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 boppr , 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 . 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 ( boppr 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 ( boppr , 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 ) . coremata are deployed in either of two ways , depending on the nature of the mating system . in most species the coremata are inflated for a brief period just prior to copulating ( birch , 1974 ) . in creatonotos gangis and c. transiens , asian arctiids , and estigmene acrea , a species common in the new world , males congregate in the early evening and inflate their coremata for extended periods ( wunderer et al . this behavior has been referred to as lekking ( willis and birch , 1982 ; alcock , 2000 ) . boppr and schneider ( 1985 ) demonstrated a remarkable morphogenetic effect of pas in creatonotus : the amount of pa ingested by the larva determines the size of the adult 's coremata ; the more pa ingested , the larger the scent organ . the behavioral , ecological , and morphological similarities between creatonotus and estigmene suggested the possibility that estigmene might exhibit a similar pa - dependent corematal development . the adult estigmene acrea examined in this experiment came from our laboratory culture , which was started with eggs collected near the bonnet carre spillway in st . larvae were fed on a commercially available salt marsh caterpillar diet ( bioserv inc . , frenchtown , nj ) . the larvae used in this experiment were from the third generation of moths reared in our laboratory , none of which had previous exposure to pas . this is important because pas can be passed between generations via the eggs ( boppr and schneider , 1985 ; eisner et al . , 2000 ) . the larvae , pupae , and adult moths were maintained at room temperature in continuous light . the larvae were raised in petri dishes ( 90 mm in diameter , 16 mm high ) with between 1 and 10 larvae per dish depending on their size . all larvae were raised under the same conditions until they reached their final larval instar . on the first day after molting into the final larval instar they were provided with the pyrrolizidine alkaloid monocrotaline n - oxide ( figure 2b ) . one experimental group ( pa+ ) received 500 g of monocrotaline n - oxide per individual . monocrotaline n - oxide was mixed into the diet so that a milliliter block of diet contained 500 g . the pa+ group was given one block containing monocrotaline and four blocks of alkaloid - free diet . the pa5 + group was given five blocks of the monocrotaline n - oxide diet , and the control group received five blocks of the control diet . after the blocks of diet were consumed , each larva was placed back on pa - free diet until it pupated . the levels of alkaloid made available to these insects are comparable to those used in previous experiments with creatonotus ( boppr and schneider , 1985 ) and to levels readily available to larval arctiids fed on their natural hostplants ( nickisch - rosenegk and wink , 1993 ) . upon eclosion into an adult , each male estigmene was placed in a plastic cup ( 1 oz ) . the coremata were obtained by removing the abdomen of the freshly killed moth with scissors . the needle of an air - filled 10 ml syringe was inserted into the anterior cut end of the abdomen and ligated in place . the coremata were deemed fully inflated when all of the corematal scales had separated at the distal tips of the coremata . at this level of inflation the coremata the overall length of a coremata was measured from the distal tip of the structure , along the centerline , to the middle of the arch that marks the proximal end of the corematal tube . scale length was determined by measuring from the outer edge of the coremata to the tip of the three longest hairs . width of the coremata was obtained by measuring the width of the coremata 2 mm from the proximal end of the corematal branch . the mean of the two tubes was then calculated and used in all further comparisons . statistical analyses were carried out using spss for windows release 11.0.1 ( spss inc . ) or statistica kernal release 5.5 ( statsoft inc . ) . the adult estigmene acrea examined in this experiment came from our laboratory culture , which was started with eggs collected near the bonnet carre spillway in st . larvae were fed on a commercially available salt marsh caterpillar diet ( bioserv inc . , frenchtown , nj ) . the larvae used in this experiment were from the third generation of moths reared in our laboratory , none of which had previous exposure to pas . this is important because pas can be passed between generations via the eggs ( boppr and schneider , 1985 ; eisner et al . , 2000 ) . the larvae , pupae , and adult moths were maintained at room temperature in continuous light . the larvae were raised in petri dishes ( 90 mm in diameter , 16 mm high ) with between 1 and 10 larvae per dish depending on their size . all larvae were raised under the same conditions until they reached their final larval instar . on the first day after molting into the final larval instar they were provided with the pyrrolizidine alkaloid monocrotaline n - oxide ( figure 2b ) . one experimental group ( pa+ ) received 500 g of monocrotaline n - oxide per individual . monocrotaline n - oxide was mixed into the diet so that a milliliter block of diet contained 500 g . the pa+ group was given one block containing monocrotaline and four blocks of alkaloid - free diet . the pa5 + group was given five blocks of the monocrotaline n - oxide diet , and the control group received five blocks of the control diet . after the blocks of diet were consumed , each larva was placed back on pa - free diet until it pupated . the levels of alkaloid made available to these insects are comparable to those used in previous experiments with creatonotus ( boppr and schneider , 1985 ) and to levels readily available to larval arctiids fed on their natural hostplants ( nickisch - rosenegk and wink , 1993 ) . upon eclosion into an adult , each male estigmene was placed in a plastic cup ( 1 oz ) . the coremata were obtained by removing the abdomen of the freshly killed moth with scissors . the needle of an air - filled 10 ml syringe was inserted into the anterior cut end of the abdomen and ligated in place . the coremata were deemed fully inflated when all of the corematal scales had separated at the distal tips of the coremata . at this level of inflation the coremata were promptly photographed side by side with a calibration scale . the overall length of a coremata was measured from the distal tip of the structure , along the centerline , to the middle of the arch that marks the proximal end of the corematal tube . scale length was determined by measuring from the outer edge of the coremata to the tip of the three longest hairs . width of the coremata was obtained by measuring the width of the coremata 2 mm from the proximal end of the corematal branch . the mean of the two tubes was then calculated and used in all further comparisons . statistical analyses were carried out using spss for windows release 11.0.1 ( spss inc . ) or statistica kernal release 5.5 ( statsoft inc . ) . the effects of the different levels of pas ingested were readily apparent when the coremata were inflated ( figure 3 ) . there was a clear positive effect of the level of pa ingested on the size of the coremata ( table 1 ) . the pa5 + coremata were 25% longer than the pa+ coremata , which in turn were 23% longer than the pa- coremata ( duncan multiple range test , p<0.01 ) . a positive pa treatment effect was also found for the width of the corematal tubes and scale length ( anova , p<0.01 in both cases ) . the corematal width of the pa5 + group was significantly larger than the corresponding measurement in the pa- group ( duncan multiple range test , p<0.01 ) . neither the pa5 + group nor the pa- group was significantly different from the pa+ group in corematal width . scale length was significantly different between the pa5 + group and the pa- group ( duncan multiple range test , p<0.05 ) , but the pa- and pa5 + groups were not significantly different from the pa+ group ( p>0.05 ; table 1 ) . an ancova comparing corematal length to the log of the body mass ( fresh weight ) with the pa level as a factor ( recommended by one reviewer ) showed a strong effect of pa feeding on corematal length ( p<10 ) with no significant effect of body mass on corematal length ( p=0.60 ) indicating that pas are not influencing the size of the coremata indirectly through an effect on body mass . in fact there is a trend towards small body masses with the highest level of pas ( table 1 ) which suggests a possible tradeoff between body mass and corematal size . the log of the body mass data easily met the assumption of parallelism for the ancova and came very close to meeting the assumption of homogeneity of variances ( cochran 's c , p = 0.044 ) . this small deviation from the assumptions should not influence the robustness of the overall levels of significance or our conclusions ( sokal and rohlf , 1995 ) . the levels of alkaloid fed in this experiment span the range readily available to arctiids from their natural hostplants ( rothschild et al . , 1979 ; nickisch - rosenegk and wink , 1993 ; trigo et al . , 1993 ) . the ingested pa monocrotaline n - oxide had a clear effect on the ontogenetic trajectory of the coremata in the estigmene acrea males that we studied . the results of the ancova indicate that the effect was specific to the corematal tissue and was not a function of overall body mass . others who have studied estigmene acrea have not seen the effect of pas on corematal development that we report . e. acrea shows no readily discernible natural variation in the size of male coremata with diet   they presented no quantitative data to support this statement , and it is possible that all of the males in their study had roughly equal access to pas either from their larval feeding or passed to them from their mothers . krasnoff and roelofs ( 1989 ) likewise reported that pas had no effect on the males of estigmene acrea . like willis and birch , however , they presented no supporting data , so it is difficult to evaluate their claim . it is also possible that the morphogenetic effect varies across populations that were different in all three studies . the molecular mechanism by which the pas exert their morphogenetic effect is unknown . in creatonotus , which shows a similar effect at comparable pa concentrations , high titers of ecdysone in the pupal stage are essential for corematal development regardless of the level of pas available to larvae ( schmitz et al . , 1989 ) . this ecdysone effect is expected since the coremata are derived from specific larval anlage , the commitment and development of which are frequently stimulated by ecdysone in insects ( nijhout , 1994 ) . how pas modulate the development of the imaginal disks is not clear . the specific attractant released by the coremata of estigmene is unknown as well , but comparison with related arctiids indicates that it is likely that it is pa - derived , and if not hydroxydanaidal , a related compound . we have found the level of hydroxydanaidal in the coremata of estigmene acrea to be highly correlated with the amount of pa in the larval diet ( jordan , jones , and conner , unpublished ) . our findings suggest that the overall size of the coremata , and thus the surface area for pheromonal release , is greater in males with access to pas . the increased surface area combined with the greater amounts of pheromone should affect the strength of a pheromonal signal downwind of a male . if this is so , it could theoretically provide a mechanism by which females could choose males with high levels of pas from a considerable distance downwind of the lek . males so chosen could provide the female with a spermatophore rich in alkaloids for her protection and the protection of her offspring , as utetheisa ornatrix males have been shown to do ( dussourd et al . , males with large coremata may produce more attractive pheromonal signals and serve as foci for lek formation . less well - endowed males may join leks to combine their signals with those of more attractive males or to intercept incoming females . estigmene acrea is common thoughout much of the united states ( covell , 1984 ; ferguson , 2000 ) and is occasionally of economic importance ( metcalf and metcalf , 1993 ) . although it is considered a generalist feeder its list of foodplants include some species that are know to contain pas ( tietz , 1972 ) . the strong morphogenetic effect of pyrrolizidine alkaloids on corematal development in this species argues that pas play a critical role in the reproductive biology of this insect . in keeping with this e. acrea has recently been shown to have a preference for pa - containing food  a preference that is likely mediated by pa receptors located on the larval galea ( bernays et al . extraordinary reproductive physiology estigmene acrea is an excellent model for the study of chemically mediated lekking behavior in insects . coremata of estigmene acrea : a. ventral view of inflated coremata of a field- collected male . coremata of estigmene acrea : b. scanning electron micrograph illustrating the elongate scales projecting from the surface of a fully inflated corema . ( top ) pa5 + male , ( middle ) pa1 + male , ( bottom ) pa- male .
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 g ) developed the largest coremata . 
 males that fed on lower levels of monocrotaline n - oxide ( 500 g ) 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 .