Abstract

Plants produce extrafloral nectar (EFN) as indirect defense against herbivores. How different types of herbivores and types of damage affect EFN secretion rates are still not fully understood. In this study, a common shrub, Clerodendrum philippinum, was exposed to three different herbivores (with the two smaller species exposed at two densities), as well as three different types of mechanical damage. Feeding by a large generalist herbivore, the locust Atractomorpha sinensis, resulted in a significantly higher EFN secretion rate than the control treatment, while the other two herbivores, the specialist beetle Hoplasoma unicolor and generalist weevil Hypomeces squamosus, only caused significant increases in EFN secretion rate when present in high densities. Under these higher-density conditions, leaf area lost also increased. With respect to mechanical damage, a significant increase in EFN secretion rate, compared to control treatments, occurred only in the treatment with leaves damaged by scratching, but not in the treatments in which leaves had a hole punched in them or were cut from the stem. The significant regression of the change in EFN secretion rate on the amount of leaf area lost also indicates that leaf area lost to chewing insects may be an important factor in EFN secretion rate change. This research suggests that the induced response of EFN secretion in C. philippinum is a matter of the amount of the leaf area lost, more than a response to whether an insect is a generalist or specialist.

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