Relationship between field captures of Mediterranean fruit flies and the residual amount and release rate of trimedlure from polymeric plugs

Detection of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), relies heavily on traps baited with trimedlure, a male-specific attractant. Originally used as a liquid, trimedlure is now dispensed from solid polymeric plugs (2 g active ingredient) that reduce volatilization and increase the effective longevity of the lure. Even so, plugs are attractive over a relatively short interval, and guidelines suggest that trimedlure plugs be replaced every 6 wk. The present study had 2 goals. First, at periodic intervals up to 10 or 12 wk, we evaluated the performance of plugs containing 4 g of trimedlure (i.e., twice the standard amount) to determine whether the increased loading resulted in an increased period of effective attractiveness. Second, we examined the relationship between trap captures and temporal changes in the residual amount and release rate of trimedlure. In 2 of the 3 field trials conducted in Hawaii and Florida, 4 g plugs weathered for as long as 8 wk, but not for 10 or 12 wk, performed as well as fresh liquid trimedlure applied to cotton wicks. In the other trial, plugs weathered for as long as 12 wk were as effective as fresh liquid. Chemical analyses revealed that the plugs were effective until the residual amount of trimedlure decreased below approximately 1.4 g and the release rate dropped below approximately 2.0 mg per h. The potential usefulness of 4 g trimedlure plugs in large-scale detection programs is discussed considering these findings.