44 BULLETIN 536, U. S. DEPARTMENT OF AGBTCULTUEE. 



it promised to become a financial asset to the islands. Even since the quarantines of 

 the Federal Horticultural Board stopped shipments of avocados to the mainland of 

 the United States shipments have been made to the Philippine Islands in cold 

 storage. The following data are the first ever published on the infestation of avocados 

 and are given here to refute arguments for reestablishing the avocado trade on its 

 former basis: • 



There are many horticultural varieties of the avocado growing in Hawaii, but there 

 appears to be little difference in their degree of susceptibility to attack. The nutmeg 

 or Guatemala variety is the only one free from attack when growing uninjured . Under 

 forced laboratory conditions adults can not oviposit through its unusually thick rind. 

 The skin of all other varieties of avocados, whether very thin or of usual toughness, can 

 be punctured by the adult fly, as proved by the examination of many fruits. The 

 avocado, like the ordinary pear, is best if picked when still hard and allowed to ripen 

 in storage. 



If left on the tree too long, the fruits drop and soften on the ground. With most 

 varieties it is not until the fruits are mature enough for gathering or dropping that 

 adults oviposit in them. As they are sufficiently soft for eating purposes within two 

 to four days after being cut from the tree, the larvae are still very young, if not just 

 hatched, and are to be found feeding close to the tough leathery rind. Their presence, 

 therefore, is seldom observed by those eating avocados served whole or cut in half to be 

 eaten with a spoon. When served cut in small pieces, with mayonnaise, the paring 

 process usually crushes the small larval burrows on the outer surface of the pulp and 

 the larvae go to the table unobserved. As thousands of larvae are thus consumed 

 yearly in Honolulu alone, it may be well to state that they do no harm. 1 Fruits in 

 which the larvae have become well grown are usually too soft for eating purposes. 



Several thousand fruits have been examined carefully by the removal of the skin. 

 Of 1,027 fruits thus examined, picked from the trees at Wahiawa and representing 10 

 separate lots of fruit, 173, or 16.8 per cent, were found to contain eggs or larvae; of 384, 

 representing six lots of fruit picked from the ground at Wahiawa, 57 fruits, or 14.8 per 

 cent, were infested. Notes on certain uninfested fruits show that of the green, varie- 

 ties 354 were thick skinned and 75 were thin skinned; of the purple varieties, 254 were 

 thick skinned and 101 were thin skinned. Of 120 infested fruits, 42 and 12 were green 

 varieties with thick and thin skins, respectively, while of the purple varieties, 32 and 

 34 were thick skinned and thin skinned, respectively. The considerably larger pro- 

 portion of thin-skinned purple fruits found infested agrees in the main with observa- 

 tions on similar fruits found on the markets. Eleven purple fruits of an early thin- 

 skinned variety picked from the tree in the Makiki district of Honolulu had an average 

 of over 41 punctures in the skin, no fruit having less than 12 or more than 119 punc- 

 tures. A fruit of a second thin-skinned purple variety grown by Mr. G. P. Wilder, of 

 Honolulu, known to be generally infested if the fruits are allowed to remain on the tree 

 too long, was hung in a jar of adult flies for about 18 hours beside a fruit similar in 

 appearance and degree of ripeness, taken from another tree. An examination after 

 removal of the fruits showed 7 eggs to have been deposited in 1 puncture in 1 fruit 

 while in the Wilder fruit 487 eggs had been deposited in 56 punctures. In a green 

 fruit with a hard, tough skin exposed to adults for 5 hours, 32 eggs were deposited in 14 

 punctures. One lot of 863 fruits of all varieties gathered by a fruit dealer from trees 

 in upper Manoa Valley and the Punahou district of Honolulu were not infested, but 

 these were picked several days earlier than they might have been picked. Avocados 

 shipped rather green from the islands of Hawaii and Kauai to Honolulu (Oahu) were 

 not found infested, but their freedom from infestation was due to the earliness of their 

 gathering. Ten thin-skinned purple fruits grown at Waikiki and purchased in the 

 market had an average of over 9 punctures per fruit, 1 fruit having 33 punctures and 



1 The writers have personally conducted experiments in which it is estimated persons have eaten 2,000 

 eggs and young larvae in plums without injurious results. 



