50 MASS. EXPERIMENT STATION BULLETIN 249 



from insect pests including the plum curculio by intelligent dusting, but in 

 these orchards this pest has never become thoroughly established. ' 



In 1927 a severely infested orchard was dusted experimentally with a 

 standard orchard dust applied with hand dui?ters of the knapsack type. Three 

 applications at opportune times yielded only 18 per cent clean fruit at har- 

 vest, but this was a gain of 10.8 per cent over the untreated plat and there 

 were about one-third less punctures per apple. Dust applications should be 

 made at the times recommended for spraying, with an additional applica- 

 tion midway between the 7-day and 3-weeks treatments whenever possible. 

 The dust must be thoroughly applied from at least two sides of the tree, 

 preferably in calm weather when it will settle slowly. Dusts containing 

 15 or 20 per cent lead arsenate are more effective than those containing less 

 poison. 



SUMMARY. 



The plum curculio, a native of North America, is found throughout eas- 

 tern and central United States and at present is the most injurious insect pest 

 of apples in Massachusetts. 



Plums are preferred as food but only slightly more than apples, and all 

 stone and pomaceous fruits may be attacked. 



Of the apple varieties, Duchess, Yellow Transparent and Gravenstein, 

 which blossom early or develop rapidly after the petals fall, are more severe- 

 ly injured in the spring than late-developing sorts such as Northern Spy 

 and Mcintosh. 



Beetles damage the fruit by making egg punctures, early feeding punc- 

 tures and late feeding punctures in it, and the larvae tunnel through it. An 

 egg puncture is distinguished by a characteristic crescent-shaped cut which 

 develops into a fan-shaped russet scar. An early feeding puncture is round 

 and usually forms a circular russet scar. Larvae eat the flesh of the apple, 

 especially near the core, and cause the fruit to fall while small. The spheri- 

 cal cavities of late feeding punctures in mellow or nearly mature fruit do not 

 heal, and are generally followed by decay. 



The plum curculio passes through four stages of development: egg, larva 

 or grub, pupa, and adult or beetle. Each female beetle lays about 175 eggs 

 from which the larvae hatch in about seven days. Young larvae burrow out 

 of sight in the fruit about two hours after hatching, and remain there approxi- 

 mately sixteen days. Pupal cells are made three inches or less beneath the 

 surface of the soil, and the insect remains in them about thirty days as larva, 

 pupa, and adult. About fifty-five days are necessary for the plum curculio 

 to develop from egg to adult. The beetles live approximately a year, from 

 August to August, and there is but one generation annually in Massachu- 

 setts. 



In confinement the beetles made an average of 236 feeding punctures per 

 pair, and feeding punctures constituted from 64 to 83 per cent of the total 

 number of punctures. 



The beetles choose leaves for hibernating cover in preference to hay and 

 stones. 



A pictorial diagram of the seasonal history of this insect in apples occurs 

 on page 35. The iirst overwintering beetles appear when the blossom buds 

 are showing pink, and the largest number enter the trees between June 10 

 and 30. The first eggs are laid about June 1, and the number deposited in- 



