Cocoon Enclosure Shifts Photoperiodic Thresholds for Diapause Termination in the Chinese Oak Silkworm, Antheraea pernyi

Abstract

Light transmission through opaque biological coverings is often evaluated using physical measurements; however, such estimates do not necessarily reflect the light environment perceived by organisms. In this study, we examined how cocoon enclosure affects photoperiodic diapause termination in the Chinese oak silkworm, Antheraea pernyi. Pupae were maintained under diapause-maintaining conditions (LD 12:12) and exposed daily to an additional 4 h light pulse of defined intensity (0, 0.1, 1, or 10 lux) immediately following the photophase. Naked pupae responded to light pulses of 0.1 lux or higher, whereas cocoon-enclosed pupae required higher intensities to induce diapause termination. At 1 lux, diapause termination was significantly lower in cocoon-enclosed pupae than in naked pupae, while both groups showed similar responses at 10 lux. These results demonstrate a shift in photoperiodic response thresholds associated with cocoon enclosure. Our findings highlight the usefulness of photoperiodic responses as an indicator of light availability and provide a simple and potentially applicable functional framework for assessing light availability within enclosed biological structures.