Arctiids

The sex attractant of the female arctiid moth contains among other components a com pound of molecular formula C21H40 that yields... 

Several families of moths utilize hydrocarbons or epoxides of hydrocarbons as their sex pheromone. Oenocyte cells produce hydrocarbons that are transported through the hemolymph by lipophorin [71]. In a study using arctiid moths it was shown that sex pheromone hydrocarbons are transported on the same lipophorin particle as the hydrocarbons destined for the cuticular surface [ 17]. Therefore, specific uptake of the sex pheromone hydrocarbon occurred in pheromone glands [17]. Similar findings have been found with other moths [72-74]. The mechanism behind this specific uptake of one hydrocarbon from a potential pool of other hydrocarbons is unknown. 

Some male arctiid moths produce their courtship pheromone from dietary pyrrolizidine alkaloids acquired during feeding by the larvae [ 126]. Conversion of monocrotaline to hydroxydanaidal by males is accomplished by aromatiza-tion, ester hydrolysis and oxidation of an alcohol to the aldehyde [7]. In the case of Utetheisa ornatirx the stereo-configuration at C7 of the dietary alkaloid is the same as the pheromone released (R). In contrast, another arctiid, Creatono-tos transiens, can convert a dietary precursor alkaloid with the (S) configuration at C7 (heliotrine) to (l )-hydroxydanaidal. The biosynthesis occurs by first oxidation-reduction at C7 to convert the stereochemistry and then proceeds through aromatization, hydrolysis, and oxidation [7]. 

FIGURE 1 Female arctiid moth in a wind tunnel. Pheromone emission as a visible stream of liquid droplets is shown. Photo by S. Krasnoff. 

A further finding concerns the stereochemistry of HD and its derivation from PA. Both HD and the primary PAs (monocrotaline, usaramine) that we know to be available to Utetheisa in the field are of the same (7R) stereochemical configuration. It was therefore not surprising to find that Utetheisa is unable to convert a PA of opposite (7S) stereochemistry (heliotrine) into HD. However, we found another arctiid moth, the Asian species Creatonotus transiens, which also produces HD in its coremata, to be able to use 7R and 7S PAs interchangeably for HD production (31). We are tempted to conclude that Creatonotus, unlike Utetheisa, has dietary access to PAs of both stereochemical configurations in its environment. 

Most PAs are ingested and sequestered intact from the host plants of larval arctiids (larval PA feeders). Others are ingested by the adults from excrescences on the surface of alkaloid-containing plants. These adult PA feeders may or may not sequester PAs as larvae. Last, other PAs are produced only by the insects from PA-related precursors ingested from plants. Herein we concentrate on arctiids that sequester PAs as larvae and adults. 

Larval PA sequestration, similar to that in U. omatrix, is common within the Arctiidae (Table 7.1). Arctiid larvae, as exemplified by Creatonotus transiens and Tyria jacobaeae, feed on plants with PAs predominantly in the A-oxide form. The A-oxides are reduced to the lipophilic free bases in the midgut and are passively absorbed (Hartmann and Ober, 2000 but see Wink and Schneider, 1988). The free bases are then reoxidized by a soluble NADPH-dependent mixed function... 

Table 7.1. Arctiids with a known association with pyrrolizidine alkaloids (PAs)a... 

Some arctiid larvae do not feed on plants containing PAs. Individuals of these species obtain PAs in a different way. They seek out PA-rich plants as adults and extract the alkaloids from deposits on the plant s surface (Plate 7.2, p. 268). This... 

The function of adult PA feeding in arctiids is most clearly illustrated by a member of the Euchromini, the scarlet-bodied wasp moth Cosmosoma myrodora. 

The third factor is that PAs are extremely effective broad-spectrum feeding deterrents. Numerous species spanning 11 plant families have made use of this attribute (Hartmann and Ober, 2000). Arctiids and other PA-pharmocophagous insects have converted antiherbivore defenses to antipredator defenses. We know little about the mechanisms by which PAs affect their unpalatability. It seems unlikely that the long-term cytotoxic and genotoxic effects of PAs are relevant to their fast-acting deterrency. Recent work has indicated that some PAs bind to acetylcholine receptors (Schmeller et al., 1997) however, further study is required to understand the mode of action of the PAs. 

The PAs and the insects that seek them have fascinated scientists for more than 40 years. More importantly, PAs and arctiids have brought attention to the interesting... 

Acharya, L. and Fenton, M. B. (1992). Echolocation behavior of vespertillionid bats (Lasiurus cinereus and Lasiurus borealis) attacking aerial targets including arctiid moths. Canadian Journal of Zoology IQ 1292-1298. 

Bell, T. W. and Meinwald, J. (1986). Pheromones of two arctiid moths (Creatonotos transiens and C. gangis) chiral components from both sexes and achiral female components. Journal of Chemical Ecology 12 385 109. 

Bell, T. W Boppre, M., Schneider, D. and Meinwald, J. (1984). Stereochemical course of pheromone biosynthesis in the arctiid moth, Creatonotos transiens. Experientia 40 713-714. 

Blest, A. D. (1964). Protective display and sound production in some new world arctiid and ctenuchid moths. Zoologica 49 161-181. 

Conner, W. E. (1987). Ultrasound its role in the courtship of the arctiid moth, Cycnia tenera. Experientia 43 1029-1031. 

Conner, W. E., Eisner T., Vander Meer, R. K., Guerrero, A. and Meinwald, J. (1981). Precopulatory sexual interactions in an arctiid moth (Utetheisa ornatrix) role of pheromone derived from alkaloids. Behavioral Ecology and Sociobiology 9 227-235. 

Conner, W. E. Roach, B., Benedict, E., Meinwald, J. and Eisner, T. (1990). Courtship pheromone production and body size as correlates of larval diet in males of the arctiid moth, Utetheisa ornatrix. Journal of Chemical Ecology 16 543-551. 

Dunning, D. C Acharya, L., Merriman, . B. and Ferro, L. D. (1992). Interactions between bats and arctiid moths. Canadian Journal of Zoology 70 2218-2223. 

Egalhaaf, A., Coelln, K., Schmitz, B Buck, M Wink, M. and Schneider, D. (1990). Organ specific storage of dietary pyrrolizidine alkaloids in the arctiid moth Creatonotus transiens. Zeitschrift fur Naturforschung 45c 172-177. 

Ehmke, A., Witte, L., Biller, A. and Hartmann, T. (1990). Sequestration, A-oxidation, and transformation of plant pyrrolizidine alkaloids by the arctiid moth Tyria jacobaeae... 

Fullard, J. H. and Heller, B. (1990). Functional organization of the arctiid moth tymbal (Insecta, Lepidoptera). Journal of Morphology 204 57-65. 

Iyengar, V. K. and Eisner, T. (1999a). Heritability of body mass, a sexually selected trait, in an arctiid moth (Utetheisa ornatrix). Proceedings of the National Academy of Sciences, USA 96 9169-9171. 

---