PREDICTION PROCEDURE. 



The Problem of Predicting the Appearance of the Codling Moth 



The codling moth is the most destructive insect infesting apples. Its 

 larva, commonly called the apple-worm, eats its way into the fruit to 

 the seeds, forming dark masses of frass, or castings, at the end of the 

 hole and in the core. It is found wherever apples are grown throughout 

 the world. It also attacks pears, quinces, wild haws, peaches, English 

 walnuts, and other fruits. Its life history, appearance, and habits, to- 

 gether with control measures used against it, have been described by 

 Metcalf and Flint* as follows: 



Liie History, Appearance, and Habits: The Codling Moth passes the win- 

 ter in the full-grown larval stage in a thick silken cocoon. The larvae are 

 pinkish-white caterpillars with brown heads and are about three-fourths of an 

 inch long. These cocoons are generally spun under loose scales of the bark 

 on the trunks of apple trees, or other shelters about the base of the trees, 

 or on the ground nearby. Many of the larvae winter in. or around, packing 

 sheds. They remain dormant, and are able to withstand low temperatures. 

 A drop in temperature to — 25° F., or below, will kill many of the larvae. Dur- 

 ing the winter, birds, especially chickadees and woodpeckers, find and eat large 

 numbers of the larvae. In the late spring the worms change inside their co- 

 coons to a brownish pupal stage and, after a period of from two to four weeks 

 or more, they emerge from the cocoons as grayish moths with somewhat irri- 

 descent, chocolate-brown patches on the back part or tip of the front wings. 

 The moths have a wing expanse of from one-half to three-fourths of an Inch. 

 During the day the moths remain quiet, usually resting on the branches or 

 trunk of the tree. The coloring of the wings is such that it blends with that 

 of the bark, making the insect very inconspicuous. About dusk of the even- 

 ing, if the temperature is above 60° F., they become active, mate, and the 

 females lay their eggs. If the temperature is low, they remain quiet, and few 

 eggs will be deposited. Each female usually deposits more than fifty eggs 

 during her life time. The eggs are white, flattened, pancake-shaped, and 

 about one-twenty-fifth of an inch in diameter. The eggs of the first generation 

 are laid one in a place, almost entirely on the upper side of the leaves, usually 

 a short distance from a cluster of apples. They are laid two to four weeks 

 after the apples have bloomed, and hatch in six to twenty days depending on 

 the temperature and, to some extent, on the rainfall. The worms feed slight- 

 ly on the leaves but in a short time crawl to the young apples and chew their 

 way into the fruit, usually entering by way of the calyx cup at the blossom 

 end. After entering the fruit, they work their way into the core, often feeding 

 on the seeds. Some of the infested fruits drop from the tree and the larvae 

 complete their growth on the ground. Upon becoming full grown, they bur- 

 row to the outside of the apple and either crawl to, or down, the trunk of the 

 tree, or drop to the ground and crawl back to the trunk or to some other ob- 

 ject on which they spin their cocoons, and change as before to the pupa, and 

 later to the adult stage. 



• The pa.=sage quoted is from "Destructive and Useful Insects," a text by C. L. 

 Metcalf and W. P. Flint, which is now (1926) being used in mimeographed form 

 (3 volumes) for instruction of classes in the University of Illinois. 



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