Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. UNITED STATES DEPARTMENT OF AGRICULTURE edeLollow WASHINGTON, D C. | PARASITISM OF THE MEDITERRANEAN FRUIT FLY IN HAWAII 1922-1924 By H. F. Wrtarp, Senior Entomologist, in Charge of Hawaiian Inspections, Plant Quarantine ‘and Control Administration, and T. L. Bissmiu, Assistant Entomologist, Division of Deciduous Fruit Insects, Bureau of Entomology } CONTENTS Page Page Pteanugiont 6h: Set ee ee a Sec 1G GSOIMMAR Yrs seers es ea er Ee ey ee ee li RECOLGS Of intestalione. 422 ee ee Qo) ALLEL LUTE sCLbe Ces = 5 Seek Sak Nn) Midna See Rehan ane 12 IPATASIDISMUTOCORGS 420 ek tsa) eed eee ods 4 INTRODUCTION When the Mediterranean fruit fly (Ceratitis capitata Wiedemann) arrived in Hawaii, where it was discovered in 1910, it found itself in an almost ideal environment. Owing to a favorable climate, an abundance and variety of host fruits, and a lack of natural enemies it spread rapidly. The temperature range in littoral Hawaii is such that this fly can reproduce rapidly during the whole year. It has been shown by Back and Pemberton (3, p. 75)” that in the lower eleva- tions of the islands 16 generations may be produced annually. There have been recorded in Hawaii 73 different varieties of fruits and other plants in which the Mediterranean fruit fly may reproduce, and at all times during the year some of these varieties are in bearing and in the proper condition for infestation. The species of insect enemies in Hawai that attacked it when it arrived were so few and ineffective that they had very little influencein checkingits spread; consequently, within a short time after it was discovered there it had become established upon all the larger islands of the Hawaiian group. The use of introduced insect parasites has been found a more prom- ising control measure under the peculiar horticultural conditions of Hawaii (where the majority of host fruits are either inedible or not worth the cost of spraying) than are the artificial control methods of spraying and the destruction of infested fruits employed in commercial fruit-growing areas in certain other parts of the world. In 1913 and 1914 the government of the Territory of Hawaii introduced and established four species of parasites which attack the larval stage of the fiy. Three of the species were braconids and one achalcid. Two braconids, Opius humilis Silvestri and Diachasma fullawayr Silvestri, and the chalcid Tetrastichus giffardianus Silvestri were imported from South Africa, and the braconid Diachasma tryoni Cameron was intro- 1 At the time of the collecting of the information contained in this circular Mr. Willard was entomologist and Mr. Bissell was plant quarantine inspector, both in the Division of Tropical, Subtropical, and Orna- mental Plant Insects, Bureau of Entomology. 2 Italic numbers in parentheses refer to Literature Cited, p. 12. 90085—30 CIRCULAR No. 109 MARCH, 1930 | ete 2 CIRCULAR 109, U. S. DEPARTMENT OF AGRICULTURE duced from Australia. Other parasites were introduced, but the four mentioned were the only ones that became established. The uniform climate of Hawaii and the constant abundance of host maggots resulted in a rapid dispersal of these parasites, and within three years after liberation they were firmly established on the main islands of the Territory and were parasitizing between 30 and 50 per cent of the fruit-fly larvae. Since these parasites became established the Bureau of Entomology of the United States Department of Agriculture has compiled a com- prehensive series of records which show the amount of parasitism accomplished by each species and the degree of infestation of host fruits by the fly. These records have been obtained by making almost daily collections of host fruits about the city of Honolulu and securing from them the maggots as they emerged. These maggots were held in rearing jars and the numbers of emerging flies and parasites care- fully recorded. In this manner the effectiveness of each species of parasite has been determined over monthly and yearly periods since 1914 for the various host fruits. The results of these observations up to ca including 1921 have already been published (1, 2, 4, 6, a9, 10): During the first few years after the parasites were liberated in Hawaii yearly reports of their activities were of much interest. In that period there was considerable yearly variation in the effectiveness of each species and in the total parasitism by all species. Conse- quently, during the years from 1915 to 1921, inclusive, these records for each year were published separately, excepting those for 1919 and 1920 which were published together in one paper (9). The records for the last five years of this period, however, show that the work of the parasites has become more or less stabilized and that there is much less variation over yearly periods. Consequently, much of the necessity for yearly reports has disappeared, and a 3-year reporting period has been adopted and put into effect in this circular. It is believed that the reader can get a more thorough and comprehensive idea of the relationship and actual work of these parasites if the information for the period is included in one report instead of three. RECORDS OF INFESTATION In connection with the recording of parasitism, an attempt has been made to note any increase or decrease in abundance of Ceratitis capitata in the field. In making this attempt the following hypothesis was adopted: An increase or decrease in the number of maggots in infested fruits will indicate that there has been an increase or decrease in the number of adult flies. As all fruits collected for records of parasitism were held in the insectary long enough to allow all maggots to emerge, and as records of the numbers of all fruits and of the maggots emerging from them were kept, the average infestation per fruit for each species of host can be computed from these records. Tables 1 and 2 give the results of these observations and computations. PARASITISM OF MEDITERRANEAN FRUIT FLY IN HAWAII 3 TABLE 1.—Records of infestation of host fruits by larve of the Mediterranean frurt jly in Hawaii during the years 1922, 1923, and 1924 Average Number of fruits | Number of larvae | number of | Average collected emerging lat yae per aes 7 i Host fruit ruit enim! ET a AOE Te La RTE, RS ee 1922 | 1923 | 1924 | 1922 | 1923 | 1924 |1922/1993|1904) inclusive Indian almond (Terminalia catappa) -.-|27, 772/17, 505)20, 408/195, 512/135, 484/100, 225) 7.0) 7.7| 4.9 7.9 Mango (Mangifera AT CICa) Paes hee ow 3 198) 2, 313) 3, 189) 18, 362] 23, 923) 21,923) 5. 7/10. 3] 6.9 5.9 @ofiee,(Cofiea: arabica) =.= s2. -2-2252. 250228 21, 15/205 647)| Bae ae 1270)2 Geo02Eoes ee Lies 4 Oi guava (Psidium cattleia- IU TOY ny ey eS A see 13, 318} 3, 813) 2,494) 21,795} 4,613) 3,059) 1.6) 1.2) 1.2 1.5 Black myrobalan (Terminalia chebula)_} 2, 036|_._.---|------ 63598 |S ee BE VA ee ee 6.0 French cherry (Eugenia uniflora) -_-_-__- 6, 453| 5, 510)12, 980} 6,056} 5,202] 16,897; .9| .9) 1.3 1.2 Satin leaf (Chrysophyllum olivae- HOITING) Pps ee Soe ee T628 oes irs oboe SrS dO ess |e ee 3:16 | fees | eee 3.3 Rose apple (Eugenia jambos)---__-__-_-- 321; 107) 1,897) 3,949 343} 22, 369/12. 3) 3. 2/11.8 9.9 West Indian medlar (Mimusops elengi)-|-_----- VG) HE ee ee 364) 2-225 a Mee POL Ge 8S Sou Carambola (Averrhoa carambola) ___---j|--_--- Say) SIS es 11 20 asl eel liars .6 Yellow oleander (Thevetia neriifolia)___; 1, 208 5,150} 422) 4,548} 26, 493 814, 3.6) 5.1) 1.9 4.0 . Loquat (Eriobotrya japonica) -____-_--- AQ | ses ee i Dili eRe |S aaa | ee ese 2.4 Chinese orange (Citrus sp.)_--_-------- 42, 195/31, 731/26, 750/119, 816) 66, 049) 58, 812} 2.8) 2.1) 2.2 2.4 Guava (Psidium guajava)..._.-_------- 4, 706| 3, 494 L 002 53, 762| 25,193} 5, 502/11. 4) 7.2) 5.5 8.2 Orange (Citrus aurantium) __._._------ 1,728) 1,121) 635) 4,270) 38,891) 1,208) 2.5) 3.5) 1.9 3.0 Tangerine (Citrus nobilis)__.._...___--- 494) 1,554) 1,460) 2,108} 1,048 817| 4.3) .7] .6 185 Lime (Citrus medica limetta) -______--_- SDA cee 3oS 386 67 CO eA ges ke .6 INoronhiaemanrginatas- 2-25 Fe seo AOGG(Rsceex (alsa se a aed pbs a aS SI 15 /S 223 | cee ies Ochrosigieilipiicas =e eee G7: eee Pe es (0) Pees ge Tce 11) eh a eas BH y/ Kamani (Calophyllum inophyllum)--.-_|.----- TGS Ed ge ee its 203) Eee ieee eS eae 3.5 Peach (Amygdalus persica) -_-.--------|------ IS eee ee pe a ADD Piette 2 lear toe 234 noes 18. 4 White sapote (Casimiroa edulis) _______- 24 eked a ee PU he a 2292s aaeien 5.9 Star-apple (Chrysophyllum cainito)_.__|}.----_|------ JB PR leh ee bs () 2h ee Oak Seon Waiawi (Psidium guajava pyriferum) __|_-____]_-__-- VAG ewe asa | eee Se Me el sale Q 25 ARermnneliaispp=.teb a ee Wena Oe ee eee ee 2S leeeen us| ene OS |e ees | G49 6.9 Grapefruit (Citrus decumana)-------_--|------|------ 6G eae ra es QA | 43 PP ACHACHS CARICA) soe as ee eee eee | Re oe ecg SO eee ao eee AB ees ees Deal eal TABLE 2.—Average number of larvae of the Mediterranean fruit fly per fruit examined in Hawaii for each year of the period 1916 to 1924, inclusive, and for the period as a whole Average number of larvae per fruit in— Host fruit Over 1916 | 1917 | 1918 | 1919 | 1920 | 1921 | 1922 | 1923 | 1924 | 9-year period 1 AM@ianralmonde ss. se ee Qe oy aS: Ol eONON Tn SKaet O50 LO; Sale CaOr eid 459 7.9 NVR Os sae eee ue ka eh B2 a Dera er Selet e244 Gk Seal) Seon wo OmMmeDa en OnsalOs9 5.9 COMCE see ee ete ae ee ay Ue ms od) .8 6 A .6 bei eee sell &) 4 SUrawibernyiguavace 2 sos le ees Bee LOE 2s Onieeeo snl Qi ae ele 5: Aue ole lO leroy emer 1.5 Blacks myrobalan 2 se (a OMPeOsOn pean Sake | OsO sO iO pais cies seo | eee 6.0 KEN CHICheniy see ee ee 28 120") 1k0 20H e140] 5159 .9 Oe 8 12 SAGUITI Ce Wem eee ae ee ee ee. ZEON Ee Coan Samed: On Paae ie |p. == 5) a ee 3.3 IROSCAD Denote = Se a ar Ne ety || Gite) | OG ee a ab tye eae WN e334 i) aha f3} 9.9 Wiest Imdianimedilar: = 2225. 925 eee Re SP Gide ee MASE G OM lee eee BY NE ee a ah 7/ Serrovore bi ele 2 ae eee eee Oe eae eee ie ea OLE fee se ee se (a ee SHOR eae OER eee Ae 7.0 CATA DO We se eek oe ee BS IES .9 gal 27 OR mess all bal .6 Mellow Oleander (ice. 22 ese ee S Ghia ROse EON OR| a leediily © le. )e=: ae BoGiie 7d. Le 1e9 4.0 LOO PERS Sh OE ae SP ee eee eee QO | LSet ou4y ee ses 4.5 Bre) | fees iB | Le ae 2.4 @himesevorangess ie eae ee ad Bal These) |i dieses We PA GN ASN PAG BAS I Oe ata 2 O 2.4 UDA YiCh ea pee a RE ek ea Tete) | eats) Ps toy, |p Ec eo Oy Ce HP Tee TS Yee yy iS 8.2 WTAE Cue ee aoe eee et Re Dae Soi ae ne NR ape. oe Bee GOW ore 2hO | Bay. Ie) 3.0 eRanverin@ieese - C7 ENE ei ee Oe Ee earls bea ee ees ek «9 [93.1 | 453 a .6 15 TMC ee ee Be Ee ae Pe bre ed WPF |e ii .o a2) © .6 INoronhiaiemarsinatas— 22 eee ip eee deo Ei eat le ch i ian pce |i bs Pah oe he |e 1.6 Ochrosiajelliptical.-- 22255. esis. nee Sel ZBR Dy) = ee ee Cee gee ateH CQ) | eee ey. ia raed Bh 7/ FRCL TA Tee eee ee mea ie leasuont paetanee cna Or OM eckaQuies —L ie fee sores IE ieaeeee 3.5 Tete (gatas eee Ra So See eee oe Gee ene ZOUSR lion gae2Ze4 sp oaO ello Ge (eas sm pte eenen D354 ee 18. 4 WHIT CIS A OUG ie epee we Ee es PEN |e ee ne eee ee. es Dials e || ses 2 U 5.9 SLGE-4)D DC ume = een. ek ee eS Oe 5s ie pa S| ce he eed .0 .0 WVU Aye en SE a es [pens ee (eee 21a eel 5 Ope 5 ea ee ee .0 ah “AM GSRTEM OIG UW, Sf Oy Oy Sok wa Om SR A me Ts [Soe ales Ses 6.9 6.9 Grapetruitaes . Orie ei ebay. ed |i oe Re S48 (ee See CE OE eRe Ne eM ee Be) Een S BS pe) Ti a ee eee | Poet flats A es ie ke el oe ee 2 cle IBY = flees 5: 1 Beal Brazilian plum (Eugenia braziliensis) - Bs jc ec | See a fe el | mI el 1, des Me i .8 1 Weighted averages. 4 CIRCULAR 109, U. 8S. DEPARTMENT OF AGRICULTURE 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 occas- ionally during the 9-year period. On the basis of comparisons only with those fruits upon which records were secured 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 ereater in 26.7 per cent of the species of host fruits, and in 1924 it was ereater 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 during 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-year 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 eent; 1921, 71.4 per cent; 1922, 42.9 per cent; 1923, 26.7 per cent; 1924, 25 per cent. These records show that during three years, 1916, 1917, and 1921, the infestation 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 Owing to the oviposition habits of the parasites of the Mediter- ranean fruit fly now established in Hawaii, the effectiveness of these enemies in controlling the fly is governed to a large extent by the nature of the fruits in which the host maggots are developing. The three opiine parasites, Opius humilis, Diachasma tryoni, and Dia- chasma fullawayi deposit their eggs within 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 afford 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, where the maggots are necessarily always near the outer surface of the fruit, parasitism is high. Tetrastichus giffardianus oviposits directly into the host maggot and must come directly in contact with the maggot before oviposition is possible. In order to reach host maggots within a fruit, it must be able to enter through some break in the skin. Fruits with tough skins which do not break readily when they fall PARASITISM OF MEDITERRANEAN FRUIT FLY IN HAWAII 9) from the trees usually have a very low parasitism by T. giffardianus. Fleshy fruits with comparatively thin skins which are broken easily offer a much better opportunity for the parasite to work. The data in Table 3 sbow the effectiveness of each species of para- site in each host fruit under observation for the second to sixth day of each month stated. Indian almond is a good example of a fruit containing a large seed surrounded by thin pulp. The opiine para- sites were much more effective than 7. giffardianus during all periods for which records were kept for the 3-year period with the exception of January, 1922, and the last five months in 1923. During those five months large numbers of this fruit were collected within an area of about four city blocks, and owing to some undetermined cause T. giffardianus was able to parasitize an unusually large number of the developing maggots. oe ISOS aS ae fa 26 re ne a | ae Gite eer e| bee ie il Via roqureydog = utes £ OT ; ae 69 Belen solec i it Fie patente | emt ant Beall nn pare An hee | alse eat he aa GO OGak | ST oe QSNBniy jroo ts ose ens="5%4=** tereqorAor ov Heres Ae 2 Rae ves) ret (eee all eset Menem eens Dl aS ose ae ee (Aaa eal ogy ees | lh cag ED "===" 19Q0400 Pettey Se eg ore” Cal Wes rs LlGr | nau ee | ace QhOGM ac om sp poe OOMese ease mae!) a= =| eh eage iad Jequ1e;dog 5 eaeeT 0‘O0T| 96% |--- > QROOT MCAS SF oes RS aT 10° (0s| boil or Sree |e a GRE cette a eae tet a aeaeteae oe L COU Gs see ~-“asnany im Boe oe ON SOs Case 0 oT 16 ORGS fi eae ene eG ceca 0 | “Oe Gralla as |iecsaonme line Saleh slant ee | OGG ae rae Aine fe ay i ae Lh eh SU Niessen al RI at ORDER al Sy Gasin Kaiee ae | ce h et CAG Palrrce toot ome tee 365] ARS ee Lae aaa (Ooo) Fe |e III IIS) 0 gly =) pegs hee eas OxCOm aa Sir Sees (0 )atc}] Oy 7 [ena | ane Cade Me ar ie reat |g Gell ean | eo 2 Os ar er ml ene tat SOR Gs reo Sa ACTA io) i eae Pane ee Sey On eee alla lel ORGowle eee s|eOG | oncn leanne (3 FB We OOS Reveal tel) (6G Kee wae 008 COCR ral aa Sete [udy ea RELY oe eames! 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It is very seldom that 7. giffardianus is reared from maggots in this fruit, but the parasitism by the opiine parasites is very high. The 11.1 per cent parasitism in October, 1924, shown in footnote 1 of Table 3, was the work of the melon fly parasite Opius fletchert Silvestri. This parasite is occasionally reared from maggots of the Mediter-. ranean fruit fly, but the high parasitism recorded during the month mentioned is very unusual. It was probably due to the fact that all of the coffee containing the maggots from which it was reared were collected in the Kona coffee fields on the island of Hawai. Around these fields the Chinese cucumber Momordica sp. grows wild and is- very abundant. The fruits of this plant are attacked freely by the- melon fly, Bactrocera cucurbitae Coq., the maggots of which in turn are highly parasitized, resulting in an abundance of O. fletcheri about the coffee fields. The mango is an example of a fleshy fruit with a comparatively tough skin which does not break easily when the fruit falls. The per-. centage of parasitism in this fruit by either the opiine parasites or the. chaleid 7. miffardianus is not high. vate The guava, which is very abundant about Honolulu, has a very thin skin and a deep pulp. The majority of maggots are beyond the reach of opiine parasites, and this results in a very low degree of para-. sitism by them. The thin tender skin of this fruit breaks easily when the fruit falls to the ground or is often punctured by birds or by coming in contact with some part of the tree. Consequently, 7. gif-- fardianus is afforded an unusual opportunity to enter this fruit, and the parasitism by this species is in almost every instance higher than. that by any of the opiine parasites. In a number of instances it was. higher than the combined parasitism of all three species of opiines. These are mentioned as examples of the influence exerted by the. structure of the infested fruits upon the effectiveness of the fruit-fly parasites, and this influence can be observed by reviewing the records in the table of the parasitism in other fruits. Table 3 shows that all four species of parasites will attack their host in most of the fruits under observation. ‘Though the structure of the infested fruit controls to a large extent the parasitism by D. fullawayi, the degree of its effectiveness in some fruits can not be attributed to this cause. This parasite in the majority of host fruits is compara- tively ineffective, whereas in coffee and yellow oleander its effective-. ness is greater than that of either of the other two opiine parasites. This may be an indication of some preference on the part of this parasite for maggots in certain fruits. Table 4 records the effectiveness of each species of parasite in all fruits collected during each month of the three years. O. humilis was first in effectiveness during three months in 1922, during no month in 1923, and during five months in 1924. Diachasma tryont was the most effective during seven months in each of the years 1922 and 1923, and during five months in 1924. D. fullawayi was the most effective during only one month of the 3-year period under consideration, namely, in December, 1924. JT’. giffardianus was the most effective parasite during two months in 1922, five months in 1923, and one- month in 1924. 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. " 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. 12 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) CIRCULAR 109, U. S. DEPARTMENT OF AGRICULTURE LITERATURE CITED Back, E. A., and PEMBERTON, C. E. 1915. PARASITISM AMONG THE LARVAE OF THE MEDITERRANEAN FRUIT FLY (C. CAPITATA) IN HAWAII DURING 1914. Hawaii Bd. Commrs. Agr. and Forestry [Bien.] Rpt. 1913-14: 153-161. and PEMBERTON, C. E. 1916. PARASITISM AMONG THE LARVAE OF THE MEDITERRANEAN FRUIT FLY (C. CAPITATA) IN HAWAII DURING 1915. Jour. Econ. Ent. 9: 306— 311. and PEMBERTON, C. E. 1918. THE MEDITERRANEAN FRUIT FLY IN HAWAII. U.S. Dept. Agr. Bul. 536, 119 p., illus. PEMBERTON, C. E., and WiLuarp, H. F. 1918. FRUIT-FLY PARASITISM IN HAWAII DURING 1916. Jour. Agr. Research 12: 103-108. and WILLARD, H. F. 1918. INTERRELATIONS OF FRUIT-FLY PARASITES IN HAWAII. Jour. Agr. Research 12: 285-296, illus. and WILLARD, H. F. 1918. WORK AND PARASITISM OF THE MEDITERRANEAN FRUIT FLY IN HAWAII DURING 1917. Jour. Agr. Research 14: 605-610. and WILLARD, H. F. 1918. A CONTRIBUTION TO THE BIOLOGY OF FRUIT-FLY PARASITES IN HAWAII: Jour. Agr. Research 15: 419-465, illus. WILLARD, H. F. 1920. WoRK AND PARASITISM OF THE MEDITERRANEAN FRUIT FLY IN HAWAII DURING 1918. Jour. Agr. Research 18: 441-446. 1923. WORK AND PARASITISM OF THE MEDITERRANEAN FRUIT FLY IN HAWAII DURING 1919 AND 1920. Jour. Agr. Research 25: 1-7. — and BissE.1u, T. L. 1926. WORK AND PARASITISM OF THE MEDITERRANEAN FRUIT FLY IN HAWAII IN 1921. Jour. Agr. Research 33: 9-15. U.S. GOVERNMENT PRINTING OFFICE: 1930 For sale by the Superintendent of Documents, Washington, D.C. - - - - Price 5d cents