Size- and density-dependent reproductive success of bagworms, Metisa plana

A study conducted in a Malaysian plantation of oil palm over 5 consecutive generations of bagworms, Metisa plana (Walker) (Lepidoptera: Psychidae), ev aluated extent and causes of variability for 3 components of reproductive s uccess: pupal mortality, mating success and fecundity. The population of M. plana in the experimental site exhibited cycles of 70-80 days with discret e generations. Females emerged before males during all generations. Relativ ely large proportions of M. plana did not reproduce, either because they di d not survive as pupa or (for females) mate as adult. Occurrence of unmated female bagworms may be attributed to complex mating procedure, short lifes pan of females, limited mating capacity of males, protogyny inducing female -biased operational sex-ratio, and/or flightlessness per se constraining ma ting success of females. Size attained at pupation is a significant compone nt of reproductive success, with large individuals having greatest survival during pupal stage, mating success and fecundity. Population density also influenced reproductive success of M. plana: female and (to a lesser extent ) male larvae on crowded palms attained small size at pupation; survival of pupae was density-dependent during 2 generations for females and density-i ndependent during 5 generations for males; mating success of females was in verse density-dependent during 4 generations. Size- and density-dependent m ating success of females may be attributed to mate choice by males, size-de pendent pheromone production by and longevity of females, and/or disorienta tion of mate-seeking males around heavily infested palms. Long-term studies are needed to determine whether and to what extent attributes of oil palm, seasonal fluctuations of abiotic factors and inter-generational variations of reproductive success influence population dynamics of M. plana.