Temporal variation in sex pheromone release from individual Chilo suppressalis (Lepidoptera: Crambidae) females and maximization of male trapping

Insects exhibit considerable variation in their sex pheromone blends, but evidence for temporal variation in individual Chilo suppressalis females has been lacking. Using solid-phase microextraction (SPME), we characterized the variability in the sex pheromone composition of C. suppressalis females and its implications for male attraction. Although the female reproductive system matures by day one, the titer and release rhythm of the major component, (cis)-11-hexadecenal [(Z)-11-16:Ald], showed substantial individual variation, particularly among females aged 1 to 3 days. Two-day-old females exhibited the most consistent detection frequency and the longest release window, accompanied by a significantly altered ratio of (Z)-11-16:Ald to the minor component (cis)-9-hexadecenal [(Z)-9-16:Ald]. A positive correlation was established between the proportion of (Z)-11-16:Ald in the blend and its absolute titer. Higher temperatures increased the release of (Z)-11-16:Ald from the pheromone gland surface, while mating drastically reduced it. Subsequent field trials demonstrated that the total dosage influenced the attractiveness of different pheromone ratios. At a low dose of 760 μg, the (Z)-11- to (Z)-9-16:Ald ratios had no significant effect, with 10:1, 16:1, and 32:1 each attracting a comparable number of males. At a medium dose of 1520 μg, the 10:1 and 16:1 ratios were most attractive, while at a higher dose of 2280 μg, the 16:1 ratio was clearly superior. Crucially, after five years of mass trapping with a fixed 10:1 blend, local populations shifted their behavioral responses: one site showed enhanced attraction to a 30:1 ratio, while another exhibited increased response to a 7:1 ratio, indicating directional adaptation. Intraspecific variation in female pheromone release and male response is substantial in C. suppressalis. Long-term use of a single pheromone blend can drive behavioral resistance, necessitating rotation of multiple blends or integration with complementary control tactics for sustainable pest management.