Impact of Psyttalia fletcheri Parasitoids on Bactrocera cucurbitae (Coq.) and Bactrocera dorsalis (Hendel) Infesting Papaya Ernest J. Harris 1, Renato C. Bautista 2, Roger I. Vargas 3, and Eric B. Jang 3 1 US Pacific Basin Agricultural Research Center, USDA-ARS, 2727 Woodlawn Drive, Honolulu, HI USA 2 Plant Pest Control Branch, Plant Industry Division, Hawaii Department of Agriculture 1428 South King Street, Honolulu, HI USA 3 US Pacific Basin Agricultural Research Center, USDA-ARS, P.O. Box 4459, Hilo, HI USA What do our findings indicate ? In Hawaii, the Mediterranean fruit fly (Ceratitis capitata) Wiedemann, the oriental fruit fly, (Bactrocera dorsalis) Hendel and the Solanaceous fruit fly (B. latifrons) Hendel, are persistent pests of fruits and vegetables. Voracious feeding by the larvae causes fruit to decay, thus rendering it unfit for human consumption. Recently, an IPM program was undertaken jointly by USDA-ARS, the University of Hawaii and Hawaii Department of Agriculture to demonstrate the potential of utilizing a package of control tactics, including biological control for suppression of fruit flies. The IPM program has provided an opportunity to assess and to quantify the potential impact of parasitoid augmentation when utilized alone as a strategy for suppression of fruit flies. In 2003, 2004, and 2005 open field releases of Fopius arisanus and Psyttalia fletcheri (egg and larval parasitoids respectively) were made in Laie, Hawaii. Kuhuku, HI served as a control site. The two North shore sites are not identical but have comparable field sizes, stands of fruit-bearing papayas, and matching patches of wild vegetation of Coccinia grandis (ivy gourd) infested by melon fly. Wild ivy gourd serves as a major source of melon flies that infest cultivated crops grown near our experimental sites. The relative abundance of melon fly and oriental fruit fly populations in our experimental sites was monitored with a) male lure and protein bait traps and b) emergence of flies and parasitoids from from infested ivy gourd and papaya fruits. The fruit fly trap data (expressed as catch per trap per day, CPTD) were supplemented with parasitoid emergence and host pupal mortality data generated from ivy gourd and papaya fruit collections. An update on the progress of our research in papaya is presented. Rationale for Our Study ? Experimental Sites Kuhuku Control Site`Laie Release Site Fig 1 Fig 2 Fig 3 Servicing male lure traps Placing fallen papaya fruit samples in field emergence boxes Experimental Sites (1) The catch, CPTDs, from February 2004 to June 2005 show the highest level of oriental fruit fly populations <800 CPTPD in both sites in July The CPTDs of melon fly populations in Laie showed six peaks <500 CPTPD (March and November 2004 and April, May, June and July 2005). The upsurge in fruit fly populations in Laie was due to melon fly infesting cucurbit crop remnants left in the field by 4-5 farmers renting the farm land near the wild ivy gourd. In Laie, protein bait traps in ivy gourd caught 3.95 fold higher numbers of melon fly than the protein bait traps in papaya. In Kuhuku, the protein bait traps in papaya caught 4 fold higher numbers of melon fly than the protein bait traps in ivy gourd. The protein bait traps in Kuhuku papaya caught 10 fold higher numbers of oriental fruit fly than the protein bait traps in Laie papaya. Oriental fruit fly and melon fly females were caught at all trap sites in protein bait traps. The farmers shifted to non cucurbit crops in mid 2005 after finding out how severe fruit fly infestations in cucurbits can be without high use of costly pesticide control measures. (2) The number of P. fletcheri parasitoids recovered from puparia infesting papaya in Laie was very low. No emergence of P. fletcheri from papaya fruits was recorded. Seven hundred and seven F. arisasnus parasitoids were recovered from a total of 2,927 papaya puparia in Laie that produced 1,189 oriental fruit fly and 31 melon fly. This evidence shows that melon flies moved from ivy gourd into papaya infesting them at a low level. The significant numbers of F. arisasnus produced came from oriental fruit fly infesting papaya it’s primary host in the natural habitat. Experimental Approach Small-scale field releases of the fruit fly parasitoid F. arisanus and P. fletcheri were carried out during the period March to August in 2003, 2004 and 2005 in Laie for augmentative biological control of Melon fly infesting wild ivy gourd. Within a short distance ( km) from the release and control site, 3 orchards of papaya were monitored for melon fly and oriental fruit fly populations with male lure and protein bait traps. Also, fruit samples were collected monthly to monitor fruit fly infestation of papaya and parasitization of fruit fly pupae by P. fletcheri and F. arisanus. Papaya fruits that fell from the trees were sampled and placed on the ground under a plastic box (0.5 m 2) ) to record emergence of flies and parasitoids from papaya fruit samples. The insects which emerged from papaya fruit were caught in stickem inside a plastic bucket on top of the emergence box. To improve the latent effectiveness of the parasitoids released, they were fed honey and males and females were held together for 5-6 days before release to ensure sexual maturity and mating before release. This procedure insures that the parasitoids are ready to search for and parasitize fruit fly hosts in ivy gourd and papaya fruits immediately after release in the field. Fig 4 (3) In Laie from January 2003 to June 2005, the number of oriental fruit fly and F. arisanus parasitoid counts recovered from papaya showed 2 peak counts of 100, June to July 2003 and June to July From September to October, November to December 2003, and November to December 2004 the oriental fruit fly and F. arisanus counts recovered from papaya ranged from 50 to 60. The most important counts recorded were the numbers of unemerged and total pupae. Three count peaks occurred. The first occurred in September 2003, the second in June 2004 and the third in November The high total numbers of unemerged pupae recovered were due to pupae death caused by parasitoid releases especially F. arisanus. (4) In Kuhuku, September 2003, October 2004 and January 2005 oriental fruit fly counts recovered from papaya exceeded 100. In November and December 2003, August, November and December 2004, F. arisanus parasitoid counts recovered from papaya did not exceed 50. Again, the most important counts recorded were the numbers of unemerged and total pupae. Three unemerged pupae counts ranged in descending order showed counts of 565, 180, and 102. Corresponding total pupae counts were 682, 297, and 180. The first count occurred in September 2003, the second in June 2004 and the third in November The high numbers of unemerged pupae recovered were due to pupal mortality caused by wild F. arisanus parasitoids. No parasitoid releases were made in Kuhuku. What May Be Gleaned From The Study The abundance of melon fly and oriental fruit fly populations can be monitored effectively with male lure traps and the impact of parasitoid releases on fruit fly infestation assessed by analyzing trends in the recovery of both tephritid fruit flies and parasitoids (P. fletcheri and F. arisanus) from infested fruit. Fruit fly trap data and fruit fly and parasitoid recoveries were identified by habitat where the flies and parasitoids were abundant and where the most damage was done to cucurbit and papaya crops. Release of the parasitoids effectively suppressed melon fly infesting ivy gourd but the parasitoids were less effective in competition against melon fly infesting crop remnants in abandoned fields of ripe cucurbits left unattended by growers. Although, oriental fruit fly infested papaya, when this fruit is harvested from the trees promptly at the mature green stage, and fallen fruit is removed and not permitted to accumulate on the ground under the trees, infestation of papaya by oriental fruit fly is greatly reduced by cultural control. Augmentative releases of the two parasitoids had major impact suppressing melon fly infesting ivy gourd but little impact on oriental fruit fly infesting papaya.