Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2012
Publication Date: May 1, 2012
Citation: Liu, Y-B. 2012. Oxygenated phosphine fumigation for control of Nasonovia ribisnigri (Homoptera: Aphididae) on harvested lettuce. Journal of Economic Entomology. 105:810-816. Interpretive Summary: Lettuce aphid, Nasonovia ribisnigri, is a common pest on lettuce in U.S. but a quarantined pest in overseas markets such as Japan and Taiwan. There has been no practical treatment except methyl bromide fumigation. However, methyl bromide fumigations cause injuries to lettuce and greatly reduces lettuce quality and shelf life. In this study, oxygenated phosphine fumigation at low temperature was explored and compared with fumigations under the normal oxygen level. Lettuce aphid was completely controlled with a 3-day low temperature fumigation with high phosphine concentrations of equal to or greater than 2000 ppm. However, the treatment was not safe to both romaine and head lettuce. In comparison, oxygen greatly increased phosphine toxicity to lettuce aphid. Complete control of lettuce aphid was achieved in a 2-day fumigation with 1000 ppm under 60% O2 at 3°C. The treatment also caused minor injuries to lettuce as compared with the controls; however, the extent of injuries was significantly less than those in the regular 3-day fumigation. The quality of lettuce subjected to the oxygenated phosphine fumigation was very good. The oxygenated phosphine fumigation should have no negative impact on marketability of lettuce and should be further developed for commercial use to control lettuce aphid on exported lettuce.
Technical Abstract: A laboratory study was conducted to compare phosphine fumigations under the normal and superatmospheric oxygen levels on toxicity against Nasonovia ribisnigri (Mosley) and effects on postharvest quality of romaine and head lettuce. Low temperature phosphine fumigation was effective against the aphid. However, a 3 d treatment with high phosphine concentrations equal or greater than 2000 ppm was needed for effective control of the insect. Oxygen at superatmospheric levels greatly increased phosphine toxicity and significantly reduced treatment time and phosphine concentration for complete control of N. ribisnigri. At 1000 ppm phosphine, 72 h fumigations under the normal oxygen level at 6°C did not achieve complete control of the insect. The same fumigation under 60% O2 achieved complete control of the aphid in 30 h. Both a 72 h treatment with 2200 ppm phosphine under the normal oxygen level and a 48 h oxygenated fumigation with 1000 ppm phosphine under 60% O2 were conducted on romaine and head lettuce at 3°C. Both treatments achieved complete control of N. ribisnigri. However, the 72 h regular fumigation caused more severe injuries to lettuce quality than the 48 h oxygenated phosphine fumigation. Although the oxygenated phosphine fumigation caused some damage to the treated lettuce, its quality remained very good and the treatment is not expected to have any negative impact on marketability of the treated lettuce. This study demonstrated that oxygenated phosphine fumigation was more effective and safety for controlling N. ribisnigri on harvested lettuce and is promising for practical use to control N. ribisnigri on exported lettuce.