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.nectar guides ͉ pollination ͉ plant defense ͉ dearomatized phloroglucinols ͉ flavonoids

The larva of the green lacewing (Ceraeochrysa cubana) (Neuroptera, Chrysopidae) is a natural predator of eggs of Utetheisa ornatrix (Lepidoptera, Arctiidae), a moth that sequesters pyrrolizidine alkaloids from its larval foodplant (Fabaceae, Crotalaria spp.). Utetheisa eggs are ordinarily endowed with the alkaloid. Alkaloidfree Utetheisa eggs, produced experimentally, are pierced by the larva with its sharp tubular jaws and sucked out. Alkaloid-laden eggs, in contrast, are rejected. When attacking an Utetheisa egg cluster (numbering on average 20 eggs), the larva subjects it to an inspection process. It prods and͞or pierces a small number of eggs (on average two to three) and, if these contain alkaloid, it passes ''negative judgement'' on the remainder of the cluster and turns away. Such generalization on the part of the larva makes sense, because the eggs within clusters differ little in alkaloid content. There is, however, considerable between-cluster variation in egg alkaloid content, so clusters in nature can be expected to range widely in palatability. To check each cluster for acceptability must therefore be adaptive for the larva, just as it must be adaptive for Utetheisa to lay its eggs in large clusters and to apportion alkaloid evenly among eggs of a cluster.Ceraeochrysa cubana ͉ Chrysopidae ͉ Utetheisa ornatrix ͉ Arctiidae ͉ pyrrolizidine alkaloid T he moth Utetheisa ornatrix (family Arctiidae) (henceforth called Utetheisa) endows its eggs with pyrrolizidine alkaloids [henceforth called alkaloid(s)]. It sequesters the chemicals as a larva from its foodplants, legumes of the genus Crotalaria (family Fabaceae), and retains them through metamorphosis into the adult stage. Both parents contribute to the egg endowment. The male transmits alkaloid to the female with the sperm package at mating, and the female allocates a portion of this gift, together with a share of her own alkaloid, to the eggs (1).Here we present evidence that the alkaloids protect the eggs against a natural enemy, the larva of the green lacewing, Ceraeochrysa cubana (family Chrysopidae) ( Fig. 1 A and B). Specifically, we demonstrate that (i) the larva, in laboratory tests, rejects alkaloid-containing Utetheisa eggs, while avidly consuming alkaloid-free eggs offered as controls; (ii) the larva exercises this discrimination in the field as well; (iii) the larva is more strongly deterred by the N-oxide form of the alkaloid than the free base form; (iv) the alkaloid in Utetheisa eggs occurs mainly in the N-oxide form; (v) the eggs in a given cluster are equally endowed with alkaloid; and (vi) the larva seems to act on this information: it abandons a cluster, no matter what the cluster size, if the first few eggs it samples are distasteful. Materials and MethodsThis study was done at our Cornell laboratories and at the Archbold Biological Station, Lake Placid, Highlands County, FL.Experimental Animals. Utetheisa occur at the Archbold Station, often in abundance, in association with stands of Crotalaria mucronata, the major local foodplant. ...

The larva of the green lacewing Chrysopa slossonae lives in colonies of the wooly alder aphid Prociphilus tesselatus upon which it feeds. It disguises itself as its prey by plucking some of the waxy "wool" from the bodies of the aphids and applying this material to its own back. The investiture protects it from assault by the ants that ordinarily "shepherd" the aphids. Larvae artifically denuded are seized by the ants and removed from the aphid colonies. A larva requires on the average less than 20 minutes to coat itself with wax. A hungry denuded larva gives the coating procedure about the same behavioral priority as feeding.

A BSTR ACTThe plant Mentzelia pumila (family Loasaceae) has leaves and stems densely covered with tiny hooked trichomes. The structures entrap and kill insects and therefore are most probably protective. But they are also maladaptive in that they incapacitate a coccinellid beetle (Hippodamia convergens) that preys upon an aphid enemy (Macrosiphum mentzeliae) of the plant. The adaptive benefit provided by the trichomes is evidently offset by a cost.The leaves and stems of many plants are beset with small hairs, hooks, spines, or scales (1, 2). These epidermal elaborations, or trichomes, which can impart on a plant a characteristic pubescent appearance or abrasive ''feel,'' generally are believed to be defensive. Indeed, a number of insect herbivores, including aphids, leaf beetles, leafhoppers, and caterpillars, have been shown to be physically deterred by trichomes (2-5). In the course of field studies undertaken by two of us (T.E. and M.E.) in southern Arizona, we came across a plant, Mentzelia pumila (family Loasaceae), that seems to reap both benefit and harm from its possession of trichomes. It benefits because its trichomes are broadly incapacitating to insects, and it is harmed because among the insects incapacitated is a coccinellid beetle that preys on an aphid enemy of the plant.The observations we made are not nearly as extensive as we would have liked. They are presented here because we do not anticipate having future occasion to study the plant. Specifically, we provide a description of M. pumila's trichomes, and data on how these structures affect insects generally and a coccinellid beetle in particular. MATERIALS AND METHODSThe Plant (M. pumila). This plant is a multibranched herb, typically 30-60 cm in height, with lanceolate toothed leaves and yellow flowers (Fig. 1A). Its range extends from Wyoming southward to Texas, Arizona, and Mexico (6). Like other members of its genus, it bears a dense covering of tiny trichomes, which render its leaves and stems characteristically sandpaper-like to the touch. We made our observations in May 1991, on stands of the plant that we located in Cochise County, AZ, northward of Douglas, along highway U.S. 80 and in the environs of Portal.Microscopy. Fresh material was photographed with a Wild M400 photomicroscope. Items viewed with a scanning electronmicroscope (pieces of M. pumila leaves and stems; insects stuck to the plant) were prepared by being dehydrated in ethanol, critical-point dried, and gold-coated (7).Insects Found Entrapped on M. pumila. These were identified to species or genus where possible, otherwise mostly to family.The Aphid (Macrosiphum mentzeliae). Two species of aphid, M. mentzeliae and Pleotrichophorus wasatchii, have been reported from Mentzelia plants (8). We found only the former feeding on M. pumila at our study sites.The Coccinellid Beetle (Hippodamia convergens). This was by far the dominant coccinellid on M. pumila at our field sites. The species occurs throughout the United States (9).Tests with H. convergens. To obtain some measure...

The arctiid moth Utetheisa ornatrix is protected against predation by pyrrolizidine alkaloids (PA) that it sequesters as a larva from its food plant. Earlier work had shown that males transmit PA to the female with the sperm package and that the female bestows part of this gift on the eggs, protecting these against predation as a result. We now show that the female herself derives protection from the gift. Females deficient in PA are vulnerable to predation from spiders (Lycosa ceratiola and Nephila clavipes). If mated with a PA-laden male, the females become unacceptable as prey. The effect takes hold promptly and endures; females are unacceptable to spiders virtually from the moment they uncouple from the male and remain unacceptable as they age. Chemical data showed that the female allocates the received PA quickly to all body parts. We predict that other instances will be found of female insects being rendered invulnerable by receipt of sexually transmitted chemicals.