12 



BULLETIN 1243, U. S. DEPARTMENT OF AGRICULTURE. 



during 1922 by L. W. Brannon. During 1922 many egg masses ob- 

 tained were not reared. All the original beetles were taken from 

 hibernation. Cages were placed in the field as well as in the insec- 

 tary, and identical results were obtained. 



These charts show overlapping of generations, due to the pro- 

 longed life of the adults, especially the overwintering generation. 

 They also show that while the insect can and does produce a maxi- 

 mum of four generations, a minimum of two is required to maintain 

 the species except in rare instances. Two generations and a partial 

 third are the rule. 



All stages of the insect occur in the field from late April or early 

 May until late October or early November about Birmingham, Ala. 

 At Thomasville ? Ga., all stages have been observed in the field from 

 April until late November or even December. A maximum of four 



L/FE CVCLE 



O^ERtV/NT£TRED 

 BEErLES 



F/RST GENERAT/ON 

 LARVAL 



F/RST GENERATION 

 BEETLES 



SECOND GENERAT/ON 

 LAR14C 



SECOND GENERATION 

 BEETLES 



TH/RO GENERAT/ON 

 LARI/AZ 



TH/RD GENERAT/ON 

 BEETLES 



FOISRTR GENERAT/ON 

 LARVsE 



FOUNT// GENERAT/ON 

 BE£:rLES 



BEErLES /N ///BERA/AT/OA/ ■ ■ 



SICT/l/E FER/O0 BEETLBS 4£& 



y^GT/KE R'ER'/<OL?—LARI^£- <^> 



Fig. 7. — Life history of the Mexican bean beetle in an open-air inseetary and field cages at Birmingham, 

 Ala., during 1922. Based on 1,590 egg-to-adult rearings. 



generations occurred there, although the duration of bean plantings 

 would permit a maximum of six generations. Two generations and 

 a partial third are the rule, as in northern Alabama. 



In the field the severest damage is done by the first and second 

 generations. 



Figure 8 represents the seasonal life history. This chart was 

 prepared from the life-history studies and records of infestation made 

 in field control experiments during 1921 and 1922. The width of the 

 bands indicates the relative abundance of the beetles and larvss, 

 calculated from injury to beans. The early records of 1921 are 

 probably unusual, and the heavy late infestations of that year were 

 not repeated in 1922. The heaviest infestation occurs in July and 

 early August, when the greatest number of larvae are present. In 

 1921 the period of heavy infestation extended over a period of about 

 three months from late June to the middle of September, but in 1922 

 this period was of shorter duration — from late June to early August. 



