PARASITISM OF MEDITERRANEAN FRUIT FLY IN HAWAII I1 
TaBLE 5.—Total parasitism of all larvae of the Mediterranean fruit fly collected in 
Hawaii from 1916 to 1924, inclusive 
Percentage of parasitism by— 
Number : 
Year of larvae ‘ Diachas- | Diachas-| 1°tas 
Opius natal: tichus Total 
umiliss |) een ; | giffar- 
tryoni lawayl dianus 
OT ere ie Se i ie er ee ee 28, 010 31.5 0.3 5.9 0.2 37.9 
101 Gee 2 TER Er Pe ee Re ee eee 83, 304 WZ 13.3 Pal .6 3o02 
TAO TY fac eS I RS SI OP 72, 139 Pd 7/ 20. 3 Loe Ga? 47.5 
TREY RSs i BS Su SA Nt SR ga 63, 480 12. 4 34. 6 2.6 6.2 55. 8 
QT O eerie Nk ae Oe A a ee 75, 9.4 19.6 1.6 7.6 38. 2 
TIS pb ke sea A Su ane RDO CD OLN ast Ep That 57, 406 9. 4 22.7 12.1 od 51.9 
TREY AS RS RR ane Me eT NSAI DENRA ae 88, 616 7.6 26.9 5.5 16.4 56. 4 
TROP PASE Re et RI pee agen me Se OSE SN 58, 562 4.6 33. 7 2.5 6.4 47.2 
TRE PAT eye he Br ROE a ae on en Sa RPE OBS 36, 191 4.1 12.2 1.6 25:13 43. 2 
AON ie cea syacte yn BAUR ANN OE eC rate 27, 262 14.5 20. 7 6.8 Bh al 45.1 
The total parasitism by all species during ine 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 
Hawau. In 1913 and 1914 three braconids, Opius humilis, Dia- 
chasma tryom, and Diachasma fullawayi, and one chalcid, Tetras- 
tichus giffardianus, were introduced and established by the Territorial 
government. ‘his 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 indicates a decrease in the abund- 
ance 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 D. tryoni during the cooler months of the year, the effective- 
ness of this parasite decreases during those months and this is accom- 
panied by a corresponding increase in effectiveness by O. humilis. 
The work of these four parasites during the three years under con- 
sideration has not varied to any great extent from that of the previous 
six years. They continued to parasitize nearly 50 per cent of the 
larvae about Honolulu, causing a corresponding decrease in infesta- 
tion of the commercial hosts. 
