Maria Eisner

Attractive and defensive functions of the ultraviolet pigments of a flower (Hypericum calycinum)

The flower of Hypericum calycinum, which appears uniformly yellow to humans, bears a UV pattern, presumably visible to insects. Two categories of pigments, flavonoids and dearomatized isoprenylated phloroglucinols (DIPs), are responsible for the UV demarcations of this flower. Flavonoids had been shown previously to function as floral UV pigments, but DIPs had not been demonstrated to serve in that capacity. We found the DIPs to be present in high concentration in the anthers and ovarian wall of the flower, suggesting that the compounds also serve in defense. Indeed, feeding tests done with one of the DIPs (hypercalin A) showed the compound to be deterrent and toxic to a caterpillar (Utetheisa ornatrix). The possibility that floral UV pigments fulfill both a visual and a defensive function had not previously been contemplated. DIPs may also serve for protection of female reproductive structures in other plants, for example in hops (Humulus lupulus). The DIPs of hops are put to human use as bitter flavoring agents and preservatives in beer.

Chemical defense of an opilionid (Acanthopachylus aculeatus).

SUMMARY The opilionid Acanthopachylus aculeatus was shown to produce a defensive secretion containing quinones (2,3-dimethyl-1,4-benzoquinone, 2,5-dimethyl-1,4-benzoquinone and 2,3,5-trimethyl-1,4-benzoquinone), confirming the findings reported nearly a half century ago in a classic study. The mechanism by which the opilionid puts the secretion to use is described. When disturbed, the animal regurgitates enteric fluid, which it conveys by intercoxal clefts to the anterolateral corners of the carapace, where the two gland openings are situated. It then injects some of its quinonoid secretion into the fluid, and conveys the mixed liquid along the length of its flanks by way of two special channels. Such a discharge mechanism may be widespread among opilionids of the family Gonyleptidae (suborder Laniatores), to which A. aculeatus belongs. In a bioassay based on a scratch reflex in decapitated cockroaches (Periplaneta americana) the liquid effluent of A. aculeatus was shown to be potently irritating. Use of the effluent was demonstrated to protect the opilionid against ants (Formica exsectoides). Wolf spiders (Lycosa ceratiola) were shown to be minimally affected by the effluent (they showed little response when the fluid was added to their mouthparts as they fed on mealworms, their normal laboratory prey), although they proved to be aversive to mere contact with the opiliond itself, and to reject the animal without inducing it to discharge. A. aculeatus may therefore contain distasteful factors besides its glandular products.

Plant Taxonomy: Ultraviolet Patterns of Flowers Visible as Fluorescent Patterns in Pressed Herbarium Specimens

Pressed flowers, in herbarium specimens, show visible fluorescent patterns matching the invisible ultraviolet patterns that the flowers show in life. The technique is taxonomically applicable since it makes an important but usually neglected floral character readily demonstrable.

Chemical defense of the mint plant, Teucrium marum (Labiatae)

Summary. The mint plant, Teucrium marum (family Labiatae), sometimes called cat thyme, contains two methylcyclopentanoid monoterpenes, dolichodial and teucrein. The former compound is potently anti-insectan. It is repellent to ants (Monomorium pharaonis) and induces preening reflexes in flies (Phormia regina) and cockroaches (Periplaneta americana). Evidence is presented suggesting that dolichodial, which is presumed to be the plants chief defensive agent, is stored in the tiny epidermal capsules that beset the leaves. It is only when the leaves are injured (and the capsules ruptured) that the leaves become repellent. Teucrein, in contrast, has no anti-insectan potency. It is present predominantly in the leaf buds, unlike dolichodial, which is present mostly in mature leaves. It is argued that teucrein is the storage compound from which dolichodial is generated during leaf development.

Chemical Defense and Sound Production in Australian Tenebrionid Beetles (Adelium Spp.)

Girdled eucalyptus trees, felled to make room for grazing pasture, are a common sight in rural Australia. In the dead and decaying stumps that are strewn through the countryside, many insects flourish. Two of these, the congeneric tenebrionid beetles ddelium percatum and .4. pustulosum (subfamily Adeliinae) possess interesting defense mechanisms that we here describe. Both have eversible abdominal glands such as are commonly found in Tenebrionidae (Roth, I945), but some features of the chemistry and biology of the glands are anomalous. Moreover, .4. pustulosum has a stridulatory apparatus that may function for acoustical reinforcement of the. chemical defense.

Defensive Chemistry of Lycid Beetles and of Mimetic Cerambycid Beetles that Feed on Them

Summary.Beetles of the family Lycidae have long been known to be chemically protected. We present evidence that North American species of the lycid genera Calopteron and Lycus are rejected by thrushes, wolf spiders, and orb-weaving spiders, and that they contain a systemic compound that could account, at least in part, for this unacceptability. This compound, a novel acetylenic acid that we named lycidic acid, proved actively deterrent in feeding tests with wolf spiders and coccinellid beetles. Species of Lycuscommonly figure as models of mimetic associations. Among their mimics are species of the cerambycid beetle genus Elytroleptus, remarkable because they prey upon the model lycids. We postulated that by doing so Elytroleptus might incorporate the lycidic acid from their prey for their own defense. However, judging from analytical data, the beetles practice no such sequestration, explaining why they remain relatively palatable (in tests with wolf spiders) even after having fed on lycids. Chemical analyses also showed the lycids to contain pyrazines, such as were already known from other Lycidae, potent odorants that could serve in an aposematic capacity to forestall predatory attacks.

Chemical defense of an earwig (Doru taeniatum).

Summary. The earwig Doru taeniatum (Dermaptera, Forficulidae) has a pair of defensive glands, opening on the 4th abdominal tergite, from which it discharges a spray when disturbed. It aims the discharges by revolving the abdomen, a maneuver that enables it simultaneously to use its pincers in defense. The secretion contains two quinones (methyl-1,4-benzoquinone and 2,3-dimethyl-1,4-benzoquinone) present in the glands as a crystalline mass, together with pentadecane and a (presumably) aqueous phase. The gland openings are minute, with the result that virtually no quinone crystals are expelled with the spray. Only the two liquid phases are discharged, together with the ca. 1% quinone they carry in solution. Such a solute-economizing discharge mechanism appears to be without parallel among insect defensive glands.

Chemical defense of a rare mint plant.

SummaryAnalyses of leaf extracts ofDicerandra frutescens, a highly aromatic mint plant from central Florida listed as an endangered species, revealed presence of 12 closely related monoterpenes. The principal of these, (+)—trans-pulegol, is a new natural product, the synthesis of which is described. The terpenes are produced in glandular capsules that release their contents upon injury of the leaf. Data from bioassays with ants and cockroaches indicate that the terpenes serve for defense against insects.Dicerandra does, however, have a leaf-eating enemy, the caterpillar of a pyralid moth,Pyrausta panopealis. The discovery of a new natural product from an endangered species raises questions about the chemical implications of species extinction.

Chemical defense of a primitive Australian bombardier beetle (Carabidae):Mystropomus regularis

SummaryThe Australian bombardier beetle,Mystropomus regularis, sprays a mixture of quinones (1,4-benzoquinone, 2-methyl-1,4-benzoquinone, 2-ethyl-1,4-benzoquinone) and hydrocarbons (principallyn-pentadecane). The defensive fluid ist generated explosively in two-chambered glands, and is ejected audibly and hot (maximal recorded temperature = 59°C).Mystropomus is a member of the paussoid lineage of bombardiers. In common with other members of the group, it has a pair of elytral flanges (flanges of Coanda), associated with the gland openings, that serve as launching guides for anteriorly-aimed ejections of spray. It is argued thatMystropomus may be the least derived of flanged paussoids, and the closest living relative of the most primitive of extant bombardiers (Metriini).

Pre-ingestive treatment of bombardier beetles by jays: food preparation by “anting” and “sand-wiping”

Summary.Evidence is presented, obtained with two species of jays, that these birds differ in the ways in which they prepare bombardier beetles for ingestion. Blue Jays subject bombardiers to “anting,” a procedure by which the beetles are induced to eject their spray into the plumage of the birds. Florida Scrub Jays, in contrast, which live in an area where the soil is sandy, subject bombardiers to “sand-wiping,” causing the beetles to eject their spray into the substrate. Both strategies lend themselves also to pre-ingestive treatment of other chemically protected arthropods. Anting is a strategy widely practiced by birds, possibly because it can be put to use no matter what the nature of the terrain. Sand-wiping, as implied by its name (which we here coin), may be of more restricted occurrence, given that it can be carried out only on loose, penetrable soil.