Friday Cat-erpillar Blogging: Playing Defense

Mandible

TOP (C): Mandible of the Burnet Moth Caterpillar
Bottom (E & F): Ingested leaf fragment and leaf material in the frass
Image: Pentzold & colleagues*

Caterpillars of the Six-spot Burnet Moth, Zygaena filipendulae sequester the cyanongenic glycosides linamarin and lotaustralin from their host plants in the Lotus family. The larvae metabolize the glycosides in a controlled manner to produce cyanide as a defense against predators. The cyanogenic glycosides are a plant defense against herbivores. When an unadapted herbivores chews on the leaf of a Lotus spp. the glycosides come in contact with the Beta-glucosidase enzymes that cause the release of toxic cyanide. How can the Burnet Moth caterpillars avoid releasing cyanide when they feed on Lotus plants?

Pentzold and colleagues* investigated the question and found multiple adpations to prevent cyanide release. The caterpillars have smooth mandibles that snip rather than macerate the leaf. Snipping avoids damage that would release glycosides and glucosidases. Maceration would disrupt the plant tissue compartments separating the glycosides and glucosidases resulting in release of cyanide. The caterpillar swallows its food in relatively large chunks. Disruption of the leaf is minimal until it reaches the midgut. The caterpillar midgut is basic; about pH 10.6. At this high pH, Beta-glucosidase activity is slow, and the cyanogenic glycosides are only slowly metabolized. The caterpillar can absorb the glycosides before substantial metabolism occurs. The plant material moves through the gut rapidly, much faster than in other caterpillar species. The speed of movement rapidly eliminates disrupted tissue that releases cyanide producing enzymes.

Six-spot Burnet Moth caterpillars do everything your mother told you not to do. They gulp their food in large chunks. They don’t chew their food. And they eat very fast. This strategy is adaptive for them.

*Pentzold S, Zagrobelny M, Roelsgaard PS, Møller BL, Bak S (2014) The Multiple Strategies of an Insect Herbivore to Overcome Plant Cyanogenic Glucoside Defence. PLoS ONE 9(3): e91337.
doi:10.1371/journal.pone.0091337

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in behavior, by jjneal, Caterpillar Blogging, Environment. Bookmark the permalink.

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