LIFE HISTORY AND HABITS. 29 



RELATION BETWEEN INJURY IN THE BEET FIELDS AND THE SIZE AND 

 ABUNDANCE OF WIREWORMS. 



As is the case with practically every destructive insect, the greatest 

 harm is done by the maturing Lirv». It is theiefore only a matter 

 of watching the progress of injury in the beet fields to tell whether 

 or not there are many mature wireworms, and whether, therefore, 

 there will be an abundance of beetles the following year. In every 

 year during which observations have been made thus far it has been 

 a simple matter to foretell this point. In 1911 injury to the beets 

 was quite heavy and general. From this it was reasonable to sup- 

 pose that there were many mature wireworms in the soil and that 

 the next year would see an abundance of beetles. Such proved to 

 be exactly the case, and beetles were quite common in the fields; 

 so much so, in fact, that it was no extraordinary feat to collect over 

 25,000 of them for the rearing work. In 1912, in the \dcimty of 

 Compton, the wireworm injury, while quite general, was light, and 

 using the same reasoning it was probalde that there would be few 

 beetles in the spring of 1913. This has been partially proven by the 

 fact that very few ot the larva^ taken in the fields during 1912 pupated 

 the same fall. The 300 wireworms collected in the summer of 1911 

 produced almost as many i)iipie in the fall of that year as the 12,000 

 wireworms collected in the summer of 1912 })roduced during the 

 succeeding fall. 



MOLTING OF THE WIREWORMS. 



The wdreworms molt in their channels, and wriggUng from their 

 old skin (PI. Ill) they lie still for some time until their new skin has 

 hardened. If the channel is larger in cross section at the place 

 where the wireworms molt, it is so Uttle larger as to be ahiiost unno- 

 ticed. When ready to molt the larvse he still for some time, in cer- 

 tain cases for several days, before the skin s})hts and they are able 

 to free themselves. In a majority of the cast skins noted the skin 

 had spht down the dorsum of the thorax. Where this occurs the 

 process of molting is simple and seldom takes more than two or 

 three hours. The cast skin is also in one piece. Now and then the 

 skin splits irregularly, and in these cases the molting process requires 

 more time, sometimes several days. In one case noted the wireworm 

 shed the skin from its head a full week after it had molted on its 

 thorax and abdomen. In such cases the skin is quite apt to be torn 

 into several pieces and is almost useless for study. 



Directly after molting the wireworm, with the exception of its 

 mandibles, is a rather sliiny opaque white. The mandibles are yel- 

 lowish, shading to brown at the tips. The \\TLreworms color quite well 

 in from one to three days, but they often remain quiescent for weeks 



