Insect identification > Coleoptera > Rhynchophora > Plum curculio

Plum curculio

The plum curculio (Conotrachelus nenuphar Hbst). - This insect is a native of the United States and formerly fed upon the wild plum and thorn fruits but now also attacks cultivated plums, prunes, cherries, nectarines, apricots, apples and peaches.

It is found practically everywhere east of the Rocky Mountains, though in the western portion of this area it seems to be of less importance than elsewhere. The adult beetle is small, being only about a fifth of an inch long, dark colored as a whole but mottled with gray and brown. Its elytra are rough and on each is a black, shining hump a little behind the middle.

This pest spends the winter, or the colder months in the South, hiding in any protected place it can find, particularly in the woods, in stone walls or under leaves. It appears about the time the plum buds open in spring and feeds more or less on the developing leaves. When the fruit begins to develop, the beetles turn their attention to it, feeding by cutting a circular hole through the skin and consuming the flesh beneath to a depth about equal to the length of the snout of the insect.

They also begin now to lay their eggs in the young plums, cutting a hole in the skin and then running the snout obliquely into the flesh beneath. In this cavity the egg is placed and it is then pushed farther in by the snout. The beetle next cuts a crescent-shaped slit through the skin close to the egg and carries this down through the flesh beneath the egg which thus comes to lie in a sort of flap which wilts and remains soft, and the crushing of the egg by the growth of firm tissue there is prevented. Several hundred eggs are laid in this way and the"spot and crescent "marks of the insect on small plums are familiar to plum growers. The fruit often pours out gum at these places, probably in an attempt to repair the injury.

The eggs hatch in a week or less and the tiny whitish grub bores through the flesh and in stone fruits passes to the stone, around which it feeds for about two weeks or until full grown. It then leaves the fruit, and, as this in most cases has fallen before this time because of the injury, the larva finds itself on escaping on the ground. Into this it now burrows an inch or two and pupates. Three to four weeks later the adult beetle emerges, comes to the surface of the ground and attacks fruit for food, egg-laying rarely if ever taking place at this season.

When cold weather comes on, it locates in some protected place for the winter. There is but one generation a year in the North. In the South, however, some of the beetles appearing in the summer will lay eggs, thus producing a partial second generation. This insect, by both its feeding and egg-laying punctures, affects the value of the fruit not entirely destroyed, not only in appearance but by the opportunity these cuts afford for the entrance of the spores of disease-producing fungi, and the destruction in the United States which it causes has been estimated at over millions of dollars annually.

When the insect attacks small apples, its punctures cause dropping of the fruit or its malformation and the production of hard, woody places in the pulp. In the fall its feeding holes in apples also cause much injury.