10 



BULLETIN 436, V. S. DEPAETMENT OF AGEICULTTJRE. 



plaster of Paris cages, consisting of 2 or 3 ounce salve boxes filled 

 with newly mixed plaster in which a cavity was bored before the 

 plaster had set. The first season that these cages were used a great 

 many larvse were reared partially but died before reaching maturity. 

 Finally efforts in this direction were rewarded and six larvae were car- 

 ried successfully through from egg to pupa (Table III) during the 

 month of June at a mean temperature of 84° F., and during this 

 time the length of the larval stage averaged from 22 to 25 days. 



Table III. — Length of larval stage of the desert corn flea-beetle {Chaetocnema ectypa) at 



Tempe, Ariz., 1915. 









Aver- 







Length 



age 



Date egg 



Date of 



of 



mean 



hatched. 



pupation 



larval 



tem- 







stage. 



pera- 

 ture. 







Days. 



°F. 



June 17 



July 9 



22 



84 



Do.... 



...do 



22 



84 



Do--.. 



...do 



22 



84 



Do... 



July 10 



23 



84 



Do.... 



July 12 



25 



84 



Do.... 



...do 



25 



84 



However, since little difficulty was experienced in securing the 

 respective lengths of the egg and pupal stages, and then the sum 

 of the lengths of the egg, larval, and pupal stages, it was possible 

 from these data to obtain the length of the larval stage by sub- 

 tracting the sum of the egg and pupal stages from the sum 

 of the three stages. Thus we had the approximate length of the 

 larval stage during practically every month in which these beetles 

 were developing. It may be seen by consulting Tables I and III that 

 this approximate length of the larval stage, under periods of the same 

 temperatures, compares favorably with the exact length of the stage 

 as noted in the case of the six larvse mentioned. By the latter method 

 the larval stage is found to vary from 20 days in the warm summer 

 months to 47 days during the cooler months of the season, an average 

 length for the larval stage of about 32 days for aU temperatures. 



FEEDING HABITS OP THE LARVA. 



Quite soon after hatching the yomig larva begins eating its way into 

 the tender succulent roots of the host plant. It thus constructs a 

 tunnel for itself as it feeds, and soon disappears from sight. Usually 

 the boring of the larva occurs in the cortex. On the roots of corn 

 (fig. 6) the tunnel will often appear to be formed between the cortex 

 and the stele or central cylinder. The reason for this attack on the 

 cortex first is doubtless because it is more tender than the rest of 

 the root. If the feeding be of prolonged duration the entire root may 

 be tunneled. Many of the roots are entirely hollowed out by these 



