8 MASS. EXPERIMENT STATION BULLETIN 375 



period of the eggs is about five days; but from 3 to 15 percent more of 

 the eggs hatched at 70° F., and this would indicate somewhat unfavorable 

 conditions for the eggs at 80° F. although the higher temperature cor- 

 responds very closely to the conditions reported in California (4). On 

 the plants, however, unhatched eggs were seldom observed and it is 

 doubtful if the mortality under natural conditions is as high as shown in 

 these experiments. At 60° F. the incubation period was two to three 

 weeks, and considering the high mortality it is apparent that this tem- 

 perature is too low for satisfactory activity or development. 



Length of Feeding Period of Larva 



According to Smith and Armitage (16) the larval feeding period in their 

 laboratories, where the temperature was approximately 80° F., lasted from 

 12 to 20 days. In preliminary experiments at Waltham in 1933, on potted 

 coleus plants heavily infested with the citrus mealybug, four larvae were 

 raised in 13 to 21 days, averaging 18 days, at 80° F. In this same experi- 

 ment, one larva at 60° F. lived more than 60 days without pupating, indi- 

 cating that development at this temperature is uncertain, if possible at all. 



In experiments in 1935 and 1937, in w^hich the larvae were fed only a 

 known number of eggs of the citrus mealybug, the larval feeding period 

 averaged 44 to 55 days at 70° F., and 32 to 53 days at 80° F. (Table 5). 

 These studies were made primarily to determine the rate of feeding on 

 mealj^bug eggs and the number of eggs necessary to bring the Cryp- 

 tolaemus larvae to maturity. During the observations a number of eggs, 

 equal to or greater tlian tlie number eaten the previous day, was supplied 

 daily, but it is apparent either that the amount of food supplied by the 

 eggs was not sufficient at critical periods of growth or that mealybug eggs 

 alone do not supply all of tlie food elements necessary for optimum 

 growth of Cryptolaemus larvae. These records also indicate that although 

 the optimum feeding period of the larvae is 18 to 20 days, this period can 

 be extended to 60 to 65 days when the larvae are feeding on mealybug- 

 eggs alone without affecting normal larval development. 



In greenhouses where Cryptolaemus have been liberated, the larvae 

 fed actively for 25 to 30 days under normal conditions existing in April 

 and May when the average day temperature is 70° to 80° F. 



Length of Pupation Period 



Table 3. Length of Pupation Period of Cryptolaemus Moxtrouzieri at 

 Constant Temperatures. Waltham, Mass., 1933. 



