CONTROL OF MEALYBUGS 19 



4. Susceptibility of Infested Plants, hi Keneral, gardenias and chrysan- 

 tliemums, especially when grown in large numbers, are adapted to the 

 use of Cryptolaemus for control of mealybug. Gardenias are semi-trop- 

 ical plants favoring high temperatures and the same plants are usually 

 grown for three or more years in the same beds. The bushy growth and 

 waxy leaves of this plant, resembling citrus, is a natural environment for 

 both the mealybug and the Cryptolaemus. Small pot plants such as 

 coleus, ivy, and geraniums, which are frequently infested with mealybugs, 

 are grown at lower temperatures and are not handled in a way favorable 

 to the development of Cryptolaemus. 



5. Use of Insecticides to Combat Other Pests. Naturally, the use of sprays 

 or fumigants during the development of the beneficial insect will affect 

 its activity, and should be avoided as much as possible. If plant lice, 

 thrips, or red spider become abundant, however, it may be necessary to 

 check them. In general, Cryptolaemus and other ladybird beetles can 

 withstand the common contact sprays and fumigants at concentrations 

 which control the more susceptible insect pests; and Pratt, Swain and 

 Eldred (9) showed that only 15 percent of the Cryptolaemus were killed 

 by a 10-minute exposure to a .2 percent concentration of hydrocyanic 

 acid gas. Haug and Peterson (7) showed that a very high percentage 

 of the convergent ladybird beetles were killed by phenothiazine and derris; 

 a moderate percentage by nicotine sulfate, Paris Green, and calcium 

 arsenate (under certain conditions); and an insignificant percentage by 

 Ijordeaux mixture, fluosilicate mixtures, pyrethrum, arsenate of lead, and 

 manganese. In our own experiments, the beetles survived fumigations 

 with nicotine smoke which effectively controlled aphids and they were 

 not seriously aflfected by application of lead arsenate for combating chew- 

 ing insects. Heavy syringing with water which broke the mealybug egg 

 masses where the eggs of the Cryptolaemus were laid reduced the rate 

 of reproduction of the beetles and was more harmful to the final beneficial 

 effect of the predators than most insecticidal treatnients. 



Theory of Mealybug Control of Cryptolaemus 



In this discussion, the first generation eggs, larvae and beetles refer to 

 those which developed from the original beetles liberated. The second 

 generation eggs, larvae and beetles refer to those which developed from 

 the first generation beetles. 



In practical application, it has been demonstrated that Cryptolaemus 

 larvae will control a moderate or heavy infestation of mealybugs on gar- 

 denia or chrysanthemum in about 60 days, provided conditions for their 

 development are favorable. Due to the check of packing and shipping, 

 the original beetles which are liberated normally lay a variable but usually 

 a small number of eggs so that the number of larvae of the first genera- 

 tion is not uniform and is dif^ficult to estimate. The function of the first 

 generation is to insure the establishment of the predatory insect. The 

 larvae and beetles of the first generation are normally active and feed 

 ravenously but in the greenhouses under observation, where liberations 

 were made at the rate of one beetle per plant or less, the first generation 

 has never given economic control. Hov.'ever. tlie activity of the first gen- 

 eration has held the mealybug in check so that the more abundant second 



