﻿26 



BULLETIN 13&3, U. S. DEPARTMENT OF AGEICULTUEE 



LENGTH OP LARVAL STAGE 



The length of the larval stage is influenced chiefly by temperature 

 and moisture. With a good food supply of normal moisture content 

 the larval stage during summer months was found to last from 19 to 

 34 days. Individual larvse showed considerable difference in the 

 length of the developmental period; thus two larvae completed their 

 development during summer in 19 and 34 days, respectively, when 

 the mean temperatures ranged from a maximum of 93° F. to a mini- 

 mum of 70° F. The longest larval development recorded by the 

 writers is 59 days, when the mean temperatures varied from 77° to 

 49° F. The development of 44 larvae is recorded in Table 5, In 

 Russia Strachov-Koltchin (65) found that the period for larval devel- 

 opment varied from 21 3^ to 84 days, according to the temperature. 



NUMBER AND DURATION OF LARVAL INSTARS 



The larva of the granary 

 weevil molts three times at 

 more or less regular inter- 

 vals. The first three in- 

 stars are usually about 

 equal in length; the fourth 

 is somewhat longer. Dur- 

 ing summer weather the 

 first three instars are of 

 from 4 to 5 da3"s' duration 

 and the fourth lasts from 6 

 to 19 days. The duration 

 of the larval instars with the 

 mean temperature for the 

 period is given in Table 5. 

 These data indicate that 

 the first larval instar was 

 from 4 to 12 days in length 

 when the temperature 

 means .were from 84° to 

 61° F.; the second instar 

 from 4 to 14 days in length 

 when the means varied 

 from 84° to 59° F.; the third instar from 4 to 17 days in length when 

 the mean temperatures for the period varied from 84° to 59° F. ; the 

 fourth larval stage from 6 to 24 days when the temperature means 

 varied from 84° to 59° F. 





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Fig. 9.— Chickpeas sectioned to reveal honeycombing of 

 interior of seed by feeding of larvae and adults of the 

 granary weevil 



THE PUPA 



After attaining its growth the larva prepares a pupal cell at the 

 end of its burrow, using a mixture of frass, borings, and larval secre- 

 tions to waU in the open end of its bmTow. If the cell is accidentally 

 broken open before the larva has transformed, the break is repaired. 

 After the cell is completed, the larva assumes a prepupal form that 

 normally lasts for one day in summer or two days in colder weather 

 before it transforms to the pupal stage. Data regarding the length of 

 the pupal stage are given in Table 6. 



