Evasion of mating disruption in Ephestia cautella (Walker) by increased pheromone production relative to that of undisrupted populations

The effect of applying high dosages of pheromone for continuous disruption of mating on sex pheromone production, fecundity, and life span was studied in inbred pairs of the almond moth (Ephestia cautella) mated in glass jars. Two experiments were conducted for six and nine consecutive generations of disruption, respectively, with a pheromone mixture (2.2-2.4 mg/jar in the first experiment and 10 mg/jar in the second experiment) composed of two components, (Z,E)-9,12-tetradecadienyl acetate (D) and (Z)-9-tetradecenyl acetate (M), in various proportions. In the first experiment pheromone emission decreased considerably in the first generation of disruption, an average of 35% lower in the control F₁ females and 47% lower amount in females of the disrupted population (exposed to an excessive pheromone dose) as compared with the amount recorded in parental (P) females (1252±84pg). The reduction in pheromone emission continued in the two treatment groups, by an average of 92 pg/generation in the control and 64pg/ generation under disruption until F₅. The same trend of reduction of pheromone production (as measured in gland extract) was also detected in the second experiment, with leveling off at 2.5 ± 2.3 and 2.7 ± 1.6 ng/ gland in F₇ and F₈, respectively, for the control population, and 5.7 ± 5.6 and 5.9 ± 5.7 ng/gland in F₇ and F₈, respectively, for the disrupted population (initial pheromone level in P was 33.8 ± 18.7 ng/gland). The confinement of the pairs in closed jars was probably the major cause for the reduction in pheromone production besides inbreeding. The higher pheromone titer in the disrupted population relative to that in the control population may represent an evasion of the pressure of mating disruption caused by selection. The mean number of progeny (per jar) gradually decreased in successive generations in both the control and disruption treatments, but no significant difference was found between the number of progeny averaged over all the generations in the two treatments. For a pheromone blend having the average composition of D:M = 77:23 in the first experiment, there was a small but significant increase in the life span among disrupted mated and unmated males (10.5 and 10.2 days, respectively) and among disrupted mated and unmated females (7.7 and 11.0 days) as compared with the respective non-disrupted control groups (9.3 and 6.5 days for the males and 6.7 and 8.6 days for the females).