Akshay Krishna
Baseline susceptibility of rice brown planthopper, Nilaparvata lugens stal(Hemiptera : Delphacidate) to selected insecticides - Vellanikkara Department of Agricultural Entomology, College of Agriculture 2025 - 76,xiip.
MSc
The development of insecticide resistance in insect pests is one of the major problems in the field of pest management. Data on baseline susceptibility to insecticides must be generated to track the evolution of resistance among different pest populations. This knowledge is vital for developing successful insecticide resistance management (IRM) strategies that aim to delay the resistance evolution and prolong the useful life of an insecticide. A comprehensive understanding of the biochemical mechanisms contributing to the shift in susceptibility is essential for ensuring the long-term sustainability of insecticide applications. In light of this, the present investigation entitled “Baseline susceptibility of rice brown planthopper, Nilaparvata lugens Stal (Hemiptera: Delphacidae) to selected insecticides” was carried out during 2022-2024 at the Department of Agricultural Entomology, with the objective of monitoring baseline susceptibility of Nilaparvata lugens to selected insecticides and studying the biochemical mechanism responsible for the change in susceptibility to insecticides. The BPH populations were collected from three major rice-growing tracts of Kerala, viz., Kuttanad in Alappuzha district, Alagappanagar in Thrissur district, and Pattambi in Palakkad district. A population maintained in the glasshouse since 2006 was procured from the Indian Institute of Rice Research (IIRR), Hyderabad. Another population, which was maintained without any pesticide exposure since 2005 at the Rice Entomology Section, Zonal Agricultural Research Station (ZARS), Mandya, was also procured to keep as a susceptible population. The collected populations were assigned respective codes, viz., KTD, TCR, PTB, HYD, and MND, and maintained separately on the rice variety, TN1, without any pesticide exposure, in a polyhouse at 29°C temperature and humidity of 75 per cent. Information on BPH outbreaks, insecticides used, and usage patterns was gathered from farmers in the sampling locations through personal inquiry. An intensive application of various insecticides, mainly imidacloprid and thiamethoxam, in doses higher than the recommended ones, was practiced in all the sampling fields. Newer molecules such as pymetrozine and triflumezopyrim were also used in the Kuttanad area. In the rice-growing regions of the Thrissur district, farmers switched to dinotefuran and reported it to be effective. In certain rice-growing regions of Pattambi, pymetrozine was also used. The laboratory bioassays were performed against imidacloprid 17.8 SL (Tatamida), thiamethoxam 25 WG (Actara), clothianidin 50 WG (Dantotsu), dinotefuran 20 SG (Token), afidopyropen 50 DC (Sefina), flonicamid 50 WG (Ulala), and pymetrozine 50 WG (Chess) to determine the median lethal concentrations (LC50). The resistance ratio (RR) was assessed by comparing the LC50 values with that of the laboratory susceptible population. All the populations of N. lugens displayed a significant shift in LC50 with respect to MND population, and were resistant to imidacloprid and thiamethoxam based on the test for the hypothesis of equality. The LC50 value for imidacloprid ranged from 150.79 ppm in KTD to 41.89 ppm in HYD, compared to 4.04 ppm in MND. The KTD population had the highest RR of 37.25-fold, followed by the TCR (31.92-fold) and PTB (24.77-fold) populations. With respect to thiamethoxam, the LC50 value ranged between 119.90 ppm in KTD (30.19-fold RR) and 79.87 ppm in HYD (20.11-fold RR), in contrast to 3.97 ppm in MND. A significant shift in susceptibility to clothianidin was recorded with KTD, TCR, and PTB populations with respective RRs of 3.35-, 2.20- and 1.36-fold. In the assay with dinotefuran, the hypothesis of equality was rejected for only KTD and TCR populations with respective LC50 values of 7.14 ppm and 6.11 ppm, as against 2.62 ppm in MND. The LC50 value for afidopyropen ranged from 1.50 ppm in KTD to 0.97 ppm in HYD, compared to 0.44 ppm in MND. According to the test for the hypothesis of equality, only KTD population showed a significant shift of 3.63-fold. However, all the populations were susceptible to flonicamid according to the test for the hypothesis of equality. A significant shift in susceptibility to pymetrozine was recorded with LC50 values ranging between 234.28 ppm in KTD and 81.70 ppm in HYD as against 40.48 ppm in MND population. The activity of detoxifying enzymes was quantified and compared with that of the susceptible population to examine the role of detoxifying enzymes in the shift in susceptibility to insecticides. The PTB, HYD, KTD, and TCR populations have shown 2.55-, 1.91-, 1.84-, and 1.62-fold increases in carboxylesterase (CarE) activity, respectively. Significantly higher titers of cytochrome P450 (Cyt P450) activity were displayed by KTD and TCR population, with 5.43-fold and 4.04-fold increase respectively. The Cyt P450 activity of PTB (1.70-fold) and HYD (1.55-fold) populations were on par. The relative activity of glutathione S-transferase (GST) was the highest in PTB (5.19-fold), followed by 5.00-fold in HYD, 3.49-fold in TCR, and the least in KTD (2.85) population. The research study revealed a shift in susceptibility and the development of resistance to some selected insecticides among the populations of N. lugens, and the result was confirmed with the test for the hypothesis of equality. The possible role of detoxifying enzymes in the shift in susceptibility was also established.
Agricultural Entomology
Rice brown planthopper
Nilaparvata lugens stal
Hemiptera : Delphacidate
insecticides
632.6 / AKS/BA PG
Baseline susceptibility of rice brown planthopper, Nilaparvata lugens stal(Hemiptera : Delphacidate) to selected insecticides - Vellanikkara Department of Agricultural Entomology, College of Agriculture 2025 - 76,xiip.
MSc
The development of insecticide resistance in insect pests is one of the major problems in the field of pest management. Data on baseline susceptibility to insecticides must be generated to track the evolution of resistance among different pest populations. This knowledge is vital for developing successful insecticide resistance management (IRM) strategies that aim to delay the resistance evolution and prolong the useful life of an insecticide. A comprehensive understanding of the biochemical mechanisms contributing to the shift in susceptibility is essential for ensuring the long-term sustainability of insecticide applications. In light of this, the present investigation entitled “Baseline susceptibility of rice brown planthopper, Nilaparvata lugens Stal (Hemiptera: Delphacidae) to selected insecticides” was carried out during 2022-2024 at the Department of Agricultural Entomology, with the objective of monitoring baseline susceptibility of Nilaparvata lugens to selected insecticides and studying the biochemical mechanism responsible for the change in susceptibility to insecticides. The BPH populations were collected from three major rice-growing tracts of Kerala, viz., Kuttanad in Alappuzha district, Alagappanagar in Thrissur district, and Pattambi in Palakkad district. A population maintained in the glasshouse since 2006 was procured from the Indian Institute of Rice Research (IIRR), Hyderabad. Another population, which was maintained without any pesticide exposure since 2005 at the Rice Entomology Section, Zonal Agricultural Research Station (ZARS), Mandya, was also procured to keep as a susceptible population. The collected populations were assigned respective codes, viz., KTD, TCR, PTB, HYD, and MND, and maintained separately on the rice variety, TN1, without any pesticide exposure, in a polyhouse at 29°C temperature and humidity of 75 per cent. Information on BPH outbreaks, insecticides used, and usage patterns was gathered from farmers in the sampling locations through personal inquiry. An intensive application of various insecticides, mainly imidacloprid and thiamethoxam, in doses higher than the recommended ones, was practiced in all the sampling fields. Newer molecules such as pymetrozine and triflumezopyrim were also used in the Kuttanad area. In the rice-growing regions of the Thrissur district, farmers switched to dinotefuran and reported it to be effective. In certain rice-growing regions of Pattambi, pymetrozine was also used. The laboratory bioassays were performed against imidacloprid 17.8 SL (Tatamida), thiamethoxam 25 WG (Actara), clothianidin 50 WG (Dantotsu), dinotefuran 20 SG (Token), afidopyropen 50 DC (Sefina), flonicamid 50 WG (Ulala), and pymetrozine 50 WG (Chess) to determine the median lethal concentrations (LC50). The resistance ratio (RR) was assessed by comparing the LC50 values with that of the laboratory susceptible population. All the populations of N. lugens displayed a significant shift in LC50 with respect to MND population, and were resistant to imidacloprid and thiamethoxam based on the test for the hypothesis of equality. The LC50 value for imidacloprid ranged from 150.79 ppm in KTD to 41.89 ppm in HYD, compared to 4.04 ppm in MND. The KTD population had the highest RR of 37.25-fold, followed by the TCR (31.92-fold) and PTB (24.77-fold) populations. With respect to thiamethoxam, the LC50 value ranged between 119.90 ppm in KTD (30.19-fold RR) and 79.87 ppm in HYD (20.11-fold RR), in contrast to 3.97 ppm in MND. A significant shift in susceptibility to clothianidin was recorded with KTD, TCR, and PTB populations with respective RRs of 3.35-, 2.20- and 1.36-fold. In the assay with dinotefuran, the hypothesis of equality was rejected for only KTD and TCR populations with respective LC50 values of 7.14 ppm and 6.11 ppm, as against 2.62 ppm in MND. The LC50 value for afidopyropen ranged from 1.50 ppm in KTD to 0.97 ppm in HYD, compared to 0.44 ppm in MND. According to the test for the hypothesis of equality, only KTD population showed a significant shift of 3.63-fold. However, all the populations were susceptible to flonicamid according to the test for the hypothesis of equality. A significant shift in susceptibility to pymetrozine was recorded with LC50 values ranging between 234.28 ppm in KTD and 81.70 ppm in HYD as against 40.48 ppm in MND population. The activity of detoxifying enzymes was quantified and compared with that of the susceptible population to examine the role of detoxifying enzymes in the shift in susceptibility to insecticides. The PTB, HYD, KTD, and TCR populations have shown 2.55-, 1.91-, 1.84-, and 1.62-fold increases in carboxylesterase (CarE) activity, respectively. Significantly higher titers of cytochrome P450 (Cyt P450) activity were displayed by KTD and TCR population, with 5.43-fold and 4.04-fold increase respectively. The Cyt P450 activity of PTB (1.70-fold) and HYD (1.55-fold) populations were on par. The relative activity of glutathione S-transferase (GST) was the highest in PTB (5.19-fold), followed by 5.00-fold in HYD, 3.49-fold in TCR, and the least in KTD (2.85) population. The research study revealed a shift in susceptibility and the development of resistance to some selected insecticides among the populations of N. lugens, and the result was confirmed with the test for the hypothesis of equality. The possible role of detoxifying enzymes in the shift in susceptibility was also established.
Agricultural Entomology
Rice brown planthopper
Nilaparvata lugens stal
Hemiptera : Delphacidate
insecticides
632.6 / AKS/BA PG