Induced-defense responses in the leaves of Chromolaena odorata consequent to infestation by Pareuchaetes pseudoinsulata (Lepidoptera: Arctiidae)

An aster, Chromolaena odorata (Linn.) R.M. King et H.E. Robinson (Siam weed), a native of the neotropics, has presently spread on to vast tracts of land in humid tropics of Africa, Asia and some of the Pacific islands. Pareuchaetes pseudoinsulata Rego Barros - a host-specific arctiid moth - feeds on the leaves of C. odorata. In less than three weeks of feeding by the larvae of P. pseudoinsulata, the leaves of C. odorata turn intensely chlorotic. Chloroplasts in the chlorotic leaves show degenerated thylakoid membranes, either as decreased numbers or as vesiculated stacks of grana, smaller starch grains, and vacant locations of plastoglobuli. Cell vacuoles include small to large, few to several electron-dense lipidic inclusions. Changes in chloroplasts during chlorosis have a specific effect on the metabolism of lipophilic materials stored in the plastoglobuli. Concurrently with the accumulation of lipidic materials from both chloroplasts and plastoglobuli into the vacuoles, chloroplast membranes get modified. These lipidic materials act as the precursors of 'novel' compounds that defend the leaf cells of C. odorata from the impact of the feeding moth. Changes in the leaf colour and chloroplasts, however, are temporary; with the physical removal of P. pseudoinsulata larvae, chlorotic leaves of C. odorata revert to green and the mesophyll cells regain their normal structure; most importantly, the mesophyll cells cease to accumulate lipidic materials in their vacuoles. Reversal of chlorotic cells to normal cells occurs only through the metabolic activation in primordial cells; mature cells killed by the physical action of mouthparts and chemical secretions from the saliva of the moth never reverse.