Proceedings of 6th International Symposium 6–10 May 2002, Stellenbosch, South Africa pp. 457–459

Successful acclimatization of Psyttalia fletcheri (: Opiinae) for biological control of the fly, cucurbitae (Diptera: ),on Réunion Island

S. Quilici*, B. Hurtrel, R.H. Messing, B. Montagneux, A. Barbet, F. Gourdon, A. Malvolti & A. Simon CIRAD Réunion, Pûle de Protection des Plantes, 7 Chemin de l’IRAT, 97410 Saint-Pierre (France)

Since its introduction to Réunion Island probably more than 40 years ago, the melon fly, Bactro- cera cucurbitae (Coquillett), has become one of the most serious pests attacking Cucurbitaceae crops on the island. In 1995, a biological control programme was initiated by CIRAD in collabora- tion with USDA Hawaii and the University of Hawaii to try and introduce the melon fly , Psyttalia fletcheri (Silvestri), from Hawaii, in order to improve the natural control of melon fly populations in areas with wild cucurbits. A laboratory colony was developed and more than 195 000 adult of both sexes were released from 1995 to 1997. P. fletcheri was first recovered in 1996 from five different sites. From 1996 to 2001, P. fletcheri was recovered from 12 sites situated all around the island. All collections were from only one host-fruit, the bitter gourd L. rates were highly variable, between 1 and 75%. From 1996 to 1998, recoveries were obtained from sites only where the parasitoid had been released. However,in 2001 P. fletcheri was recorded far from any release site,confirming its ability to disperse effectively. The parasitoid can now be considered to be acclimatized on Réunion Island and it will be useful to analyse the evolution of its parasitism rates over several years in order to assess its impact on populations of the local Dacini species, and particularly on populations of B. cucurbitae.

INTRODUCTION fruit, placed in oviposition units, and presented Since its introduction to Réunion Island probably to female parasitoids (minimum age, two days) for more than 40 years ago, the melon fly Bactrocera 24 hours. Parasitoids were maintained in plastic cucurbitae (Coquillett) has become one of the cages (300 × 210 × 350 mm) and provided with most serious pests attacking Cucurbitaceae crops diluted honey. A piece of organdy was used to in the island (Etienne 1982; Vayssières & Carel restrain host larvae in an oviposition unit 1999). In 1995, a biological control programme (plastic lid; diam. 50 mm; height 4 mm). Before was initiated by CIRAD in collaboration with packing, larvae were rinsed and the excess media USDA Hawaii and the University of Hawaii to try squeezed out. After exposure to parasitoids, host and introduce the melon fly parasitoid Psyttalia larvae were removed from the oviposition units fletcheri (Silvestri) (Braconidae: Opiinae) from and placed with their media in plastic boxes Hawaii, in order to improve the natural control of (355 × 235 × 130 mm) containing dry sawdust for melon fly populations in areas with wild cucur- pupation. Pupae were screened out 3 or 4 days bits. This parasitoid species had been previously later and placed in a plastic box (diam. 80 mm, introduced to Hawaii in 1916 (Clausen et al. 1965). height 50 mm) in an emergence cage. This programme was coupled with an evaluation Both melon fruit and parasitoids were held of parasitism of fruit flies attacking Cucurbitaceae in a room at 25 ± 1°C and 60 ± 10% RH, with indi- by indigenous parasitoids or by parasitoids rect natural light. introduced in previous biocontrol programmes. Releases MATERIALS AND METHODS P. fletcheri releases were made with the colla- boration of UDAC (natural enemies production Rearing procedures unit), a local structure of the FDGDEC (Fédéra- Mated females of B. cucurbitae were allowed to tion Départementale des Groupements de oviposit into ( pepo L.) for 24 Défense contre les Ennemis des Cultures). hours. After this, were removed from the Sexually mature parasitoid adults were released cage and placed into a plastic box on potato at a site where their host was present in abun- flocks. Six days later, larvae were removed from dance. This site had to be free of chemical treat-

*To whom correspondence should be addressed. ment,and frequently consisted of a non-cultivated E-mail: [email protected] area with wild cucurbits (such as the bitter gourd 458 Proceedings of the 6th International Fruit Fly Symposium

A

B

Fig. 1. Biological control programme against Bactrocera cucurbitae with Psyttalia fletcheri on Réunion Island. A, release sites of P. fletcheri, 1995–1997; B, percentage parasitism by P. fletcheri in bitter gourd samples, 1996–2001.

Momordica charantia L.; Cucurbitaceae) (see RESULTS Table 1). A laboratory colony was developed in 1995 and releases were made from 1995 to 1997, totaling Fruit sampling more than 195 000 adult parasitoids of both sexes Cucurbit fruits were collected in various areas (see Fig. 1A for release sites). of the island to assess the presence and abun- This exotic parasitoid was first recovered in 1996 dance of P. fletcheri or other parasitoid species. from five different sites. Then, from 1996 to 2001, These fruits were collected mostly in non-culti- P. fletcheri was recovered from 12 sites situated vated areas to obtain pesticide-free material. all around the island (Fig. 1B). All recoveries were Samples were numbered, weighed, and kept in from only one host-fruit, the bitter gourd Momor- the laboratory at 25 ± 1EC, with a photoperiod of dica charantia L. (Cucurbitaceae). Parasitism rates 12L:12D, and 80 ± 10% RH. Pupae were collected were found to be highly variable, between 1 and weekly from the sample and maintained in small 75% (Fig.1B). Whereas from 1996 to 1998 recover- plastic boxes for emergence. After all adults had ies were obtained from sites where the parasitoid emerged and died, they were identified, num- had been released, in 2001 P. fletcheri was recor- bered and their sex was recorded. ded far from any release site, confirming its abil- Quilici et al.: Successful acclimatization of Psyttalia fletcheri for biological control of melon fly on Réunion 459

Table 1. Parasitism by Psyttalia fletcheri on Dacini damaging cucurbits, evaluated from bitter gourd fruits (Momordica charantia) collected from 1996 to 2001.

Year of Site no. No. of fruits No. tephritids No. of P. fletcheri % Parasitism recovery (B. cucurbitae/ D. ciliatus)

1996 1 195 472 68 12.6 3 15 80 2 2.4 4 28 8 1 11.1 5 104 266 22 7.6 12 34 18 27 60.0 1997 2 6 114 6 5.0 3 84 29 2 6.4 58 38 68 6 8.1 28 1 3 75.0 1998 5 10 44 13 22.8 6 385 576 20 3.4 9 20 65 2 3.0 2001 7 23 100 1 1.0 10 56 196 50 20.3 11 42 82 24 22.6 ity to disperse effectively. Further laboratory studies would be needed to Among the other parasitoid species collected, determine its specificity in relation to the other the most frequently recovered was Tetrastichus dacine species attacking Cucurbitaceae on Réunion giffardianus (Silvestri) (Eulophidae). This larvo- Island [Dacus ciliatus Loew and D. demmerezi pupal parasitoid had been introduced onto (Bezzi)]. Réunion in the period 1972–75. Parasitism by this species appears low in many cases. However, REFERENCES CLAUSEN, C.P., CLANCY, D.W. & CHOCK, Q.C. 1965. Bio- it would be interesting to study in more detail logical control of the Oriental fruit fly (Dacus dor- its status (primary or secondary parasitoid) in rela- salis Hendel) and other fruit flies in Hawaii. Technical tion to P. fletcheri . Bulletin, United States Department of 1322: 67–102. ETIENNE, J. 1982. Étude systématique, faunistique et CONCLUSION écologique des Téphritides de la Réunion. Thèse Psyttalia fletcheri can now be considered as Ecole Pratique des Hautes Études, Paris. acclimatized on Réunion Island. It will be useful VAYSSIÈRES, J.F. & CAREL, Y. 1999. Les Dacini (Diptera: to analyse the evolution of its parasitism rates Tephritidae) inféodés aux Cucurbitaceae à la Réunion: over several years in order to assess its impact gamme de plantes-hôtes et stades phénologiques préférentiels des fruits au moment de la piqûre pour on populations of local Dacini species, and des espèces cultivées. Annales de la Société Ento- particularly on melon fly populations. mologique de France 35: 197–202.