Insect Sex Pheromones: Formulations to Increase the Stability of Conjugated Dienes1

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Abstract
Formulation substrates were tested for their ability to suppress isomerization of pheromone components containing the conjugated diene structure. Formulation substrates compared were red natural rubber septa (sleeve-type stopper); gray halo-butyl isoprene blend elastomer septa (sleeve-type stopper); black halo-butyl elastomer septa, containing carbon filler (flange-type stopper, designated 55C); and black halo-butyl elastomer septa (flange-type stopper, designated 50C). All substrates except for 55C contained mineral filler. Red septa were cured with sulfur and the others were cured with phenolic resin. During the first 2 weeks of field exposure, isomerization of (E, Z)-7,9-dodecadien-1-ol acetate was fastest in red septa followed by 55C black (5-fold slower), and the gray (7-fold slower). Isomerization of (Z, E)-9,11-tetradecadien-1-ol acetate was fastest in red septa and slower in 55C black (8-fold during the first 2 weeks). Isomerization of (E, E)-8,10-dodecadien-1-ol was fastest in red septa, followed by 55C black (3.7-fold slower during the first 2 weeks) and gray (4.7-fold slower). After 43 days in direct sunlight, the (E, E)-8,10-dodecadien-1-ol acetate isomer content decreased from ca. 96% of total isomers by 16.7, 16.8, and 13.0% in the gray, 50C black, and 55C black, respectively. Type of filler, carbon or mineral, had no effect on stability, and differences in stability of the conjugated dienes in the nonsulfur-cured formulations substrates were minimal. Because of its convenient shape, gray is the preferred substrate for minimizing isomerization of conjugated dienes. Based on these data, conjugated dienes with field lives of 2–3 days in red rubber septa are predicted to last 2–3 weeks in gray septa. The most important factors for minimizing isomerization were avoiding isomerization catalysts such as sulfur and minimizing exposure to sunlight.