Here’s a turn-up for the books. Potato plants in which a tuber is infested by the larva of the Gautemalan Potato Moth Tecia solanivora — “considered one of the most economically important potato pests in Latin America” — produce 2.5 times more marketable potatoes than uninfected plants. Something in the caterpillar’s saliva spreads through the plant and promotes tuber growth, giving a greater yield even when up to one in five of the tubers are infected.
Did indigenous Colombian potato farmers know of this? I couldn’t discover why the researchers had decided to investigate. In any case, the Guatemalan Potato Moth is clearly no pest. Researchers are now looking at “herbivore-derived chemical clues” and “induced compensatory plant responses to herbivory” as new ways to boost production.
It seems to me that tecia is a pest at high densities. But what a surprise that it can be beneficial at lower densities.
The reported size of the benefit is humongous. Yields that more than double with a little chemical stimulus?
Under field conditions, I can reason a part of it away. The fewer tubers a plant has, the lower its changes of getting infected. Are yields of unifected plants low, or are low-yielding plants less likely to be infected? Probably a bit of both.
Even so, the greenhouse experiments leave little room for doubt. Something is going on. Time to get into the regurgitant spraying business.