Abstract
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.
Highlights
Crops are exposed to increased pressure from insect pests, partly due to climate change which affects the distribution of pest insects (Battisti and Larsson 2015; Castex et al 2018)
Leaf-disk assays are commonly used to evaluate plant resistance against insects with chewing mouthparts by measuring the area of tissues consumed (Jermy et al 1968; Jones and Coleman 1988; O’Neal et al 2002; Sharma et al 2005). They are relevant to study stem borers because adult females deposit their eggs on the plant surface, as neonate larvae graze on the leaf surface, and young larvae need to bore a tunnel through the leaves to reach the inner tissues
Leaf-consumption by young larvae can be used as a proxy to evaluate plant resistance and to find and evaluate the effectiveness of feeding deterrents extracted from plants or of synthetic origin (Arnason1985; Belles et al 1985; Shields et al 2008; Yencho et al 1994)
Summary
Crops are exposed to increased pressure from insect pests, partly due to climate change which affects the distribution of pest insects (Battisti and Larsson 2015; Castex et al 2018). Pests placed in new biotic and abiotic conditions may become invasive, as they lack their usual natural enemies, face plants with poor defenses against them (Sakai2001), and may even become more adaptable and colonize new hosts as documented in Drosophila suzukii (Little et al 2020). These changes place plant selection under pressure because it means existing cultivars need to be re-examined for their resistance or. While disk assays have drawbacks such as the damage inflicted
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