Miriam Rothschild

Calystegines in Solanum and Datura species and the death's-head hawk-moth (Acherontia atropus)

Abstract Polyhydroxylated tropane alkaloids, not hitherto recorded from the potato ( Solanum tuberosum ), were detected in the leaves and tubers of this plant. They are potent inhibitors of glycosidases and may be responsible for neurological disorders in livestock. These alkaloids were also extracted from a sphingid moth and an ithomiine butterfly, the larvae of which feed on Solanum .

A strophanthidin glycoside in siberian wallflower: A contact deterrent for the large white butterfly

Abstract In the greenhouse the Large White butterfly ( Pieris brassicae L.) does not oviposit on the Siberian wallflower ( Cheiranthus x allionii ) or Erysimum scoparium . From the leaves of Cheiranthus x allionii we extracted a strophanthidin glycoside (also present in washings from the leaf surface which when sprayed onto cabbage leaves inhibited egg laying. These extracts were tested in a dual choice chamber. Assayed on the butterflys tarsal receptors the strophanthidin glycoside produced a high, to very high impulse frequency, which is phasi-tonic, with only one cell firing. It appears to be the first natural contact oviposition deterrent recorded for the Lepidoptera.

Cycasin in the endangered butterfly Eumaeus atala florida

Abstract The strikingly beautiful aposematic hairstreak butterfly, Eumaeus atala florida , its pupa and brightly coloured, gregarious larva, all contain cycasin, the β-D-glucoside of methylazoxymethanol (MAM), which is also present in the food plant. It is suggested that the sequestration and storage of this toxin by the butterfly protects it from potential predators and that its various, highly specialized, warning attributes indicate a long association with the plant host.

Acyanoglucoside, sarmentosin, from the magpie moth, Abraxas grossulariata, geometridae: Lepidoptera

Abstract A bitter tasting cyanoglucoside, sarmentosin, was isolated from the Magpie moth. The high concentration in the imago (650,μg insect −1 suggests a defensive role for this substance. The concentration of carotenoids was also found to be exceptionally high.

SOME PECULIAR ASPECTS OF DANAID/PLANT RELATIONSHIPS

The two South American subspecies Danaus plexippus megalippe and D. plexippus erippus were reared on Asclepias curassavica (Oxford strain). The former became more emetic (tested on the pigeon) than extracts of the food plant, while the latter was much less so. The cardiac glycosides stored by D. p. erippus were insufficient to exert a characteristic digitalis‐like effect on the isolated rats heart. In our greenhouse both adult butterflies sequester pyrrolizidine alkaloids (PAs) from the juices of Senecio and Heliotropium and it is suggested that, for danaids as a group, especially Euploea and Amauris, the PAs may constitute the principal predator deterrents. In addition, it was shown that these butterflies themselves secrete cardioactive substances which can be demonstrated in larva and pupa reared on artificial diet (lacking leaf powder) if tested on the isolated rats heart. These substances are not emetic, but, since they are lacking in cryptic species of Lepidoptera, it is thought that they may function as part of the Danaids defence mechanism.

Lack of response to background colour in Pieris brassicae pupae reared on carotenoid-free diet

THE Large White butterfly (Pieris brassicae L.) is a toxic species1, aposematic at all stages of its life-cycle. Probably for this reason, the pupa responds to the colour of its background in a somewhat different manner from that of many other Pierid species, displaying heterochromy (background contrasting) rather than homochromy (background matching). In this respect, there is some genetical variation between different strains (M. R., unpublished).

Toxicity induced in the tobacco horn-worm (Manduca sexta L.) (Sphingidae, Lepidoptera)

INSECTS feeding on toxic plants demonstrate three fairly distinct types of life-style1–3. There are cryptic species, which metabolise or rapidly excrete the toxic substances present or avoid their ingestion by selective feeding; aposematic or warningly coloured species which store plant toxins in their tissues unchanged or slightly modified4; and aposematic species which superficially resemble or mimic toxic species—without actually storing poisonous plant products—or those warningly-coloured non-storers which secrete their own toxins. It is generally agreed that the cryptic life-style is more ‘successful’ than either of the other two, which are relatively rare, and it is difficult to envisage the evolutionary steps necessary to enable a species to change to the more hazardous warning life-style. If, however, circumstances favour a switch to certain toxic host plants, a cryptic insect is frequently destined to become warningly coloured1,5. On the basis of experiments with Manduca sexta, the tobacco horn-worm, we suggest that the evolution of an aposematic poisonous insect, from the more common, harmless, cryptic type, may simply involve a change to a related food plant containing different toxic properties from those of its usual host. Storage and the acquisition of toxicity and warning colour could follow this crucial switch.

Egg protection by the Atala Hairstreak butterfly (Eumaeus atala florida

Abstract The Atala Hairstreak places bright orange/red scales from the anal tuft round its egg batch. Mixed with these scales are a few larval spines. Unlike other Lycaenids which camouflage their eggs with concealing scales, the Atala draws attention to their presence with an aposematic decoration. There can be little doubt that the eggs, like the imago, contain cycasin.

Phytochemical selection of aposematic insects

Abstract Phytochemical selection and the evolution of certain aposematic insects is based on the relationship between plants containing storable toxins and the insects feeding upon them.