Scyphophorus Yuccae) in a Flowering Field of Yucca Whipplei
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Great Basin Naturalist Volume 57 Number 1 Article 4 3-7-1997 Dispersal characteristics of the yucca weevil (Scyphophorus yuccae) in a flowering field of Yucca whipplei Travis E. Huxman California State University, San Bernardino Kimberly A. Huxman California State University, San Bernardino Marc R. Stamer California State University, San Bernardino Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Huxman, Travis E.; Huxman, Kimberly A.; and Stamer, Marc R. (1997) "Dispersal characteristics of the yucca weevil (Scyphophorus yuccae) in a flowering field of Yucca whipplei," Great Basin Naturalist: Vol. 57 : No. 1 , Article 4. Available at: https://scholarsarchive.byu.edu/gbn/vol57/iss1/4 This Article 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 Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Great Basin Naturalist 57(1), © 1997, pp. 38-43 DISPERSAL CHARACTERISTICS OF THE YUCCA WEEVIL (SCYPHOPHORUS YUCCAE) IN A FLOWERING FIELD OF YUCCA WHIPFLEI Travis E. HuxmanI ,2, Kimberly A. Huxman1,2, and Marc R. Stamerl ABSTHhcT.-Dispersal charactcristics wcre measured for a population of yucca weevils (Scyplwplwrus YUGcae) in a plot consisting of flowering and nonflowering Yucca whipplei. We compared weevil dispersal to yucca distribution, phe nology, and caudex temperature. We also compared weevil movement to wind patterns and time ofday. Captured weevils were marked and released into both flowering and nonflowering home plants in the field. Distance traveled, weevil flight direction, and tm'get plant characteristics were recorded. We found that yucca weevils moved only between 1600 h on the release day and 0600 h of the following day. We recorded movement from both nonflowering and old flowering (>1;2 stalk had reached anthesis) yuccas to new flowering (> 1/2 stalk pre-anthesis) yuccas. The pattern ofweevil movement did not match the pattern offlowering yuccas in the field. Yucca weevils moved a mean distance of33 ± 8 m. Caudex temper ature appeared to be important for maintaining a population ofweevils on a plant. Wind direction was the best predictor ofweevil dispersal direction. Weevils consistently moved into the wind, suggesting that they are active fliers. Dispersal characteristics ofthe yucca weevil have implications for the evolution ofthe semelparous flowering strategy ofY. whipplei and S. ytllXae life history. Key words: Yucca whipplei, Scyphophorus yueeae, yucca weevils, insect dispersal. Only 2 species in the genus Scyplwphorus produce between several bundred and several are known to exist in the New World (Vaurie thousand flowers (Haines 1941), which can 1971). Scyphoplwru. acupunctatus Gyllenhae result in up to 150 fruit (Aker 1982b) and more and Scyphophorus yuccae Horn. (CurcuHoni than 15,000 seeds (Huxman 1996). The flower dae: Rhynchophorinae) are found exclusively on ing season for the population of Y. whipplei either agaves or yuccas, respectively (Vaurie in the San Gabriel Mountains (San Bernardino 1971). The organism we studied was S. yuccae, County, California) is typically from April the monophagolls yucca weevil, which feeds througb June, with individual plants in flower on Yucca whipplei Torr. and other members of for a period that lasts between 2 and 7 wk (Aker the genus Yucca in the southwestern region of 1982a). The inflorescence often develops for the United States and Baja California (Waring about 2 wk, reacbing a height of2 m before any 1986). The yucca weevil is a fully winged, flat flowers open, and extending to a final height tened black beetle without scales or dorsal ofapproximately 4 m. hairs, usually 10-19 mm long (Vaurie 1971). Adult weevils usually occupy a low position There is some evidence that S. yuecae damages on the plant (on both flowering and nonflower the inflorescence of 1'. whipplei in such a way ing rosettes); however, they feed and reproduce that it influences the reproductive strategy of on the base of the flowering stalk (Coquillelt the plant (Huxman and Loik 1996). Therefore, 1892). During the summer and fall, S. yuccae dispersal characteristics of this weevil may be lalVae bore into the caudex and inflorescence important in better understanding its influence of the yucca (Blaisdell 1892). They tben travel on plant reproduction. up the inflorescence, making a network oftun Yucca whipplei Torr. ssp. whipplei is a mono nels and eventually reaching a position high in carpic perennial distributed throughout south the stalk wbere they pupate and exit tbe plant, ern California, from the San Diego coast east often before the plant drops seeds in September and north into the Mojave Desert (Haines 1941, (Huxman and Loik 1996). Damage to the yucca Aker 1982a). Each rosette has a several-year inflorescence caused by tunneling weevils vegetative cycle and then produces a single makes tbe plant more susceptible to wildfire large inflorescence. The inflorescence may damage (Huxman and Loik 1996). Fire damage IDepartment of lIiolol,,'Y, Cllifijrnia Stale University-San Ikrnardino, San Bernardino, CA 92407-2397. 2prcwTll addrc~s: Department ofBiological Sciences, University ofNevada, 4505 Maryland Parkway, Box 4004, Las Vegas, NV 89154-4004. 38 1997] YUCCA WEEVIL DISPERSAL 39 and weevil tunnels can subsequently lead to was subsequently marked on the pronotum with the greater loss of small seed crops as com a small dot of Testor's (Testor Corporation, pared to large seed crops in Y whipplei (Hux Rockford, IL) brand acetate paint and released man and Loik 1996). into 1 of2 field experiments. In this study we test the hypothesis that S. In the 1st experiment we marked and re yuccae actively disperses in a nonrandom pat leased weevils into 8 randomly chosen home tern within a flowering field ofY whipplR.i. We plants: 6 nonflowering and 2 flowering rosettes. speculate that S. yuccae disperse in a direc Between 4 and 8 marked weevils were placed tional-oriented pattern that is related to fac in each plant. Each individual home plant and tors such as yucca phenology, wind patterns, its introduced weevils were marked with the or yucca caudex temperature. Because weevils same paint color, but different colors were damage small yucca inflorescences at a greater used for different plant and weevil combina rate than large inflorescences (Huxman and tions. Weevils were released in the morning Loik 1996), the dispersal characteristics of S. before 0800 h. In the afternoon of the release yuccae may be important in selecting for a day (between 1600 hand 1800 h) we sampled large reproductive output and in the general the plots to look for any dispersed weevils. All evolution ofsemelparity in Y whipplR.i. Y whipplei within the plot were sampled, and we repeatedly covered more than 3 X 104 m2 METHODS during each sampling event. This represented the area within a 100-m radius from the Study Site release point of any weevil. In the morning The experimental plot is located within the (0600 h) and afternoon (1600 h) of the day fol San Bernardino National Forest in Day Canyon lowing release, all Y whipplR.i were sampled Wash (34' ll'N, 117'32'W, 893 m). The plotis again. We measured the distance dispersed on alluvium. bisected by a permanent stream. weevils had traveled from their specific home Surrounding vegetation consists of a riversid plant and noted the time of day as either ian sagebrush scrub and chaparral mix com morning or afternoon. In addition, plants on posed of Salvia apiana Jeps., Salvia mellifera which dispersed marked weevils were found Greene, Eriogonum fascirolatum Benth., Adeno during sampling were categorized as either stoma flUlciculatum Eastw., Quercus dumosa nonflowering, young flowering (>1/2 of flow Nutt., and Ceanothus spp. The plot is bordered ers on stalk were pre-anthesis), or old flower to the north and west by the foothills of the ing (> 1/2 flowers on stalk had reached anthe San Gabriel Mountains; no geographic bound sis). This process was repeated 5 times within aries exist to the south or east. All experiments a 5-wk period from May through June 1990 were carried out approximately 1 km from the and once in 1994. base ofthe mountains to maintain a large homo In 1994 we mapped every Y whipplR.i within geneous plot with respect to topography. a 100-m radius of a single home plant. The Yearly rainfall estimates for Day Canyon Wash 100-m radius was greater than the maximum are 40-110 em of precipitation, all as rain. Dur distance recorded for weevil dispersal in the ing the 1994 experimental period, temperature 1990 field season. This mapped portion of the for winter ranged from 4' to 15'C, while sum field was used for a 2nd experiment. Marked mer temperatures ranged from 17' to 34 'c. weevils were released in the morning (before 0800 h) into the single home plant. Plots were Experimental Design then sampled in the afternoon and morning of During May and June 1990 and 1994, yucca the following day to look for dispersed weevils weevils were randomly removed from rosettes in yuccas. We repeated this routine 5 times adjacent to the experimental plot. Early in the within a 3-wk period during May and June flowering season, weevils were taken from non 1994, using the same home plant each time. flowering plants, but later they could be found During each release we marked the weevils only on flowering plants. Five to 10 weevils with a different color paint. We released 28, were taken from each plant. Once captured, 11, 20, 20, and 21 weevils, respectively, on 5 they were kept in a container for no longer separate occasions and measured distance and than 5 min, as extended periods of time could direction weevils dispersed from the home cause incidental flight upon release.