20 .MASS. EXPERIMENT STATION BULLETIN 375 



generation larvae have been able to devour all available mealybugs. In 

 each case observed, a few mealybugs have been protected by soil, mulch, 

 or parts of the plants where the Cryptolaemus larvae did not find them 

 and, therefore, eradication was not complete. 



The average life cycle of the beetle in favorable conditions is 40 days 

 (p. 5) and the incubation of eggs of the second generation will require 

 about 8 days. Thus, the larvae of the second generation will start to feed 

 on the mealybugs about 48 days after the original beetles are introduced. 



The activity of the second generation larvae of Cryptolaemus is more 

 uniform and can be estimated from the calculations in Table 11. At 70' 

 F. there are 269 eggs in a mealybug egg mass. The Cryptolaemus larva 

 eats an average of 27.21 eggs per day. Therefore, each larva will eat all 

 the eggs in a mealybug egg mass in 9.89 days. At 80° F., 10.89 days will 

 be required, by similar calculations. During its life, the larva eats an 

 average of 1338.8 eggs which is equivalent to the number of eggs in 4.94 

 mealybug egg masses. 



The calculated number of second generation larvae which will develop 

 from each pair of beetles of the first generation is 39.9. Thus, each of 

 about 40 larvae will be eating all the eggs in a mealybug egg mass in 9.89 

 days, and each larva will eat 4.94 mealybug egg masses during its life. 

 In other words, under normal conditions of reproduction and development, 

 each pair of Cryptolaemus beetles which become established in the first 

 generation after liberation will produce a sufficient number of larvae to 

 destroy about 200 mealybug egg masses during their life. 



Actually, the older larvae eat all stages of the mealybug instead of the 

 eggs only, thus influencing the number of eggs eaten and the length of the 

 feeding period of larva. At the same time, many larvae are killed by 

 accidents and by cannibalism so that the increase in population is less 

 than the theoretical number. It should also be noted in Table 11 that 

 the average length of life cycle of Cryptolaemus at 70° F. is about equal 

 to that of the mealybug, but at 80° F. the life cycle of the beetle is 16.6 

 days shorter. Thus, at the higher temperatures, the activity of the pred- 

 ator is stimulated to a much greater extent than that of the mealybug. 



Table 11. Theoretic.xl Control of Mealybugs bv Cryptolaemus. 



At so° V. At 70° F. 



Average luiniber of mealybug eggs per oKg mass* ::i.">l.l> 



Average length of life cycle of mealybug in days* 7.3 



Average length of life cycle of Cryptolaemus in days 5(!.3 



Average number of mealybug eggs eaten by Cryptolaemus larva di i- 



ing feeding period 1 8'2i.'J 



Average nundier of mealybug oggs eaten l)y Cryptohicinns lar\a per 



day 8 li. 1 4 



Number of days required for the average Cryptolaemus larva to eat 



eggs in average mealybug egg mass 10. si) 



Number of mealybug egg masses eaten by the average Cryptolaemus 



larva during feeding period ;l7 7 



Average number of eggs laid by Cryptolaemus lieetles 122.9 



Percent of larvae hatched from total eggs laid 40.2'J 



Number of larvae hatched in succeeding generation 49.5 



*1935 records only; all others are the average of 1935 and 193', 



