Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2004
Publication Date: 9/5/2004
Citation: McInnis, D.O., Tam, S.Y., Lim, R.R., Komatsu, J., Kurashima, R.S., Albrecht, C.P. 2004. Development of a pupal color-based genetic sexing strain of the melon fly, Bactrocera cucurbitae (Diptera: tephritidae). Annals of the Entomological Society of America. 97: 1026-1033. Interpretive Summary: The first practical genetic sexing strain for the melon fly, Bactrocera cucurbitae, based on pupal coloration was developed in Hawaii. Male flies emerge from normal brown pupae, and females emerge from mutant white color pupae. This strain was created through a genetic manipulation of the sex chromosome (Y) of the male, leading to the sex separation based on color. High speed color sorting machines can sort the two sexes apart in the pupal stage prior to release in a sterile fly program. Preliminary tests in the laboratory and in the field demonstrated that the strain can rear reasonably well, and has very good fitness as adults. The flies mate very well compared to wild insects and can survive as well as wild insects in outdoor field cages. With these results, the strain has been mass-reared and open field sterile fly releases of all males has now been carried out on 3 Hawaiian islands beginning in 2002 on the Big island of Hawaii, then on Maui in 2003, and finally on Oahu in 2004. Results have been very good in the field confirming the results we got in the small scale field tests and in the laboratory.
Technical Abstract: The first genetic sexing system for the melon fly, Bactrocera cucurbitae (Coquillett) based on pupal color was developed. The recessive white pupae mutant, wh, was used in a putative chromosome translocation linking the wild type allele to the male sex. This system permits the separation of males (wild-type brown pupae) from females (mutant white pupae). Results from the laboratory studies indicated that egg hatch averaged 42% for flies 2-5 weeks old, with higher rates (ca. 50%) for younger flies in this age range. Male larvae left the diet to pupate earlier than females, averaging over 60% of the pupae in the first day of collection, while only ca. 40% on the 4th day of collection. Adult emergence rate was normal, averaging ca. 92%. Adult egg fecundity and fertility (both sexes) were very low (< 1% of normal) after irradiation at 100 Gy 1, 2, or 3 days before emergence. Adult flight ability from standard 20-cm tubes averaged ca. 65%. Irradiated females landed on, and oviposited into, zucchini fruit significantly less than non-irradiated females. Field cage survival tests indicated that the new strain survived as well (over 80%) as wild males over a 7-d period when provided with food and water. Mating tests indicated that males-only sterile flies mated significantly more (ca. double) with wild females than sterile males from bisexual (male and female) sterile populations competing with wild males. Males fed only sugar until tested in the cages failed to mate at all with wild females, while males fed a low protein diet (6:1 sugar:protein) or fed the standard 3:1 diet mated as well as wild males for wild females. Finally, males exposed to the attractant, cuelure, failed to improve their mating performance compared to control, unexposed males. The results were discussed in the context of the potential for using the new strain in current or future melon fly SIT programs in Hawaii and elsewhere.