60 MASS. EXPERIMENT STATION BULLETIN 233 



Egg laying usually begins the third to fourth week of May, and may last 

 until late July. Oviposition corresponds very closely with the emergence 

 of moths, and is very irregular since it is governed by the temperature at 

 dusk or in early evening when most of the eggs are deposited. If the 

 temperature is 60° F. or less at this time, the moths show little activity and 

 very few eggs are laid. A sudden drop in temperature, or showers in late 

 afternoon, decreases the number of eggs laid that day. Prolonged cold and 

 unfavorable weather during the egg laying period greatly influences both 

 the time and amount of the season's oviposition. 



Hatching. In hatching, the young larvae break througli the upper surface 

 of the egg shell, usually close to the margin. They have never been found 

 to emerge through the under surface even when eggs are laid on the fruit. 

 The larvae, therefore, do not bore directly into the fruit witliout crawling 

 somewhat over tlie surface. 



The incubation period of the eggs varies from four to twelve days, 

 but most of them require six to seven days. The wide variation is due to 

 the fact that, in this stage, the codling moth is particularly sensitive to cli- 

 matic conditions and responds very quickly to any sudden rise or fall in 

 temperature. The close correlation can be seen from the following record 

 obtained in our studies in 1923. 



Daily maximum temperature Eggs hatched in 



56°— 65° F. 9—10 days 



73°— 80° F. 7— 8 " 



85°— 94° F. 6— 7 " 



87°— 89° F. 6 " 



92°— 97° F. 5 • " 



Larval Development. Tlie young larvae, or "worms" may be expected 

 to appear in about two weeks after the emergence of tlie moths. Their 

 appearance marks the period when infestation of the fruit takes place. 

 When it is recalled that moths are emerging over a period of six weeks or 

 more, it is easy to see the necessity for timely sprays to protect tlie rapidly 

 growing fruit from infestation. 



The length of time spent by the "worms" inside the fruit has been found 

 to be very uniform year after year. Protected as they are within the fruit, 

 they are not greatly affected by outside conditions. On the average 

 twenty-one to twenty-three days elapse from the time the newlv-hatched 

 "worms" enter the fruit until they emerge as full-grown larvae. 



The period during which they mature and are leaving the frijit varies 

 considerably according to the season. In a typical year, mature larvae 

 are found about the first week of July. In 1925, an early season, they 

 were leaving the fruit by the 25th of Jime; in 1926 a backward season, none 

 were found until July 20. 



Among those larvae which transform in the summer, there is much 

 irregularity in the time elapsing between their emergence from fruit and 

 pupation. Such wide variation is hard to explain. It appears to be an 

 individual matter. A few pupate at once upon leaving the fruit. Most 

 of them transfonn within six to nine days. A number, however, were 

 found to have delayed for seventeen, nineteen, twenty-eight, and, in one case, 

 thirty-one days before pupating. Larvae of the same age often pupated one 

 to two weeks apart. 



