Creating a Test to Measure Bug-Killing Substances on Soybean Leaves

Greg Howard
1st February, 2024

Creating a Test to Measure Bug-Killing Substances on Soybean Leaves

Cotton Bollworm Moth (Helicoverpa armigera), a major pest to Bt cotton used as the test insect in the study.

Photo adapted from: Donald Hobern / CC BY (Source)
Controlling agricultural pests is a constant challenge, relying heavily on insecticides. However, many traditional insecticides have drawbacks, including harmful effects on beneficial insects like bees and the development of resistance in the pest populations themselves. This resistance is a significant problem, as seen with the cotton bollworm, Helicoverpa armigera, which has developed resistance to multiple insecticides, including those used in Bt cotton[2]. Bt cotton is genetically modified to produce a toxin from the bacterium Bacillus thuringiensis (Bt) that is harmful to the bollworm, but widespread use has led to the evolution of resistance. Researchers at the University of the Sunshine Coast sought to address the need for a reliable laboratory method to test new, potentially more sustainable insecticides. The study focused on developing a new laboratory model to assess the effectiveness of insecticidal agents. Currently, there’s a lack of standardized methods that accurately reflect real-world conditions when testing these agents. The researchers from the University of the Sunshine Coast developed a “leaf disk assay” (LDA) using the cotton bollworm (Helicoverpa armigera) as a test insect. This assay involves feeding newly hatched bollworm larvae soybean leaves treated with different insecticides. The LDA aims to mimic how insects feed in the field, providing a more realistic assessment of insecticide effectiveness than traditional methods. The LDA was used to test the effectiveness of several insecticides, including Bt toxin and the neonicotinoid imidacloprid. Neonicotinoids, while effective, have raised concerns due to their potential harm to pollinators like honeybees[3]. The study found that both Bt toxin and imidacloprid were effective in killing the bollworm larvae, with imidacloprid showing a faster effect. Importantly, the researchers also investigated the potential of combining Bt toxin with insecticidal compounds derived from arachnid venoms – the poisons of spiders, scorpions, and related creatures. They discovered that certain arachnid venoms enhanced the effectiveness of Bt toxin, even when used at lower, sub-lethal doses. This finding is particularly interesting in light of the increasing resistance to Bt toxins observed in bollworm populations[2][4]. The study suggests that combining Bt with other insecticidal agents, like those found in arachnid venoms, could be a strategy to overcome resistance and improve pest control. The observed synergy – where the combined effect is greater than the sum of the individual effects – could allow for lower doses of Bt toxin to be used, potentially slowing down the development of further resistance. The study also builds on previous research into the metabolic mechanisms of insecticide resistance in Helicoverpa armigera[2]. That research showed that resistance to Bt toxins and other insecticides is often linked to increased activity of enzymes that break down the toxins, effectively detoxifying them. Combining Bt with an arachnid venom might overwhelm these detoxification mechanisms, or target different pathways, leading to increased effectiveness. Furthermore, understanding how insect digestive systems adapt to different diets[5] could also inform strategies for enhancing insecticide delivery and effectiveness. The LDA developed in this study provides a valuable tool for investigating these interactions. The researchers propose that the Helicoverpa armigera LDA is a reliable and practical method for evaluating the insecticidal potential of new compounds, particularly for controlling lepidopteran pests – the group of insects that includes moths and butterflies. This new model offers a more realistic assessment of insecticide effectiveness, potentially accelerating the development of more sustainable and effective pest control strategies.

AgricultureBiotechPlant Science

References

Main Study

1) Development of a soybean leaf disc assay for determining oral insecticidal activity in the lepidopteran agricultural pest Helicoverpa armigera.

Published 1st February, 2024

https://doi.org/10.1016/j.toxicon.2023.107588

Related Studies

2) Field evolved resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) to Bacillus thuringiensis toxin Cry1Ac in Pakistan.

https://doi.org/10.1371/journal.pone.0047309

3) Impairments in learning and memory performances associated with nicotinic receptor expression in the honeybee Apis mellifera after exposure to a sublethal dose of sulfoxaflor.

https://doi.org/10.1371/journal.pone.0272514

4) Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India.

https://doi.org/10.1002/ps.2127

5) Characterization of the Mamestra configurata (Lepidoptera: Noctuidae) larval midgut protease complement and adaptation to feeding on artificial diet, Brassica species, and protease inhibitor.

https://doi.org/10.1002/arch.20381


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