Insect pests of rainfed wetland rice in the Philippines: population densities, yield loss, and insecticide management

Abstract

Rainfed wetland rice (RWR) had more species in common with irrigated wetland than dryland rice agroecosystems. Across ecosystems, higher pest densities and losses were recorded in RWR sites. We hypothesise that under low pressure from natural enemies, vegetative stage losses became particularly high due the combination of whorl maggot and caseworm damage combined with the physiological stress of transplanting shock. Both of these pest groups benefited from an expanded vegetative period common in RWR agroecosystems. Losses in older rice were probably due to stemborers. RWR is more prone to an array of physiological stresses than irrigated rice that we believe minimises crop compensation to accentuate insect losses. Chemical control is uneconomical mainly due to the low yield potential of RWR and the poor efficacy of applied insecticide.

Keywords:

• rice insect pests
• yield loss
• natural enemies
• action thresholds
• chemical control
• crop compensation
• crop stresses
• integrated pest management

Acknowledgements

We are indebted to the field work performed by our site staff in Oton Iloilo, Manaoag Pangasinan, and Solana Cagayan without whose help this research would not have been possible. We are grateful for the assistance of Nonnie Bunyi and Josie Lynn Catindig at IRRI in providing references and technical information. In addition the assistance provided by three anonymous reviewers is gratefully appreciated.