<p>Fallow field biotopes are expected to compensate for wetland habitats in paddy environments. However, the optimal timing of plowing to support aquatic insect diversity (Odonata, Hemiptera, and Coleoptera) remains unclear. We conducted field experiments to investigate whether early summer plowing in biotopes suppresses vegetation cover and promotes aerial colonization by aquatic insects. We managed 10 abandoned paddy fields as two types: paddy fields and biotopes. The biotopes were not plowed in the early summer of 2023, but both the biotopes and paddy fields were plowed in 2024. We evaluated the indirect effects of vegetation cover differences between the biotopes and paddy fields on the abundance of each aquatic insect species yearly. In 2023, we confirmed that dense vegetation covers suppressed colonization, reducing the abundance of aquatic insects in biotopes than in paddy fields, including the endangered giant water bug, <i>Kirkaldyia deyrolli,</i> which reproduces in early summer. In 2024, early summer plowing resulted in no notable differences in vegetation cover between the biotopes and paddy fields, thereby nullifying the indirect negative effects of vegetation cover. Early summer is the optimal timing for plowing, as reducing vegetation cover at this time could promote the colonization of species that reproduce in early summer.</p>