Insect Pollinators of Three Rare Plants in a Florida Longleaf Pine Forest
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308 Florida Entomologist 85(2) June 2002 INSECT POLLINATORS OF THREE RARE PLANTS IN A FLORIDA LONGLEAF PINE FOREST THERESA L. PITTS-SINGER1, JAMES L. HANULA1 AND JOAN L. WALKER2 1U.S.D.A. Forest Service, Forestry Sciences Laboratory, 320 Green St., Athens, GA 30602 2U.S.D.A. Forest Service, Department of Forest Resources, Clemson University, Clemson, SC 29634 ABSTRACT As a result of human activity, longleaf pine (Pinus palustris Miller) forests in the southern United States have been lost or drastically altered. Many of the plant species that histori- cally occupied those forests now persist only as remnants and are classified as threatened or endangered. In order to safeguard such species, a better understanding of their pollination ecology is needed. We identified insect visitors and potential pollinators of Harperocallis flava (McDaniel) (Amaryllidaceae), Macbridea alba Chapman (Lamiaceae) and Scutellaria floridana Chapman (Lamiaceae) that occur in longleaf pine habitat on the Apalachicola Na- tional Forest in Florida. We observed that potential pollinators of H. flava were Halictidae, of M. alba were bumble bees (Apidae: Bombus), and of S. floridana were Megachilidae and Halictidae. However, the rates at which these insects visited the flowers were very low. Our results raise important concerns about how forest management practices affect the survival of rare plants, as well as their pollinators. Key Words: Harperocallis flava (McDaniel), Macbridea alba Chapman, Scutellaria floridana Chapman, Pinus palustris Miller, threatened species, endangered species RESUMEN Como resultado de la actividad humana, los bosques de pino de hoja larga (Pinus palustris Miller) del sureste de los Estados Unidos han desaparecido o han sido drasticamente altera- dos. Muchas de las especies de plantas que historicamente ocupaban estos bosques persisten en la actualidad como restos y estan clasificadas como amenazadas o en peligro de extincíon. Para salvaguardar estas especies es necesitario entender la ecologia de su polinizacíon. Para ello, identificamos los insectos visitadores y polinizadores potenciales de Harperocallis flava (McDaniel) (Amaryllidaceae), Macbridea alba Chapman (Lamiaceae) y Scutellaria flori- diana Chapman (Lamiaceae) que existen en el habitat del pino de hoja larga del Bosque Na- cional de Apalachicola en Florida. Observamos que los polinizadores potenciales de H. flava eran Halictidae, de M. alba eran abejorros (Apidae: Bombus), y de S. floridiana eran Mega- chilidae y Halictidae. Sin embargo, los niveles de visitacion de estos insectos a las flores era muy bajo. Nuestros resultados crean dudas importantes acerca de como practicas de mante- nimiento de los bosques afectan a la supervivencia de plantas amenazadas, asi como a sus polinizadores. The longleaf pine ecosystem is a conservation ical and ecological requirements of these plants in priority area within the U.S. Department of Agri- order to develop appropriate recovery plans. culture Conservation Reserve Program (Food Se- Studies of potential management effects on rare curity Act of 1985, Title XII). Longleaf pine (Pinus plants in some fire-disturbed habitats have consid- palustris Miller) forests once occupied >24 million ered the response of plants to management prac- ha in the southern United States. Today, <1.3 mil- tices e.g., Hessl & Spackman 1995; Brewer 1999; lion ha remain as small isolated parcels (Outcalt Lesica 1999), but not the effects on their pollinator & Sheffield 1996). The diversity of groundcover systems. One reason for this lack of information is plants per unit area (e.g., 140 vascular plant spe- simply that the effective pollinators are unknown. cies/1000 m2 in mesic longleaf woodlands) illus- Pollinators are critical to the long-term survival of trates the remarkable species richness of longleaf many flowering plants because they provide a pine ecosystems (Peet & Allard 1993). At least 30 mechanism for ensuring seed set and develop- endangered or threatened plant species now re- ment, and often facilitate gene flow between plants side in the few remnant understory communities and plant populations. In return for pollination of longleaf pine forest, and populations of at least services, the flowers provide vital floral resources 191 taxa of vascular plants have been reduced to for the foraging insects (Proctor et al. 1996). low levels (Hardin & White 1989; Walker 1993). A worldwide pollination crisis is at hand, and Thus, it is important to understand the physiolog- environmental degradation from habitat destruc- Pitts-Singer et al.:Pollinators of Rare Plants 309 tion, modification, or fragmentation can disrupt during the growing season and usually occurs plant-pollinator interactions and jeopardize their from May to July (U.S. Fish & Wildlife Service existence (Rathcke & Jules 1993; Kearns et al. 1992, Madsen 1999). Some information available 1998). Tepedino et al. (1997) express a need for concerning this flower species relies on insect pol- “extended care” in conservation. When rare linators. Madsen (1999) found that when insects plants are imperiled, their extended families of were excluded from M. alba flowers, almost no pollinators also must be considered. It is impor- seeds were produced. tant to “maintain the integrity of ecosystems by Scutellaria floridana was also placed on the preserving interactions between plants and their federal threatened species list in 1992 (U.S. Fish pollinators” (Tepedino et al. 1997). & Wildlife Service 1992). It is found in Franklin, Our study investigates the pollinator-plant Liberty, and Gulf Counties, Florida. The stem is relationships of Harper’s beauty, Harperocallis simple or sparingly branched, and its solitary flava (McDaniel) (Amaryllidaceae), white birds- purple flowers are well separated in the axils of in-a-nest, Macbridea alba Chapman (Lamiaceae), short, leafy bracts. The corolla (2.5 cm in length) and Florida skullcap, Scutellaria floridana Chap- has 2 lips, the lower one being white in the mid- man (Lamiaceae). All of these plants are federally dle. The preferred habitat of S. floridana is simi- listed species and are endemic to the longleaf pine lar to that of M. alba, although it is more ecosystem in the Apalachicola lowlands of the restricted (Kral 1983; U.S. Fish & Wildlife Service Florida panhandle (Kral 1983; Walker 1993). They 1992). This perennial herb is reported to flower in are fire-dependent species (Kral 1983; Walker May or June (Kral 1983). 1993), and the local USDA Forest Service uses We monitored arthropod visitors to flowers of prescribed fires to help maintain their habitats. these plants, identified them, and evaluated their For H. flava pollination, insects may not be as importance as pollinators. The results of our important as for the other species in this study, if study are an important first step towards under- they are important at all. Allozyme studies have standing the interactions between these rare indicated that H. flava individuals and popula- plants and their pollinators in this Florida tions are genetically uniform (Godt et al. 1997). longleaf pine ecosystem. Further, a preliminary study by Wagner & Spira (1996) indicated that H. flava flowers are self- MATERIALS AND METHOD compatible and capable of selfing. Mature fruits were produced from flowers that were open-polli- All study sites were located on the Apalachi- nated, cross-pollinated, and self-pollinated. cola National Forest near Sumatra and Wilma, Harperocallis flava was first listed as an en- Florida. Field observations were made to deter- dangered species in 1979 (U.S. Fish & Wildlife mine which insects frequently visited flowers and Service 1992). It occurs in Franklin and Liberty how they behaved. In the summers of 1999 and Counties, Florida, in open pineland bogs and 2000, we selected and tagged 10-25 flowers (or in- along moist roadside ditches. This perennial spe- florescences) at each site, and then monitored the cies has a single yellow flower with 6 tepals (each flowers for 3- or 5-min periods throughout the day being 9-15 mm in length) produced atop a stalk for 2-5 days. Arthropod activity and the time they that emerges from stiff, grasslike leaves. Flower- were present on the flowers were recorded during ing occurs from mid-April through May and fruits the observation period. The visits of arthropods to mature in July. Kral (1983) reported that the den- flowers were counted only when they occurred sity of H. flava has declined since its discovery in during the observation period for that flower, al- 1965 primarily because of lack of fire in the area. though visits to other tagged flowers in the vicin- Presently, the USDA Forest Service manages a ity could be seen during this same time. Franklin County location and carries out periodic Observations were not made at the same time controlled burns to help maintain the open habi- each day. Because the 1999 sites did not produce tat required by this species (U.S. Fish & Wildlife enough flowers for study in 2000, sites chosen in Service 1992). 2000 were not the same as those used in 1999. In Macbridea alba was first listed as a federally summer 2000, we also used a video camcorder to threatened species in 1992 (U.S. Fish & Wildlife record insect activity on focal flowers. Service 1992). It occurs in open savannahs as well The video equipment consisted of a tripod- as in drainage areas in pine stands in Bay, Gulf, mounted Sony CCD-VX3 Video Recorder that was Franklin, and Liberty Counties, Florida (Kral auto-controlled via a Dell Latitude Xpi Laptop 1983; U.S. Fish & Wildlife Service 1992). This pe- computer with custom-developed “VideoSpy” soft- rennial herb usually has only one stem, which ware (Mark Evans, John Deere Commercial Prod- may be branched. Brilliant white flowers are clus- ucts, Inc., unpublished). The custom software tered in terminal compressed thyrses on erect allowed us to set a filming schedule for each day stems. Each flower has a green calyx (1 cm in using “record” times (3 or 5 min) and “wait” times length) and a white, 2-lipped corolla (3 cm in (10-15 min) so that up to 2 h of video could be re- length).