PARASITISM OF MEDITEEEANEAN FRUIT FLY IN HAWAII 



11 



1915. This parasite is usualh' the most effective of any of the four 

 species. It has shown a fairly uniform degree of parasitism since it 

 became well established in 1916. In 1923, as has been noted, Tetra- 

 stichus giffardianus was the most effective over a yearly period for the 

 first time since its introduction. 



Table 5. — Total parasitism of all larvae of the Mediterranean fruit fly collected in 

 Hawaii from 1915 to 1924, inclusive 





Number 

 of larvae 



Percentage of parasitism by— 



Year 



Opius 

 humilis 



Diachas- 



ma 



tryoni 



Diachas- 

 maful- 

 lawayi 



Tetras- 

 tichus 

 giffar- 

 dianus 



Total 



1915 



28,010 

 83, 304 

 72,139 

 63, 480 

 75, 406 



57, 406 

 88, 616 



58, 562 

 36, 191 

 27, 262 



31.5 

 17.2 



12.7 

 12.4 

 9.4 

 9.4 

 7.6 

 4.6 

 4.1 

 14.5 



0.3 

 13.3 

 20.3 

 34.6 

 19.6 

 22.7 

 26.9 

 33.7 

 12.2 

 20.7 



5.9 

 2.1 

 7.3 

 2.6 

 1.6 

 12.1 

 5.5 

 2.5 

 1.6 

 6.8 



0.2 



7^2 

 6.2 

 7.6 

 7.7 



16.4 

 6.4 



25.3 

 3.1 



37.9 



1916 -. 



33.2 



1917- 



47.5 



191S 



55.8 



1919 



1920 



38.2 

 51.9 



1921.- 



56.4 



1922 



47.2 



1923 



1924 - 



43.2 

 45.1 











The total parasitism by all species during the 3-year period covered 

 by this report was comparatively uniform, ranging from 43.2 per cent 

 to 47.2 per cent. During the three previous years, the total para- 

 sitism ranged from 38.2 per cent to 56.4 per cent. A comparison of 

 the average parasitism during the two 3-year periods shows that it was 

 nearly the same, although it was a little higher during the period 

 1919-1921. 



SUMMARY 



The Mediterranean fruit fly, since it was discovered in Hawaii in 

 1910, has been a major fruit pest in all parts of the Territory. Of 

 the various methods employed in different parts of the world to con- 

 trol this pest, the use of introduced parasites is the only one which 

 has been found adapted to the peculiar horticultural conditions of 

 Hawaii. In 1913 and 1914 three braconids, Opius humilis, Dia- 

 chasma tryoni, and Diachasma fuUawayi, and one chalcid, Tetras- 

 tichus giffardianus, were introduced and established by the Territorial 

 government. This circular records the effectiveness of these parasites 

 during the 3-year period 1922 to 1924, inclusive, and is a continua- 

 tion of similar records made since 1914. 



The infestation of fruits by the fly during the three years under 

 consideration was less in the majority of hosts than the average in- 

 festation per fruit over the 9-year period 1916 to 1924, inclusive. The 

 decrease in infestation of host fruits indircates a decrease in the abun- 

 dance of adult flies. 



Parasitism by Opius humilis reached its minimum, 4.1 per cent, in 

 1923, owing probably to the effect upon it of the two species of 

 Diachasma. In 1924 the parasitism (14.5 per cent) by this species 

 was greater than for any year since 1916. Owing to the hibernation 

 habits of Z>. tryoni during the cooler months of the year, the effective- 

 ness of this parasite decreases during those months and at the same 

 time there is a corresponding increase in effectiveness by 0. humilis. 



