Field surveys revealed that in south Florida the recently established Mikania micrantha Kunth (Asterales: Asteraceae: Eupatorieae) had a lower diversity of monophagous insect herbivores compared to the native Mikania spp. or Chromolaena odorata (L.) R. M. King & H. Rob. (Asterales: Asteraceae: Eupatorieae). In addition, Mikania micrantha served as a host for pests of agricultural and ornamental crops in Florida.
Mikania micrantha Kunth (Asterales: Asteraceae: Eupatorieae) is native to Central and South America, and because of its negative impacts in adventive regions, is considered one of the world's worst invasive species (ISSG 2014). It was discovered for the first time in North America in Oct 2009 near Homestead, Florida (Weaver & Dixon 2010), and has since been found at > 50 sites in the same area. Plant managers have raised concerns about the potential spread of M. micrantha into natural areas, particularly the Everglades National Park, located just a few miles west of the current infestation. The genus Mikania belongs to the tribe Eupatorieae in the family Asteraceae. In North America, this tribe is represented by a large number of native species, including Mikania scandens (L.) Willd., Mikania cordifolia. (L. f.) Willd., and Chromolaena odorata (L.) R.M. King & H. Rob. These species can be found in wet areas as well as in uplands throughout central and south Florida (Wunderlin & Hansen 2008). Upon their arrival to an adventive region, exotic plants encounter biotic factors including herbivorous arthropods as well as plant pathogens which could prevent their establishment and spread (Levine et al. 2004). The diversity and impact of natural enemies is predicted to be greater in regions containing native species closely related to the exotic plant (Darwin 1859; Ricciardi & Mottiar 2006). Therefore, the objective of this study was to assess the diversity of arthropods associated with Mikania spp. and C. odorata.
To find arthropods on these plants, we surveyed natural infestations located in central and south Florida. Sites with M. micrantha were located only in Homestead, while sites with M. scandens, M. cordifolia and C. odorata were located in Homestead and Fort Pierce, Florida. The distance between Fort Pierce and Homestead is approximately 200 km. Because it mostly occurs near nurseries, the M. micrantha sites were disturbed locations along fences or hedgerows. Sites with M. scandens were along canals in Fort Pierce and Homestead, whereas sites with M. cordifolia and C. odorata were in uplands in natural areas and along roadsides in Fort Pierce and Homestead. The collection of insects and mites was opportunistic and conducted in daylight hours from Jul 2011 to Jul 2013. We did not examine roots, flowers or seeds. Most of the adult insects and mites were hand collected and placed in killing jars or in alcohol. Immature insects were reared to adults inside cages on their host plants. Insect rearing was conducted in walk-in rearing rooms maintained at 25–26 °C, 60–70% RH and 14:10 h L:D photoperiod. Adult parasitoids emerging from insects were placed in alcohol for later identification. Identification of insects and mites was conducted using morphological methods by experts at several institutions including the Florida Department of Agriculture and Consumer Services (FDACS), Gainesville Florida; the National Museum of Natural History (USNM), Smithsonian Institution, Washington, D.C.; the Systematic Entomology Laboratory, Agricultural Research Service, United States Department of Agriculture; Falkultaet Biologie, Universtaet Bielefeld, Germany; and Agriculture-Agri-Food, Canada. Feeding habits of herbivores were classified as polyphagous, oligophagous and monophagous and were obtained from identification reports of experts and literature.
Results of our surveys revealed the presence of 16, 11, 34 and 18 species of herbivorous arthropods on M. micrantha, M. cordifolia, M. scandens and C. odorata, respectively (Table 1). The proportions of monophagous herbivores were 0, 22, 9 and 25% for M. micrantha, M. cordifolia, M. scandens and C. odorata, respectively. The combined proportions of oligophagous and polyphagous herbivores were 100, 78, 91 and 75% for M. micrantha, M. cordifolia, M. scandens and C. odorata, respectively. Twelve herbivores reared from M. micrantha were classified as polyphagous and included mites and insects, and represented new host records in the state of Florida. Feeding habits of the herbivores collected from all plants included scrapers (Acarina), leaf chewers (mostly Lepidoptera), leaf miners (Diptera and Lepidoptera), stem borers (Diptera), gall inducers (Diptera) and sapsuckers (Hemiptera). Of the herbivores collected from M. micrantha, 35% were shared with at least one of the sampled native plants (Table 1). The most speciose insect group reared from M. micrantha was leafminer flies. Mikania micrantha hosted several crop pests including Tetranychus sp. (Trombidiformes: Tetranychidae Acarina), Aphis spiraecola Patch (Hemiptera: Aphididae), Amorbia sp. (Lepidoptera: Tortricidae: Tortricinae), Phenacoccus parvus Morrison (Hemiptera: Pseudococcidae), Nemorimyza maculosa (Malloch) (Diptera: Agromyzidae) and Bradybaena similaris (Férussac) (Gastropoda: Helicoidea: Bradybaenidae). Two new species were discovered during this survey; the leafminer Bucculatrix n. sp. (Lepidoptera: Bucculatricidae) (Donald R. Davis, personal communication) was found on leaves of M. scandens in Fort Pierce during the summer of 2011, and a second leafminer, Cremastobombycia chromolaenae Davis, (Lepidoptera: Gracillariidae) was found on leaves of C. odorata in Fort Pierce late in the fall of 2011 (Davis et al. 2013). The stem galler Phestinia costella (Hampson) is a monophagous species on C. odorata (Solis et al. 2008) and a new US record (Dr. Alma Solis, personal communication). We did not find Melanagromyza eupatoriella Spencer (Diptera: Agromyzidae) and Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae), which are reportedly common herbivores of C. odorata in Florida (Zachariades et al. 2011).
Arthropod herbivores collected from M. micrantha (exotic), M. cordifolia, M. scandens and C. odorata in Florida during 2011–2013.
Predators and parasitoid collected from M. micrantha, M. cordifolia, M. scandens and C. odorata in Florida during 2011–2013.
We identified 4 predator species and 1 parasitoid species associated with insect herbivores on these plants (Table 2). The parasitoid Hyphantrophaga sellersi (Sabrosky) (Diptera: Tachinidae) was reared from the pupae of the specialist herbivore Cosmosoma myrodora Dyar (Lepidoptera: Erebidae) and represented a new host record. Because of the recent arrival and the limited distribution of M. micrantha, further studies are needed to assess whether local specialist insect herbivores will utilize this exotic weed in Florida. This study demonstrated that M. micrantha not only lacks specialist herbivores but also is a host of pests of agricultural and ornamental crops. Funding for this study was provided in part by the Animal Plant Health Inspection Service, United States Department of Agriculture.