Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2010
Publication Date: 2/1/2011
Citation: Hallman, G.J., Thomas, D.B. 2011. Evaluation of the efficacy of the methyl bromide fumigation schedule against Mexican fruit fly (Diptera: Tephritidae) in citrus fruit. Journal of Economic Entomology. 104:63-68.
Interpretive Summary: Fumigation of fruit using methyl bromide is an important quarantine treatment against many pests, including fruit flies. The Mexican fruit fly is a quarantine pest of citrus and other fruits in Texas, Mexico and Central American countries. There have been some live larval finds in fruit supposedly properly fumigated with methyl bromide. Therefore, this research was conducted to explore the reliability of the previously approved USDA-APHIS treatment schedule: 2.5 pounds of methyl bromide at fruit temperatures between 70-80 degrees F for 2 hours. When fumigating naturally-infesting grapefruit, the most methyl bromide tolerant stage was the last larval instar followed by the second which was more tolerant than the first larval instar and egg. Insertion of larvae into fruit is sometimes used in quarantine treatment research. However, in the case of Mexican fruit fly inserted into grapefruit, it was harder to control than larvae in naturally infested fruit. A few larvae were still moving 5 days after fumigation when held at room temperature. Cooler temperatures between 71.4 and 81 degrees F resulted in more larvae moving, pupariating, and emerging as adults 24 hours after fumigation. Coating grapefruit with Pearl Lustr(R) 2-3 hours before fumigation did not significantly affect the proportion of third instars moving or surviving 24 hours after fumigation. In conclusion, efficacy of fumigation with 40 g/m(3) of methyl bromide for 2 hours at fruit temperatures greater than or equal to 80 degrees F is supported, and although a few larvae were found moving 24 hours after fumigation, they do not develop further.
Technical Abstract: Methyl bromide fumigation is a major phytosanitary treatment for a wide variety of quarantine pests, including tephritid fruit flies. Mexican fruit fly, Anastrepha ludens (Loew), is a quarantine pest of a number of fruits, including citrus exported from Texas, Mexico and Central American countries. In recent years live larvae of A. ludens have been found with supposedly correctly fumigated citrus fruit. This research investigates efficacy of the previously approved USDA-APHIS treatment schedule: 40 g/m(3) of methyl bromide at fruit temperatures between 21 and 29.4 degrees C for 2 hours. Tolerance of Mexican fruit fly to methyl bromide in descending order when fumigated in grapefruits and measured as completion of development is third instar greater than second instar, greater than first instar, greater than egg. Two infestation techniques were compared, insertion into fruit of third instars reared in diet and oviposition of adult A. ludens into fruit and development to the third instar. Inserted larvae were statistically more likely to survive fumigation than oviposited larvae. When fruit were held at ambient temperature, a small proportion of larvae was still moving 5 days post fumigation. Temperatures between 21.9 and 27.2 degrees C were positively related to efficacy measured as larvae moving greater than 24 hours after fumigation, pupariation, and adult emergence. Coating grapefruit with Pearl Lustr(R) 2-3 hours before fumigation did not significantly affect the proportion of third instars moving 24 hours after fumigation, pupariating, or emerging as adults. In conclusion, efficacy of fumigation with 40 g/m(3) of methyl bromide for 2 hours at fruit temperatures greater than 26.7 degrees C is supported, and although a few moving larvae greater than 24 hours post fumigation may be found, they do not pupariate.