Influence of iridoid glycoside containing host plants on midgut ?-glucosidase activity in a polyphagous caterpillar, Spilosoma virginica Fabricius (Arctiidae)
Iridoid glycosides are secondary plant compounds that have deterrent growth reducing or even toxic effects on non-adapted herbivorous Insects To investigate the effects of iridoid glycoside containing plants on the digestive metabolism of a generalist herbivore larvae of Spilosoma virginica (Lepidoptera Arctiidae) were reared on three plant species that differ in their secondary plant chemistry Taraxacum officinale (no iridoid glycosides) Plantago major (low iridoid glycoside content) and P lanceolata (high iridoid glycoside content) Midguts of fifth instar larvae were assayed for the activity and kinetic properties of beta-glucosidase using different substrates Compared to the larvae on T officinale the beta-glucosidase activity of larvae feeding on P lanceolata was significantly lower measured with 4-nitrophenyl-beta-D-glucopyranoside Using the iridoid glycoside aucubin as a substrate we did not find differences in the P-glucosidase activity of the larvae reared on the three plants Heat inactivation experiments revealed the existence of a heat-labile and a more heat-stable beta-glucosidase with similar Michaelis constants for 4-nitrophenyl-beta-D-glucopyranoside We discuss possible mechanisms leading to the observed decrease of beta-glucosidase activity for larvae reared on P lanceolata and its relevance for generalist herbivores in adapting to iridoid glycoside containing plant species and their use as potential host plants (C) 2010 Elsevier Ltd All rights reserved