22 THE GRAPE KOOT-WORM. 



SEASONAL HISTORY. 



The grape root-worm attains its growth during the feeding period 

 of the larvse. The pupal stage, following the long larval period, is a 

 process of transformation, whereby all the internal organs, and to 

 some extent the external parts, become reconstructed, resulting, with 

 the throwing off of the pupal skin, in the appearance of the beetle. 

 It is during this latter stage and in the early part of the summer that 

 reproduction occurs. 



The diagram (fig. 12) will, it is believed, greatly aid the reader in 

 comprehending the development and the activit}^ of the grape root- 

 worm in its various stages throughout its life cycle. This illustra- 

 tion has been compiled from both field and rearing observations 

 and represents the life of a single beetle under average conditions. 



In the following consideration of the life history of the grape root- 

 worm is presented the results of rearing experiments and field obser- 

 vations for the year 1909. In most respects that year was normal 

 as regards climatic conditions and the insect developed as might be 

 expected under average conditions. In view of the extreme varia- 

 tions in the development of the insect during 1907 and 1908, the 

 records of observations for these years have been treated under 

 the topic ''Seasonal variations in the life history of the grape root- 

 worm." The rearing and experimental methods relating to the tables 

 of the life-history work are described separately on pages 44-50. 



THE ADULT OR BEETLE. 

 THE PROCESS AND TIME OF EMERGENCE. 



Prior to its emergence the beetle spends several days in the pupal 

 cell and at the time of the shedding of the pupal skin is of a light 

 turbid yellowish cast, and is comparatively soft and for a time help- 

 less. On an average the beetles remain 4 days in the cell, while the 

 parts of the body harden. In Table XV (p. 38) are given 25 observa- 

 tions on the length of time the beetles remain in the cell after trans- 

 formation. In one instance a beetle remained in the cell 7 days. 

 The minimum length of time was 2 days. Dead beetles have been 

 found in cells, both in the breeding cages and in the ground in vine- 

 yards. This occurrence, however, has not been found sufficiently 

 common to cause any material reduction in the number of insects. 



The time required by the beetle in passing through the soil to the 

 surface varies considerably with the distance to be covered and the 

 texture and moisture of the soil. It has been possible to make only 

 a few observations on the process of emerging. These were made in 

 breeding cages with glass sides, in which the beetles have worked 

 their way out to the edge of the soil next to the glass. One beetle 

 which left the cell July 6 emerged July 9. On its way upward it had 



