showed highest synergistic activity against both the organophosphates tested followed by DEM and TPP. Highest synergistic activity against synthetic pyrethroids also was shown by PBO, followed by TPP and DEM. The results obtained from the present study revealed that PBO at 1:4 ratio showed higher synergism with the test insecticides against the resistant populations of S.litura and proved to be an effective molecule alternate for breaking the resistance against conventional organophosphates and synthetic pyrethroids.

Dissipation of Chlorpyriphos and Profenophos in Cabbage (Brassica oleracea var. capitata L.)

The persistence of organophosphorus insecticides chlorpyriphos and profenophos @ 300 and 500 g a.i. ha−1 in cabbage following two foliar applications at 15 d interval during the head formation stage, is reported. Samples collected at 0 (2h), 1, 3, 5, 7, 10 and 15 d after the last (second) spray were extracted by QuEChERS method and residues estimated by gas liquid chromatography equipped with flame photometric detector (FPD). The mean initial deposits of chlorpyriphos and profenophos were 1.52 and 1.02 μg g−1 respectively which dissipated with time and reached below the quantitation level of 0.05 μg g−1 within 15 d with half-life values of 1.91 and 2.01 d, respectively. The Limit of detection (LOD) and limit of quantitation (LOQ) of the two insecticides in cabbage were 0.01 and 0.05 μg g−1, respectively.

Bioefficacy of certain new insecticide molecules against spotted pod borer, Maruca vitrata (lepidoptera: crambidae) of cowpea

Studies on the management of resistant populations of Maruca vitrata (F.) revealed that 100% mortality was recorded in the population treated with spinosad 75 g a.i. ha−1, emamectin benzoate 10 g a.i. ha−1 and indoxacarb + acetamiprid 100 g a.i. ha−1 after 12 h of treatment under laboratory trial. No significant difference was observed in the mortality when treated with chemicals like chlorantraniliprole 30 g a.i. ha−1, indoxacarb 60 g a.i. ha−1, flubendiamide 100 g a.i. ha−1 and acephate + imidacloprid 518 g a.i. ha−1 which showed a per cent mortality of 93.33 per cent each and less mortality was recorded in population sprayed with chlorpyriphos 600 g a.i.ha−1 (20%) and novaluron 100 g a.i. ha−1 (33.33%) after 24 h of treatment under laboratory trial.