67 



On the 17th and 18th of Augast, two beetles hatched from the 

 worms sent me by Dr. Boardman, and, as he had surmised, proved 

 to be Diabrotica Longicornis, Say. 



Besides the knowledge of what was doing the damage, we had 

 some of its habits from the Doctor's observations ; but another letter 

 from him, under date of August '/!Oth, gives a few more items of its 

 history, together with some facts as to the extent of its ravages. 

 He says : 



"Your favor of the 17th inst. reached me this evening, and I hasten 

 to reply. The next day after sending you those specimens, I found, 

 on examining some hills of corn, that the worms were gone, or nearly 

 so, but on digging a little in the dry dirt below the hill, I found a 

 quantity of the pupa3 of Diabrotica, and on looking still further, I 

 found large numbers of D. Longicornis on the corn. It is my im- 

 pression that they are more than one-brooded, as I still find some 

 larvae not more advanced than those I sent you. I find now no 

 larvae in the fibrous roots, but in the brace roots they are still at 

 work, while the pupae among the fibrous roots (or where they were 

 before they were eaten up) have nearly all changed to the imago, 

 and are swarming everywhere. Yesterday, on sweeping the ragweed 

 (Ambrosia Trifida) with the bug net, I could sweep them off by the 

 hundreds ; in fact, they are swarming in immense numbers. There 

 is no mistake as to the correctness of your results in hatching. 



"The damage to the corn crop is much greater than I had at first 

 anticipated, and I find, on more extensive inquiry, that it is wide- 

 spread. Your article in the 'Prairie Farmer' has led a great many 

 to examine their cornfields, and they find that the injury done 

 their crops, which they had attributed to the dry weather, is due in 

 a great measure to this insect. Hon. J. H. Lewis, of Knox county, 

 informs me that there are hundreds of acres of corn in that county 

 that will not pay the rent this year, and some pieces in the circle 

 of his acquaintance are entirely destroyed. Over this county (Stark) 

 the injury will be very great. Occasionally we see a field that is unin- 

 jured, and those are on new ground or on ground that was in oats 

 last year. So far as I can learn, the most serious injury is on lands 

 that have been cultivated in corn for several years in succession. 

 Last year my crop was nearly destroyed by the Aphides [Aphis 

 Maidis), but this year I have escaped injury (from Aphis) on the 

 same ground. Some little injury has been done in some places this 

 year by the Aphides, but it is slight in comparison with the Diab- 

 rotica. 



"As to remedies, I fear that unless we can get the help of some 

 other insect to destroy them, they will prove a serious pest, in spite 

 of remedies. I think your suggestion of rotation of crops, is probably 

 at present the most effective remedy. I have noticed for the last 

 few years that they were quite abundant in the ragweed growing 

 along the roadsides, especially on the kind known as the horseweed, 

 or great ragweed {Ambrosia Trifida). This appears to be one of 

 their favorite food plants. Might we not accomplish something 

 towards their destruction by cutting down and destroying this vile 

 weed? I think it of importance that we study more closely their 

 habits, for judging from this year's work, they will prove a formid- 

 able enemy. So far as I can yet determine, they do not stay long 

 on the corn after hatching, but resort to the weeds." 



