Changes in plant physiology during cultivation periods influence the hydrogen isotope ratio of the water-insect relationship

O_LIThe hydrogen stable isotope ratios ({delta}2H) in tissues of terrestrial insects are widely applied to estimate natal origins in field populations. The hydrogen isotopes of insect tissues incorporate those of environmental waters through the insects metabolic processes. Water sources and abiotic environmental factors reflect changes in plant physiology, as indicated by the {delta}2H values of plants. However, the influence of plant physiology on the assimilation of hydrogen in insect tissues derived from water through feeding diets is still unknown. C_LIO_LIWe experimentally examined the influence of water on the {delta}2H values of maize leaf and of forewings of Mythimna separata (Lepidoptera: Noctuidae) and Spodoptera frugiperda (Noctuidae). We prepared five specific water samples for cultivating maize, aiming to replicate the gradient of {delta}2H values observed in environmental waters across the Japanese archipelago. C_LIO_LIThe mean-percentage contribution of water to hydrogen in maize leaves was 17.6% (July-August) and 25.1% (September-October). Linear analyses indicated that 17.4% and 32.7% of hydrogen in M. separata and S. frugiperda forewings were derived from water through the consumption of maize leaves. The slope values of linear regression between the insect forewings and the maize leaves supplied in the final instar were closest to 1.0. These results indicated that the {delta}2H values of maize leaves and insect forewings reflected those of water resources. C_LIO_LIThis study presented the seasonal changes in climate conditions that affected the {delta}2H values of host plants and insect tissues. Changes in plant physiology with seasonal variations may influence the interpretation of the linear relationship between water and insect tissues on the estimation of natal origins. C_LI