[Illustration:  The curculio in its stages of growth, and its fruit injury.]

There are four distinct stages in its life cycle:  (1) The egg, (2) the larva, or “worm,” (3) the pupa, and (4) the adult, or beetle.

The curculio passes the winter in the adult stage under accumulations of partly decayed leaves, among the closely-packed dried grass of sod-covered orchards, and probably wherever suitable protection from the winter may be found.  Its depredations are usually worse near woods, so it probably finds here very suitable places for wintering.

In the spring, when the fruit buds are unfolding, the beetles begin to emerge from their winter quarters and feed to some extent on the blossoms and tender leaves of the fruit trees.  Mating soon begins, and by the time the fruit is well set the beetles make this fruit the chief object of their attention.  The circular punctures in the skin are feeding punctures, while the crescent-shaped ones are egg-laying punctures.  A single egg is deposited in a puncture, although several may be placed in a single fruit.  From one to eight eggs may be deposited daily by an individual female, which may be continued for several months.  The great majority of the eggs, however, are deposited by the end of eight weeks.  These eggs hatch in from three to seven days, being influenced greatly by the weather.

The egg hatches into a larva, or “worm,” which bores into the fruit.  It becomes full-grown in from twelve to twenty days and bores out of the fruit.  It enters the soil, burrows to a depth of one-half to two inches, and forms an earthern cell in which to pupate.  In three or four weeks it emerges as a full grown beetle and attacks the ungathered fruit and the foliage.  On the approach of cold weather the beetle seeks a protected place in which to pass the winter.

The character of the injury is very nearly alike in all fruits.  In the plum the fruit often falls to the ground before mature.  In seasons of short crops very little fruit may remain to ripen.  The punctures cause the fruit to become mis-shaped and to exude masses of gum.  The ripe fruit becomes “wormy.”  The late varieties may be seriously injured by the new generation of adults.  In the apple the injury to the fruit is about the same as in the plum, except that the infested fruit is not so likely to fall to the ground and that the egg rarely hatches into the grub there.  The fruit becomes knotted and pitted.  The late varieties may also be injured by the new generation of adults.  In the peach, cherry and other stone fruits, the injury closely resembles that of the plum.

Although the plum curculio has some natural enemies that tend to reduce its numbers somewhat, yet they are not important enough to be considered as effective means of control.  Some of these natural enemies are parasites of various kinds, birds, chickens and the like.

There are several remedial measures practiced, varying in their degree of effectiveness.  Away back in the early days of horticulture in this country, when the curculio became very abundant rewards were offered for an effective method of combating it.  Several were proposed, but only a few were at all effective.  The best of these methods is what is called “jarring.”