50 MASS. EXPERIMENT STATION BULLETIN 315 



branches and trunk of the trees and spun cocoons under the bark and in crotches 

 rather than dropping to the ground. This migration down the tree took place 

 mostly during rain, partly because the rain softened the rolls and facilitated 

 emergence and partly because they were not exposed to hot sun and dry wind 

 at that time. After the maggots have become mature, their emergence is greatly 

 influenced by rain. Only a small number of the maggots appear to transform into 

 the succeeding generation, and the majority hibernate. 



Practically all infested leaves dried and fell before August 10. 



Cyanogas and naphthalene applied under the trees as soil insecticides reduced 

 the number of adult midges collected in cloth cages from 11.5 to an average of 

 1.83 per square foot, but in spite of this reduction, migration and emergence from 

 cocoons on the tree produced a heavy infestation on the treated trees. 



Sprays containing sulfur, nicotine, and rotenone killed exposed eggs and newly 

 hatched maggots in the laboratory but when applied to infested potted apple 

 trees the results were disappointing. 



Plum Curculio. (W. D. Whitcomb, Waltham.) The practical application of the 

 relation of temperature to control of the plum curculio by spraying was attempted 

 by spraying one row of heavily infested trees with lead arsenate and fish oil each 

 second day for twelve days beginning May 22, four days after the calyx applica- 

 tion. Based on the maximum daily temperature, the most timely sprays would 

 have been applied May 27 to 29. The results showed that, except in one row which 

 yielded only 81 apples, the amount of curculio-injured fruit decreased regularly 

 from 48.92 percent on May 22 which was too early, to a minimum of 18 percent 

 on May 28 which was the estimated most effective date, and again increased to 

 44.66 percent on June 1 which was too late for satisfactory protection. 



Adaptability of Cryptolaemus to the Control of Mealybugs in the Greenhouse " 



(W. D. Whitcomb, Waltham.) After having practically eliminated a heavy in- 

 festation of the citrus mealybug in the greenhouse of the Waltham Field Station 

 soon after being introduced, the colony of the mealybug predator, Cryptolaemus 

 montrouzieri Muls., nearly died of starvation; but the few survivors developed in 

 sufficient numbers to keep the pest under commercial control without the aid of 

 insecticides for eighteen months, and they are now in a position to accomplish 

 practical control of the mealybug whenever the pest should increase. 



Introductions of this predatory insect were supervised in two commercial 

 greenhouses, one growing gardenias infested by the citrus mealybug, Pseudococcus 

 citri Risso, and the other growing chrysanthemums infested with the Mexican 

 mealybug, Phenacoccus gossypii T. & Ckll. In both cases control almost to the 

 point of eradication resulted when a second generation of the ladybird larvae 

 developed. In each case, however, the mealybug developed so rapidly during the 

 inactive and developmental periods of the ladybird beetles that considerable 

 injury resulted to the plants or the use of insecticides was necessary before the 

 predators controlled the pest. 



These records show definitely that both P. citri and P. gossypii can be practi- 

 cally and economically controlled by Cryptolaemus montrouzieri when the beetles 

 are properly manipulated, and that the successful establishment of these beetles 

 is dependent on, (1) the comparative rate of reproduction of the pest and the 

 predator, (2) the abundance of the pest at the time of introduction, (3) the num- 

 ber of predators introduced, (4) the season when the predators are introduced 

 as it affects the relation of temperature to development, and (5) the type of plants 

 infested by the mealybugs. 



