Many recent studies have shown that plants can mount active an active defence against herbivores (insects, mammals or others). When leaves are being consumed, many species of plants release a chemical signal, methyl jasmonate. The process, however, takes some time and the plant might be destroyed by the time the chemical moves through all the leaves. But neighbouring plants may heed the signal and release the chemical. As a result, their foliage becomes less palatable.
A Wisconsin research team investigated the response of tomato plants to an attack by a beet armyworm, a pest which (despite its name) consumes many types of crops. Beet armyworms will devour tomato leaves when the plant defences are low. However, the researchers found that the armyworms preferred to eat each other rather than eat leaves with high levels of methyl jasmonate.
The end result is the chemical release leads to less plant damage. Fewer caterpillars are around (because many have been consumed). The cannibalistic caterpillars survive but they eat less plant tissue because they have filled up on caterpillar tissue.
Source: Induced defences in plants reduce herbivory by increasing cannibalism. John Orrock, Brian Connolly & Anthony Kitchen. Nature Ecology & Evolution. July. 2017.
- Janet Wallace