Insect Herbivory

Higher tree species diversity leads directly to higher diversity of leaf-eating insects, scientists report in a new study.

It may be obvious that forests with greater numbers of tree species should support a wider variety of leaf-eating insects than do less diverse forests, but no one had ever done the experiment to rule out the major alternative explanation: that insect species in the tropics eat the leaves of a smaller number of host trees and are thus more host specific, which would also result in more insect species in a given area.

In this study, scientists compared 850 species of leaf-eating insects from 14 tree species in temperate floodplain forest sites in Moravia and from 14 tree species in lowland tropical sites in Papua New Guinea (PNG). They also compared caterpillars from 8 trees in Slovakia, and 8 trees in PNG. Tree species were chosen such that they would have the same evolutionary relationships at each site, making the comparisons equivalent and eliminating another confounding factor.

After collecting the insects, researchers ran feeding trials by presenting larval and adult insects with foliage. They gathered and analyzed a total of 26,970 feeding observations.

Based on this latitudinal comparison they concluded that individual temperate and tropical tree species support similar numbers of leaf-eating insects. Host specificity did not differ significantly between temperate and tropical communities therefore, the greater number of tree species in the tropics is the best explanation for higher insect diversity.

The study was detailed in the July 13, 2006 online version of the journal Science.

--LiveScience Staff

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Credit: Marcos Guerra, STRI