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 
eebea BOA 
OVERWINTEFRED 
BLEEILES. 
_a 
+IRST, GENERA TION omen IIS 
EE. = SMEG 7/ON 
BEETLES 
SECOND GENEFAT/ONV 
{ LAALZE 
SECOND GENEFATIO, 
BEETLES 
THIPD GENERAT/ION 
LARIE 
TH/FD GENERAT/ION 
BEETLES 
FOURTH GENEFAT/O 
LAR KE 
FOURTH GENERATION 
SLETILES 
BEETLES /NM HIBERNATION a8 = 
ACTIVE PER/IOD --ZEETLES ae 9) 
ACTIVE PERIOD --LARVE ae x 
Fic. 7.—Life history of the Mexican bean beetle in an open-air insectary 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 larvee, 
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 larve 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. 
