Defoliation of the Mangrove Avicennia marina in Hong Kong: Cause and Consequences

In Hong Kong, the mangrove Avicennia marina (Forsk.) Vierh. experiences intense herbivory every summer such that within 3 months all trees are defoliated. Rapid regeneration of the canopy follows, but reproductive output is severely impaired as defoliation coincides with flowering. The causal herbivore is the caterpillar of Nephopterix syntaractis Turner (Lepidoptera: Pyralidae), as demonstrated in investigations of caterpillar densities and leaf consumption rates. The effect of N. syntaractis on leaf area damaged, leaf tannin content, and reproductive output of A. marina was investigated by applying insecticide over trees in marked plots. In comparison with the control plot, spraying reduced leaf damaged and increased flower and propagule production in the treated stand. Tannin levels showed no increase with level of leaf damage but did differ between sprayed and control plots, reflecting a raised tannin content of regenerated leaves. The consequences of defoliation of the stand are discussed.