4 CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



in the egg, and the day before the worm hatches" a black spot, the 

 head of the worm, is easily seen. Most of the first-brood eggs are 

 laid on the leaves. 



The earliest-laid eggs are usually subjected to cool weather and 

 the worms do not hatch for 12 to 14 days. As the temperature 

 becomes higher, the incubation period of the egg shortens, the mini- 

 mum being 5 days, although in extremely cool weather it may be as 

 long as 3 weeks. Worms are hatching from eggs and entering the 

 fruit for about 5 weeks, and are most numerous during the first half 

 of June. These worms feed in the fruit for about 3 weeks and then 

 leave it and spin cocoons. About 75 percent of them continue their 

 development into pupae and moths, but the others remain in their 

 cocoons until the following season. The worms that transform pass 

 through the pupal period in about 2 weeks, and the first individuals 

 of the second brood of moths appear early in July. After this time 

 moths are present in large numbers until cool weather in the fall, the 



Figure 4.— Codling-moth eggs: Left, natural size on apple leaf; right, single egg, 35 times natural size. 



first period of stormy weather in September usually ending the 

 activities of the moths for the season. Many eggs of the second brood 

 are laid on the fruit, and during the warm weather of July and 

 August they ordinarily hatch in 6 or 7 days. The worms often remain 

 in the fruit for more than a month in the fall, and many of them are 

 still there when it is picked. They may leave the fruit before it is 

 packed, and for this reason large numbers of wintering worms in their 

 cocoons may be found in picking boxes and packing sheds. 



The codling moth is very sensitive to variations in temperature. 

 In the warmer localities there is often a partial third generation, but 

 at greater elevations and along the coast there is no third generation 

 and the second generation is smaller than elsewhere. In any locality 

 the yearly abundance of worms varies greatly, as it is dependent on 

 weather conditions. Winter temperatures of —15° F. or colder kill 

 some of the overwintering worms. Probably the most important 

 effect of temperature occurs during May and June, when large num- 

 bers of first-brood eggs are laid if the weather is warm, but the number 

 is greatly reduced if it is cold or rainy. Thus an early, warm season 

 produces many worms, but a late cool season has the opposite effect. 



