Jerrold Meinwald

Precopulatory sexual interaction in an arctiid moth (Utetheisa ornatrix): Role of a pheromone derived from dietary alkaloids

SummaryMales of Utetheisa ornatrix have a pair of brushlike glandular structures, the coremata, which they evert from the abdomen during close-range precopulatory interaction with the female. Males experimentally deprived of coremata are less acceptable to females. The principal chemical associated with the coremata, identified as a pyrrolizine (hydroxydanaidal), has a proven pheromonal role: males raised under conditions where they fail to produce hydroxydanaidal are also less likely to succeed in courtship, and the compound itself, as its (-)-isomer, is capable of inducing the principal receptive response (wing raising) of the female. Evidence is presented indicating that Utetheisa derive hydroxydanidal from defensive pyrrolizidine alkaloids that they sequester from their larval foodplants (Crotalaria spp.). It is proposed that in addition to signalling male presence to the female, hydroxydanaidal may provide the means whereby the female assesses the alkaloid content of the male and therefore his degree of chemical protectedness. The argument is made that such pheromonal assessment of defensive capacity may occur also in other insects, including danaid butterflies, many of which share with Utetheisa a dependence on pyrrolizidine alkaloids for sex-pheromone production.

Defensive Use by an Insect of a Plant Resin

Larvae of the sawfly Neodiprion sertifer (Hymenoptera: Diprionidae), when disturbed, discharge an oily oral effluent essentially identical chemically to the terpenoid resin of its host plant (Pinus sylvestris). The resin is sequestered by the larva upon feeding, and stored in two compressible diverticular pouches of the foregut. The fluid is effectively deterrent to predators. The defensive use by an insect of a plant resin provides an instance of secondary utilization by a herbivore of the protective chemical weaponry of its host.

Sex attractant of an arctiid moth (Utetheisa ornatrix): a pulsed chemical signal.

SummaryThe sex attractant pheromone produced by the female of the moth Utetheisa ornatrix was shown to contain Z, Z, Z-3, 6, 9-heneicosatriene. The compound, whose structure was confirmed by synthesis, proved active in electroantennogram and field bioassays. Pheromone emission occurs discontinuously, in the form of short pulses (pulse repetition rate=1.5±0.2 pulses/s). It is argued that such temporal patterning — which had not previously been demonstrated for an airborne chemical signal — can provide close-range orientation cues to the male moth as it seeks out the female.

Grass roots chemistry: meta-Tyrosine, an herbicidal nonprotein amino acid

Fine fescue grasses displace neighboring plants by depositing large quantities of an aqueous phytotoxic root exudate in the soil rhizosphere. Via activity-guided fractionation, we have isolated and identified the nonprotein amino acid m-tyrosine as the major active component. m-Tyrosine is significantly more phytotoxic than its structural isomers o- and p-tyrosine. We show that m-tyrosine exposure results in growth inhibition for a wide range of plant species and propose that the release of this nonprotein amino acid interferes with root development of competing plants. Acid hydrolysis of total root protein from Arabidopsis thaliana showed incorporation of m-tyrosine, suggesting this as a possible mechanism of phytotoxicity. m-Tyrosine inhibition of A. thaliana root growth is counteracted by exogenous addition of protein amino acids, with phenylalanine having the most significant effect. The discovery of m-tyrosine, as well as a further understanding of its mode(s) of action, could lead to the development of biorational approaches to weed control.

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.

Scent organ development in Creatonotos moths: regulation by pyrrolizidine alkaloids

7-Hydroxy-6,7-dihydro-5H-pyrolizine-1-carboxaldehyde is the major volatile component of the scent organs in males of two species of Creatonotos (Lepidoptera, Arctiidae). The biosynthesis of this presumed pheromone depends on the presence of pyrrolizidine alkaloids in plants that are ingested by the larvae. In addition, these secondary plant substances control the morphogenesis of the scent organs. This morphogenetic effect of an alkaloid has not been observed previously.

Alkaloid-derived pheromones and sexual selection in Lepidoptera

Publisher Summary This chapter discusses alkaloid-derived pheromones and sexual selection in Lepidoptera. In certain insects, foreplay is basically a sexually selective process, involving assessment by the female of certain male traits that are a measure of an eventual benefit to the offspring. The foreplay is in the nature of a pheromone-mediated dialogue, and the insects are certain butterflies and moths. What kindled the interest in this area of research was the seminal paper by Brower et al. on the courtship of the queen butterfly, Danaus gilippus, and the motion picture that these investigators made of this behavior. Their data showed clearly that the two brushlike structures, or hairpencils, that the males ordinarily keep tucked away in their abdomen are in fact everted and splayed during courtship, and are brushed against the female prior to copulation. The hairpencils of Danaus gilippus turned out to be chemically similar to those of Lycorea. While they lacked the esters, and had instead the viscous terpenoid alcohol, they too were laden with danaidone. It became clear that danaidone and closely related pyrrolizidines are very generally present in the hairpencils of these insects, having been found in a number of genera beside Danaus and Lycorea. Accompanying compounds are also present, but these are variable and have been identified in only a few species.

Courtship pheromone production and body size as correlates of larval diet in males of the arctiid moth,Utetheisa ornatrix

Hydroxydanaidal, the corematal courtship pheromone of maleUtetheisa ornatrix, shows pronounced quantitative variation in natural populations of the moth. Males that, as larvae, fed on seed-bearing rather than immature food plants (Crotalaria spectabilis orC. mucronata) produce higher levels of hydroxydanaidal. Such males also have higher systemic loads of pyrrolizidine alkaloid, the known metabolic precursor of hydroxydanaidal, whichUtetheisa sequester from their larval diet and which is concentrated in the seeds ofCrotalaria. Males raised on seed-bearing plants also achieve higher adult weight. In the context of sexual selection, therefore, femaleUtetheisa could, through assessment of male hydroxydanaidal levels, gauge both the alkaloid content and body weight of their suitors.

Defence mechanisms of arthropods—I The composition and function of the spray of the whipscorpion, Mastigoproctus giganteus (Lucas) (Arachnida, Pedipalpida)☆

Abstract Mastigoproctus giganteus possesses a pair of voluminous glands, the secretion of which consists of 84 per cent acetic acid, 5 per cent caprylic acid, and 11 per cent water. The secretion is ejected forcibly as a finely dispersed spray that can be aimed accurately in almost all directions. It acts as a strong deterrent to predator attack, being repellent to arthropods and vertebrates alike. The presence of caprylic acid adds considerably to the effectiveness of the weapon as it is used against arthropods. By acting as a wetting agent, caprylic acid promotes the spread of the spray droplets over the cuticle of the predator, hence increasing the effective area of contact of the poison. In addition, caprylic acid exerts a marked accelerating effect on the penetration of the secretion, presumably by increasing the permeability of the epicuticular lipid barrier.

Red Cochineal Dye (Carminic Acid): Its Role in Nature

Carminic acid, the well-known red dyestuff from cochineal insects (Dactylopius spp.), is a potent feeding deterrent to ants. This deterrency may be indicative of the natural function of the compound, which may have evolved in cochineals as a chemical weapon against predation. The behavior of an unusual predator is described—the carnivorous caterpillar of a pyralid moth (Laetilia coccidivora)—which is undeterred by carminic acid and feeds on cochineals. The animal has the remarkable habit of utilizing the ingested carminic acid for defensive purposes of its own.