10 CIRCULAR 109, U. S. DEPARTMENT OF AGRICULTURE 
TaBLe 4.—Total parasitism of larvae of the Mediterranean fruit fly from all fruits 
collected in Hawaii in 1922, 1923, and 1924 (averaged by months) 
=— 
Percentage of parasitism by— 
Total para- 
Number of larvae sitism (per 
Opius Diachasma | Diachasma | Tetrastichus cent) 
Month humilis tryoni fullawayi | giffardianus 
1922 | 1923 | 1924 |1922)1923)1924)1922)1923/1924/1922|1923)/1924 1922/1923) 1924|1922|1923/1924 
pee eee eee ed ee ee okt pe OS! (ad PE — Pat: 
January see. 952) 1,019} 1,144) 1.4) 1.2) 9.3) 8.9)20. 5/23. 9} 1.8) 0.4) 0. 7/26. 6/15. 1) 1. 7/38. 7|37. 2/35. 6 
Bebruary-2-----—- 458 96) 2,642)10.5) .3/26. 2) 7.0) 8. 7/14. 1) 1.5] . 5) 1.4) 9.4) 5.6} 2.9)28. 4115. 1/44. 6 
Marches Sie 798) 1,469) 4, 530)12.8) .5)25.9] 9. 6/12. 1/22.7) 2.0) .9] 7.1) 7.911. 0) 2.9)32. 3/24 5/58. 6 
Aprils 2oe% elo: 2,617) 4,264)  961/16.0) 3. 3/28. 7)15. 0/17. 5) 8.4) .9) .5/-_-_| 6.0) 3.8] . 6/87. 9/25. 1/37. 7 
INGER YS olen eros 9, 877| 1, 732] 2, 117)14. 2) 3. 4/15. 9/39. 3)21. 2) 5.2) .5) 1.2) .5) 1.2) 8.2) . 2/55. 2/34. 0/21.8 
MUNG See eee SN Be 7, 176} 1,925) 1,175) 1.2) .9) 8.3/48. 7/12. 9) 5. 7} 3.6) 1. 1)/-_-_| 4.0) 8.6! . 7/57. 5)23. 5/14. 7 
yea 2,261) 2,749) 1,758] 1.9} .4) 3.3)13. 7) 7. 1/47. 6) 5.4) 4.7) .3/15.4/11.3) . 9/36. 4/23. 5152.1 
JNU CADIS fe Se ee 9, 525) 9, 236} 4,003) 1.0) 2.7) 5.9)20. 4/12. 7/25. 8} 3.1] 1.0) .1) 6.8)19.3) 2. 0/31. 3/35. 7/33. 8 
September--_.-_-- 8, 984! 7,512) 2,354) 1.8) 6. 1/17. 2/21. 4) 7. 2/25. 1] 1.7) 1.5) .2) 6.1151. 4) 9. 9/31. 0.66. 2/52. 4 
Octoberz==2=2 8, 367| 3, 257) 2,959} 1.9) 5. 8)16. 9/58. 0) 4. 5)20.6) .3) 1.0) 1.6) 5.8/60. 2) 5. 9/66. 0/71. 5145.7 
November. .------- 4,697) 1,844) 387) 2. 3/16. 2/11. 6/37. 6/24. 4/14. 5) 9.5) 5. 9/15. 8) 5. 4/16. 5/20. 4/54. 8/63. 0/62. 3 
December.-_--_---- 2,850} 588] 3, 232) 2. ‘| 3.7) . 4/84. 0/16. 7/18. 3} 1.2 Sr lag 9/18. 6)18.4) . 4/56. Re 8/61. 0 
10.7 per cent of the parasitism shown in this total was accomplished by Opius fletcheri. 
O. humilis did its most effective work during the early months of 
the year. This can be attributed to the control of O. humilis by either 
species of Diachasma when it occurs in the same host maggot with 
them. It has been shown in a previous publication (5) that O. humilis 
is always eliminated under these conditions. Both species of Dia- 
chasma have been shown (7, p. 480) to hibernate to a considerable 
extent during the cooler months of the year, whereas O. humilis does 
not show this tendency. Consequently, with the advent of the cooler 
months, which begin about December, D. tryont and D. fullawayr 
become less effective and do not retard the development of O. humilis 
to so great an extent as during the warmer months. ‘The increase in 
the effectiveness for O. humilis begins at about that time. 
The unusually high percentage of parasitism accomplished by 
T. giffardianus during the latter part of 1923 is due to the fact already 
mentioned that the records included larvae contained in fruits of 
Indian almond collected in one locality where the parasitism was 
abnormal. Should these records be discarded the parasitism by 
T. offardianus would be less than half the figures shown. 
The records in Table 5 are given to show the effectiveness of each 
species of parasite and the combined effectiveness of all four species 
since their establishment in 1915. In 1915, Opius humilis was respon- 
sible for the greater part of the total of 37.9 per cent of the parasitism. 
From that time its effectiveness gradually decreased until a minimum 
of 4.1 per cent was reached, in 1923. During 1924, however, it para- 
sitized 14.5 per cent of all the larvae under observation and was more 
effective during that year than for any yearly period since 1916. 
Diachasma tryoni was less effective in 1923 than in any year since 
1915. This parasite is usually the most effective of any of the four 
species. It has shown a fairly uniform amount 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. 
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