16 MASS. EXPERIMENT STATION BULLETIN 261 



of eggs hatching in the control cabinet was probably abnormally low as can 

 be seen by comparison with the results in Table III. The length of the in- 

 cubation period was approximately a day and a half below that at 32°. The 

 number of days required for development was slightly less than the calculated 

 figures. 



When temperatures were alternated about 22°, good hatches were secured 

 with 27° and 17° (Table IV, 22°). The poorest hatches were obtained in 

 the 32° combinations where the unfavorable effects of the high temperature, 

 previously discussed, were not fully overcome by eight or sixteen hours' ex- 

 posure at 22°. The percentage of eggs hatching in low humidity conditions 

 was much less than in high humidity environments, especially when the mois- 

 ture content of the cabinet was below 4.5 per cent. The stimulatory effect 

 produced by varying the conditions is shown in the table. • 



The data secured from varied conditions about 17° with low humidity are 

 not as extensive as with 22° (Table IV, 17°). All of the eggs failed to hatch 

 when exposed to 32° for eight or sixteen hours. When alternated with 22°, 

 the percentage of eggs hatching was low in the drier environment, while the 

 combination with humidity above 45 per cent gave much better results. 



Constant and Varied Environments. The effects of temperature and mois- 

 ture on the eggs can he illustrated further by plotting the data in Tables III 

 and IV (figs. 2 and 3). The percentage of eggs hatching is given in Figure 

 2, and the length of the incubation jjeriod in Figure 3. The two figures are 

 discussed together. 



Three general zones are rather sharply defined, although more data are 

 needed in the low humidity region between 22° and 17°. Under field condi- 

 tions the region that falls below 17° is automatically taken care of by the 

 negligible num)ber of eggs laid below this temperature (Tables I and II) ; but 

 from a scientific viewpoint it would be well to conduct experiments with tem- 

 peratures below 17°. A suitable, intermediate, and unfavorable zone is indi- 

 cated for the two conditions, — percentage of hatch and length of incubation 

 period. It is evident that Zones I of the two figures do not agree. Since 

 both factors are vital in the life cycle of the bean beetle, a position favorable 

 to both of the above factors must be selected. The temperature limits then 

 would fall on the upper line of Zone I of Figure 2 for high temperature, and 

 the lower line of Zone I of Figure 3 for low temperature. This gives a de- 

 cidedly small temperature range (about 6°) that is favorable for incubation 

 of the egg.s, although it nuist be remembered that lower temperatures merely 

 delay the time of hatching and do not kill the embryos. The moisture limits 

 are in much closer agreement in the two figures. The upper limit is not de- 

 terminable from the data at hand, although favorable results were obtained 

 in 93 per cent himiidity. The lower limit probably falls between 40 and 50 

 per cent humidity. Thus the incubation period is shown to be an extremely 

 vital one in the economic distribution of the bean beetle, as both high tem- 

 peratures and low humidity are very destructive. However, low temperature 

 is not necessarily detrimental unless continued for prolonged periods. The 

 physical conditions just described would need to occur among the growing 

 bean plants in the field to affect the eggs of the bean beetle. 



Summary. A temperature of 37° destroyed the embryos in botli wet and 

 dr\' environments. 



A temperature of 32° gave similar results in constant conditions, but with 

 varied temperatures a few larvae hatched in the moist environment at 22°. 



