The role of herbivorous insects and pathogens in the regeneration dynamics of Guazuma ulmifoliain Panama

A significant proportion of mortality of rainforest trees occurs during the early life stages (seeds and seedlings), but mortality agents are often elusive. Our study investigated the role of herbivorous insects and pathogens in the early regeneration dynamics of Guazuma ulmifolia (Malvaceae), an important tree species in agroforestry in Central America.We reared pre-dispersal insect seed predators from G. ulmifoliaseeds in Panama. We also carried out an experiment, controlling insects and pathogens using insecticide and/or fungicide treatments, as well as seed density, and compared survivorship of G. ulmifoliaseeds and seedlings among treatments and relative to untreated control plots. We observed (1) high pre-dispersal attack (92%) of the fruits ofG. ulmifolia, mostly by anobiine and bruchine beetles; (2) negligible post-dispersal attack of isolated seeds by insects and pathogens; (3) slow growth and high mortality (> 95%) of seedlings after 14 weeks; (4) low insect damage on seedlings; and (5) a strong positive correlation between seedling mortality and rainfall. We conclude that for G. ulmifoliaat our study site the pre-dispersal seed stage is by far the most sensitive stage to insects and that their influence on seedling mortality appears to be slight as compared to that of inclement weather. Thus, the regeneration of this important tree species may depend on effective primary dispersal of seeds by vertebrates (before most of the seed crop is lost to insects), conditioned by suitable conditions in which the seedlings can grow.