MONITORING RESISTANCE TO ACARICIDES IN TETRANYCHUS URTICAE (KOCH) UNDER PROTECTED CULTIVATION.
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Date
2019-07-23
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CSKHPKV, Palampur
Abstract
Investigations on “Monitoring resistance to acaricides in Tetranychus urticae (Koch) under protected cultivation” were carried out during 2018-19. The study was aimed to determine the level of resistance in field populations of T. urticae and to formulate a strategy for resistance management. Intrinsic toxicity of three chemical acaricides (fenazaquin, hexythiazox and propargite), one biopesticide (azadirachtin) and two natural products (Tamarlassi and Darekastra) against T. urticae was determined. For this, mite population was reared in laboratory for more than 25 generations without exposing it to any chemicals. The median lethal concentration for azadirachtin, Darekastra, fenazaquin, hexythiazox, propargite and Tamarlassi was 0.00013, 4.01176, 0.00125, 0.00056, 0.00681 and 2.49950 per cent, azadirachtin being most toxic and Darekastra the least. Field populations of T. urticae collected from six localities in Zone I and II of Himachal Pradesh revealed maximum resistance ratio to exhibit in Una population for all the chemical acaricides(3) followed by Kullu(3) > Solan(2) > Sundarnager(2) > Kangra(3) and least for Palampur(3). Among acaricides, T. urticae populations were found most resistant to propargite (3.47 to 5.63) followed by fenazaquin (3.62 to 4.26) and hexythiazox (1.88 to 2.45). Fenazaquin resistant strain was developed by giving selection pressure based on the LC50 values till the extremely high level of resistance was achieved after eight generations of selectivity and was designated as fenazaquin resistant strain (FR-strain) exhibiting extremely high level of resistance (216.74). Growth and development parameters studied for FR- and S-strain revealed the FR- strain to be bigger in size but their generation time, adult longevity and fecundity were reduced significantly when compared to S-strain. Resistance incorporated in FR-strain was not stable and declined by 26.7 per cent in three generation of non-selectivity. FR-strain exhibited low cross resistance to azadirachtin, Darekastra, hexythiazox, propargite and Tamarlassi, being non- significant. The results indicated that T. urticae can quickly develop resistance to fenazaquin. It also exhibited low level of cross resistance, being non-significant to acaricides belonging to different mode of action and natural products suggesting their incorporation in mite resistance management plan.
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