176 Annals Entomological Society of America [Vol. XIII, 



that even the inherent tendencies toward periodicity may not 

 be altered. In general those forms which are found in more or 

 less uniform environmental conditions respond most readily 

 to changes of the environment. Examples of this may be found 

 among the beetles which live in stored food products. On the 

 other hand, the beetles which feel the effects of the periodic 

 changes of the season, having their food available for a limited 

 period of each year, often have developed a periodicity with 

 regard to their life phenomena. 



Tribolium conjusum has its egg stage shortened from ten to 

 five days by a rise of from 24° to 34°, and it will develop one 

 generation after the other throughout the year. On the other 

 hand, the life cycle may be prolonged by a reduction of the 

 amount of moisture and also by a limitation of the quantity 

 or quality of the food. Thus the length of life and the number 

 of broods may be altered by changing any one or all of these 

 three factors. A larva now under observation has had its life 

 prolonged from thirty to ninety days due to food conditions, 

 and during this time it has molted twelve times rather than the 

 normal six times. 



So far as is known, all beetles have their lives shortened 

 by an increase of temperature, over that which they normally 

 experience. But some of them will not produce more broods 

 in a year under high temperature than under low. The cotton 

 b)oll weevil, a native of the south, has been reported to have as 

 many broods a year as time, temperature, and humidity will 

 allow, but the potato beetle always has two broods a year. 

 Those forms which are not subject to an inherent periodicity 

 have more broods in the south than in the north, but those with a 

 fixed periodicity cannot be so changed. Shelford reports that 

 a certain cicindelid has the last larval , instar prolonged to 

 extend over the period of hibernation in Canada, while the same 

 ■species has a shorter larval life in the vicinity of Chicago. 



The Buprestidas as a family hibernate in the larval stage, but 

 Taphrocerus which mines in the leaves of the floodplain bullrush 

 as a larva, emerges and hibernates in the adult stage. In this 

 case the larval life is confined to about six weeks in the early 

 part of the summer and the adult beetles emerge and feed 

 about on the leaves, but no eggs are deposited until the following 

 spring. On the other hand, the larvae of Agrilus bilineatus, a 

 wood-boring buprestid, may mature in August and form their 



