Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2003
Publication Date: October 30, 2003
Citation: Prokopy, R.J., Miller, N.W., Pinero, J.C., Barry, J.D., Tran, L.C., Oride, L.K., Vargas, R.I. 2003. Effectiveness of gf-120 fruit fly bait spray applied to border area plants for control of melon flies (diptera: tephritidae). Journal of Economic Entomology. 96(5):1485-1493.
Interpretive Summary: The melon fly has become a major pest of cucurbit crops in Hawaii since its introduction in the late 19th century. In the past attempts to control melon flies have been made with protein baits combined with malathion applied to crop borders, where females spend the night. Current emphasis in melon fly control in Hawaii is on use of GF-120 Fruit Fly Bait containing the toxicant spinosad. Spinosad is known for its extremely low mammalian toxicity and reduced non-target effects. However, baits containing spinosad must be ingested by hungry flies where baits that contained malathion killed mainly by contact. This study found that GF-120 was very effective at stopping protein-starved female melon flies from entering field plots but that it was less effective at stopping protein-fed females. Cage tests showed that GF-120 looses half of its attractiveness after 5 hours and all attractiveness after 24 hours under dry conditions. Cup tests showed that despite the loss of attractions, spray droplets remained toxic to female melon flies 24 hours after application.
In a field study in Hawaii, color-marked protein-deprived and protein-fed male melon flies, Bactocera cucurbitae Coquillett, were released within canopies of unsprayed sorghum plants outside of a border area of unsprayed or bait-sprayed sorghum plants or open space that surrounded cucumbers, a favored host of melon flies. Application of bait sprays to sorghum or sugarcane surrounding host plants of melon flies is a common practice for melon fly control in Hawaii. GF-120 fruit fly bait spray proved very effective at preventing protein-deprived females from landing on cucumbers (23% of released females were observed dead on bait-sprayed sorghum, 0% were observed alive on cucumbers), but proved less effective in suppressing protein-fed females (14% of releases females were observed dead on bait-sprayed sorghum, 11% were observed alive on cucumbers). No females were found dead on unsprayed sorghum. Compared with open space surrounding cucumbers, the presence of unsprayed sorghum as a surrounding border area neither significantly inhibited the ability of either type of female with respect to finding cucumbers. Greenhouse cage tests revealed that GF-120 Fruit Fly Bait spray droplets were highly attractive to protein-deprived females within 1 hour of bait spray application to sorghum, but lost about half of their attractiveness within 5 h and all of it within 24 h under dry conditions. Laboratory cup tests showed that bait spray droplets remained highly toxic to protein-deprived females 24 hours after application, but lost about half of their toxicity within 4 d under dry conditions and nearly all of it after ~ 8 mm of rainfall. Combined findings suggested that application of GF-120 Fruit Fly Bait spray to non-host plants for melon fly control either be made often enough to overcome loss of attractiveness of bait sprays to females or that bait sprays be applied to non-host plants that are themselves attractive to females.