Posts Tagged ‘plant defense’

Latex lovers

So the title of this post is a little misleading I have to admit.  I wouldn’t say these insects particularly love latex, but the words tolerate and sequester come to mind.  With the alternatives being avoid, succumb to, die from…not the most pleasant options.

In the title, I’m referring to the common milkweed plant Asclepias syriaca and its associated herbivores. What a group they are!

Photo courtesy of Folks Butterfly Farm

Milkweed is particularly known for its chemical defenses against herbivory, producing latex and cardenolides for protection.  Usually, these compounds are toxic to insect herbivores.  But, as always in the insect world, there are exceptions.  A handful of insects are specialists on milkweed, feeding on one or a few species because they have evolved a mechanism to overcome the plant defense.  For a full list of specialist herbivores, see here.  The most common milkweed associated insects I see around here include monarch butterflies, the common milkweed beetle, and the small milkweed bug.  But I haven’t been looking very closely.

Photo courtesy of Rhode Island Bugs

Notice the striking color of the beetle, bug, and butterfly.  Their bright coloration is known as aposematic coloration, or warning coloring.  They’re telling predators, “I’m not very good to eat.”  Monarchs, in particular, sequester the toxic cardenolides as caterpillars and butterflies.  The result?  Birds spew their last meal.

The thing I’d like to introduce is the amazing monarch migration across North America.  These butterflies overwinter in lower latitudes as adults, congregating in Monterey, California and Michoacán, Mexico.  Given that we just had (hopefully the last) snow in Ithaca, maybe I should go to Mexico too!

Photo courtesy of Wanderlust Images

For more about this awesome migration and ways to tag and get involved, see here.

I love ant. Part 3.

Ants and fungi: Leafcutter ants
If you’ve never had the opportunity to see leafcutter ants in action, watch this.

Cool, eh?

Ants cultivate a particular fungus to feed their young.  The fungus is farmed by the ants who provide cut leaves that the fungus decomposes.  The ants are sensitive to any parasitic fungus and have a further symbiosis with a bacteria to protect their farmed fungus.  The fungus is dependent on the ant to grow, and ants in turn are dependent on the fungal farm. Voila! Myrmecophily.

Image courtesy of Alex Wild

I love ant. Part 2.

Ants and arthropods: Lycaenid caterpillars
Ants have mutualist associations with many different arthropods, many of which happen to be liquid feeding bugs (order Heteroptera). Honeydew is the liquid excretion of these insects, rich in sugar and very attractive to ants. A unique group of caterpillars in the family Lycaenidae (order Lepidoptera) secrete honeydew-like substances to attract ants.  In fact, they have special organs dedicated to these liquid secretions.  In exchange for the sugar rich liquid, ants protect caterpillars from parasitic wasps that would otherwise kill them.

But some caterpillars cheat! In an extreme way of using the ants for protection, some Lycaenids chemically mimic ant species, essentially send out a “lost young” signal. The ants take the parasitic caterpillars back to their nest site where the caterpillars chomp away on the brood.  Who said there’s no free lunch?

Image courtesy of Alex Wild

I love ant. Part 1.

Thanks to numerous lectures by a visiting professor, I’ve learned quite a bit about myrmecophily: the beneficial associations between ants and other organisms such as plants, arthropods, or fungi.  These I gladly share with you over the next few posts.

Ants and Plants: The Bullhorn Acacia
The bullhorn acacia, Acacia cornigera, is commonly found in association with Pseudomyrmex ant species.  In exchange for defense, the Acacia provides shelter for ants (domatia), carbohydrate rich nectar (extrafloral nectar), and lipid-protein packets (food/Beltian bodies).  The ants protect the tree against herbivory by other arthropods or even mammals.  There is evidence that the Acacia tightly monitor their relationship with mutualistic ants.  One way is by pre-digesting sugar for ants that lack such digestive enzymes.  Evolutionarily cool.

Image courtesy of Alex Wild

Om nom nom

Not only is the title of this post a common greeting in my household, it accurately suggests something delicious.  At least in most cases.  While providing nourishment and pleasure for some (e.g. deep dish pizza from The Nines), food can also be the way to kill a bug, particularly those pesky plant eating insects.

Plant defense and insect offense: same story, new insights.  This cycle, known as a co-evolutionary arms race, goes something like this: insect herbivores consume plant matter; plants don’t want to get eaten so they find a way to defend themselves; insects retaliate and find a way to overcome these plant defenses; plants evolve a new mechanism; repeat indefinitely along an extended evolutionary timescale.  And the escalation is riveting!

So how does it work?  In this study, researchers focused on tomato plants and caterpillars.  They found an enzyme specific to tomato and other Solanaceous plants that is activated only in the gut of caterpillars.  The enzyme breaks down a key nutrient needed for caterpillar growth.  And the caterpillars essentially starve to death, wah wah wah.

Poor little dudes, but they keep eating my tomatoes…conundrum!

Tobacco hornworm, Manduca sexta

***Editor’s note***
Serious Eats has just informed me that “nom nom” has been officially recognized in the Oxford English Dictionary.