THE POTATO TUBER MOTH. 



31 



noticeable development for a few days at a time when the average 

 mean temperature is low. 



Experiments were carried on in the storage rooms of an ice company 

 at Pasadena to determine if low temperature acting for some time 

 would kill the various stages of the moth or whether they could 

 hibernate successfully. For these experiments the following stages 

 were taken : Adults, pupfe, mature larvse in cocoons, and eggs. Two 

 experiments were carried on at the same time. One lot was kept at 

 32° F. for three weeks, while the other lot was kept for 35 days at a 

 temperature of 38°-40° F. 



The results are summarized in Table 10: 



Table 10.— 



-Effect of 



ow temperatures on stages of the potato tuber moth. 



Time. 



Tempera- 

 ture 

 (constant). 



Adults. 



Pupae. 



Mature 

 larvae. 



Eggs. 



21 days.. 



32° r 



40° r 



Most alive and active 



Alive 



...do 



Alive 



...do 



Alive. 





Over half were dead 



Do. 













In the cases where the various stages were alive they developed 

 normally when taken from storage. In both experiments develop- 

 ment was stopped in all stages while the material was in storage. 

 These results show that the tuber moth may hibernate successfully 

 where conditions demand it and that no development takes place 

 below 40° F. Prof. Picard (83) says that no development takes place 

 below 50° F. 



DISSEMINATION. 



The tuber moth is disseminated by two means, natural and arti- 

 ficial. Of- these two the former (by flight of the moth) is much the 

 slower and, as it can hardly be controlled, is relatively unimportant. 

 The most important spread of the tuber moth takes place through 

 the movement of infested potato tubers. In this way the insect is 

 assured of an abundance of food, and since the tubers are not allowed 

 to freeze, the temperature is always favorable. In interstate and 

 international shipments the moth is given every opportunity to 

 spread and has probably been introduced at some time into every 

 civilized country on the globe. 



It is even possible that a careful inspection will show that it is 

 established in many localities where it is now unknown. This is 

 especially likely to be the case in districts where the climate is cold 

 and wet and therefon^ unfavorable for the insect's normal develop- 

 ment. 



MORTALITy OF THE STAGES. 



^Hie mortality in the various stages must be considered from the 

 standpoint of whether the insect is working on potato tops or on 

 stored potatoes. Under field conditions as a leaf minor the mortality 



