Iridoid Glycoside Content Research Articles

Fate of iridoid glycosides in different life stages of the Buckeye,Junonia coenia (Lepidoptera: Nymphalidae)

The buckeye butterfly,Junonia coenia (Lepidoptera: Nymphalidae), specializes on plants that contain iridoid glycosides. To determine the fate of these compounds in larvae, pupae, and adults of this species, we reared larvae on artificial diets with and without iridoid glycosides, and on leaves of a host plant,Plantago lanceolata (Plantaginaceae). Quantification by gas chromatography showed that newly molted third-, fourth-, and fifth-instar larvae reared on leaves ofP. lanceolata contained means of 5.13, 2.88, and 6.83% dry weight iridoid glycoside. In contrast, the mean iridoid glycoside concentration of actively feeding fifth-instar larvae was 0.28% dry weight, that of pupae was 0.19% dry weight iridoids, and adults contained no detectable iridoids. Feeding experiments suggested that this reduction in actively feeding larvae was due to the metabolism of iridoid glycosides.P. lanceolata leaves in these experiments contained a mean of 1.00% dry weight iridoid glycoside, with a 2:1 ratio of aucubin to catalpol. Calculation of iridoid consumption and utilization indices showed that larvae fed artificial diets consumed, digested, and sequestered aucubin and catalpol in similar ways. When these indices were calculated for larvae fed leaves ofP. lanceolata, catalpol was sequestered twice as efficiently as aucubin.

The behaviour of grey jays, Perisoreus canadensis, towards palatable and unpalatable Lepidoptera

Grey jays were fed a set of six species of lepidopterans, predicted to be palatable or unpalatable based on their coloration and the fate of ingested host plant allelochemicals. Each of four birds received the entire series of insects. Junonia coenia (Nymphalidae) and Ceratomia catalpae (Sphingidae) were highly palatable as predicted based on their relatively cryptic coloration and lack of chemical defence. Three Euphydryas (Nymphalidae) species were predicted to be unpalatable: larvae and adults are warningly coloured and they sequester iridoid glycosides. However, Euphydryas gillettii was quite palatable, E. anicia was intermediate and E. phaeton was unpalatable. These differences may be due to differences in the iridoid glycoside content of these butterflies. Eumaeus atala (Lycaenidae) sequesters cycasin from its hostplant in the Cycadaceae and larvae and adults are warningly coloured. Adult E. atala were unpalatable.

Iridoid glycosides of Aureolaria flava and their sequestration by Euphydryas phaeton butterflies

Four iridoid glycosides were isolated and identified from Aureolaria flava (Scrophulariaceae): aucubin, gardoside methyl ester, 8-epiloganin, and 8- O-acetylharpagide. The iridoid glycoside content of Euphydryas phaeton (Nymphalidae), a principal herbivore of A. flava, was quantitatively determined by gas chromatography. In general, only aucubin was found in the butterflies, and amounts of this compound were low and variable among individuals.

Host plant utilization and iridoid glycoside sequestration byEuphydryas anicia (Lepidoptera: Nymphalidae)

The iridoid glycoside content of individual adultEuphydryas anicia butterflies from two Colorado populations was quantitatively determined. At one site (Red Hill), larval host plants wereCastilleja integra andBesseya plantaginea, while at the other site (Cumberland Pass) a single host plant,B. alpina, was used. At Red Hill, macfadienoside and catalpol were sequestered, while at Cumberland Pass, catalpol and aucubin were sequestered. Artificial diet studies showed that larvae hydrolyzed a major iridoid ofB. plantaginea, 6-isovanilIylcatalpol, to catalpol (which was sequestered) and isovanillic acid (which was excreted). Large year-to-year and individual variation in butterfly iridoid content was established as was a female-male difference in macfadienoside vs. catalpol content. Larval host plant distributions and numbers were determined at Red Hill for two years and compared with changes in butterfly populations and sequestered iridoids.