10 



CIECULAE 10 9, U. S. DEPARTMENT OF AGEICULTURE 



1923, and during five months in 1924. Diachasma tryord was the 

 most effective during seven months in each of the years 1922 and 1923, 

 and during five months in 1924. D.fuUawayi was the most eft'ective 

 during only one month of the 3-year period under consideration, 

 namely, in December, 1924. T. gifardianus was the most effective 

 parasite during two months in 1922, five months in 1923, and one 

 month in 1924. 



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) 



Month 



Percentage of parasitism by- 



Number of larvae 



Opius Diachasma 

 humilis tryoni 



1922 1923 1924 192219231924 



1922 1923 1924 



Diachasma 

 fullawayi 



1922 1923 1924 



Tetrastichus 

 gifiardianus 



1922 1923 1924 



Total para- 

 sitism (per 

 cent) 



1922 1923 1924 



January 



February. . 



March 



April 



May 



June 



July 



August 



September. 



October 



November. 

 December.. 



2,6i: 



7,176 

 2,261 

 9,525 

 8,984 

 8,367 

 4,697 

 2,850 



1,019 

 596 

 1,469 

 4,264 

 1,732 

 1,925 

 2,749 

 9,236 



7, 512; 



3,257| 



l,844l 



588! 



1,144 1. 

 2, 642 10. 

 4, 530 12. 



961 16. 

 2, 117 14. 

 1,175 1. 

 1,758: 1. 

 4,003' 1. 

 2,354 1. 

 2,959 1. 



387i 2. 

 3.232 2. 



.2 9. 

 .3 26. 



. 5125. 

 ,3i28. 



4:15. 

 ,9: 8. 



4i 3. 



7; 5. 



117. 



8! 16. 

 2lll. 



7 . 



3: 8. 



2, 7. 

 9 9. 

 7 15. 

 9 39. 

 3 48. 

 3:13. 

 9 20. 

 221. 

 9 58. 

 6 37. 

 4134. 



9 20. 



0: 8. 

 6 12. 

 17. 

 321. 

 7^2. 

 7; 7. 

 4^12. 

 4 7. 

 4. 

 6 24. 

 016. 



5 23. 



7il4. 

 122. 



5j 8. 

 2i 5. 

 9 5. 

 Ii47. 

 7|25. 

 2,25. 

 5 20. 

 4:14. 

 71 18. 



.5 

 7| 3.6 

 6| 5.4 

 8! 3.1 

 1! 1.7 



el .3 

 5; 9.5 

 3 1.2 



26.6 

 9.4 

 7.9 

 6.0 

 1.2 

 4.0 



15.4 



15.1 

 5, 



11.0 

 3. 



8.2 



8.6 



11.3 



19.3 



6. 1 51. 4 



5. 8 60. 2 



Si 5.4!l6.5 



918. 6| 18. 4 



2.0 

 9.9 

 5.9 

 20.4 

 .4 



38.7 37. 



28.4115. 

 32. 3:24. 

 37. 9:25. 



55. 2 34. 

 57.5 23. 

 36. 4:23. 

 31.3 35. 

 31. 66. 

 66.0i71. 

 54. 8163. 



56. 2|38. 



2 35. 

 144.6 



1137. 7 

 0:21.8 

 5 14.7 

 5 52. 1 

 7|33. 8 

 2 52. 4 

 5'Mb.l 

 62.3 

 8 61.0 



1 0.7 per cent of the parasitism shown in this total was accomplished bj" Opius fletchcrl. 



0. humilis did its most effective work during the early months of 

 the year. This can be attributed to the control of 0. 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 0. humilis 

 is always eliminated under these conditions. Both species of Dia- 

 chasma have been shown (7, p. 430) to hibernate to a considerable 

 extent during the cooler months of the year, whereas 0. humilis does 

 not show this tendency. Consequent^, with the advent of the cooler 

 months, which begin about December, D. tryoni and D. JuUawayi 

 become less effective and do not retard the development of 0. humilis 

 to so great an extent as during the warmer months. The increase in 

 the eft'ectiveness for 0. humilis begins at about that time. 



The unusuall}^ high percentage of parasitism accomplished by 

 1 . gifardianus 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 

 J. gifardianus 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 ail 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 



