Seeds of Acacia trees survive attacks by parasitic beetles by attracting herbivores whose digestive juices kill the parasites' larvae.

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"The species of acacia whose umbrella shape is so typical of the plains of East Africa encloses its seeds in small twisted pods. These are very rich in protein and many of the plant-eating animals on the plain relish them. Those seeds that remain uneaten on the ground seldom if ever germinate, whereas those that are swallowed with the pods do. It used to be thought that this was because stewing in digestive juices weakened the covering of the seeds and made it possible for the infant plant within to break out. The truth, however, is somewhat different. Within a few hours of the acacia tree shedding its pods, large numbers of a particular kind of small beetle fly in, pierce the pods with their sharp ovipositors and lay their eggs within. The eggs hatch rapidly and the tiny grubs then proceed to feed on the acacia's seeds. Unless, that is, the pods are eaten by an animal such as an elephant. Although the elephant grinds up the pods with its teeth, many of the seeds remain unharmed and are swallowed with the mash. In the stomach all the beetle eggs are killed stone dead by the digestive juices. So when the seeds finally return to the outside world with the animal's droppings, they have been freed from their insect pests by the elephant, just as effectively as seeds of wheat that have been treated by a farmer with insecticide." (Attenborough 1995:29-30)

Book
The Private Life of PlantsBBC BooksAugust 21, 1995
David Attenborough

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