Melon fly

(= Dacus aureus Tseng and Chu, 1982, Dacus yuiliensis Tseng and Chu, 1992)

Figure 96

Distribution (Fig. 129). Widespread throughout tropical Asia, from Pakistan to Taiwan and south to New Guinea (introduced) and Solomon Islands (introduced); introduced to Africa, the Middle East, and various islands in the Indian and Pacific Oceans (see distribution map in Vargas et al. 2015). Papua New Guinea (mainland, New Britain, New Ireland, Manus, Bougainville). Solomon Islands (Shortland Group, Choiseul, Vella Lavella, Gizo, Kolombangara, New Georgia, Isabel, Russell, Guadalcanal, Malaita). Hawaii (all islands; detected 1895). Guam (detected 1936, eradicated 1965 but re-introduced from Northern Mariana Islands in 1981). Northern Mariana Islands (detected 1936). Kiribati (Christmas Island; detected 1987, eradicated 1989). Nauru (detected 1982, eradicated 1999, reintroduced 2002).

Male lure. Cue-lure. Weak attraction to zingerone, dihydroeugenol, and methyl-isoeugenol (Royer et al. 2018).

Host plants. Category A severe pest of cucurbit crops (Vargas et al. 2015), also bred from a diversity of other families, with a total of 136 host taxa in 30 families (Allwood et al. 1999; McQuate et al. 2016).Records in Guam, Nauru, Northern Mariana Islands, Papua New Guinea, and Solomon Islands: CUCURBITACEAE: Citrullus lanatus, Coccinia grandis, Cucumis sativus, Cucurbita pepo, Luffa acutangula, L. cylindrica, Momordica charantia, Trichosanthes cucumerina. FABACEAE: Phaseolus vulgaris, Vigna unguiculata. MALVACEAE: Abelmoschus esculentus. SOLANACEAE: Solanum lycopersicum.

Edible hosts common names. Angled luffa, bittergourd, common bean, cucumber, ivy gourd, luffa, okra, snakebean, snakegourd, squash, tomato, watermelon.

Biology. Adults mate at dusk (Waterhouse 1993). Rate of development was summarized by Waterhouse (1993). Female flies start laying eggs, primarily on cucurbits, 11–12 days after their emergence from pupae. Eggs are laid in batches of 1– 40 eggs in young to ripe fruits, but also on flowers, buds and even leaf stalks and stems of host cucurbits. One female may lay over 1000 eggs during her life. Oviposition peaks occur in the morning and late afternoon. Eggs hatch in about 24 hours. Development time varies from 4 to 17 days (larva) and 7 to 13 days (pupa), depending on temperature and host. In the Solomon Islands, development from egg to adult takes 13 days at 29°C. In Hawaii, at 24°C, eggs hatch in 1.3 days, larval development takes 6.6 days and pupal stage lasts 10.2 days (Vargas et al. 1996). Adults are long-lived, typically up to 150 days, but as long as 240–460 days under cooler temperature. This species is uncommon in the forest. Monthly trapping data is illustrated on Figures 137, 138, and was also published in Hollingsworth et al. (1997). The parasitoid Psyttalia fletcheri (Silvestri) was introduced from India to Hawaii in 1916, and subsequently from Hawaii to the Mariana Islands in 1950 (Waterhouse 1993) and the Solomon Islands in 1997 (Hollingsworth 2003).

Notes. Heat tolerance was studied in Hawaii (Jang 1986). Melon fly was eradicated from the Northern Mariana Islands in 1963 through sterile insect releases (Steiner et al. 1965a), but re-introduced from Guam in 1981 (Wong et al. 1989). It was first detected in the Solomon Islands on Shortland in 1984, then Kolombangara, Choiseul and Gizo in 1985, Isabel in 1988, Malaita in 1994, and Guadalcanal in 1995, where initial attempts for eradication were unsuccessful (Waterhouse 1993; Hollingsworth et al. 1997; Vagalo et al. 1997). It was also detected on Christmas Island (Kiribati) in 1987, and eradicated through a 2-year interruption in cucurbit cultivation (Waterhouse 1993). It was easily eradicated from Nauru in 1998–1999, using male annihilation and limited protein bait spray applications, aided by a drought that had reduced host fruit availability (Allwood et al. 2002). It was, however, re-introduced to Nauru in 2002, likely aided by Air Nauru passenger flights from Guam (SPC 2002).