The “mother knows best” hypothesis states that adults should choose hosts for oviposition on which their offspring will best perform, maximizing their own fitness. In other words, mothers will lay eggs in places where there’s good food for their children.
It has been hypothesized that this is especially important for wood-boring insects because the larvae are not able to switch hosts. Instead, they’ve got to feed on whatever tree their eggs were laid on.
Now scientists from Ohio and Michigan have tested the hypothesis using the emerald ash borer (Agrilus planipennis Fairmaire), an invasive wood-boring insect that causes millions of dollars of damage in the U.S. each year. Their research was recently published in the Annals of the Entomological Society of America.
While some species of ash trees that are native to Asia are inherently resistant to the emerald ash borer — also known as EAB — species of ash trees from North America are not, making them better hosts for the EAB larvae.
For two years the researchers observed two gardens containing both Asian and North American ash trees, and they found that “ash species native to North America, which are highly susceptible to the emerald ash borer, consistently received more ova than Manchurian ash, which is indigenous to Asia and more resistant to the emerald ash borer,” proving the “mother knows best” hypothesis, at least in this case.
The susceptible North American trees received 93 times as many eggs in one garden, and as many as 25 times in the other, irregardless of tree size or health, and the researchers also observed higher numbers of adult exit holes in the North American ash trees.
“Collectively, our results demonstrate that the emerald ash borer prefers to oviposit on species on which its offspring will best perform, suggesting that there is strong selection for the ability to recognize host cues that predict better larval survival and performance,” the authors wrote.
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