Bess, H.A.

Haramoto, F.

Van Den Bosch, R.

Proceedings of the Hawaiian Entomological Society

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Vol. XIV, No. 1, March, 1950 29Progress and Status of Two Recently Introduced Parasites of theOriental Fruit Fly, Dacus dorsalis Hendel, in Hawaii1By H. A. BESS, ROBERT VAN DEN BOSCH, and FRANK HARAMOTOUNIVERSITY OF HAWAII AGRICULTURAL EXPERIMENT STATION(Presented at the meeting of December 12, 1949)In June of 1948, N. L. H. Krauss, Entomologist with the TerritorialBoard of Agriculture and Forestry, began shipping fruit fly puparia containing parasites to Honolulu from Malaya. Two of the braconids, Opiuspersulcatus (Silvestri) and Opius longicaudatus (Ashmead), reared fromthe puparia were released in relatively large numbers throughout theTerritory during the following twelve months. The establishment, spreadand increase in abundance of these parasites have been studied fairlyintensively since the initial releases were made.2 This paper shows theprogress and status of these parasites in Hawaii through 1949.RELEASESTable 1 summarizes the numbers of O. persulcatus and O. longicau-datus that have been liberated in the Territory and on Oahu where moreintensive studies have been made on their establishment, spread, andabundance. The early releases were predominantly O. longicaudatus.However, several small liberations of O. persulcatus were made during thefall and winter of 1948-49 in the general vicinity where the bulk of theinformation given in this paper was obtained.Table 1.—Summary of liberations of O. longicaudatus and O. persulcatusin Hawaii.LiberationsJuly-Sept., 1948Oct.-Dec, 1948Jan.-Mar., 1949Apr.-June, 1949July-Sept., 1949TOTALNo. parasites liberated3O. persulcatusOahu651,35766510,59320012,880all islands651,4825,28114,2081,63422,670O. longicaudatusOahu1,41418,4945,54310,6755,48841,614all islands1,71440,05818,13822,66021,781. 104,3511 Published with the approval of the Director of the Hawaii Agricultural Experiment Station asTechnical Paper No. 194.2 G. B. Mainland and S. Shimono, former members of the entomological staff, obtained an appreciable part of the information presented on the establishment and spread of the two parasites duringthe fall and winter of 1948-49, and spring of 1949.8 All parasite liberations were made by the Board of Agriculture and Forestry.30 Proceedings, Hawaiian Entomological SocietyESTABLISHMENT AND SPREAD OF PARASITESWithin a few weeks after liberation of O. longicaudatus recoveries weremade from fruits collected at several liberation sites and adults were alsoreadily observed at these places. Furthermore, the parasites spread to adistance of at least one-quarter mile within two months after liberationand one to four miles in four months. By the fall of 1949, O. longicaudatus adults were commonly seen on mangoes and other fruits throughoutthe island of Oahu, and at a number of places on Hawaii, Kauai, andMaui.O. persulcatus apparently became established from the small liberationsmade in the fall and winter of 1948-49 but until the fall of 1949 wasrecovered from only a few places. However, it has now spread a distanceof at least six miles from two different liberation points and occurs generally throughout the Honolulu, Kailua, and Waimanalo areas on Oahu.To date it has been recovered on the outer islands only in the vicinitiesof a few liberation points.INCREASE IN ABUNDANCE OF PARASITESO. longicaudatus increased rapidly after its release in Manoa Valley(Table 2) and similar increases were observed in several other liberationareas. Parasitization by this species was frequently as high as 50 per centTable 2.—Parasitization of D. dorsalis from guava fruits collected inManoa Valley (Oahu).Date12- 1-4812-15-482-16494- 5-497-29-499- 9-4910-25-4912- 2-4912- 7-49No insample727206722581215340476192246No. parasitized byO. persulcatus000019272351138159O. longicaudatus141313137832421749Totalper centparasitized0.119.94.353.945.189.482.685.284.6Ratio ofpersulcatus tolongicaudatus........6"i8.58.48.13.2in fruit collections made in the spring and summer of 1949 on Oahu. Theincrease on the outer islands has been slower but in a few localities parasitization has exceeded 40 per cent. During the late spring and summer of1949, the adults of this parasite became conspicuously abundant locallyat several places on Oahu and Maui. In these areas hundreds of adultscould be seen flying over and resting on low vegetation. However, whereclose examinations were made, it was found that males predominated inthese high populations. In early October O. longicaudatus adults (malesand females) were seen generally on the slopes of Haleakala (Maui) below3,000 feet elevation. However, fruit collections at that time indicatedVol. XIV, No. 1, March, 1950 31that parasitization was for the most part below 50 per cent. Furthermore,collections made at the same places a month later gave parasitization ofless than 10 per cent.In the shipments from Malaya, O. persulcatus predominated to theextent of about 22 to I.4 In Hawaii the initial increase of O. persulcatuswas considerably slower than that of O. longicaudatus. However, relativelyfew of the former species were liberated until late in the spring of 1949.As stated above, prior to the fall of 1949 O. persulcatus had only beenrecovered in numbers from a few localized areas. Nevertheless, collectionsmade in Manoa Valley (Table 2), Waimanalo (Table 3) and at pointsthroughout a large part of Oahu (Table 4) in the fall of 1949 revealedthat O. persulcatus had increased in abundance tremendously. In can beTable 3.—Parasitization of D. dorsalis from guava fruits collected atWaimanalo, Oahu.Date6- 7-10-499-204910- 5-4911- 7-4912-13-49No. insample354135111403335No. parasitized byO. persulcatus613467248192O. longicaudatus741572549Totalper centparasitized38.136.366.667.771.9Ratio ofpersulcatus tolongicaudatus0.82.39.69.93.9Table 4.—Summary of parasitization of different instars of D. dorsalis byO. persulcatus and O. longicaudatus from 52 collections takenon Oahu during October, November, and December, 1949.Instar1st2nd3rdTOTALNo. fliesemerged4062,3172,0314,754No. parasitesemergedO. persulcatus1921,5011,9143,607O. longicaudatus123358661,213Per centparasitized byO. persulcatus31.536.139.837.7O. longicaudatus2.08.118.012.7Totalparasitization33.544.2-57.850.4seen from Table 2 that in the samples taken from Manoa Valley in September, October and December, 1949, O. persulcatus alone parasitized65 to 80 per cent of the larvae of D. dorsalis. Many other collections takenon Oahu during this period gave similar high percentages of parasitization by this species. Not only has O. persulcatus increased in relativeabundance during the fall and winter of 1949 but there has been a greatincrease in the ratio of this species to O. longicaudatus. The combinedparasitization by the two species in several collections has exceeded 80per cent.4 Figures obtained from rccoids submitted by the Territorial Board of Agriculture and Forestry andfrom the U. S. Bureau of Entomology and Plant Quarantine.32 Proceedings, Hawaiian Entomological SocietyPARASITES REARED FROM DIFFERENT LARVAL INSTARSDuring October, November, and December, 1949, several collections ofripe guavas, Psidium Guajava L., gathered for the most part from theground, were made at points well distributed over the greater part ofOahu. Within a day after collection, the D. dorsalis larvae were removedfrom the fruit, segregated into instars, and allowed to complete theirdevelopment in papaya pulp medium. In this manner parasitization ofthe different larval groups (instars) at the time of collection, was obtained.A summary of the numbers of parasites reared from the different instarsis given in Table 4. This summary is based on rearings from 52 collections, each of which produced both species of parasites. The parasitesthat emerged from the first instar groups represent parasitization due toattack of only first instar larvae, those that emerged from the second represent parasitization of the first and second instars, and emergence fromthe third represents parasitization due to attack in all three stages. It isobvious that such figures do not show the maximum parasitization expected in the different stages in the field. From the information given inTable 4, from additional data on parasitization from other collections andfrom observations of adult behavior, there is considerable evidence thatO. persulcatus commonly oviposits in younger larvae than those normallyattacked by O. longicaudatus. The ratios of O. persulcatus to O. longi-caudatus in the different instars obtained from the data in Table 4 are asfollows: first instar, 16.0 to I; second instar, 4.5 to 1; third instar, 2.2 to 1.Females of O. longicaudatus are commonly seen inserting their ovipositors in fruits on the ground, whereas adults of O. persulcatus apparentlyrarely occur on fruits on the ground. Furthermore, it can be seen fromthese figures that there was relatively little increase in parasitization byO. persulcatus in the later instars. On the contrary, there was an appreciable increase in the parasitization by O. longicaudatus in the largerlarvae. There is the possibility that many young larvae stung by O. longi-caudatus are killed and therefore that the species may actually attack alarger number of young larvae than the figures indicate. Despite this possibility, it now appears probable that O. persulcatus has a greater influence on first instar larvae than does O. longicaudatus.SEX RATIO OF PARASITESThe available information indicates that more females than malesoccur in the populations of O. persulcatus and that the sexes occur inabout equal numbers in the populations of O. longicaudatus. This condition prevailed in the shipments from Malaya as well as in the collectionstaken from the field on Oahu. In the imported collections, out of a totalof 12,7105 O. persulcatus received, females predominated 2.1 to 1, and ina total of 587 O. longicaudatus, females occurred at a ratio of 1.0 to 1.From the 52 Oahu collections referred to above, a total of 3,607 O. persulcatus and 1,213 O. longicaudatus were reared. The figures show that5 Figures obtained from records submitted by the Territorial Board of Agriculture and Forestry andthe U. S. Bureau of Entomology and Plant Quarantine.Vol. XIV, No. 1, March, 1950 33the ratio of females to males was 1.8 to 1 for O. persulcatus and 1.0 to 1for O. longicaudatus. These ratios are quite similar to those obtainedfrom the Malaya collections.Table 5.-Sex ratio of O. persulcatus and O. longicaudatus reared fromD. dorsalis larvae of different instars at the time of collection.[nstar1st2nd3rdTOTALO. persulcatusNo. reared1921,5011,9143,607Ratio offemales/males1.81.81.81.8 .O. longicaudatusNo. reared123358661,213Ratio offemales/males' 0.20.71.11.0Table 5 shows the sex ratios of the parasites reared from the differentinstars of D. dorsalis larvae. The sex ratio of O. persulcatus was the samefor the groups reared from all three host instars, whereas the ratio offemales tP males of O. longicaudatus increased with the later instars. Thetrue sex ratio of O. longicaudatus that develop from larvae parasitized inthe first instar may be quite different from that shown in Table 5 sincerelatively few individuals were reared. It would appear from the morefavorable sex ratio of O. longicaudatus obtained from the third instar thatthis parasite is better adapted to development in older larvae. Furthermore, the favorable sex ratio of O. persulcatus reared from all threeinstars indicates that it is well adapted for development in the smallerlarvae.DISCUSSIONSufficient time has not elapsed to determine what the final status ofO. persulcatus and O. longicaudatus will be in Hawaii, or what relationthe species will have to each other. However, both parasites have becomewell established and give promise of playing an important role in reducing the abundance of D. dorsalis in the Islands. During the late summerand fall of 1949 O. persulcatus increased tremendously in abundance andby the end of the year had become far more numerous than O. longicaudatus in several localities. Since O. persulcatus is the predominant speciesin Malaya and there has been a shift in that direction recently in Hawaii,it may possibly become the more important of the two species here.

Progress and Status of Two Recently Introduced Parasites of the Oriental Fruit Fly, Dacus dorsalis Hendel, in Hawaii

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Progress and Status of Two Recently Introduced Parasites of the Oriental Fruit Fly, Dacus dorsalis Hendel, in Hawaii

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