THE MEXICAN BEAN BEETLE 19 



A temperature of 27° produced a fair number of larvae in moist surround- 

 ings but none in dry conditions with constant environments. Good hatches 

 were obtained in vari«d conditions with 22°, but not with 32°. 



A temperature of 22° produced good hatches in moist environments and 

 with temperature combinations below 32°. 



A temperature of 17° was favorable to good hatching of the eggs with 

 humidity above 45 per cent and with temperature combinations below 32°. 



Experiments with Larvae and Pupae. 



Constant En-eironments. A high temperature of 37° was as disastrous for 

 the larvae as for the egg and adult stages of the bean beetle, regardless of 

 the humidity used (Table V, 37°). It is evident that the temperature is the 

 limiting factor. 



The effect of moisture on the larvae was brought out very clearly in the 32° 

 series (Table V, 32° Moisture Constant). The results of two lots of experi- 

 ments are listed in the table. The larvae in the first lot were fed at 8 a.m., 

 4 p. m., and 10 p. m., but the leaf petioles were not placed in water to keep 

 the leaves fresh. A low humidity of 32 per cent was sufficiently favorable to 

 enable half of the larvae to complete development. When the humidity was 

 increased to 92 per cent, a few of the larvae reached the pupal stage but 

 faUed to transform into adults. In the earlier series where the food was not 

 kept fresh, the same tendencies can be seen, as a few larvae were able to 

 reach the pupal stage in 40 per cent humidity but none completed the feeding 

 stage in the higher humidities. Undoubtedly starvation was an important 

 factor in the earlier series. This is indicated by the lengthened feeding period 

 that was required. Alternation of the larvae between dry and wet condi- 

 tions gave slightly more favorable results than high humidity alone as a few 

 of the larvae developed to the pupal stage (Table V, 32° Moisture Varied). 

 The pupae in the high humidity were about one-half below normal in size. 

 The adults that emerged in these conditions were undersized, and all of them 

 were crippled. Some of the individuals had distorted wings or elytra, or 

 both, while about 50 per cent had disfigured abdomens. The shrunken condi- 

 tion of the abdomens was noticeable with some individuals while still in the 

 pupal stage. Much of the distortion was great enough to prevent mating and 

 reproduction. Probably the moisture problem for the larvae is to eliminate 

 moisture, since they take in large quantities of water with their food. This 

 elimination would occur through excretion, respiration, and evaporation 

 through the body wall. Excretion and respiration are probaMy the important 

 means of water elimination. Loss of water through respiration would be 

 greatly reduced in high humidity environments, and the process possibly 

 might be refversed. This may be the explanation for the deaths of the larvae 

 in high humidity conditions at 32°. 



At 27° the larvae developed well, and the majority completed growth as 

 long as the food was kept fresh (Table V, 27°). The data from three differ- 

 ent series of experiments are shown in the table. The larvae in the first series 

 were fed at 8 a.m. and 8 p.m. during the first part of the experiment, and 

 at 8 a.m., 4 p.m., and 10 p.m. during the latter part of the experiment, but 

 the food became rather dry at times. Fresh food was given to the second 

 series at 8 a. m., 4 p. m., and 10 p. m., but the frequent feedings were not 

 sufficient to keep the food fresh in the drier environments. Ninety-three per 



