There are several thousand species of sawfly, all of which resemble a cross between a fly and a wasp. Unlike a wasp, however, the sawfly does not sting. Its name comes from the female’s use of her ovipositor to cut slits in plant leaves, stems or shoots into which she lays her eggs.
Although the adults are important pollinators of crops and flowering plants, these slits can expose the plant to disease. In addition, depositing eggs inside the plant can result in galls, abnormal outgrowths in the tissue of the plant.
Larvae: the main problem
It is the larva, however, that is the most destructive life-cycle form. It targets a wide variety of crops and plants, such as cabbage, kale, fruit, and ornamental and wild trees. The larva eats the soft flesh of the leaf, leaving only the midrib and
Although a mature plant may be able to sustain such an attack, small or immature plants are particularly vulnerable to this type of damage. Fortunately, sawflies tend to be host-specific, and do not generally roam from one plant species to another.
The tiny maggot-like larvae hatch several weeks after the eggs have been laid. At first glance, the larvae resemble small caterpillars. Unlike caterpillars, though, they have three pairs of true legs on the abdomen and seven or eight pairs of false fleshy legs.
The growing larva feeds for about a month. When mature, it spins a cocoon in which it pupates. Some species pupate on the plant and others on the ground. If the weather is unfavourable for pupation, the pupa will over-winter until the following spring.
Control measures: manual is best
Fortunately for the farmer, sawfly infestations are usually nowhere near as extensive as those of caterpillars. That said, they can cause significant economic damage. The best means of control is to remove the larvae manually and kill them.
Alternatively, douse them in insecticidal soap, or forcibly remove them by spraying them off the plant with water. Ground-dwelling predators will eat them. In the unlikely event of a large outbreak (more