The Biology and Ecology of Rice-Stem Borers in Sarawak (Malaysian Borneo)

Abstract

At least five species of lepidopterous stem borers are known to occur in rice in Sarawak. These are the pyralids, Tryporyza incertulas (Walk.), T. innotata (Walk.), Chilo suppressalis (Walk.), C. auricilius Dudg. and the noctuid, Sesamia inferens (Walk.). A dipterous borer, Hydrellia sp. nr. sasakii Y. & I. (Ephydridae) commonly occurs in wet rice during the peak tillering phase, and larvae of a beetle, Anadastusfiliformis (F.) (Languriidae), also occasionally bore the stems of heading rice plants. Specimens from Sarawak originally identified as Chilo polychrysa (Meyr.) have since been identified as C. auricilius; larvae of C. polychrysa described in Rothschild (1967) were from Malaya. The relative abundance of borer species in samples collected from rice areas throughout Sarawak is shown in Table 1. Tryporyza incertulas is generally the dominant species in wet rice fields while T. innotata predominates in hill plantings; overall borer density in dry sites is, however, usually low. Sesamia is the next most common borer in both wet and dry rice crops.