226 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



THE WHITE BLOTCH OAK LEAF MIJs^ER. 



{Lithocolletis hamadryadella Clemens.) 

 Order LepidopterA; family Tineidae. 



Makiur^ a -n-hitish blotch mine upon the upper surface of the leaves of different oakg, 

 a niwuiie, dat, homy, footless, active, hrownish-yellow larvii, which traustbrms 

 within the mine in a delicate discoid silken cocoon. (Plate IV, tig. 4.) 



In tLe latter part of June, 1879, the leaves of many of the oaks on the 

 department sfrounds were seen to be badly spotted by the mines of this 

 interesting little insect. Although each mine by itself caused but an 

 insignificant blotch, yet these insects were present in such enormous 

 numbers as to promise serious injury to some of the trees. It is safe to 

 say that with a few trees every leaf contained, on an average, four or 

 five miners, and with many leaves the entire parenchyma on the upper 

 side of the skeleton was entirely eaten out, leaving the upper epidermis 

 as dry as parchment. The vitality of the tree had made efforts to re- 

 pair the injury, but the constant drain upon the tree, supporting these 

 hundreds of thousands of living beings, sadly weakened ifc. before the 

 end of the season. 



Of American oaks the foUowing species were affected: Quercus lyrata^ 

 Q.prinuSj Q. ruhra, Q. tinctoria, Q. robusta, Q. panonica, Q. macrooarpa. 



Of foreign oaks gTOwing upon the grounds the following had been 

 attacked: Quercus cerris, of Southern Europe; Q. rohur, of Great Brit- 

 ain; Q. pyrenaica, from the Pyrenees; Q. aegilops^ from the Levant; 

 Q. sideroxylon, of Mexico ; Q. daimio, of -Japan ; Q. sp. from Japan. 



The character of the mine varied more or less with the variations in 

 size, pubescence, and thickness of the epidermis of the leaf. A leaf of 

 Q. lyrata^ for instance, when extensively mined, presents an entiiely 

 different appearance from a leaf of Q.prinm. Chambers states in gen- 

 eral that the mine of L. hamadryadella is a "whitish blotch on the up- 

 per side of the leaf." Upon different species of oak, however, the color 

 of the blister-like blotch caused by the mine varies from whitish through 

 yellow to dark brown. 



The upper epidermis of the leaf being removed and the bottom of the 

 mine exposed to view, it is seen in every case to be curiously spotted with 

 the excrement of the larva, as is well shown in the plate. The leaf 

 therein represented is no worse affected than the average one upon 

 many trees. Upon the under side of the leaves the evidence of the 

 extensive mining upon the upper surface is usually very slight, and the 

 most careful examination reveals only a slight discoloration. 



Upo^i examining the edge of the mine with the microscope, usually 

 one or more extremely minute eggs will be found, either empty or un- 

 hatchcd. These eggs average .112'"™ in diameter (.004 inch), and are 

 almost spherical in shape. They are tinged with brown before hatch- 

 ing, but after hatching are transparent. No markings are discernible. 



The young hirvae present a most curious appearance, as shown in 

 figure hoi the plate. They are nearly flat, with the first thoracic segment 

 much larger than any of the others, the hind body tapering gradually to 

 the end. The head is small also in comparison \dth the size of the first 

 segment. As the larvae increase in size they still retain their flat form 

 and as they approach full growth and have but one more molt to undergo 

 tliey present the appearance of figure c. Upon the back of each seg- 

 pient is a shiny brownish homy i)late, and the head and last segment are 



