What is the Shelf Life of Trimedlure Plugs? Comparing Lure Content and Captures of Male Mediterranean Fruit Flies (Diptera: Tephritidae) Between Newly Manufactured and 5–7-Year-Old Trimedlure Plugs

Abstract

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), is a major agricultural pest, and many countries operate trapping networks to detect incursions or monitor infestations. These networks rely primarily on trimedlure (TML), a compound attractive to C. capitata males that is dispensed from polymeric plugs (2 g a.i.) placed within traps. As large numbers of traps are deployed and re-baiting occurs relatively frequently, detection programs purchase TML plugs in large batches that meet demand over several years. To avoid any interruption in trapping, a batch of new plugs is received prior to the exhaustion of the preceding batch. Typically, newly purchased plugs are not deployed until all plugs from the previous batch have been used. However, older stock is occasionally overlooked, and, when later discovered, TML plugs manufactured ≥2 years earlier may be deployed in the field. Such plugs are assumed to be effective, but supporting data are not available. Here, we determined whether TML content of plugs declines appreciably over time by comparing—within the same production batch—the TML content at the time of manufacture with the content after plugs were stored for 5 or 7 years. Second, we assessed whether the attractiveness of TML plugs declines over time by comparing field captures of wild male medflies in traps baited with newly manufactured plugs or 5-year-old plugs. Results showed that the absolute and proportional amounts of TML decreased significantly over 7 years but not over 5 years. The decrease over 7 years was slight, however, and both 5- and 7-year-old plugs were found to be as attractive as new plugs.