FLAT-HEADED BORERS AFFECTING FOREST TREES. 3 



in the adult stage before emerging. Feeding begins soon after emer- 

 gence, and mating, egg-laying, and death soon follow, the whole 

 being completed before the end of summer. 



SPECIAL HABITS. 



So far as known to the writer only two of our genera (Agrilus and 

 Eupristocerus) cause the formation of galls (PL VIII, figs. 3, 6) on 

 the host plant, and in these cases it seems to be more the special 

 nature of the plant to produce the galls than it is the special work 

 of the insect that causes them to be produced. Thus, the same 

 species of inse'ct will produce galls on some plants and not on others, 

 or on one part of a plant and not on other parts of the same plant. 

 A common western form, Agrilus, that infests the alder often pro- 

 duces galls in eastern Oregon, while it seldom does so in eastern Cali- 

 fornia. The common Agrilus bilineatus Web. of the Eastern States 

 hardly ever produces galls, but it will do so sometimes when it works 

 on the smaller branches of the oak. 



Besides the enlarged roughened galls, some species cause "splotch" 

 mines to form in the bark of young shoots or branches. 



Clirysopliana placida Lee. usually works in the heartwood of dead 

 branches, tops, fire scars, etc., but recently Mr. P. D. Sergent found 

 it mining the cones of the knobcone pine (Pinus attenuata) in southern 

 Oregon (PL VIII, fig. 5) . 



In pupating, it seems to be the most natural habit for the bark- 

 borers to pupate in the bark, and most of them will do so if the bark 

 is thick, but where it is thin they will go into the outer wood. The 

 natural habit of the wood-borers is to pupate in the wood, but some 

 will pupate in the bark. 



Although the usual food of the adults is the foliage of the host plant 

 (PL VIII, fig. 4), some are pollen feeders, and, as has been determined 

 recently by Mr. F. C. Craighead, some will feed on the spores of fungi. 

 In this instance the adult Agrilus bilineatus is of some benefit in de- 

 stroying the spores of the destructive chestnut blight fungus. Mr. 

 L. E. Ricksecker mentions (Entomologica Americana, 1885) having 

 seen adult Melanopliila consputa Lee. devouring scorched white ants 

 (termites) on an old spruce log. 



SPECIAL STRUCTURAL CHARACTERS. 



The larvse of the genus Agrilus (PL VI, fig. 2) and of the genus 

 Eupristocerus (PL VI, fig. 1) bear on the thirteenth or last segment a 

 pair of strong, heavily chitinized, toothed forks or forceps. These 

 are absolutely distinct from any structure possessed by any other 

 member of the family. Polycesta larvae have a pair of sunken brown- 

 ish spots on the head, one on each side of the jaws, a pair on the 

 postero-dorsal surface of the third segment, and a pair on the antero- 

 ventral surface of the fourth segment. The function of these spots 



