Evaluation of Bt resistance in Helicoverpa zea (Lepidoptera: Noctuidae) strains using various Bt cotton plant tissues

Abstract

BACKGROUND Diet‐overlay bioassays suggest that Helicoverpa zea (Lepidoptera: Noctuidae) field populations have developed resistance to some of the Bt insecticidal proteins that are constituents of the pyramids expressed in the second and third generation Bt cotton technologies. Unfortunately, these bioassays are not always a reliable indicator for how a seemingly resistant population will perform in an actual cotton field, and thus, leaf tissue bioassays have been suggested as a method to better assess field performance. However, bollworm larvae typically prefer to feed on floral tissue rather than leaf tissue, and an alternative cotton structure type may be more ideal for use in plant tissue‐based bioassays. A series of diet‐overlay bioassays using Bt proteins and Bt cotton plant tissue were conducted with laboratory susceptible (Bz‐SS) and resistant (Cry‐RR, resistant to Cry1Ac and Cry2Ab) H. zea strains to determine if plant tissue overlays could detect resistance and which cotton plant structure type would be most ideal for use in bioassays. RESULTS Results suggest that diet overlays using lyophilized plant tissue were able to detect resistance. Lyophilized tissue from white flowers was most ideal for use in bioassays, whereas tissue from non‐Bt bolls and leaves affected larval health and behavior, confounding assay results. CONCLUSION Overlays using white flower tissue could potentially be used to supplement Bt protein overlays and provide an improved assessment of larval performance on Bt cotton technologies. © 2021 Society of Chemical Industry.

Cross‐resistance and redundant killing of Vip3Aa resistant populations of Helicoverpa zea on purified Bt proteins and pyramided Bt crops

“…Conversely, H. zea field populations exhibiting tolerance against the Vip3Aa protein were highly susceptible to the Cry proteins. 41,42 Collectively, these findings indicate that strong positive cross-resistance is not present between Cry and Vip proteins, which is not surprising given that these proteins do not share binding sites and are not similar in structure. Evidence of weak negative cross-resistance between Cry and Vip3Aa proteins in this study could provide insight for managing Vip3Aa resistance in major lepidopteran pests.…”

Effects of Methoxyfenozide-Loaded Fluorescent Mesoporous Silica Nanoparticles on Plutella xylostella (L.) (Lepidoptera: Plutellidae) Mortality and Detoxification Enzyme Levels Activities

“…The great expression of P450 for pyrethroids, esterase for novel insecticides, carbamates as well as pyrethroids, and GST for parathion in P. xylostella were checked. Xenobiotics including nanoparticles, insecticides, and insecticide-loaded nanoparticles in the organisms can interrupt the normal functioning of enzymes, causing the production of reactive oxygen species, results in reduction or inactivation of detoxification enzymes [ 62 , 63 ]. The relationships between insecticide resistance and enzyme activity have been studied.…”

Effects of cross‐pollination among non‐Bt and pyramided Bt corn expressing cry proteins in seed mixtures on resistance development of dual‐gene resistant Helicoverpa zea

“…H. zea is a major target pest of pyramided Bt corn in the USA and primarily feeds on corn kernels. Here, we used a strain of H. zea that shows resistance to both Cry1 and Cry2 Bt proteins, a susceptible strain and their F 1 heterozygous progeny 34–36 . We compared the survival and development of these three genotypes of H. zea in the laboratory on non‐Bt and pyramided Bt corn ears collected from mixed plantings and structured plantings in the field.…”

“…Here, we used a strain of H. zea that shows resistance to both Cry1 and Cry2 Bt proteins, a susceptible strain and their F 1 heterozygous progeny. [34][35][36] We compared the survival and development of these three genotypes of H. zea in the laboratory on non-Bt and pyramided Bt corn ears collected from mixed plantings and structured plantings in the field. We found higher fitness for F 1 heterozygous insects than for the susceptible insects of H. zea on both pyramided Bt corn and non-Bt corn in the mixed plantings.…”