Western North American Naturalist

Volume 62 Number 4 Article 15

10-28-2002

Removal of Rhododendron macrophyllum petals by Camponotus modoc

Michael D. Weiser University of Oklahoma, Norman

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Recommended Citation Weiser, Michael D. (2002) "Removal of Rhododendron macrophyllum petals by Camponotus modoc," Western North American Naturalist: Vol. 62 : No. 4 , Article 15. Available at: https://scholarsarchive.byu.edu/wnan/vol62/iss4/15

This Note is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 62(4), © 2002, pp. 498–499

REMOVAL OF RHODODENDRON MACROPHYLLUM PETALS BY CAMPONOTUS MODOC

Michael D. Weiser1

Key words: Formicidae, nectivory, pollination, pollinator.

Most research on the relationship between I made all observations reported here in and plants has focused on mutualistic inter- H.J. Andrews Experimental Forest, Willamette actions in which plants benefit from the pres- National Forest, in the Western Cascade Range ence of ants (Hölldobler and Wilson 1990). of Oregon. My initial observation, in full sun While there are examples of ants removing at 1400 hours on 2 June 1997, was of R. macro- petals as a food source (Cerdá et al. 1992, Höll- phyllum in flower in a clear-cut experimental dobler and Wilson 1990), I know of no report plot at ~650 m. Several C. modoc workers were of ants removing petals specifically to access clipping petals off apparently normal R. macro- floral nectaries. There are few reports in the phyllum flowers. The workers, typically a sin- literature of ants collecting floral nectar (Tobin gle individual to a flower, were cutting around 1994), but ants will readily accept floral nectar the base of the petals with their mandibles, when it is accessible (Schubart and Anderson clipping off the entire corolla intact, which then 1978, Guerrant and Fiedler 1981, Haber et al. fell to the ground. The remaining flower had 1981). Herein I report observations of Cam- very little or no petal remaining (i.e., all pink- ponotus modoc removing petals from Rhodo- colored portions of the flower were removed.) dendron macrophyllum flowers, a behavior that The ants remained on the flower head after may have impacts on R. macrophyllum polli- removing the corolla and appeared to collect nectar from the base of the flower. They placed nation biology. their mouthparts on the base of the flower and Camponotus modoc (: Formi- their gasters appeared distended, indicating cidae: ), a common carpenter of that they had taken up liquid from the plant. the Pacific Northwest, nests at the base of live None of the flowers I observed being clipped trees, as well as in dead logs in old-growth had any serious damage to their petals (e.g., forests. In clear-cuts they often nest in and browning or wilting) before cutting by the ant. under stumps. Rhododendron macrophyllum I observed this behavior on 6 other R. macro- (Ericaceae) is a common shrub of moist to dry, phyllum in the immediate area. Two R. macro- coniferous or mixed forests ranging from British phyllum in the area had C. modoc on them, Columbia south to California. In the Western but I did not observe petal removal. I saw this Cascade Range of Oregon, R. macrophyllum behavior over several days at this single site, flowers in May and June. Flowers have large but not on R. macrophyllum at other localities pink blossoms that are collected in racemes of within H.J. Andrews. I also observed at least 20 or more flowers. Individual flowers last a 10 species of flying , including Hymen- few days, and then the entire corolla (individ- optera, Lepidoptera, and Diptera, landing on ual petals are fused to each other) wilts, turns intact flowers. The only flying insects observed brown, and falls off the flower. Rhododendron landing on flowers lacking petals were asilid macrophyllum is bee pollinated (Halverson flies that used them as perches. 1986), but many other insects and humming- While speculative, I suggest that C. modoc birds visit Rhododendron flowers for nectar workers removed the petals to access the floral (Pojar 1975). nectar of R. macrophyllum and that removing

1University of Oklahoma, Department of Zoology, 730 Van Vleet Oval, Room 314, Norman, OK 73019-0235. Present address: University of Arizona, Department of Ecology and Evolutionary Biology, 1041 E. Lowell Street, Tucson, AZ 85721.

498 2002] NOTES 499 petals allowed the ants to monopolize the nec- energy budget of R. macrophyllum, as non-pol- tar source. It is possible that the petals limited linating nectar-feeders such as hummingbirds C. modoc access to the inside of the corolla. would not access flowers lacking petals. As the Two smaller species of ants (Tapinoma sessile flowers clipped by ants look superficially simi- and Formica sp.) were observed within intact lar to flowers that have naturally dehisced flowers. Several small C. modoc were observed their corolla, this behavior has implications for within corollas of unclipped flowers, but many field studies of R. macrophyllum, specifically more were observed on the outer surface of in the examination of seed set and pollination the flowers, which may indicate that petals success. limit C. modoc access to the floral nectaries. Given that removal of the corolla was almost LITERATURE CITED complete, pollinators, which use the showy pink petals as a cue to find floral nectar, would CERDÁ, X., J. RETANA, S. CARPINTERO, AND S. CROS. 1992. Petals as the main resource collected by the ant, be less likely to visit flowers lacking these cues. Cataglyphis floricola (Hymenoptera: Formicidae). As only C. modoc and asilid flies were seen Sociobiology 20:315–319. visiting clipped flowers, the nectaries were, in GUERRANT, E.O., JR., AND P. G . F IEDLER. 1981. Flower effect, monopolized by the ants. defenses against nectar-pilferage by ants. Biotropica To differentiate between the hypotheses 13(suppl. 2): 25–33. HABER, W.A., G.W. FRANKIE, H.G. BAKER, I. BAKER, AND that flower clipping behavior was for access or S. KOPTUR. 1981. Ants like flower nectar. Biotropica monopolization (or both), one could manipu- 13:211–214. late petals of R. macrophyllum in the presence HALVERSON, N.M. 1986. Major indicator shrubs and herbs of ants and observe their behavior. For exam- on national forests of western Oregon and south- western Washington. R6-TM-229. U.S. Department ple, if a portion of the corolla large enough for of Agriculture, Forest Service, Pacific Northwest the ants to pass through were removed, then the Region, Portland, OR. access hypothesis predicts that they would not HÖLLDOBLER, B., AND E.O. WILSON. 1990. The ants. Belk- continue clipping petals. The monopolization nap Press of Harvard University Press, Cambridge, hypothesis predicts complete petal removal. MA. POJAR, J. 1975. Hummingbird flowers of British Colum- I observed more than 10 flowers being cut bia. Syesis 8:25–28. from a single plant in 2 hours. Estimating 150– SCHUBART, H.O.R., AND A.B. ANDERSON. 1978. Why don’t 200 flowers on the plant, one can easily extrap- ants visit flowers? A reply to D.H. Janzen. Biotropica olate the potential impact of this behavior on 10:310–311. TOBIN, J.E. 1994. Ants as primary consumers: diet and the pollination biology of R. macrophyllum. abundance in the Formicidae. Pages 278–309 in J.H. Ants are not effective pollinators (Hölldobler Hunt and C. Napela, editors, Nourishment and evo- and Wilson 1990), and removal of petals should lution in societies. Westview Press, Boulder, reduce the number of potential pollination CO. events by reducing blooming time for individ- Received 20 November 2000 ual flowers. Petal removal also may affect the Accepted 17 October 2001