Insect sex pheromones: Determination of half-lives from formulations by collection of emitted vapor.

A new method for determining half-lives for the evaporation of sex pheromones from formulations has been developed. A previously unexploited mathematical relationship makes possible the determination of half-lives of over 1000 days by collecting evaporated pheromone for 1-4 hr and measuring the amount collected and the amount left in the formulation. Purified nitrogen flows over the test material and the evaporated pheromone is qualitatively collected on an adsorbent of 80-100 mesh silica gel silanized with octadecyltrichlorosilane. Quantitation is by gas chromatography. Quantitative mass balance was achieved and half-lives determined by this new method are in agreement with half-lives previously determined by measuring the amount of pheromone left in septa after a sequence of time intervals. Previously undetermined half-lives for acetates and alcohols are reported.

Insect sex pheromones: Evaporation rates of alcohols and acetates from natural rubber septa.

The half-lives (t 1/2) of alcohol sex pheromones, 1-alkanols, acetate sex pheromones, and an epoxide (disparlure) were determined on natural rubber septa. Thet 1/2 values for the homologous alcohols from decanol to heptadecanol increased regularly from 2.2 to 1117 days, but thet 1/2 of octadecanol was 609 days. Thet 1/2 values of (Z)7-, (E)7-, and (Z)9-tetradecen-1-ol acetates were 154, 168, and 199 days, respectively, whereas those of five other tested 14-carbon acetates ranged from 310 to 350 days. The dependence oft 1/2 values on chain length and double-bond position is consistent with the hypothesis that molecular size is an important variable affectingt 1/2 values. Also, in accordance with the hypothesis, when aZ-alkenyl compound has a much shortert 1/2 than the corresponding saturated compound, thet 1/2 values of theZ compound and itsE isomer may be quite different. Thus, (E)-9-tetradecen-l-ol acetate had at 1/2 of 331 days. Thet 1/2 of disparlure was 180 days. The effect of thecis-7,8 epoxide group is apparently similar to that of the olefin group in lowering thet 1/2 below the value that would be expected solely on the basis of chain length.