Rearing History, Larval Density, and Larval Developmental Stage Affect Volatile- and Light-Mediated Diel Hiding Behavior in Mythimna unipuncta

Abstract Our previous study has shown that plant volatiles and light jointly influence the diel hiding behavior of Mythimna unipuncta larvae using the third instars of the laboratory colony. Here, we investigated the effect of rearing history, larval density, and developmental stage on the diel hiding behavior of M. unipuncta larvae under controlled laboratory conditions. Third-instar larvae from a newly established, field-derived colony exhibited more frequent hiding behavior in the presence of maize volatiles, regardless of the light regime, whereas third-instar larvae from a long-term laboratory colony (> 5 years) showed no change in response to volatiles. Larval density during the second instar also altered responsiveness; low-density cohorts from the new colony exhibited increased hiding in response to volatiles, whereas high-density cohorts exhibited a decrease. Furthermore, developmental stage also influenced behavior. Second instars from the new colony consistently exhibited increased hiding when exposed to volatiles, regardless of light conditions. In contrast, under light condition, the fifth–sixth instars hid more with volatiles than without. Under dark condition, however, they hid less with volatiles than without. Our results demonstrate that diel hiding behavior in M. unipuncta larvae is shaped not only by immediate environmental cues such as light and plant volatiles but also by larval rearing history, social context (density) and the developmental states. This study provides novel insights into the behavioral adaptations underlying diel activity patterns in herbivorous insects.