Late-instar monarch caterpillars sabotage milkweed to acquire toxins, not to disarm plant defence
Betz A, Bischoff R, Petschenka G. Proceedings. Biological sciences, February 2024.
Read the paper Free to read · doi:10.1098/rspb.2023.2721
What this paper is about
Monarch caterpillars cut the veins of a milkweed leaf before eating it, and the textbook explanation is that this stops the latex reaching the feeding site. This study found that only young caterpillars avoid the latex.
Late-instar caterpillars drink the latex as it leaks out, which suggests vein cutting becomes a way of harvesting cardenolides rather than dodging them. A related butterfly that does not store cardenolides behaved differently.
Summarised here from the abstract below. Not the authors’ words.
Abstract
Sabotaging milkweed by monarch caterpillars (Danaus plexippus) is a famous textbook example of disarming plant defence. By severing leaf veins, monarchs are thought to prevent the flow of toxic latex to their feeding site. Here, we show that sabotaging by monarch caterpillars is not only an avoidance strategy. While young caterpillars appear to avoid latex, late-instar caterpillars actively ingest exuding latex, presumably to increase sequestration of cardenolides used for defence against predators. Comparisons with caterpillars of the related but non-sequestering common crow butterfly (Euploea core) revealed three lines of evidence supporting our hypothesis. First, monarch caterpillars sabotage inconsistently and therefore the behaviour is not obligatory to feed on milkweed, whereas sabotaging precedes each feeding event in Euploea caterpillars. Second, monarch caterpillars shift their behaviour from latex avoidance in younger to eager drinking in later stages, whereas Euploea caterpillars consistently avoid latex and spit it out during sabotaging. Third, monarchs reared on detached leaves without latex sequestered more cardenolides when caterpillars imbibed latex offered with a pipette. Thus, we conclude that monarch caterpillars have transformed the ancestral 'sabotage to avoid' strategy into a 'sabotage to consume' strategy, implying a novel behavioural adaptation to increase sequestration of cardenolides for defence.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
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title = {Late-instar monarch caterpillars sabotage milkweed to acquire toxins, not to disarm plant defence (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/late-instar-monarch-caterpillars-sabotage-milkweed-to-acquire-toxins-2024/},
note = {Accessed DATE}
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