4 CIECULAE 10 9, U. S. DEPAETMEXT OF AGEICULTUEE 



The records in Table 1 show for each species of host fruit the num- 

 ber of fruits under observation, the number of maggots emerging, and 

 the average infestation per fruit for each year of the 3-year period 

 under consideration. The average infestation per fruit for the 9-year 

 period, 1916-1924, inclusive, is given to show how these yearly 

 records compare with the average for the nine years. By referring 

 to Table 2 it will be noted that some fruits were collected only occa- 

 sionally during the 9-year period. On the basis of comparisons only 

 %\ith those fruits upon which records were secm^ed during five or 

 more of the nine years. Table 1 shows that during 1922 the average 

 infestation per fruit in 42.9 per cent of the species collected was greater 

 than the average for the 9-year period. In 1923 this average was 

 greater in 26.7 per cent of the species of host fruits, and in 1924 it was 

 greater in 25 per cent of the host fruits. The percentage of host 

 fruits having a higher infestation than the average has been well 

 under 50 per cent dm^ing each of the three years of this period and has 

 shown a decrease each year, indicating an actual decrease in infes- 

 tation and in the number of adult flies. 



Table 2, showing the average infestation per fruit for each species 

 of host during each year and for the 9-year period, 1916-1924, 

 inclusive, is given to indicate the fluctuation of infestation from year 

 to year. On the same basis as that outlined in the preceding para- 

 graph, this table shows that the percentage of fruits having a higher 

 average number of larvae per fruit in any yearly period than the 

 average for the 9-vear period is as follows: 1916, 56.2 per cent: 1917, 

 50 per cent: 1918^ 41.2 per cent; 1919, 46.7 per cent: 1920, 38.9 per 

 cent; 1921, 71.4 per cent; 1922, 42.9 per cent; 1923, 26.7 per cent; 

 1924, 25 per cent. These records show that dm^ing three years, 

 1916, 1917, and 1921, the mfestation was above the average in 50 

 per cent or more of the fruits under observation. During the other 

 six years less than 50 per cent of the host fruits showed infestation 

 above the average, and in 1924 the percentage of 25 indicates that 

 the infestation during that year was lower than for any other year 

 covered by the table. 



PARASITISM RECORDS 



Owmg to the oviposition habits of the parasites of the Alediter- 

 ranean fruit fly now established in Hawaii, the eft'ectiveness of these 

 enemies in controlling the fly is governed to a large extent b}^ the 

 nature of the fruits in which the host maggots are developing. The 

 three opiine parasites, Opius humilis, Diachasma iryoni, and Dia- 

 chasma jullawayi deposit then eggs ^\ithin the host larva by piercing 

 the skin of the fruit and the integument of the larva with the ovi- 

 positor. The host maggot must therefore be near the surface of the 

 fruit in order to be within reach of the parasite. Consequently, in 

 fleshy fruits which aft'ord an opportunity for maggots to burrow some 

 distance beneath the skin parasitism is low, whereas in small fruits 

 and those containing a large seed covered by thin pulp, vrhere the 

 maggots are necessarily always near the outer surface of the fruit, 

 parasitism is high. Tetrastichus gifardianus oviposits directly into 

 the host maggot and must come directly in contact \Y\ih. the maggot 

 before oviposition is possible. In order to reach host maggots 

 ■^-ithm a fruit, it must be able to enter through some break in the skin. 



