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Mentions: Androconial organs are common in moths and play an important role in their courtship (Birch, 1974, 1979; Phelan and Baker, 1987; Birch et al., 1990). In tiger moths (Lepidoptera: Arctiidae) they often take the form of impressive inflatable tubes projecting from the ventral surface of the abdomen or from the genital valves (Birch and Hefetz, 1987; Hauser and Boppré, 1997; Weller et al., 1999). In the tiger moth Estigmene acrea the coremata are composed of two medially curved, air-filled tubes that extend ventro-laterally from the intersegmental membrane between the seventh and eighth abdominal segments (Figure 1a). When fully inflated they are sparsely set with elongate scent scales projecting perpendicular to their surface (Figure 1b). The coremata of E. acrea have been shown to carry the dihydropyrrolizine, hydroxydanaidal (Figure 2a; Krasnoff and Roelofs, 1989), a chemical that is known to have pheromonal activity in some arctiid species (Conner et al. 1981; Davidson et al., 1997, Iyengar et al., 2001). Females of Utetheisa ornatrix prefer to mate with males with high levels of hydroxydanaidal, which provides information on the quality of the male as a mate (Iyengar et al., 2001). The presence of hydroxydanaidal has been linked to the larval ingestion of dietary pyrrolizidine alkaloids (PAs) in Utetheisa ornatrix (Conner, 1981), Creatonotus gangis (Boppré and Schneider, 1985), Phragmatobia fuliginosa, Pyrrharctia isabella, and Estigmene acrea (Krasnoff and Roelofs, 1989). PAs are bitter tasting and hepatotoxic secondary chemicals that are thought to protect more than 300 plant species in 11 families from herbivory (Mattocks, 1986; Hartmann and Ober, 2000). Paradoxically, PAs have been shown to be phagostimulatory for the specialist feeder Utetheisa ornatrix (Bogner and Eisner, 1991) and some generalist feeders such as Creatonotus gangis (Boppré, 1990) that sequester the alkaloids. For Utetheisa the ingested alkaloids protect the larvae, pupae, and adult stages from predation (Eisner et al., 2000 and references therein).
Dietary alkaloids and the development of androconial organs in Estigmene acrea
Bottom Line: Adult males that fed on high levels of the pyrrolizidine alkaloid monocrotaline N-oxide (2500 microg) developed the largest coremata.Males that fed on lower levels of monocrotaline N-oxide (500 microg) or no alkaloid, while normal in body weight, had coremata that were progressively smaller and less robust.The size of the coremata and their commensurate pheromonal charge may have behavioral consequences in the unusual mating system of this species.
Affiliation: Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA.
Male salt marsh moths, Estigmene acrea (Lepidoptera: Arctiidae), possess inflatable androconial organs called coremata. Prior to mating males form aggregations and inflate their coremata en masse. The communal display attracts additional males and females for the purpose of mating. The coremata are known to carry the plant-derived dihydropyrrolizine, hydroxydanaidal. This pheromonal substance is derived from secondary plant chemicals called pyrrolizidine alkaloids found in the larval diet. When E. acrea larvae were raised on semi-synthetic diets containing different levels of the pyrrolizidine alkaloid precursors the alkaloids triggered a pronounced morphogenetic effect. Adult males that fed on high levels of the pyrrolizidine alkaloid monocrotaline N-oxide (2500 microg) developed the largest coremata. Males that fed on lower levels of monocrotaline N-oxide (500 microg) or no alkaloid, while normal in body weight, had coremata that were progressively smaller and less robust. The size of the coremata and their commensurate pheromonal charge may have behavioral consequences in the unusual mating system of this species.
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