Hydroglyphus geminus

Hydroglyphus geminus is a species of predatory diving beetle belonging to the family Dytiscidae, order Coleoptera. While often found in natural freshwater habitats, this insect has become recognized as a significant pest in paddy fields, particularly affecting rice cultivation in warm climates.

The primary host crop for this pest is rice (Oryza sativa). Both adult beetles and their larvae infest flooded fields, where they feed on the succulent tissues of young rice seedlings. This behavior is most destructive during the early vegetative stage, leading to significant thinning of crop stands.

The biology of the pest involves a complete life cycle. Eggs are deposited in aquatic environments. The larvae, which are typically predatory, adapt to agricultural settings by feeding on plant sprouts when aquatic prey is scarce or when the population density is high, causing mechanical injury to the plants.

Damage symptoms include ragged leaf margins, severed stems, and overall stunting of young plants. The economic impact is linked to yield loss due to reduced plant density and the physiological stress imposed on the crop, which may require extensive replanting if infestations are severe.

Management strategies focus on integrated pest management (IPM). Key practices include water level management, where temporary drainage of paddy fields disrupts the larval environment. Chemical control using selective insecticides is applied when thresholds are exceeded, ensuring minimal impact on non-target aquatic organisms.