Jan. IS, 1920 Mediterranean Fruit Fly in Hawaii in igi8 



445 



Table III. — Total parasitism of all larvce of Ceratitis capitata collected in Hawaii 

 during igi8, arranged by months 



Month. 



Number 



of 

 larva. 



Percentage of parasitism. 



Opius 



humilis. 



Dia- 

 chasma 

 tryoni. 



Dia- 



chasma 

 fulla- 

 wayi. 



Tetra- 

 stichus 



giffard- 



Total 

 for 



1918. 



Total 

 for 



1917. 



Total 

 for 



1916. 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



Average for 19 18 

 Average for 191 7 

 Average for 1916 



5.219 

 3, 600 

 4,404 

 4,675 

 5,854 

 14, 388 

 8,827 

 4,850 



4,471 

 6,885 

 8,659 

 1,648 



4.8 



2-3 

 24. I 



10.3 



16.5 



II. 8 



2. o 



•7 

 2.4 



6-5 

 25-3 

 21.5 



9.6 



2-5 



7-9 



27.8 



17- 3 



48.6 

 e,2. 2 

 38.1 

 28.0 

 22. o 

 21. 7 

 37-7 



6.2 

 1.6 

 2-3 

 5-0 



2. I 

 3-8 

 3-4 

 3-2 

 •5 

 •4 



0.8 

 . 2 



3-2 

 •4 



2. o 



3- 7 

 3-6 



7-9 



9-4 

 II. 2 

 10. 9 



21.4 

 6.6 



37-5 

 43- S 

 36.0 

 64.9 

 59-9 

 50-5 

 47- I 

 41. I 



58-7 

 70-5 



59- o 



32- 9 



63-5 



43-3 



40. 9 



36. I 



51.0 



33- 



52- 



45- 



72. 



34- 



63, 480 

 72, 139 

 83) 304 



12.4 

 12. 7 

 17. 2 



34-6 

 20.3 

 ^3-3 



2.6 



7-3 

 2. I 



6.2 

 7.2 



.6 



55-8 



47-5 



19-5 



14.7 

 37-64 

 26. 69 

 27.81 

 18.52 



37- S 

 45-2 

 44-3 

 44-3 

 44- I 



33- 



Previous publications (1-4) give data that show the consistent as- 

 cendancy of the parasite Diachasma tryoni over Opius humilis during 

 the warmer months of the year and the predominance of O. humilis in 

 the cooler months. This interchange in the effectiveness of these two 

 parasites is due to the ability of D. tryoni to destroy O. humilis when both 

 occur in the same host larva, coupled with the decreased activity of the 

 former during the cooler months (5). Records of parasitism for 191 6 

 and 1 91 7 {3-4) show that O. humilis gained this predominance for five 

 and three months, respectively; while during 1918, as shown by Table III, 

 this species was able to gain the ascendancy for only two months — 

 March and November. This yearly decrease in the effectiveness of 

 0. humilis is directly due to the yearly increase in numbers of D. tryoni, 

 which is shown by the average yearly parasitism records given at the 

 bottom of Table III. The average parasitism by D. tryoni increased 

 from 13.3 larv'ae to each fruit in 1916 to 20.3 in 1917 and to 34.6 in 1918, 

 while the average parasitism by O. humilis consistently decreased. Al- 

 though the parasitism by both D. fullawayi and Tetrastichus giffardianus 

 was less in 1918 than in 1 91 7, the total percentage of parasitism for the last 

 year, on account of the increased effectiveness of D. tryoni, had increased 

 8.3, making the total parasitism for 1918, 55.8 per cent of all the fruit- 

 fly larvae under observ^ation. 



The carefully recorded data concerning the activities of the Medi- 

 terranean fruit-fly parasites in Hawaii show that their value as destroj-ers 

 of this pest has consistently increased each year since their introduction, 



