gus or bacterial disease, than by the ainoimt of food provided the 

 grub. (When grubs succumbed to the Metarrhizium fungus during^ 

 the second or third instars, it was found that the earlier instars had 

 been above normal in length.) 



From the fact that larvte of ^lay-beetles are always in a coiled 

 position, and seldom straighten out to crawl as do the grubs of Rute- 

 lids and Dynastids, it is very difficult to measure their length. It 

 was ascertained, however, that the length is just double the measure- 

 ment across the coiled body, so that the length of grubs in the various 

 instars was determined in this way. 



At the time of hatching from the egg, the grub of vandinei is 

 about 6 nun. long and 1.75 mm. to 1.8 mm. across the head. Before 

 molting to the second instar (see Plate III, fig. 3) it reaches a length 

 of 17 ram. to 18 mm., and the head reaches a diameter of 1.9 mm. to 

 2 nmi. (PI. V, fig. 1.) 



The head does not grow like the body, l)ut that it enlarges some- 

 what in size may be shown by the following brief table, from actual 

 measurements with sliding calipers from living grubs :^ 



HEAD OF FJRST-IXSTAR GRUBS. 



An average from 5 grubs varying from 5 to 10 mm. in length; head 1.8.5 

 mm. wide. 



An average from 29 grnbs varying from 11 to la mm. in length; head 1.96 

 mm. wide. 



An average from 11 grubs varying from 1(5 to 18 mm. in length; head 2.01 

 mm. wide. 



During the first instar no damage is done by the grub of vandinei, 

 since it lives entirely upon vegetable matter in the soil. It is only 

 during the very last days of the instar, or more commonly in the early 

 part of the second instar, that the grub l)egins to eat living roots. 



The second instar. — The average duration of the second instar 

 (see Plate III, tig. 4) was found to be 47 days; the maximum, 103 

 days; the minimum, 26 days. Or, reduced to months, the average 

 was one and one-half months; the maximum, three and one-third 

 months; and the mininuim, somewhat under one month. It is seen 

 that the maximum duration of this instar was more than four times 

 tlie minimum. 



At beginning of the second instar the length of the grul) is 17 nun. 

 to 18 mm.: at end of the instar, and just before molting to the third 

 instar, the length is 28 mm. to 30 mm. The average width of head, 

 taken from 43 second instar grubs, was 3.33 nun. (See Plate V, fig. 2.) 



1 Note. — ^Measurements of small objects made with sliding calipers are very apt to 

 average from .1 mm. to .15 mm. above actual size. 



74 



