Diversity of aquatic insects in Agusan Marsh floodplain and its relation to insect pest management in adjacent lowland ricefields

Aquatic insect diversity and community structure in the Agusan marsh floodplain and their implications on biodiversity conservation in natural habitats and pest management in rice fields were investigated. The fern-dominated swamp, sedge-dominated swamp, sago forest, Terminalia forest, and Bangkal forest, and their adjacent rice fields were selected as study sites. Agusan Marsh had 59 species and taxa of aquatic insects, with water beetles having 28 species, aquatic bugs with 17, while the odonates had 11. Some species were unique to particular natural habitats. The sedge-dominated swamp and adjacent ricefields and the ricefield near the Sago forest had the most species in the wet season, while the Bangkal forest and adjacent ricefield had the least number. The water beetles were the most abundant insects, followed by aquatic bugs and dragon flies. The non-predaceous insects were more abundant than predaceous species. Species diversities were relatively high (3.15-3.71), with the sedge-dominated swamp and adjacent ricefield having the highest diversity. Water depth and community structure of aquatic insects were significantly correlated. The rainy months of February and July had higher diversity than the dry months of May and October. Rice fields possibly serve as corridors for aquatic insects especially during dry months. Likewise, species similarities differed among habitats regardless of proximity to each other, with higher levels in the dry season. Predaceous insects of natural habitats acted as natural control agents against rice insect pests, such as planthoppers and leafhoppers. Only dragon flies foraged above ground and have a wider range of prey, including moth pests were found, indicating relations to pest management in rice fields. The use of GIS in monitoring the extent of human intrusion and the status of natural habitats was considered important in assessing the success of biodiversity conservation in the Agusan Marsh Wildlife Sanctuary. Recommendations for resolving the demand for increased food production and the need to conserve biodiversity in the protected area were presented.