IRIDOID GLYCOSIDE SEQUESTRATION BY THESSALIA-LEANIRA (LEPIDOPTERA, NYMPHALIDAE) FEEDING ON CASTILLEJA-INTEGRA (SCROPHULARIACEAE)

A small population of a polyvoltine checkerspot butterfly, Thessalia l eanira fulvia (also known as Chlosyne leanira ssp. fulvia), was found to use Castilleja integra as a larval food plant at a localized site ( Burnt Mill) southwest of Pueblo, Colorado. Field-captured adult butter flies contained the major iridoid glycosides (catalpol and macfadienos ide) of the Castilleja. The content of a third iridoid glycoside, meth yl shanzhiside, was also relatively high in the collected butterflies even though most individual Castilleja plants at Burnt Mill contained little or no methyl shanzhiside. Only a few plants, restricted to a sm all area, did contain appreciable methyl shanzhiside. Most of the plan ts that lacked the ester methyl shanzhiside contained shanzhiside, the corresponding free carboxylic acid. Thessalia larvae did not normally methylate the acid to produce methyl shanzhiside. Larvae that stopped feeding at an early instar, but yet survived several weeks, did conta in major amounts of methyl shanzhiside. It is suggested that only larv ae that overwinter or otherwise enter diapause convert shanzhiside to methyl shanzhiside. The Castilleja food plant also contained iridoids other than catalpol and macfadienoside, sometimes in major amounts, bu t these were never found in larvae, pupae, or butterflies.