THE MEXICAN BEAN BEETLE 15 



When the eggs were incubated at 27°, entirely different results were ob- 

 tained (Table III, 27°). Larvae were secured in all moisture environments 

 from 60 to 93 per cent humidity. The failure to hatch any larvae from 1700 

 eggs incubated under the 32 per cent moisture condition emphasized the un- 

 favorable effects of a dry atmosphere at this temperature. The hatching 

 periods of the eggs in the medium to moist cabinets ranged from 5.5 to 6.0 

 days, showing a close similarity in all conditions. The number of larvae 

 hatching in the 80 and 85 per cent humidity environments was much below 

 those in the other conditions, but the 79 and 93 per cent surroundings pro- 

 duced the best hatches, thus indicating that a moisture environment of 60 per 

 cent humidity, or higher, at 27° is favorable to incubation of the eggs. The 

 unfavorable limit would fall somewhere between 32 and 60 per cent hvmiidity. 



The effects of, moisture on incubation of two dift'erent series of eggs at 22° 

 gave rather irregular results (Table III, 22°). Probably the first series — 

 40, 60 and 90 per cent — shows a much lower percentage of hatching than is 

 normal for these conditions. When this series is compared with the results 

 in Table IV (22°), which are in agreement with the second series of this 

 table, the jsrobability of an abnormally low percentage of hatching is made 

 doubly certain. A much better hatch was obtained in the cabinets with high 

 humidity. The incubation period was about one day less in the high than in 

 the low humidity chambers, but was about one and one-half days longer than 

 was required at 27°. The percentage of eggs hatching under most conditions 

 at 22° was considerably above that at 27°, indicating that the former is a 

 more favorable temperature. The alternation of eggs between wet and dry 

 environments gave results similar to those obtained under constant conditions 

 (Table III, 22° Moisture Varied). 



The influence of a temperature of 17° with 50 per cent humidity was 

 favorable to hatching of the eggs (Table III, 17°). Good hatching resulted 

 but the incubation period was nearly twice as long as at 22°. 



Varied Environments. A discussion of these environments is given under 

 this heading for the adult stage. A high temperature of 37° was excluded 

 from the varied series, as none of the eggs had hatched at that temperature 

 in the constant environments (Table III). 



The results of alternations of temperature with 32° are given in Table IV 

 (32°). Combinations of 32° with 17° and 27° failed to produce any larvae 

 regardless of the humidity used. When 22° was used, sixteen hours of ex- 

 posure at 32° killed the embryos in both high and low humidity, but when 

 the exposure was reduced to eight hours at 32°, one egg hatched in the low 

 and 21.5 per cent in the high humidity. The number of eggs hatching in both 

 cases was low, but is significant for the high moisture environment. Eggs 

 hatched in about half of the egg masses used in this moist condition. This 

 shows that a high moisture environment is preferable to dry conditions and 

 may indicate that 22° is near the optimum temperature for incubation of the 

 eggs. The incubation period of the single individual emerging in the drier 

 environment was more than twenty-four hours longer than the average for 

 those in the wetter condition. The longest incubation period in the high hu- 

 midity cabinet was eight days. 



The eggs were incubated in the varied conditions about 27° with high hu- 

 midity only (Table IV, 27°). Good hatches were obtained from the eggs in 

 the temperature coml)ination of 27° and 22°, while either eight or sixteen 

 hours at 32° was sufficient to prevent hatching of the eggs. The percentage 



