189 



a field in SalirK; county, an assistani, Mr. K. I>. r'orhes, lonnd .Inly 29, 

 IS!)!), an avcra^f; of .seven or ei<:;lii hei^iles (jatinji; t}i(; I'nisli silk at the 

 tip o(" each younj^ ear. "'i'fie beetle," iie says, "makes its way as fast 

 as j)ossibl(! into Hk; closely coni|)resse(l silk, which it then feeds upon. 

 As tJK! threads are cut off they diy up iuid fall to the ji;round in hi'ovvn 

 lociks, the tij) of the ear b((ing loft d(;nuded." 



It lias been suj)|)os(!d that this injury must result in the bhisliiiff of 

 th(! (;ar throu^ijh fjulurc; of fertili/>;i,tion, but this coiuilusion is rc^ndcrcd 

 doubtful both by observations 

 made in tlu; field and by 

 known facts concernirif^ t})e 

 growtfi of the corn silk. We 

 have noticed, for (!xamf)le, that 

 tli(! be(;tles usually })(!gin thcii- 

 injury at the c(!nter of the 

 tuft of silk, first cutting off the; 

 inner filaments, which fertilize 

 the smaller and poorer kerruils 

 at the tip of the ear. Again, 

 in fields of fairly early corn, 

 v(!ry many of the (!ars are 

 fully IVirtilized bcsfore the beetles 

 appear in any considerable 

 inimbers, and these ears an; 

 of course not injured in the 

 least })y the loss of their silks. 

 It is further well known that the 



corn silk grows indefinitely until it is eflV'ctively act(;d upon by th(; pollen, 

 and that its growth thereupon ceases. It is consequently quite possible, 

 as suggested to me by Professor P. O. Ifolden, that the silks will continue 

 to grow after mutilati(jn, pr<;s(!nting a fresh effective; surface to the j^ollen 

 grains, and that unless cf)ntinuously eaten away until the power of 

 growth is exfiaustecJ, no final injury to tlie (!ar may be done, (.'oriifjara- 

 tiv(! observations, backed by experiment, will be needed to show whether 

 an injury of any economic consequence is done by the various insects 

 which eat tlu; fresli corn-silk, or by those which kill it by sucking its sap. 



Diahrotica alripennis is the last of the four Illinois Sfx^cies here 

 njferred to. It is a black beetle with reddish or black thorax. The 

 larval liabits are unknown. The adult was seen by Webster eating corn 

 pollen and corn silk before fertilization had taken place. It usually feeds 

 on the pollen of Compositce and has been taken on Siiphiurn. Chittenden 

 found the adults d(;vouring Ijlossoms of Lima beans in Maryland. 



Fl<;. 180. Tho Noitlieni Com Root-worm, Din- 

 lirolica lonificorniH, adult. J^ength aboiit oik; liftli 

 inch. 



