436 Journal of Agricultural Research vol. xx, No. 6 



at Moiliili were found variously infested. They state also that the 

 ordinary cucumber, when very young, is the most resistant to melon-fly 

 attack of all the cucurbits cultivated in Hawaii, but that inasmuch as 

 the fly has been permitted to increase unchecked since its introduction 

 it has become so abundant that slight differences in inherent resistance 

 to attack are not evident among host fruits growing in the field. The 

 condition of cucumbers offered for sale in Honolulu during the first 

 eight months of 191 9 indicates that O. fletcheri, while not being able 

 completely to control the melon fly on the island of Oahu, has been able 

 to reduce its numbers to such an extent that the infestation of cucumbers 

 has been greatly decreased. During this period there have been good 

 quantities of this vegetable on the market at all times, a very small 

 portion of which has shown evidences of melon-fly attack. The writer 

 has observed on several occasions at different plantations wagon loads 

 of cucumbers that had been selected for market, among which it was 

 difficult to find any great number that had been attacked. While col- 

 lecting cucumbers during the past year from the different gardens for 

 parasitism records, it has often been difficult to get a sufficient quantity 

 of well-infested fruits. These observations, as compared with those 

 made previous to the establishment of O. fletcheri, would lead to the 

 conclusion that this parasite has already become of much value, even 

 while attacking its host in the larger cucurbits. 



The ability of Opius fletcheri to reach and parasitize the majority of 

 host larvae developing in the smaller fruits is clearly shown by data 

 collected during the past five years in the Kona district of the island of 

 Hawaii. In this district it comes nearer to controlling the melon fly 

 completely than in any other locality that has been observed. This 

 great degree of control is without doubt due to the great abundance of 

 the wild Chinese cucumber (Momordica sp.). The fruits of this plant 

 are small, about % to \ l /i inches in diameter by 1 to 2 inches long. The 

 following observations give a good conception of their susceptibility to 

 melon-fly attack and of the ability of Opius fletcheri to decrease their 

 infestation greatly by parasitizing a large percentage of the larvae de- 

 veloping in them. 



From observations made in this district, Back and Pemberton state ' 

 that— 



From Momordica vines covering a patch of pasture land 6 feet square, 331 fruits 

 were gathered during November, 1914, of which only 12 had not been infested. These 

 fruits, which were of all sizes up to \% inches in diameter, averaged between three and 

 four punctures per fruit, with a maximum of 15 punctures on the more exposed fruits. 

 From 7 feet of stone wall 442 fruits were gathered, and of these 193 were so badly- 

 affected that they had dried up without developing seeds, and only 11 were not 

 affected. From 250 fruits placed over sand 1,586 larvae, or an average of 6.5 larvae 

 per fruit, were reared. 



1 Back, E. A., and Pemberton, C. E. the melon fly in Hawaii. U. S. Dept. Agr. Bui. 491, 64 p., 

 24 pi., 10 fig. 1917. (See p. 17-18.) 



