Volume 63, Number 2 83 Journal of the Lepidopterists’ Society 63(2), 2009,83-88 SEX BIAS ADULT FEEDING FOR GUMWEED (ASTERACEAE) FLOWER NECTAR AND EXTRAFLORAL RESIN BY A WETLAND POPULATION OF LYCAENA XANTHOIDES (BOISDUVAL) (LYCAENIDAE) Paul M.Severns Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331; [email protected] (author for correspondence) AND Evrim Karacetin Environmental Sciences Department, Oregon State University, Corvallis, OR 97331; present address: Erciyes University, Muhendislik Fakiiltesi, Qevre Miihendisli i Boliimu, 38039 Kayseri, Turkey ABSTRACT. With the exception of some tropical genera, most butterflies rely on nectar as the primary adult resource and feed on non-flo¬ ral resources, like tree sap, opportunistically. We found that an isolated wetland population of Lycaena xanthoicles (Boisduval) (Lycaenidae) in western Oregon, USA, frequently uses both flower nectar and extra-floral resin of Grindelia integrifolia DC. x G. nana Nutt, var nana (Aster- aceae) as an adult food resource. There were sex biases in nectar- versus resin-feeding preferences, with males feeding on Grindelia flower nec¬ tar more frequently than resin, and females feeding on resin more frequently than nectar. A combination of taste tests and sucrose estimates through a handheld refractometer suggested that the Grindelia resin may be a source of sugars, while a Kjeldahl analysis detected organic ni¬ trogen at 2.6 ppm in the resin. We propose that the wetland population of L. xanthoides has either evolved or is evolving to use Grindelia resin as an adult resource because it is predictable in abundance over the landscape, unlike alternate non-floral adult resources. Additional key words: nectar preference, Grindelia, butterfly behavior, adult butterfly resources, butterfly conservation In temperate zones worldwide, butterflies typically butterflies that have obligate associations with one or a rely on flower nectar as an adult energy source (Gilbert few preferred adult resources, the combination of larval & Singer 1975; Boggs & Ross 1993; Boggs 1997a; and adult resource distribution will determine whether Rusterholz & Erhardt 2000; Tooker et al. 2002) while a particular piece of habitat is suitable for colonization feeding on non-floral resources such as feces, carrion, and population persistence. In the case of rare species rotting fruit (Gilbert & Singer 1975), aphid honeydew that are of conservation concern, understanding what (Rosenberg 1989; Corke 1999), and tree sap (Rosenberg resources are preferred and the strength of the insect- 1989; Krenn et al. 2001; Warren 2005) appears to be resource interaction is essential for estimating habitat largely opportunistic and likely supplemental to the quality and providing appropriate targets for restoration primary diet. In tropical regions, specialization of adult (Severns et al. 2006). butterflies on non-floral resources, like rotting fruit In this paper, we report on the adult feeding behavior (DeVries et al. 1997; Krenn 2001; Knopp & Krenn of a rare wetland population of Lycaena xanthoides 2003; Fischer et al. 2004; Molleman et al. 2005), is a (Boisduval) (Lycaenidae) in the Willamette Valley of strategy for acquiring resources infrequently used by western Oregon, USA, and its frequent use of an extra¬ temperate butterflies. Consumption of adult butterfly floral herbaceous plant resin. We furthermore provide resources can directly influence population evidence that butterflies may derive sugars and nitrogen demographics by increasing fecundity (Boggs & Ross from this abundant, predictable extra-floral adult 1993; Boggs 1997a; Fischer & Fiedler 2001; Fischer et resource, and that the contribution of plant resin to the al. 2004), contributing to a longer lifespan (Hill & adult diet is an important interaction for local Pierce 1989; Karlsson & Wiekman 1990; Fischer & conservation planning in this butterfly species. Fiedler 2001), and providing energy for flight (Corbet Materials and Methods 2000), which is related to both survival and fitness. Spatial and temporal aggregation of adult resources Study species. Lycaena xanthoides is a western across a patchily distributed landscape of resources may North America butterfly primarily found in various dry also concentrate adult butterflies (Wiklund 1977; habitats throughout northern Mexico, California, and Peterson 1997; Schneider et al. 2003; Auckland et al. southern Oregon (Scott 1986). However, two wetland 2004), increasing opportunities for mating. For populations of L. xanthoides occur in the Sacramento 84 Journal of the Lepidopterists’ Society Valley of central California (Shapiro 1974) and in the Feeding observations and analysis. We were southern Willamette Valley of western Oregon (Severns careful to record feeding; on nectar or resin only if the & Villegas 2005). In these wetland populations, L. proboscis was extended either into an open Grindelia xanthoides females lay eggs that survive seasonal disc flower or resin on the phyllaries of the inflorescence flooding and adults are restricted to the local wetlands head. We recorded as many nectaring observations for (Severns et al. 2006; A.M. Shapiro pers. com. 2006). each individual as possible. Because the study Western Oregon (Willamette Valley) L. xanthoides population of L. xanthoides is small, it was relatively appeared to be historically rare and was presumed easy to find identifying wing characteristics (e.g. wing extinct until recently rediscovered (Severns & Villegas tears, maculation differences, size, wing wear patterns, 2005). The butterfly population remains precariously etc.) for individuals to be accurately followed. To avoid small, with an estimated 97 total individuals (L90%=70, resampling of individuals, nectaring observations were U90%=215) among three subpopulations (Ramsey & gathered on two different occasions separated by 12 Severns 2008 in press). Immediately following its days. On both observation dates, male and female rediscovery in the Willamette Valley an attempt was butterflies were encountered and at least 10% of the made to understand butterfly-environment interactions Grindelia heads contained open disc flowers. that would enhance L. xanthoides restoration projects. We pooled the data within an individual to generate A key interaction identified was that the Willamette the per individual ratio of feeding on Grindelia resin or Valley wetland population of L. xanthoides had a strong flower nectar (i.e. the number of flower nectaring preference (> 85%) for flowers of perennial Grindelia observations for individual #1/ total number of feeding integrifolia DC. x G. nana Nutt. var. nana (Asteraceae) observations for individual #1). Ratios of nectar to resin plants (hereafter Grindelia and see Chambers 1998 for feeding by individual were analyzed for adult resource a taxonomic treatment) despite a conspicuous feeding differences between sexes using a proportions abundance of alternate nectar sources which other co¬ test (Ramsey & Schafer 2002). We used a one-sided occurring butterfly species prefer (Severns et al. 2006). Wilcoxon signed-rank test to determine if within sex Although not reported previously (Severns et al. 2006), choice of food resource could be explained by random observations of female nectaring were not as common as chance. We chose a non-parametric statistical test male nectaring, despite a nearly equal number of males because data were not normally distributed and no and females observed. Females commonly perched on other transformations (other than a rank the buds of Grindelia, but it was not noticed until the transformation) improved the data distribution. summer of 2006 that butterflies may use resin secreted Statistical analyses were performed using S-PLUS 6.1 by the plant as a food source. Resins secreted by for Windows Professional Edition (Insightful Corp Grindelia plants are generally most abundant on the 2002). flower heads of the plant, followed by the leaves, and Simple sugar and nitrogen resin analysis. We then the stems (Hoffmann & McLaughlin 1986). A gathered Grindelia flower buds from the field during combination of dense glandular trichomes and resin the flight period of L. xanthoides, placed the buds in a canals (Hoffmann et al. 1984) produces conspicuous amounts of resin that appear on flower buds as either a white, sticky, viscous liquid, or a covering of clear, less viscous resin coating the phyllaries (Fig. 1). The clear, less viscous liquid appears while the glands are actively secreting resin, and as the resin dehydrates it becomes more viscous and sticky. Grindelia in western Oregon secretes resins beginning before the flower heads open and continues through the end of flower anthesis. Grindelia typically has 20 to 40 heads on a flowering plant but particularly large plants can have hundreds of flower heads. Each head has 20-50 disc flowers and 10-35 ray flowers that are open throughout the months of July, August, and September. Since the flight of L. xanthoides and Grindelia anthesis coincide, the abundance of flowering Grindelia plants is unlikely to Fig. I. A). Female Lycaena xanthoides feeding on Grindelia be limiting in the study populations as flower heads resin, B) a Grindelia hud covered with resin, and C) magnifica¬ tion of the proboscis placement from 1A. easily number in the thousands. Volume 63, Number 2 85 plastic bag on ice, and transported the buds to a laboratory where the resin was extracted. We extracted resin by gentlv squeezing the phyllaries until a small droplet of resin, approximately 2-8 |jL per head, was collected with a micropipette and placed into a centrifuge tube. Approximately 400 |J I. of exudate were collected from 50 unopened flower heads. The Brix concentration, an index of sucrose concentration, was estimated by taking the mean of five replicates (20 pL/sample) of pooled resin using an Atago ATC-1E handheld refraetometer under manufacturer recommended conditions. Total inorganic and organic Fig. 2. Bar graph of median resin and flower nectar feeding nitrogen (TKN) was estimated from 50 piL of pooled with error bars representing the 1st and 3rd quartiles. A pro¬ portions test indicated that there was a difference in adult re¬ resin exudate by an acid Kjeldalil digestion (Strickland source choice between male and female L. xanthoides (Z = - & Parsons 1972) which measures the amount of organic 5.093, p = 0.000000176). The percentage of resin and flower N in a given sample, excluding nitrites and nitrates nectar feeding instances indicates that females selected resin over nectar (Wilcoxon signed rank test: 110 = number of nectar (D'Elia etal. 1977). visits < number of resin visits, Z = 2.446, p = 0.0072), while males preferred nectar over resin (Wilcoxon signed rank test: Results HO = number of resin visits < number of nectar visits, Z = - 2.2713, p-value: 0.0116). ° = statistically significant difference Twenty individuals were reliably followed and the between medians. mean number of feeding observations per individual was 4.6 occasions (± 0.72 S.E.). A proportions test small, our data suggest that female Willamette Valley L. indicated that male L. xanthoides used flower nectar xanthoides preferred to feed on plant resin over more frequently than females, while females fed on Grindelia (lower nectar, while males appeared to choose Grindelia resin more commonly than males (Fig. 2). ffower nectar over plant resin (Fig. 2). Rusterholz & Among the twelve males observed, most of the Erhardt (2000) suggested that, within a species, male individuals preferred to forage on flower nectar and and female butterflies prefer different nectar species small number preferred resin (Fig. 2). Among the eight despite having the opportunity to feed from the same females observed, most preferred to feed on Grindelia array of flowers. In some instances, sex-specific resin instead of flower nectar (Fig. 2). No other differences for nectar resources was linked to the butterfly species were observed feeding on Grindelia availability of amino acids (Aim et al. 1990; Mevi- resin during the course of this study. Schiiutz & Erhardt 2002, 2003), which females may use Chemical analyses of Grindelia resin suggest that to increase their fecundity (Murphy et al. 1983; Boggs there was. a small amount of available resources for adult 1997b). We do not know if any amino acids are L. xanthoides. The Brix concentration was ca. 2.5% (± available in Grindelia resin, but it does appear that 0.3% SEM), suggesting that simple sugars, primarily soluble nitrogenous compounds are present in the resin, sucrose, was an available resource in the resin (for a Brix at low concentrations (ca. 2.16 mg/L of resin). scale comparison, a ripened banana has a Brix Grindelia resin may also contain a low concentration of measurement between 10 and 12%). Total Kjeldalil sugars as the solution tasted sweet and the Brix nitrogen was 2.16 mg N/L of Grindelia resin, indicating concentration of the resin was approximately 2.5%. that a small amount of organically bound nitrogen may Handheld re I lactometers, like the one used in this be available for butterfly use. study, are known to measure compounds other than sucrose and do not measure other disaccharides and Discussion most simple sugars (Corbet 2003). Our Brix estimate of Both sexes of Willamette Valley L. xanthoides fed on sugars in Grindelia resin may be an overestimate of extra-floral Grindelia plant resin as well as flower nectar, some sugars but is also likely to underestimate others. A and resin appears to have both simple sugars and a small more rigorous chemical analysis is needed to amount of organically bound nitrogen available for use. understand the quantity and diversity of carbohydrate The sugars are concentrated enough to be tasted by the and nitrogen resources available for butterfly use in human tongue (Severns pers. obs.) and the amount of Grindelia resin and flower nectar. organically bound nitrogen is positioned at the lowest Perhaps the most interesting aspect of L. xanthoides end of ranges documented to support insect larvae use of Grindelia resin as an adult resource is that the (Mattson 1980). Although the observation number is resins produced by Grindelia species are known to 86 Journal of the Lepidopterists’ Society contain chemical deterrents effective against adult resource. However, it is possible that other lepidopteran larvae (Glendinning et al. 1998). It is temperate butterflies may use Grindelia resin as a food unclear which compounds within the resin protect resource because members of this genus are common Grindelia plants from herbivory, but it may be due to throughout western North America and arid areas of grindelic acid (e.g. Mahmoud et al. 2000), a diterpene South America (Steyermark 1937), and at least one that is similar in structure to diterpenes found in trees of species is currently under cultivation for resin the Pinaceae (Langenheim 2003). This suggests the production in arid regions of North and South America possibility that females may use secondary plant (Timmermann & Hoffmann 1985; Zavala & Ravetta compounds to provision progeny with chemical 2001). Grindelia species, with a broad geographic range, predator deterrents. Since female L. xanthoides a predictable extra-floral resin resource, and relatively appeared to prefer resin over flower nectar while males high local abundance may be a significant non-nectar displayed an opposite trend under the same adult resource lor other Lepidoptera. environmental and site conditions (Fig. 2), gender The Willamette Valley population of L. xanthoides is associated resource selection may be due to chemical a target species for wetland conservation, in part due to resources that are present or more plentiful in resin that its rarity and local wetland endemism (Severns & are not in Grindelia nectar. Villegas 2005; Severns et al. 2006). It was recently To our knowledge this is the only lycaenid population argued that there was an important association between in temperate zones that has been documented to the flower nectar of Grindelia and the distribution and consistently use plant resin as an adult resource. habitat preference of adult butterflies (Severns et al. Nymphalid butterflies in temperate zones do use tree 2006). It appears that the importance of Grindelia may resin opportunistically as an adult resource (Tolman & have been underestimated to the remaining Willamette Lewington 1997; Scott 1986; Layberry et al. 1998; Valley L. xanthoides population. In past studies Corke 1999; Omura & Honda 2003), but tree sap is not (Severns & Villegas 2005; Severns et al. 2006), likely a dependable enough resource to annually individuals that perched on Grindelia buds, that were support a butterfly population. For example, Rosenberg likely feeding on resin, were not recorded doing so. (1989) found that Limenitis weidemeyerii Edwards Thus, the local dependence of L. xanthoides on (Nymphalidae), Vanessa atalanta (L.) (Nymphalidae), Grindelia resources was likely underestimated. Since and Nymphalis antiopa (L.) (Nymphalidae) fed on flower nectaring observations in past studies indicated willow (Salix) tree sap from wounds created by yellow- that L. xanthoides neetared on Grindelia flowers = 90% bellied sapsuckers, Sphyrapicus varins (L.) (Pieidae). of the time without accounting for resin feeding, it is For tree sap to be a dependable resource for butterflies, likely that interaction between Willamette Valley L. birds must be present annually, and tree wounding must xanthoides and Grindelia as an adult resource is an be frequent and substantial enough for sap to be obligate association. The natural extension of this available throughout the butterflies’ adult life span. In information to management of the Willamette Valley L. comparison to fruit production by tropical trees and xanthoides is that conservation and restoration of habitat resin production by Grindelia plants, the sap available must focus on two obligate butterfly resources - the from a wounded tree is a more unpredictable and host plant and Grindelia - for conservation projects to limited resource. Willamette Valley L. xanthoides may have the greatest chance of success. be evolving a preference for Grindelia resin because it is a predictable, abundant resource in the remnant Acknowledgements wetland prairies of western Oregon. Furthermore, this We thank E. Bradford for helping gather field nectaring data, two anonymous reviewers for providing helpful comments on relationship between Grindelia resin and L. xanthoides this manuscript, and S. Villegas (Eugene, Oregon District, Bu¬ may be more geographically widespread. Lycaena reau of Land Management) for support of this project and ac¬ xanthoides in central California appear to prefer cess to the study site. Grindelia (lowers (Scott & Opler 1975; Shapiro & Literature Cited Manolis 2007) and may even be selective when given a Alm, J., T.E. Ohnmeiss, & J. Lanza. 1990. Preference of choice of Grindelia species (Shapiro & Manolis 2007), cabbage white butterflies and honeybees for nectar that but these authors did not note resin feeding. Other contains amino acids. Oecologia 84:53—57. butterflies in the Willamette Valley either do not nectar Auckland, J.N., D.M. Debinski, & W.R. Clark. 2004. Survival, movement, and resource use of the butterfly on Grindelia flowers, or the species that do visit Pamassius clodius. Ecol. Entomol. 29:139-149. Grindelia flowers do not feed on resin (Severns pers. Boggs, C.L. 1997a. Reproductive allocation from reserves obs.). 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