MARTA DEL CAMPO: It is really fun to work with insects. They're fascinating creatures. They have this amazing behavior that most people maybe miss, first, because they don't have much contact with nature and, second, because insects are really tiny. I've been interested on insect-plant interactions for a long time. And I've been working on Manduca sexta, the tobacco hornworn.
In order to have enough animals, what we do is [INAUDIBLE] them on the artificial diet that has the nutrients altogether. But we have to start with the moths that are in the greenhouse-- is where everything starts. After the females lay eggs in the cage, what we do is we collect the eggs. Carefully, we'll remove them from the leave that we provide them. And in here, the animals start to hatch. But what happens in this cup is that they are too crowded.
They need some more space. So we put them in little cups where we [INAUDIBLE] them individually. In here, you see this caterpillar was transferred just this morning. And, of course, they continue growing and growing. And there is a point that the cup begins to get really, really small for it, so they have a need for a larger home. And in here, you can see they go into a larger cup and then become really larger caterpillars.
They will finish their larval developmental stage and become a pupa. Because in the lab we cannot provide the space for having a large chamber for each animal, we put them in these wooden blocks where they can actually go inside. And after a few days-- I'm worried that [? all are ?] [? gonna fall-- ?] and here we have a Manduca pupa. These pupae eventually hatch as moths. And here you can see an example.
The animals have not become host-restricted or adapted to a host plant. They are polyphagous. They can eat and accept almost anything I can give them. That means in simple words that they can easily shift from feeding on a plant that is completely unrelated to artificial diets. They will try to feed on your finger. They will try to feed on a pipette, on anything they encounter.
But when they feed on a solanaceous plant, just after a few days, two to four days, is enough for them, and they become kind of hooked on it. They become dependent on the chemistry of the plant to actually continue growing and developing. And they will reject even up to death any plant or food that you provide them that is not solanaceous. But there's some particular compound that [? leaves ?] we isolated from potato that they use to identify like a label that says this is food. And when they learn to recognize this compound, what happens is that they cannot detect the other plants as food.
When the animal encounters a leaf or it's sitting on a plant and it gets hungry, what they start to do is actually to tap the surface of the leaves with their taste organs. In caterpillars, there's a big difference if you compare them with our cells for example, because we taste our food with our tongue, but in caterpillars they have taste receptors that are outside. They're like little hairs protruding from their chin, if you want to call it, or on the side of their mouth parts. So they're able to taste the food before they start eating on it.
If those sensor receptors are removed and the animal has been growing on solanaceous plants, it will completely lose their ability to discriminate. And they will be able to feed on almost anything it finds around. Well, the thing is solanaceous plants are loaded with chemicals that are really toxic. And that means when the caterpillars hatch, they have to really change their whole system in the digestive system, in their sensory system.
So it's really costly to become adjusted to the chemistry of the plant. Why they hatch as polyphagous, feeding on anything? Why not be host-restricted from the beginning, from the moment they hatch as many other caterpillars do? And that we believe it's due to the mother's choice. When the mother choose plants in nature to oviposit the egg, she's taking a very risky decision.
And the reason for that is that if the egg is left alone-- because the egg is left alone, it's really important that she chooses the right plant for the caterpillar to grow. And when they oviposits on a salacious plant, is everything perfect. However, [? in ?] sometimes in nature and it is known the caterpillars-- well, actually the females oviposit on plants that are not solanaceous. In that case of course, it will be critical for the survival of the caterpillar be able to feed on a non-solanaceous plant.
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Marta del Campo explains how the larvae of Manduca sexta, a moth nicknamed the tobacco hornworm, can become so chemically dependent on their favorite foods--the leaves of eggplant, potato, or tomato plants--that they would rather starve to death than eat leaves from other plants.
Tobacco hornworms raised on an artificial diet will eat any kind of plant material. Yet after only four or five days of feeding on a solanaceous plant such as tobacco, tomato, or hot pepper, they will refuse any other kind of plant food. Having become host specific, they will use taste organs located on hairs near their mouths to search out particular chemicals. In the absence of these chemicals, the caterpillars will not feed. If these hairs are removed, the caterpillars will once again return to feeding on any plant.