152 



THE MONTHLY BULLETIN. 



and there is a possibility that varying conditions such as altitude and 

 climate might make them unreliable elsewhere. In case there is any 

 doubt, however, as to the cause of the trouble, carefully cut away the 

 bark on one of the dead twigs and in case it is beetle work that has 

 caused an abnormality which has made itself manifest, the burrows 

 and accompanying "frass" will be noted. The larva is a very slender 

 delicate little creature, and will be overlooked or cut away if care is not 

 taken. The insect wnll usually be found at a point near the union of 

 dead and living wood. 



Life-history. 



Little seems to be known relative to the various stages in the trans- 

 formation of this beetle. The author has casually watched the develop- 

 ment and growth of the species while attending Stanford University, 

 where the insect is found abundantly. 



From the various collecting dates that have been recorded with the 

 insects that have been taken in various years it would appear that the 



Fig. .55. — Larva and adult of the oak 

 twig girdler, Agrilus politus. About 

 twice natural size. (Original.) 



adults may issue as early as April. The beetle has been reared from 

 infested twigs by the writer and the emergence of the adult has never 

 occurred before the first of June. Weather conditions and the variable 

 supply of available foodstuffs in different trees doubtless have a great 

 deal to do with the time the insects make their appearance. The time 

 of the is.suance of the adult is very important in the control of the pest, 

 and this work should be undertaken during the fall and winter. This 

 precaution will greatly reduce the infestation for the following year. 

 The eggs or egg-laying has not been observed, but must take place 

 soon after emergence for the young larvae show considerable growth by 

 the first of August. From the fact that the yoimg grubs begin their 

 burrow.s at some weakness that the small twig affords, i. e., at the base 

 of a leaf or at a branching point of the small twig where there is an 

 irregularitv in the bark surface, the egg-laving habits of the twig girdler 



