How? Call in the enemy of their enemy. Think you know how? Well a somewhat recent study from 2011 lays out the 911.
I learn so much from Cornell Cooperative Extension, and I rarely share it here, mostly because I think it might bore your socks off. The University has remarkable studies in every department from, ecology, evolutionary biology, entomology, botany, and horticulture. I recently read this study rather than contacted the researcher, which I have done on occasion.
You have all heard of beneficial insects. My guess is you might think of them flying around on the prowl actively searching for their prey. There is a slight problem with this scenario in that the insects they are looking for are quite small. So how do they find them so readily?
One study caught my eye done by Professor Andre Kessler, professor of ecology and evolutionary biology. He and Ian Baldwin of Max-Planck Institute for Chemical Ecology did a study and subsequently released a paper called, The enemy of my enemy is my friend. You can download the 2011 abstract in pdf form for further reading. Pressem_Kessler2001_en
The paper noted four ways to benefit when plants emit infochemicals.
- They signal to herbivores the plants defenses have been activated.
- The released volatiles let other herbivores know that the plant is under attack and to avoid further competition, they should decide to feed elsewhere.
- They let the predators know that their prey awaits.
- Because the plant attracted predators, it signals the hungry herbivores “that it is a well-guarded fortress.”
Now this does not occur with every plant because some are toxic to herbivores in their own right, and have little need to attract predators. But…
The study found that some plants are not passive when under attack by munching herbivores and will give off a distress signal.
So interesting is that the plants will release volatile organic compounds like a dinner bell to parasitoids and predators. They essentially put out word to the insect world, “here is an insect worth eating” or worse, one to feed and incubate their young. This in turn attracts predators to act as the plant’s bodyguard and savior.
An example you might be familiar with is the case of the cabbage plant and the Cabbage Moth. Those little caterpillars do quite a number on the cabbage plant.
But, the cabbage plant has defenses and emits the specific VOC that will attract a species of parasitic wasp, Cotesia glomerata that will be happy to swoop in and attack the moth or butterfly eggs and any caterpillars that have hatched from them. We have the Cabbage White butterfly here, and it too is attacked by Trichogramma brassicae and Cotesia glomerata.
The caterpillar incubates the wasp brood as it develops, with the larvae feeding on the caterpillar from the inside out. Damage is done to the plant but the caterpillar will be dead as a result of this act of nature. If you are curious as to how this process unfolds….
The really amazing part of this drama is the parent wasp might never have found the prey had the plant not sent out the invitation.
“These herbivores are small and don’t smell a lot. They’re difficult to find,” said Poelman, of Wagenigen University in the Netherlands. “We had an idea that these wasps might use something that was already detectable.”
It is the odor of the VOC that acts as the olfactory cry for help. Kessler was not part of the Dutch study, but noted the signal can be interpreted by any available predator that is able to read it, which means it could also be attracting uninvited insects to the dinner table.
The plant loses control once the signal is sent, because “plant-insect interactions are played out in an ecological arena that is larger than the plant itself and incorporates many community-level components,” says Kessler.
Pretty amazing how plants actively react to threat. Did you know they also give off the distress signal after a lawn mowing? Now how cool is that. Pretty confusing to the parasitoids though.
What is new to the thinking here is that what was commonly once thought a twosome pairing of partners now is an active threesome. Think about the complexity of this. It is not just the hunted and the hunter. The plants and insects evolve right along making this complex world pretty darn amazing.
I had no images of caterpillars getting eating from the inside out, but do have a Drone Fly and Cicada suffering a similar malady. Both insects were alive despite such horrific damage. The Cicada was almost completely hollowed out, possibly from the fungus Massospora cicadina, even into the head. Nature is cruel in many respects. This is another example of a threesome in play. The mating pair, genetics, and good old-fashioned passing off the fungus to the offspring.
Upcoming… Bugs We Love and Plants They Hate. Why not bug the bugs before they bug YOU!