THE MEXICAN BEAN BEETLE 7 



was consumed in the higher luiinidities in either series. Possibly the inability 

 of the beetles to eliminate water in the higii moisture environments was an 

 important factor in producing death. These results show that a constant 

 temperature of 32° can be very favorable to the oviposition rate and length 

 of life of the bean beetle with a low humidity, and extremely unfavorable with 

 a high humidity. When the beetles were varied between dry and wet environ- 

 ments, the number of eggs obtained was intermediate between the yields 

 obtained in the constant conditions (Table I, 32° Moisture Varied). A cal- 

 culation of the number of eggs to be expected according to the hours of 

 exposure imder regularly varied conditions of humiditj', as determined by the 

 results with constant himiidity, gives figures which agree fairly closely with 

 tlie actual number laid. Apparently the inhibitory action of 92 per cent hu- 

 midity on egg production of the beetles was not carried over to any great 

 extent into periods when the percentage of moisture was reduced to 32 

 per cent. 



A tennjcrature of 27° proved to be m,uch more favorable to heavy egg pro- 

 duction than 32° (Table I, 27° Moisture Constant). Three different series of 

 experiments are given, but all of them show the same tendencies. The first 

 series was made up of beetles of unknown ages collected in the field in 

 September. Many of these beetles had been laying previous to exposure to 

 the experimental conditions. Humidities of 60 per cent or above were favor- 

 able tc heavy oviposition, while a low humidity of 32 per cent showed a re- 

 duction of over one-half in the number of eggs deposited. A sufficient num- 

 ber of eggs was laid in the dry conditions for the bean beetle to maintain 

 itself in nimibers as far as egg production is concerned. A slight reduction 

 in the egg yield occurred in 8.5 and 93 per cent humidity. 



The varied moisture conditions gave results similar to the constant environ- 

 ments (Table I, 27° Moisture Varied). The beetles used in this series were 

 collected in September after the natural oviposition period had ended. Many^ 

 of the females had probably laid a large number of eggs previous to collec- 

 tion. A rather wide range of humidity appears to be suitable for good egg 

 production at 27°, although a reduction in oviposition occurred in both high 

 and low moisture environments. The two varied conditions in which the 

 lieetles were kept in 93 per cent humidity for sixteen hours show a markedly 

 large reduction below the expected number of eggs, which is only partially 

 accounted for by the death of a few of the beetles. This result indicates that 

 this high humidity at 27° was slightly unfavorable to egg production. 



The results secured at 22° were not as extensive as at 27°, but they are 

 very similar in so far as they are comparable. Data from two experimental 

 series are shown (Table I, 22°). One cage of beetles in the 40 per cent humid- 

 ity showed a lowered egg production indicating a possible inhibitory effect 

 in this low humidty. A similar decrease in egg production in the 90 per cent 

 humidity cabinet indicated that this high moisture environment was still un- 

 favorable, as was found with higher temperatures. 



The results secured in the 17° environment with 50 per cent humidity are 

 very important (Table I, 17°). Since this humidity is near a critical point 

 between favorable and unfavorable moisture conditions for egg production at 

 higher temperatures, care must be used in interpreting the data. It is quite 

 probable that 17° is very close to the minimum effective temperature for ovi- 

 position of the bean beetle. This conclusion becomes more certain when the 

 varied data are analyzed (Table II, 17°). The number of eggs laid appears 



