Severe and unprecedented outbreaks of bagworms and nettle caterpillars occurred on oil palm plantations in the Malaya in late 1950s to early 1960s, caused by applications of organochlorine insecticides, which killed insect natural enemies more effectively than they did the pests. Outbreaks mostly declined when applications ceased, sometimes with resurgence because the pesticides also upset the co-ordination of pest and enemy life cycles. Selective pesticides were found (‘integrated control’), and there was general freedom from serious outbreak until around 1990. Incidence, particularly of bagworms, then again became common, with parallel increase in pesticide use. A range of investigations have progressed over the years. During the 1960s, clean weeding had been indicated as conducive to caterpillar pest outbreak by removing shelter and floral food of the natural enemies. Field trials have shown that several beneficial plant species could extend the life of parasitoids, and where planted, bagworm numbers declined whilst natural enemy numbers relatively increased. On-going studies screened additional chemicals mostly emphasising selective potential through stomach action and specific lethality to caterpillars. Microbial pathogens were sought in the field for testing on bagworms by applying suspensions of ground up cadavers, as proven effective for nettle caterpillars. Strong attraction of male bagworms to a female pheromone was demonstrated, suggesting promise of a practical trapping technique. Predators such as Sycanus dichotomus build up in high caterpillar populations, indicating potential of rearing for mass field release to quickly reduce outbreaks. All of these methods could aid in restoring and maintaining subeconomic levels of leaf-eating caterpillars in a balanced and sustainable agroecosystem.