26 MASS. EXPERIMENT STATION BULLETIN 261 



vironnients. The increased n.etabolisin occurring at temperatures above 17° 

 was probably sufficient to oxidize the pigment. 



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

 ture on the larvae are shown graphically in Figures 4 and 5, which were con- 

 structed from the data in Tables V and VI. The length of the developmental 

 periods was plotted in Figure 4 and the percentage of larvae reaching ma- 

 turity in Figure 5. 



The length of the developmental periods shows rather wide variations in 

 environments that are very much alike. When development was completed 

 at high temperatures, th^ time needed to reach maturity was favorable to 

 the species. On the low temperature side the developmental period was great- 

 ly lengthened, indicating that a temperature below 20° would be rather un- 

 favorable to the bean beetle. The average period was somewhat shorter 

 when the humidity was high, but it is impossible to determine the limits of a 

 suitable moisture range for length of developmental period from the data at 

 hand. When the percentage of larvae reaching maturity is considered (fig. 

 5), the upper temperature limit of Zone I was one to two degrees below that 

 in Figure 4, while the lower limit was still lower in comparison. The mois- 

 ture limits are not indicated in Figure 4, but for the percentage of larvae 

 reaching maturity (fig. 5) the lower limit was near 3.5 per cent. The mois- 

 ture range, then, for favorable larval development lies between 3-5 and 9.5 

 per cent. 



It is quite evident that neither the length of the developmental period nor 

 the percentage maturing can be used as a criterion for determining the de- 

 gree of favorableness for larval development necessary for the insect to main- 

 tain itself in economic nun.bers. Therefore a combination of Zones I of the 

 two figures must be used. A high percentage of the larvae must complete 

 development in a reasonably short time for the insect to maintain itself in 

 abundance. Thus if a line is drawn from A to B (the lower Hmit of Zone I 

 in Figure 4) in Figure 5, the resulting area of Zone I above this line would 

 probaibly represent the con binations of temperature and moisture in which 

 the bean beetle would beccn e injurious in so far as larval development is 

 concerned. 



Summary. A temperature of 37° was very destructive to the larvae in all 

 humidities used. 



Half of the larvae con.pleted development at a temperature of 32° when 

 the humidity was low, while all of them succumbed in high moisture environ- 

 ments. The adults from larvae reared in these conditions were badly dis- 

 torted. All of the larvae died in varied humidity at this temperature. The 

 death rates were much reduced when the temperature was alternated, but 

 most of the resulting adults were monstrosities. 



A temperature of 27° was favorable for larval development with high hu- 

 midity, while the death rate was very high in dry environments. Alternated 

 environments with 32° were unfavorable. 



A temperature of 22° was very favorable for larval development in all mois- 

 ture conditions used. The number pupating was much reduced with 32° in 

 the alternating teniperature experiments. 



A temperature of 17° was favorable for the larvae completing development, 

 but growth was very slow. High percentages of the larvae matured in alter- 

 nating conditions but the tin'.e necessary was greatly increased. 



