204 LEAF-MINING INSECTS 



berry, turnip, cabbage and other plants. The beetle is a 

 small black species, measuring less than a twelfth of an 

 inch in length and possessing yellow antennae and legs. 



Sagrinae. This small tribe is represented in our fauna by 

 the following single leaf-mining genus. 



Zeagophora 



The cottonwood leaf-mining beetle, Z. scutellaris, makes 

 great black blotch mines on the upperside of the leaves of 

 poplars, often seriously disfiguring and damaging the trees. 

 (See fig. 54 , 2.) The following notes of this species are based 

 on Strickland's excellent paper (1920), together with obser- 

 vations made by the senior author at North Fairhaven, New 

 York, while obtaining the additional data on larval head 

 structures already given in the introduction to this chapter 

 (p. 185). 



Before egg-laying begins the adult beetles feed openly 

 upon the leaves nibbling at the first leaves of the season, 

 eating out little patches of parenchyma generally from the 

 underside, leaving the upper epidermis intact. A brownish 

 corky tissue later develops around the injured area. Other 

 smaller holes are also made for the reception of the eggs. 

 The eggs are thrust singly into these latter holes, that ex- 

 tend from the lowerside puncture diagonally upward. After 

 the egg is inserted, the injured tissue about it turns brown, 

 and a spot of that color about 1 mm. in diameter appears 

 upon the green upper surface. 



The egg is short, cylindric or oblong, measuring about 

 1.5 mm. Judging by the cast skins found in the mines, 

 there appear to be three larval instars. 



The larva on hatching begins at once to cut a way through 

 the palisade tissue next the upper epidermis. Only rarely 

 is a mine found next the lower side of the leaf, and then only 

 the lowermost layers of mesophyll are eaten. The tissue 



