Leaf Tissue Assay for Lepidopteran Pests of Bt Cotton

Little, Nathan S.; Mullen, R. Michelle; Allen, Charles T.; Tyler, Heather L.

doi:10.3958/059.042.0414

Cited by 7 publications

(7 citation statements)

References 17 publications

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“…While the leaf-disks method is commonly used to screen for plant resistance or to evaluate antifeedant compounds, this approach has the drawback of using an excised plant tissue, which may desiccate, and which is injured. Hence, most experimenters place the disks over agar to limit desiccation during the experiment (Escoubas et al 1993;Little et al 2017). To limit these effects, we collected the leaf disks in the field on the day of the experiment, placing them immediately in the cages together with 1% agarose, and sandwiched them between two glass plates as shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

High-Throughput Feeding Bioassay for Lepidoptera Larvae

et al. 2021

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Finding plant cultivars that are resistant or tolerant against lepidopteran pests, takes time, effort and is costly. We present here a high throughput leaf-disk consumption assay system, to screen plants for resistance or chemicals for their deterrence. A webcam capturing images at regular intervals can follow the feeding activities of 150 larvae placed into individual cages. We developed a computer program running under an open source image analysis program to analyze and measure the surface of each leaf disk over time. We further developed new statistical procedures to analyze the time course of the feeding activities of the larvae and to compare them between treatments. As a test case, we compared how European corn borer larvae respond to a commercial antifeedant containing azadirachtin, and to quinine, which is a bitter alkaloid for many organisms. As expected, increasing doses of azadirachtin reduced and delayed feeding. However, quinine was poorly effective at the range of concentrations tested (10–5 M to 10–2 M). The model cage, the camera holder, the plugins, and the R scripts are freely available, and can be modified according to the users’ needs.

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Section: Discussionmentioning

confidence: 99%

High-Throughput Feeding Bioassay for Lepidoptera Larvae

et al. 2021

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“…The homogenized concentrations were pipetted into the bioassay tray at 0.5 ml/well. Leaf tissue assays with non- Bt , Bollgard II, and Bollgard III leaves were conducted as described by Little et al [ 36 ] using 2.54 cm leaf disks in 36.9 ml clear containers with a 5 mm layer of agar. Four replicates were performed for each H .…”

Section: Methodsmentioning

confidence: 99%

Differences between two populations of bollworm, Helicoverpa zea (Lepidoptera: Noctuidae), with variable measurements of laboratory susceptibilities to Bt toxins exposed to non-Bt and Bt cottons in large field cages

et al. 2019

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Interpreting variable laboratory measurements of Helicoverpa zea Boddie susceptibility to toxins from Bacillus thuringiensis Berliner (Bt) has been challenging due to a lack of clear evidence to document declining field control. Research that links laboratory measurements of susceptibility to survival on Bt crops is vital for accurate characterization and any subsequent response to the occurrence of an implied H. zea resistance event. In this study, H. zea survival and the resultant damage to plant fruiting structures of non-Bt, Bollgard II, and Bollgard III cottons from two insect colonies with differing levels of laboratory susceptibility to Bt toxins were evaluated in large field cages. Laboratory bioassays revealed resistance ratios of 2.04 and 622.14 between the two H. zea colonies for Dipel DF and Cry1Ac, respectively. Differences between the two H. zea colonies measured via bioassays with Bollgard II and Bollgard III cotton leaf tissue in the laboratory were not statistically discernable. However, there was 17.6% and 5.3% lower larval mortality in Bollgard II and Bollgard III for the feral relative to the laboratory colony of H. zea, respectively. Although H. zea larval numbers in cages infested with the laboratory susceptible colony did not differ between the two Bt cottons, there were fewer larvae per 25 plants in Bollgard III than in Bollgard II cotton in cages containing tolerant insects. Cages infested with tolerant H. zea moths had higher numbers of total larvae than those containing the laboratory susceptible colony in both Bollgard II and Bollgard III cottons. Bollgard II and Bollgard III cottons received 77.4% and 82.7% more total damage to total plant fruiting structures in cages infested with tolerant insects relative to those containing the laboratory susceptible colony. The damage inflicted to fruiting structures on Bollgard III cotton by a feral H. zea colony with decreased measurements of laboratory susceptibility to Dipel DF and Cry1Ac indicate that the addition of Vip3A to third generation Bt cottons may not provide sufficient control in situations where infestations levels are high.

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“…It is possible that this laboratory resistant strain developed a form of resistance that would not be viable in the field or that the comparison of this strain with highly susceptible laboratory strains yielded a resistance ratio that is not biologically relevant to the levels of Bt proteins expressed in transgenic crops. Thus, cotton leaf tissue assays have been proposed as a method to assess H. zea populations under conditions that are more ecologically significant than diet‐based assays 8 …”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the Bt cotton varieties available today express a suite of proteins, and larvae are simultaneously exposed to multiple Bt proteins in the field. The leaf tissue assays described by Little et al 8 . allow for the collective assessment of the suites of Bt proteins that are available in Bt cotton rather than individual assessments of each Bt protein.…”

Section: Introductionmentioning

confidence: 99%

“…However, considering the points above, it is apparent that the kind of plant tissue used in resistance assays could substantially influence the results. Terminal leaves have been shown to contain a high concentration of Cry1Ac relative to other cotton plant structures, 12,13,27,28 and they seem to be a logical and easily accessible tissue to utilize in assays 8 . Although bollworm larvae are known to feed on leaf tissue, 29 they have a preference for floral structures ( i.e ., squares, flowers, bolls) 30 .…”

Section: Introductionmentioning

confidence: 99%

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

Kerns

Yang

Kerns

et al. 2021

Pest Management Science

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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.

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Leaf Tissue Assay for Lepidopteran Pests of Bt Cotton

Cited by 7 publications

References 17 publications

High-Throughput Feeding Bioassay for Lepidoptera Larvae

High-Throughput Feeding Bioassay for Lepidoptera Larvae

Differences between two populations of bollworm, Helicoverpa zea (Lepidoptera: Noctuidae), with variable measurements of laboratory susceptibilities to Bt toxins exposed to non-Bt and Bt cottons in large field cages

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

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