Insecticide bioassay

Published: 03-03-2021| Version 1 | DOI: 10.17632/hhbgcfbrjs.1
Contributor:
Amit Paschapur

Description

The insect pests like Helicoverpa armigera Hubner, Spilarctia oblique (walker), Raphidopalpa foveicollis (Lucas), Chauliops choprai and Lipaphis erysimi Kaltenbach cause severe yield losses to hill crops in the Indian Himalayas. Considering the pest severity, a total of 23 insecticides (conventional and novel groups, botanicals and microbials) were screened. The insecticides belonging to diamide, spinosyn and avermectin group were highly toxic against lepidopteran pests. Emamectin benzoate and Flubendiamide recorded lowest LC50 value of 97.49 and 22.8 ppm against the 3rd instars of H. armigera and S. obliqua respectively. Moreover, for management of sucking pests, insecticides belonging to thiourease, neonicotinoid and Pyiridine azomethine group were found to be effective with Difenthiuron recording lowest LC50 value of 20.61 and 0.703 ppm against C. choprai and L. erysimi respectively. For management of R. foveicollis, two insecticides belonging to synthetic pyrethroid group Deltamethrin and Lamdacyhalothrin were found effective with LC50 value 12.97 and 21.33 ppm respectively. However, the botanicals and microbial insecticides did not show promising results as their median lethal values were much higher than other green label insecticides.

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Test insect cultures All the test insects used for insecticide evaluation were collected from the fields of ICARVPKAS (Vivekananda Parvatiya Krishi Anusandhana Sansthan), Experimental farm, Hawalbagh, Almora, Uttarakhand, India (29.630N and 79.630E, 1250 m) (details in table 1). Insecticides evaluated In order to test the efficacy of insecticides and fix the baseline susceptibility, a total of 23 insecticides were evaluated (details in Table 2). The test insecticides belonging to conventional groups, botanicals, entomopathogenic based, microbial based, insect growth regulators and novel groups were used for the study. A minimum of 10 insecticides belonging to different modes of action were used against a single test insect. A thorough market survey was conducted in the Indian Himalayas before selecting the insecticide for bioassay and due care was taken to select only those insecticides and formulations that were commercially available in the market and widely used by farmers for pest management in hill agriculture. Bioassay studies Different concentrations (in ppm) of technical grade insecticides were prepared by serial dilution in double distilled water and leaf dip bioassay technique was followed against all the insect pests as recommended by Insecticide Resistance Action Committee (Anonymous 1990). The leaf discs of 90 mm diameter were cut and dipped in the insecticide solution for 60 seconds and after thorough incubation the leaves were transferred to an autoclaved Petri dish and 10 numbers of insects was released in each plate. Whereas, in case of H. armigera, diet contamination method was followed (Rafiei et al. 2008) and the treated diet was placed in small 50 mm Petri plates and single 3rd instar larvae was released into each plate to avoid cannibalism. The treated insects were placed in a temperature (25±20C) and relative humidity (70±5%) controlled chamber for 72 hours and the mortality data was recorded after every 12 hours. The insects were counted dead when they showed no visible moments after gentle probing with a brush or blunt probe. A minimum of three replicates for seven insecticide concentrations and one control (untreated) were used for each test insecticide. Data analysis The mortality data of the treated insects recorded after 48 hours of insecticide exposure was corrected by Abbott's (1925) formula and the obtained data was subjected to probit analysis (Finney 1971) using the software package PoloPlus (LeOra Software 2013). Abbott’s corrected mortality = % mortality in treatment (T) % mortality in control (C) X 100 100% mortality in control (C)