394 



THE AGRICULTURAL NEWS 



Decembee 15, 1917 



INSECT NOTES. 



THE MELON FLY IN HAWAII. 



From time to time within recent years articles have 

 appeared in this column of the Afiricultural News dealing 

 with fruit flies. Some of these articles were devoted 

 entirely to the Mediterranean fruit fiy, as bein j perhaps the 

 most important of this group of pests. Another member of 

 this group, however, has been attracting considerable atten- 

 tion in various parts of the world, mainly in the East. The 

 insect in question is the melon fly (Bactrocera rucur/dtae, 

 Coq.), which has been recorded from India, Ceylon, Java, 

 Timor, Northern Australia, Singapore, the Philippine Islands. 

 Southern China, Japan, and the Hawaiian Islands. It is in 

 the last named country that the melon fly has assumed the 

 greatest importance, and a brief account of this insect, as it 

 occurs in Hawaii, is taken from Bulletin Jfil of the United 

 States Department of Agriculture by E. A. Back and C. E. 

 Pemberton, who have done much valuable work in fruit fly 

 investigations in Hawaii, 



It is now considered by Bezzi and other entomologists 

 that the melon fly had its native home in India. Its spread 

 to other widely separated countries has been due, not to 

 natural agencies, but to the assistance of man. 



Its introduction into the Hawaiian Island.s took place 

 about 1895, and when discovered in 189" it was already 

 a serious pest. The favourable climate and abundant food 

 supply prevailing in Hawaii have enabled the melon fly tf> 

 increase to such an extent that at the present time the free 

 cultivation of many of the crops grown by market gardeners 

 has been rendered impossible. This pest not only attacks 

 such cucurbitaceous crops as sijuashes, pumpkins, vegetable 

 marrows, melons, cucumbers, etc., but it is also destructive to 

 tomatoes, cowpeas, and string beans. The annual loss due 

 to the melon fly in Hawaii is estimated at $750,000, 



t.IFE-CYCLE 



L'nder favourable warm weather conditions in Hawaii, 

 the egg, larval, and pupal stages may C'ccupy as few as twelve 

 days, or as many as twenty-eight and a half days. At lower 

 temperatures the duration of the immature stages may be 

 greatly lengthened and occupy as much as three and a half 

 to four months. It has been found that the adult flies can 

 be kept alive for a period of 431 day.s, although adult* 

 deprived of food and Witer never live more than lOi! hours, 

 or more than 120 hours without food but with water. 



The complete life-cycle may, therefore, take from 443 

 to 459 days under favourable conditions of food and climate, 

 but will take longer under les.s favourable conditions. 



Under natural conditions the adult flies live chiefly on 

 the honeydew secreted by such insects as aphids, leaf hoppers, 

 and scale insects, upon the juices of host plants, and the 

 nectar of flowers. The flies are rapid fliers, but apparently do 

 not indulge in long-sustained flights. In captivity, mating 

 does cot begin until about twenty days after emergence, and 

 egg-laying under these conditions first takes place in about 

 another twelve days. It was found by Messrs, Back and Pem 

 berton that when fed on cucumber in captivity, mating will 

 begin when the adults are only ten days old, and egg-laying 



will take place the next day. This is when the temperature 

 and humidity conditions are favourable. After egg-laying 

 has begun the adults continue to deposit e^gs everj- few days 

 throughout life, and it has been estimated that a vigorous 

 and long-lived fly would be capable of laying as many as 1,000 

 eggs during the year or more of her existence. 



The eggs are laid within the tissues of the host pi uit 

 or fruit by means of a sharp ovipositor. No portion ot the 

 plant is free from attack, since the eggs may be depo.si'ed on 

 almost all portions of the plant and fruit. 



The larvae on hatching usually bore their way to- 

 the centre of the plant or fruit, but the place of feeding 

 is determined largely by the moisture content of the host. 

 In the case of young seedlings the larvae may burrow into 

 the tap root and kill the plant. In juicy plants «vhich have 

 made a good ^ rowth they bore through the leaf petioles and 

 stalks, causing the death of the parts attacked. The young 

 fruits of all cucurbitaceous crops are badly attacked arid 

 destroyed as a rule but the older fruits of some species are 

 more resistatit to attack. They are, however, usually 

 deformed by the presence of numerous colonies of larvae in 

 open surface wounds. 



After passing through three instars the larvae leave the 

 host and pupate in the soil, u.sually beneath the host. The 

 larvae after leaving the fruit are able to jump a few inches, 

 in stages, and can thus find more suitable places to pupate, 

 and if they cannot enter the soil they will pupate on any- 

 hard surface. 



There are as many as eight to ten generations of the 

 melon fly a year in Hawaii, so that the pest is able to multiply 

 very rapidly. The n.elon fly is spread largely in the larval 

 .stage, being carried in fruits from one country to another, 

 and it is constantly being intercepted at the Californian 

 ports in .ships arriving from Hawaii. The local spread from 

 one town to another maj' occur in the adult or in the pupal 

 stage. 



CONTROL MEASURES. 



Under Hawaiian conditions there are at present no 

 natural agencies, such as parasitic and predaceous enemies, 

 that can check the abundance of the melon flies. Further, 

 no satisfactory artificial means of control have been success- 

 ful in controlling this pest under Hawaiian conditions. The 

 writers consider that these methods are not likely to be 

 successful so long as the cultivation of the chief host plants 

 of the ration fly is carried on by uneducated orientals, who 

 do not practice clean cultivation or co operate in applying 

 remedial measures. 



J.C.H 



A NEW METHOD OF KILLING WEEDS^ 

 IN OANE FIELDS. 



In the last issue of this Journal December 1, 1917, 

 notice was drawn to a speech of the Hon. Charles Hedley 

 Strutt on the subject of progress in tropical agriculture, in 

 which was emphasized the vital importance for every 

 manager of a tropical estate never to rest .satisfied with 

 the methods of agriculture which were thought satisfac- 

 tory a few years ago, but always to be on the alert to 

 experiment with and adopt new methods uTid new appli- 

 ances, in order not to be left behind in the race for success. 



An article in the Internatioiiil Sugar ■lournal, October 

 1917, much of which i.~ reproduced below, shows the alertness 

 of mind, and the readiness to receive new ideas, with the 

 determination to find out their value and employ iliem to 

 the utmost when found useful, which the Hawaiian sugar 

 planters are exhibiting in the conduct of their business. It 



