NATURAL ENEMIES OF THE BAGWORM, METISA-PLANA WALKER (LEPIDOPTERA, PSYCHIDAE) AND THEIR IMPACT ON HOST POPULATION REGULATION

The bagworm, Metisa plana (Lepidoptera: Psychidae) is an important pes t of oil palm, capable of being present as outbreak, which could cause a crop loss of up to 44%. Circumstantial evidence has long indicated that natural enemies play an important role in the population regulati on of this pest. However, direct field data on the enemies themselves has been lacking. A field study on a population of M. plana was made a t PORIM Kluang, Johor, Malaysia from September 1988 to December 1992. The population of bagworm was initially high (late 1988, up to 38 larv ae/frond, and in early 1994 up to 30 larvae/frond) but remained extrem ely low in the subsequent period (<10 larvae/frond). The population of M. plana was affected by both primary and secondary parasitoids and p redators. Among the primary parasitoids, Dolichogenidea metesae was th e most pronounced larval parasitoid of M. plana. This parasitoid was c ommonly attacked by hyperparasitoids, particularly Pediobius anomalus and Pediobius imbreus. A hypothetical life table constructed from the mortality figures of the declining part of the population during late 1988 confirmed that the natural enemies played a key role in suppressi ng the bagworm population. The present study confirmed that overlappin g generations were vital for the persistence of parasitoids of M. plan a. The paper also suggested a possible need of alternative hosts. An a ctive predator, Callimerus arcufer was also commonly encountered.