18 -MASS. EXPERnrENT STATION BULLETIN i75 



twig where they were hatclied and do not migrate to adjacent infested 

 stems unless they become hungry. To permit the development of a heavy 

 mealybug infestation usually causes more damage to the plants than is 

 practical in profitable flower production, and is so contrary to good green- 

 house operation that florists do not favor it. Sucii a condition was pur- 

 posely allowed to develop in liberation No. 5, and although the final con- 

 trol of mealybug was excellent, the crop of flowers previous to control 

 was below normal and unprofitable. 



2. Number of Beetles Liberated. In these observations the heaviest libera- 

 tion was at the rate of one beetle per plant, and this number gave satis- 

 factory control of mealybugs on gardenias in about 60 days, or after the 

 second generation of larvae had developed. Theoretically, the more beetles 

 that are liberated the more quickly the infestation will be brought under 

 control. In liberation No. 5, Table 10, the infestation on large gardenia 

 plants was extremely heavy and it did not appear that liberations at the 

 rate of three or four per plant would eradicate the pest in one generation, 

 while a liberation at the rate of three for each four plants was very eflfec- 

 tive after the development of the second generation. A supply of beetles 

 equal to three or four per plant would increase the expense, apparently 

 without proportionately greater benefits, and under normal infestations 

 the liberations of beetles at the rate of one per plant seems most satisfac- 

 tory on gardenias. 



Chrysanthemums not only grow close together in the beds but are also 

 a comparatively short-time crop. A treatment that required two months 

 to produce results would probably permit too much injury by the pest 

 before the benefits took place to meet the practical requirements of the 

 florist. 



In liberation No. 3, Table 10, Cryptolaemus beetles liberated at the rate 

 of one for each two plants of chrysanthemums satisfactorily controlled a 

 heavy infestation of the Mexican mealybug by the time the second gen- 

 eration of larvae had developed. However, this did not occur until many 

 of the flowers had been cut for sale, and the results were generally unsat- 

 isfactory to the florist. If the liberation had been made two or three weeks 

 earlier, the results would have been much more profitable, and beetles 

 at the rate of one per plant rather than one for each two plants would 

 iiave prevented serious damage to the plants before actual control was 

 obtained. Tiiis observation indicated that liberations should be made not 

 less than 10 weeks before control is desired. 



3. Time of Introducing Beetles. As shown in the studies on the effect of 

 temperature, development of the Cryptolaemus beetles is not satisfactory 

 below 70° F.; therefore these beetles should not be liberated unless the 

 average temperature will be maintained at about 70° F., or higher, while 

 the beetles are developing through two generations. Greenhouse tem- 

 peratures are generally less than 70° F. during the winter and heating 

 costs would prohibit the maintenance of such temperature during the cold 

 weather. Therefore, liberation of Cryptolaemus beetles is practical only 

 from about April 1 to July 1 when the prevailing greenhouse temperature 

 will be 70°' F. or higher in the following ten weeks. These points were 

 demonstrated in the case of liberation No. 4 made on October 10, when 

 cool weather in November and December so delayed beetle activity and 

 development tliat only a 50 percent reduction in mealybug resulted. 



