AMERICAN JOURNAL OF UNDERGRADUATE RESEARCH VOL. 2 NO. 2 (2003) The Relationship of Apis mellifera with Exotic and Native Plants in Boulder County, Colorado Kira Krend and Christina Murphy Department of Ecology and Evolutionary Biology University of Colorado at Boulder Boulder, Colorado 80309 USA Received: May 20, 2003 Accepted: August 5, 2003 ABSTRACT Since honeybees (Apis mellifera) were introduced to North America in the 1600’s, their influence has been profound and widespread. As pollinators, honeybees are extremely valuable economically and are vital to crop pollination. However, their presence has affected native ecosystems, including the plains ecosystem in Colorado. Using recruitment and other unique foraging characteristics, honeybees may be out-competing native pollinators for nectar and pollen resources. Our study was designed to determine if A. mellifera has a preference for exotic or native plants. We observed patches of exotic plants and patches of native plants and recorded the type of bee (exotic or native) that visited each flowering head. We also examined data from Kearns and Oliveras (unpublished), which illustrates that invasive plant species are also popular with native bees, and may draw vital pollinators away from native plants. Our results indicate that honeybees prefer to visit exotic invasive plant species to native plants. Consequently, honeybees may contribute to the spread of exotic plant species and the decline of native plant species, reducing biodiversity. Thus, native plants are doubly jeopardized. The invasion of exotic flora and fauna into native ecosystems on the plains of Colorado is part of a worldwide phenomenon of species invasion, and researchers must continue to investigate interspecies relationships to minimize the potential negative effects of invasive species. I. INTRODUCTION mellifera would visit and pollinate exotic plants more than the native plants of the The infiltration of exotic species into an area Front Range. can change ecological processes. Any The honeybee, Apis mellifera, is at disturbances to a food web can affect the the forefront of what ecologists deem a entire ecosystem. Exotics can often out- “pollination crisis:” an imbalance of the compete native species for resources and critical pollination ecosystem of flowering introduce new diseases and parasites [1]. plants [2]. The economic value of flowering Three things are clear about exotics: 1) it is plants is enormous, and most angiosperms impossible to know where an exotic species depend on insect pollinators, such as bees, will become established; 2) when it will for sexual reproduction. Changes in the happen; 3) and how it will affect an populations of pollinating insects directly ecosystem [1]. The effects of introduced affect the plants they pollinate. This shift honeybees on native ecosystems are still could potentially have serious unclear; few studies have been done, and consequences for the world’s food supply. those few found differing levels of effect. Part of a worldwide phenomenon of species The purpose of this project was to examine invasion, A. mellifera has been introduced the attractiveness of exotic and native plants from Eurasia and Africa into most of the rest to the exotic honeybee, Apis mellifera, by of the world [3]. Although introduced looking at visitation rates in Boulder County, honeybees may contribute to the decline of Colorado. Our hypothesis was that A. native pollinators, and consequently native 5 AMERICAN JOURNAL OF UNDERGRADUATE RESEARCH VOL. 2 NO. 2 (2003) plants, the economic importance of area to area [6]. This evidence suggests honeybees cannot be denied as they honeybees may be poor pollinators of some pollinate a significant proportion of flowering native flora. plants [4]. Yet some research suggests that While the concept that pollinators honeybees may negatively affect the native are more attracted to plants with which they biota [5]. Balancing the economic value and have co-evolved makes intuitive sense, very ecological consequences of honeybees, as few studies have been conducted regarding well as many other species, is a complex this association. In residential areas of issue that has yet to be resolved. Berkeley, California, Frankie et al. [7] found that exotic plants had a low attraction for a. Study Pollinators native bees. The authors believed the low attraction may be attributed to horticultural Apis mellifera is native to Europe, selection where humans have selected for Africa, and northwest Asia. It was first aesthetically pleasing traits, such as showy introduced into North America through petals, and not for large amounts of nectar Jamestown, Virginia, between 1630 and and pollen, resulting in reduced rewards for 1663 [5]. Since that time, honeybees have bees. Additionally, native bees may be less spread to every terrestrial environment in attracted to exotic plants because they did North America and number in the billions. not co-evolve with the exotic plants. Native Honeybees often out-compete other plants were four times more likely than pollinators; however, the extent to which exotic plants to attract native bees. they have replaced native species is Many people think of wax and unclear. Honeybees’ success can be honey production as the primary economic attributed to many factors. First, they find importance of honeybees. However, flowers quickly and promptly determine if the Buchmann and Nabhan [4] estimated that flowers are worth the time to visit. Secondly, honeybee pollination of crops is 50 to 60 if a good source of nectar is found, percent more valuable than their production honeybees can communicate the location of of honey and wax. Unfortunately, many the flowers to the rest of the hive through ecologists believe that both native recruitment, a tactic not used by most native pollinators and honeybees are in rapid pollinators. Consequently, honeybees decline [2]. Some reasons for the drop in harvest nectar and pollen before native honeybee populations include the use of pollinators have a chance [6]. While solitary pesticides and infectious parasitism by mites bees only live for one generation, honeybee [4]. Also, in regions of the United States that colonies are long-lived [6]. Thus, knowledge have been invaded by aggressive of flower patch locations can be used by Africanized bees, many beekeepers have honeybee colonies for generations, while been driven out of business due to rising solitary bees must learn these locations insurance costs against attacks [4]. This independently. decline could mean lower crop yields, with Honeybees are generalists and not serious consequences to the world’s food faithful to any single plant species. This supply; one in every three mouthfuls of food generality is in contrast to many native eaten is pollinated by animals, including pollinators that are specialized visitors of honeybees [4]. certain plants for nectar and pollen [6]. Studies that have attempted to look Additionally, honeybees usually pack their at competition between native bees and A. pollen with nectar and saliva, which limits mellifera have reported mixed results. pollen viability and causes less pollen to fall Some studies argue that honeybees change on a flower’s stigmatic surface [6]. On some the foraging behavior and population size of flowers, honeybees are able to collect pollen native bees [7]. For example, Gross [8] without ever coming into contact with the found that native bees were less likely to flower’s stigma, avoiding pollination of the forage on plants where honeybees are flower. Many ecologists believe that native present. Paton [9] determined that native flower species have not been able to adapt bees of North and South America switch to to honeybees’ particular method of less profitable flower resources when pollination, because a colony’s taste honeybees were present. Though changes from season to season and from honeybees are blamed for out-competing 6 AMERICAN JOURNAL OF UNDERGRADUATE RESEARCH VOL. 2 NO. 2 (2003) native pollinators, not pollinating native results with a broad range of implications, plants effectively, and increasing the which help to illustrate the complexity of success of weeds, Huryn [3] notes that not plant-pollinator relationships. In our study, much data have been collected to support we predicted that A. mellifera would exhibit a these accusations. higher visitation to rate to exotic plant species than native plants. b. Study Plants All plants in this study are members II. METHODS of the family Asteraceae. The two plant species native to the Front Range that were We examined flower patches of included in this study were golden aster each species, Heterotheca villosa, (Heterotheca villosa) and gumweed Centaurea diffusa, Grindelia squarrosa, and (Grindelia squarrosa). The two exotic Cirsium arvense in the prairie and foothills of o species in the study were Canada thistle Boulder County, (40 00' N latitude, and o o (Cirsium arvense) and diffuse knapweed between 105 20'W and 105 30'W) (Centaurea diffusa). Data were also Colorado, USA. Each species of flower was examined from (but not analyzed, see observed four to six times. Different patches Results) sunflowers (Helianthus pumilus, of flowers were observed on different days native) and chicory (Cichorium intybus, for ten-minute periods from July through exotic). Originally a Eurasian immigrant, September 2002. During the study, we Canada thistle is considered a pest in towns, observed approximately equal numbers gardens, fields, and pastures, and is (average 1235 heads) of open flower heads common in the region. Chicory was also available for pollination on each plant imported from Europe and is common on the species. We noted whether each visiting plains, often along roads, fields and ditches bee was a honeybee (A. mellifera) or a from July to October [10]. The third exotic native bee, and attempted to identify the plant, diffuse knapweed, will be elaborated native bee visitors to family. We captured on below, as it is a paradigm of an exotic representative bees after the observation plant species that has invaded an area and period was complete, and later identified may be harming native ecosystems.