262 



MISSOURI AGRICULTURAL REPORT. 



Where one rotates corn with grain or grass or other crops except sor- 

 ghum and broom corn, these insects are held in check because of the 

 fact that the larvae will not, so far as known, feed upon any other plant 

 than corn. Hence when one finds the corn fields infested with these in- 

 sects, all that is necessary to do in order to rid the field of their presence 

 is to put the field in some other crop for a year or two and use another 

 field for the production of corn in the meantime. This simple rotation 

 of the corn crop every two or three years is all that is necessary to 

 keep these insects within reasonable numbers. 



THE SOUTHERN CORN ROOT-WORM. 

 Diabrotica 12-punctala, Oliv. 



In the southern, especially the southeastern portion of Missouri, 

 the roots of the corn plant are more liable to be attacked by a corn root- 

 worm known as the southern corn root- 

 worm. This insect in the adult condition 

 is a small beetle, shown in figure 22, enlarged 

 five and two-thirds diameters. It is frequent- 

 ly spoken of as the squash and cucumber 

 beetle, and, in fact, is found upon these plants 

 frequently in connection with the true squash 

 and cucumber beetles, and is known to feed 

 more or less upon these plants, as well as 

 upon the fruit, into which it occasionally 

 mines a short distance. These beetles lay 

 their eggs in corn fields and the larvae 

 mine through the larger roots to the crown, 

 and also here and there through the crown 

 or even the base of the stalk, differing in this 

 ^^S '«^.1-oS''"i2'^°pT«5a?.': respect in their habits from the northern 

 fwo-Vhi?ds' d^kmeS;r' '''' ^"'^ corn root-worm, which is more commonly 

 distributed over tlic larger part of Missouri. The complete life history 

 of this beetle has never been worked up. The insects arc more trouble- 

 some south of Missou- 

 ri, and are not found 

 in the northern half of 

 our State. 



The effect of the 

 presence of these in- 



Fig. 23. — Southern 

 five diameters. 



Corn Root-Worm, Larva ; enlarged 



sects in the corn field 

 is similar to that of the northern corn root-worm. However, we have 



