44 BULLETIN 491, U. S. DEPARTMENT OF AGRICULTURE. 



SEASONAL HISTORY. 



In littoral Hawaii there may be from 8 to 10 generations of the 

 melon fly a year when one considers the length of a generation as 

 extending from the time the eggs are laid until the female of the 

 next generation begins to deposit eggs. As the females are capable 

 of living many months and of depositing eggs at frequent intervals 

 throughout life, the generations so overlap each other that adults 

 present in the field at any one time may belong to generations started 

 in any month of the year. It is possible for females ovipositing on 

 January 1 to be still alive and ovipositing the following January 

 along with the progeny of the tenth generation of her descendents. 



In the Hawaiian Islands, where the climatic conditions permit 

 breeding throughout the year, adults of the melon fly are abundant 

 at all seasons in the littoral regions, where, for the most part, host 

 plants are grown. There is no evidence of seasonal broods or genera- 

 tions of adults. That the cooler weather of the winter months does 

 lengthen the duration of the immature stages has already been proved 

 by data. This slowing down of development naturally results in the 

 emergence of fewer adults, and in forcing these to feed for a greater 

 period of time before becoming sufficiently developed to oviposit. 

 Unfortunately the length of adult life and the capacity of the females 

 for continued egg laying makes it difficult for market gardeners to 

 benefit to any marked extent from the effects of cool weather upon 

 development if they allow their fruits to remain unprotected. The 

 fewer adults, coupled with the shorter hours during the day when 

 they are sufficiently active to oviposit, does result in greater success 

 in saving fruits by the use of various protective coverings than would 

 follow the use of the same measures in the summer. At an elevation 

 of 1,500 to 2,000 feet in the Kona district of Hawaii, where the winter 

 mean averages about 68° F., and where the melon fly can breed in 

 large numbers in wild hosts, fully 50 per cent of the pumpkins and 

 squashes are able to mature even if left uncovered. Adults were 

 present at an elevation of 4,000 to 4,500 feet in the island of Hawaii 

 and ovipositing in young squashes. These squashes were examined 

 and found to contain eggs and larvae. As the vines bearing these 

 fruits were later killed by frosts, it seems possible to conclude, at 

 least for this locality, that the melon fly is able to survive in climates 

 too cold to permit its host plants to grow continuously throughout the 

 year. 



METHOD OF SPREAD. 



The melon fly is probably more often carried from one locality or 

 country to another in the larval stage than in any other form. 

 Maskew (42) has recorded finding living larvae in host fruits arriv- 

 ing at San Francisco on ships from Honolulu, and his records prove 

 that the melon fly in the larval stage is able to bridge the 6 or 7 days 



