Dec. 22, 1923 
Biology of Four-Spotted Bean Weevil 
615 
ttPT 11 ^ first two-thirds of the laying period, indicated in Table 
ill, the constant increase in the length of the average developmental 
Pf™® 2* weevils from eggs laid on successive days is a good illustration 
of the effect of the approach of winter. Our understanding of heat unit 
values at different temperatures with respect to the rapidity of develop¬ 
ment of Bruchus quadrimaculatus is not equal to the task of correlating 
these progressively lengthened periods with the thermal environment by 
an analysis of the thermograph records. There are, however, certain 
points which should be briefly discussed. 
That the mortality of young larvae is higher than that of older individ¬ 
uals has been noted, and it is reasonable to suppose that they are very 
responsive to temperature changes, because they are not deeply buried 
in the seeds. In the fall, young larvae hatched on successive days are 
usually exposed to optimum temperatures for progressively shorter 
periods, and a difference of a few days of warmth at the beginning of the 
development of two groups of weevils at that season may be magnified 
to a greater difference in their developmental periods. Thus, in the case 
of the eggs deposited September 18 and 19, a difference of one day in die 
duration of the exposure of the eggs and young larvae to warm weather 
at the beginning of the period of growth resulted in a difference of four 
days m the average time required for all the weevils from these eggs to 
emerge, as shown in the last column of the table. Likewise, in the case 
of eggs deposited September 18 and 27 (the latter being the date of a 
cold storm), a difference of 9 days of warmth at the beginning of the life 
of the weevils seems to be responsible for the ultimate Hi (T erence of 29 
days m the average period required for emergence. 
Toward the end of the egg laying (October 4 to 15) the small number of 
individuals concerned probably tended to make the last few average 
developmental periods inconsistent with the constant increase of the 
preceding ones. 
The mean monthly temperatures in the laboratory during the period 
covered by the development of the brood were as follows: September (18 
to 3 °J’^ 8 : 5 ° F-; October, 61.5 0 ; November, 58°; December, 6i°; January, 
59-5 ; February, 59.5°; March, 6o°; April, 63°; May, 64°. 
Considerable variations were noted in the length of the periods re¬ 
quired for the development of individual weevils from eggs laid by the 
same female on the same day. An example illustrating this point is 
given in Table IV, which also shows one of the most nearly typical egg 
records, including the diminishing number and vitality of the eggs toward 
the end of the laying. (See also fig. 1.) The results of the oviposition 
ot all the females, similarly worked out, are abstracted in Table II. 
Data used to prepare figure 1 show that there was a greater percentage 
of hatching of eggs laid early in the life of a female than toward the end, 
and an even more marked preponderance of the earlier eggs produced 
adults. Figure 1 applies to all the eggs of all the females, consolidated 
on the basis of the individual reproductive life. That is, the first day’s 
eggs of all the 61 females are consolidated under “laying day” 1, etc. 
Only three females extended their oviposition over 15 laying days! 
Dates, as well as days on which individuals laid no eggs, are not consid¬ 
ered, the 61 egg records of the series being in effect telescoped so that 
.j'eginmngs are coincidental. The tendency toward heavy oviposi- 
tion durmg the first few laying days and the decreasing number and 
fertility of the eggs as the females approached death are shown. The 
higher degree of vitality which characterizes the earlier eggs of an indi- 
