Helicoverpa armigera (Hubner) Associated Cross Resistance Patterns in South Indian Crop Ecosystem

Aim: To study the cross resistance patterns associated with Mahaboobnagar, Raichur, Nagpur populations of Helicoverpa armigera (Hubner).Study design: BioassayPlace and Duration of Study: The experiment was carried out from February 2010 to May 2011 at Department of Entomology, College of Agriculture, Rajendranagar, Hyderabad, Telangana.Methodology: Helicoverpa armigera was selected for indoxacarb in F1 and F2 continuously then the population subjected to different selected insecticides to know the cross resistance patterns associated.Results: Mahaboobnagar population recorded 1.109 and 0.816 fold resistance at LD50 and LD90, respectively, while Raichur population has developed still higher levels of relative resistance by 1.591 and 0.846 fold when compared with the Nagpur population at LD50 and LD90, respectively. Similarly, the Raichur population has developed 1.435 and 1.037 folds relative resistance at LD50­ and LD90, respectively as compared with the Mahaboobnagar population.The Mahaboobnagar population resistant to indoxacarb at F3, when subjected to selected insecticides like cypermethrin, methomyl, spinosad showed a negative cross resistance ratio of 0.665, 0.830, 0.916 to cypermethrin, methomyl, spinosad respectively, and a positive cross resistance ratio of 1.019 to indoxacarb, while similar trend was displayed by Raichur population showing a negative cross resistance ratio of 0.932, 0.565, 0.803 to cypermethrin, methomyl, spinosad respectively and positive cross resistance of 1.036 indoxacarb further, same trend was shown by Nagpur population by displaying a negative cross resistance ratio of 0.610, 0.735, 0.519 to cypermethrin, methomyl, spinosad and positive cross resistance ratio of 1.026 to indoxacarb.Conclusion: Continuous application of single insecticide belonging to a specific group across the generations increases the resistance from F1 to F3. Alternating the new chemistries with old conventional chemicals resulted in no cross resistance development as it was observed in all test populations.

Screening of Tropical Maize Inbred Lines by Artificial Infestation for Resistance against Invasive Fall Armyworm in India

Aim: This study was aimed to find resistance sources against FAW. Study Design: Randomised Block Design. Place and Duration of Study: The Present study was conducted at Maize Research Centre, Hyderabad with promising germplasm during Kharif-2021, Rabi-2021-22 and Kharif-2022. Methodology: Field-collected FAW egg masses were reared using maize leaf- and stalk-based diet at 27 ± 1 °C, 60 ± 5% relative humidity and 12 h day length. The resulting neonates were used to infest the seedlings of 34 diverse tropical maize inbred genotypes. Results: A total of 15 genotypes were found to have recorded a leaf damage score of less than 5 with the least score recorded in BML 2 (3.24), followed by BML 11 (3.34), BML 7(3.37), BML 5 (3.37), BML 8 (3.49), CM 201 (3.60), BML 32-2 (3.91), CM 132 (3.97), BML 10 (4.01), BML 6 (4.02), BML 13 (4.34), CM202 (4.34), CM 131 (4.68), BML 90 (4.82), BML 45 (4.95) and displayed moderate resistance. Conclusion: Out of 34 inbred lines studied 15 were found to be moderately resistant to fall armyworm based on LIR and cob damage score under artificial infestation.

Cross Resistance Patterns Associated with Spinosad Resistant Helicoverpa armigera (Hubner) in South India

Aim: To study the cross resistance patterns associated with Helicoverpa armigera (Hubner) in south India. Study Design: Bioassay. Place and Duration of Study: The experiment was carried out in the Department of Entomology, College of Agriculture, Rajendranagar, Hyderabad,Telangana from February 2010 to May 2011. Methodology: Spinosad resistant Helicoverpa armigera population in F1 and F2 subjected to different insecticides to know the cross resistance patterns associated. Results: American bollworm population of Mahaboobnagar has developed 0.308 and 0.646 folds and 0.284 and 0.624 folds in Raichur population as compared with the Nagpur baseline population at F1. Mahaboobnagar population displayed a negative cross resistance ratio of 0.677 fold to cypermethrin, 0.806 fold to methomyl, 0.935 fold to indoxacarb and positive cross resistance of 1.039 fold to spinosad, similar trend was followed in Raichur population with a negative cross resistance ratio of 0.918 fold to cypermethrin, 0.543 fold to methomyl, 0.642 fold to indoxacarb and 1.060 fold to spinosad. Further, the Nagpur population exihibited a similar trend with a negative cross resistance ratio of 0.604 fold to cypermethrin, 0.690 fold to methomyl, 0.570 fold to indoxacarb and positive cross resistance ratio of 1.077 fold to spinosad at F3. Conclusion: The present study revealed that the continuous application of same insecticide across the generations increases the resistance from F1 to F3. Alternating the new chemistries with old conventional chemicals results in no cross resistance development as it was observed in all three populations studied.