February, '15] 



RUGGLES: OBEREA TRIPUXCTATA 



81 



The Egg 



The egg is 2| mm. long and 0.7 mm. in width; cylindrical, with 

 round ends, smooth and of a j^ello^dsh tinge. Many eggs were 

 found on one stem, each in its characteristic position, but all the eggs 

 between the complete girdling next the main stem and the end of the 

 twig soon perished. Fig. 2 shows the methods of placing the egg in 

 the t"^ag. The arrow in Fig. 1 and the x in Fig. 2 show the position 

 of the egg. 



Larv^ and Work 



The eggs began to hatch June 21, just one week after rny first obser- 

 vation, and no more eggs were found after June 28. The entrance hole 

 of the larva was just below the lower end of the egg. In the majoritj^ 

 of the burrows examined, the larvse first tunneled upward and later 

 returned to continue the burrow downward. Many perished by 

 emerging at the girdled end. This may be due to their inability to 

 turn around after emergence or possibly due to attacks of an enemy. 

 Along the burrow, at short intervals, 6 mm. or more, the larva made 

 holes through the bark or through an aborted bud out of which it 

 pushed its borings. Up to October 30, 1911, the longest burrow^ made 

 was 75 mm. The majority of the burrows, however, were much 

 shorter. The larvse at this time measured 5 mm. in length and had a 

 head measurement of 0.6 mm. This, according to the theory of head 

 measurement, would place the hibernation period in the third instar. 

 By the last of July, 1912, practically all the larvse had reached the last 

 stage, having a head measurement of 1.2 mm. In September, 1912, 

 some burrows were six inches and more in length and in the terminal 

 portion of the burrow, the larva hibernated. In Minnesota, therefore, 

 it takes two years for this beetle to complete its life-cycle. 



In wood-boring insects, it is very difficult to find moulted skins in 

 the burrows and practically, therefore, impossible to tell the number of 

 instars. I have been doing some work on the head measurement of 

 these wood-boring insects, and a few species of wood-boring beetle 

 larvse in all their stages have been examined. The head measurement 

 appears quite constant for a given period which we believe would 

 correspond to the length of an instar, and therefore, this measure- 

 ment is preferred to merely length measurements which are sometimes 

 given with descriptions of larvse. For Oberea tripundata larvse, the 

 following measurements and descriptions are given : 



First Instar. — Head measurement, .36 mm.; length, 0.8 mm. to 2.6 

 mm. The young larvse are lemon-yellow in color, at times having an 

 orange cast. The anterior part of the head and mandibles are a very 



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