Herbivorous insects associated with Ludwigia peploides (Onagraceae) in the southern United States.
One critical ecological aspect of floating primrose-willow that has been examined only marginally is that of the herbivorous insect fauna associated with the species. Surviving feeding by insects is important to competitive success in plants and contributes to composition of plant communities (Lodge, 1991), so it is necessary to document which species of insects impact plants. Based on published accounts, examination of associated herbivores has occurred mostly in South America, including that by Cordo and DeLoach (1982a, 1982b) who reported Ochetina bruchi (Coleoptera: Curculionidae), Tyloderma (Coleoptera: Curculionidae), Auleutes bosqi (Coleoptera: Curculionidae), Onychylis nigrirostris (Coleoptera: Curculionidae), and Lysathia flavipes (Coleoptera: Chrysomelidae) feeding on floating primrose-willow in Argentina. In the USA, herbivorous insects associated with floating primrose-willow include Perigaster cretura (Coleoptera: Curculionidae) and Lysathia ludoviciana (Coleoptera: Chrysomelidae; Clark, 1976; Haag et al., 1986), and two species of Altica (Coleoptera: Chrysomelidae; J. G. Nachtrieb, pers. comm.). Although not reported directly on floating primrose-willow, several caterpillars (Lepidoptera) and weevils (Coleoptera: Curculionidae) have been associated with Ludwigia in the USA (Lange, 1956; Herlong, 1979; Wibmer, 1981; Haag et al., 1986; Stoops et al., 1998; Anderson, 2002). These likely are generalist feeders using multiple species in the genus as a source of food.
Understanding which species of insect feed on floating primrose-willow will, in addition to furthering our understanding of the ecology of the plant, provide researchers and managers with a starting point for developing new management strategies by identifying potential agents for biological control. The advantage to management is two-fold in that any discovered agents can be used not only within the native range, but also in foreign areas. In the USA, when floating primrose-willow becomes problematic, surveys can indicate whether or not herbivorous species are present. If not, herbivores can be released in infested areas to help provide a means of control. One great advantage to this approach is that their introduction can be made without the oversight required when foreign insects are brought into the USA. In those instances, insects must undergo rigorous testing in quarantine to ensure the safety of introducing the agents. In addition to potential domestic use, insects that feed on floating primrose-willow may prove suitable for biological control of foreign populations of this species.
During 2007-2009, cultures of floating primrose-willow were kept in four wooden boxes (1.5 by 6.1 by 0.6 m deep) at the Lewisville Aquatic Ecosystem Research Facility, Lewisville, Denton County, Texas. Cylindrical, 6.7-L plastic containers (35.6-cm diameter, 10.2-cm depth) were filled with pond-substrate, saturated with pond-water, planted with floating primrose-willow, and then placed in the boxes. All floating primrose-willows were harvested from existing ponds at the Lewisville Aquatic Ecosystem Research Facility and both fragments containing nodes and whole plants with roots were transplanted into the substrate. Levels of water were adjusted periodically to allow plants to grow out from the substrate over the surface of the water, as is common in its natural habitat. Insects were allowed to colonize naturally and were observed periodically throughout summers. Insects feeding on plants were collected at random intervals by hand and preserved in 70% ethanol for later identification.
In addition to cultures of floating primrose-willow, invertebrates were collected opportunistically from other sites (Table 1). Specimens were preserved in 70% ethanol and subsequently identified. Specimens from culture boxes and field sites were collected both by hand and sweeping through vegetation with a net.
Nine species of insects were associated with floating primrose-willow from eight sites in five states (Table 1), including three species of leaf beetles, four species of weevils, and two species of caterpillars. Representatives of each species of weevil were deposited in the Canadian Museum of Nature Collection, Ottawa, Ontario, and leaf beetles were deposited in the Canadian National Collection, Ottawa, Ontario.
Species of leaf beetles recovered include Lysathia ludoviciana, Altica litigata, and Chaetocnema. Lysathia ludoviciana feeds on both floating primrose-willow (Campbell and Clark, 1983; Haag et al., 1986) and Myriophyllum aquaticum (parrotfeather; Habeck and Wilkerson, 1980) and has been considered for use as a agent for biological control of the introduced Ludwigia grandiflora (large-flower primrose-willow) in the southern USA (McGregor et al., 1996). Altica litigata feeds on multiple species of Ludwigia and economically important Lagerstoemia (crape myrtle; Cabrera et al., 2008). Chaetocnema has not been reported previously from floating primrose-willow and because we were unable to contact an expert to obtain identifications of species, it is not possible to speculate on host-specificity. There are 59 species of Chaetocnema recognized in the USA and Canada, many with economic importance to agriculture (Riley et al., 2002).
Four species of weevils were collected, including two species of Auleutes, Tyloderma sphaerocarpae, and Perigaster cretura. Exploration in Argentina by Cordo and DeLoach (1982b) revealed both Tyloderma and Auleutes feeding on floating primrose-willow, although neither association has been reported previously for the USA. The two Auleutes we collected were not identified to species due to a much-needed revision of the genus, but probably belong to undescribed species (R. Anderson, pers. comm.). Although specific host cannot be ascertained, A. bosqi was considered to be host specific to floating primrose-willow in Argentina (Cordo and DeLoach, 1982b), indicating a possibility of narrow specificity for one or both of the Auleutes collected in our surveys. Tyloderma sphaerocarpae has been collected previously from multiple species of Ludwigia, including L. sphaerocarpa (globefruit primrose-willow), L. repens (creeping primrose-willow), and L. glandulosa (cylindricfruit primrose-willow; Wibmer, 1981). Of the weevils collected, only P. cretura has been reported previously as a herbivore of floating primrose-willow in the USA (Clark, 1976). This species also feeds on L. alternifolia (seedbox; Knab, 1915) and L. repens (Mitchell and Pierce, 1911).
Although not collected, the caterpillars of Eumorpha and Spilosoma were observed feeding on floating primrose-willow at the Lewisville Aquatic Ecosystem Research Facility. Eumorpha fasciata has been reported from L. octovalvis (Mexican primrose-willow; Center et al., 1999) and L. leptocarpa (anglestem primrose-willow; Dominick, 1972). Spilosoma has been collected and reared previously from other species of aquatic plants at the Lewisville Aquatic Ecosystem Research Facility, including Nymphaea odorata (white waterlilly) and Sagittaria. Caterpillars were not collected from plants in this survey because species observed have generalist diets and feed on multiple taxa of plants (Bruner, 1891; Dominick, 1972; Center et al., 1999); therefore, making them unsuitable as agents for biological control.
An unknown species of leafhopper (Homoptera) was consistently on leaves of floating primrose-willow at the Lewisville Aquatic Ecosystem Research Facility, but was not identified. We believe the specimens are Draeculacephala inscripta (waterlettuce leafhopper), which is known to feed on Ludwigia (Center et al., 1999). Its occurrence on floating primrose-willow may be coincidental. It is a common herbivore of Pistia stratiodes (waterlettuce) and cultures of that species were kept nearby at the Lewisville Aquatic Ecosystem Research Facility for other research on biological controls.
Managers of domestic plants may consider using these insects as part of a management program, especially for new infestations of floating primrose-willow in which herbivores have not spread naturally to the new infestations. In contrast to classical biocontrol programs, in which the biocontrol agent is assumed to be free of, or subject to minimal, parasitism-predation, the domestic goal of using these insects should be only to suppress, and not eradicate, populations of floating primrose-willow. Because these insects surely will be affected by parasitism-predation in their native range, it is not likely that their populations will increase sufficiently to completely control floating primrose-willow. Cultures of floating primrose-willow at the Lewisville Aquatic Ecosystem Research Facility are subject to constant feeding by herbivorous species, and by the end of summer, cultures are defoliated completely. Based on our observations, A. litigata and L. ludoviciana tend to attack plants early in summer and populations ofP. cretura increase toward the end of the growing season. This temporal partitioning may allow for the diversity of herbivorous species collected from floating primrose-willow. In addition, understanding population dynamics of the insects could aid in management, so that timing of releases coincides with natural growth of population of the insects. Foreign managers of plants should use caution when considering use of A. litigata and L. ludoviciana because of their apparent polyphagous diet. Until more is known regarding diet and life history of T. sphaerocarpae and Auleutes, it is not clear what role they may have in management of floating primrose-willow.
This research was conducted under the United States Army Corps of Engineers Aquatic Plant Control Research Program, United States Army Engineer Research and Development Center. We thank B. Anderson and L. LeSage for assistance in identifing specimens. Assistance in the field was provided by G. Pitchford and J. Leidi. Specimens were collected from the Rio Grande in Texas by C. Owens. We also thank S. Garcia for translation of the abstract and J. Nachtrieb and G. Dick for their review of the manuscript.
Submitted 21 April 2010. Accepted 12 June 2011. Associate Editor was Jerry L. Cook.
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NATHAN E. HARMS * AND MICHAEL J. GRODOWITZ
University of North Texas-Lewisville Aquatic Ecosystem Research Facility, 201 East Jones Street, Lewisville, TX 75057 (NEH)
United States Army Engineer Research and Development Center, 3909 Halls Ferry Road, Vicksburg, MS 39180 (MJG)
* Correspondent: Nathan.E.Harms@usace.army.mil
TABLE 1--Herbivorous species of insects associated with floating primrose-willow (Ludwigia peploides). Number of sites where Taxa of insects Order and family Life stage collected Chaetocnema Coleoptera, Adult 1 Chrysomelidae Lysathia Coleoptera, Adult, larval 4 ludoviciana Chrysomelidae Altica litigata Coleoptera, Adult 2 Chrysomelidae Auleutes 1 Coleoptera, Adult 1 Curculionidae Auleutes 2 Coleoptera, Adult 1 Curculionidae Perigaster Coleoptera, Adult, larval, 3 cretura Curculionidae pupae Tyloderma Coleoptera, Adult 1 sphaerocarpae Curculionidae Eumorpha (b) Lepidoptera, Larval 1 Sphingidae Spilosoma (b) Lepidoptera, Larval 1 Arctiidae Coordinates of Taxa of insects Collection site collection sites Chaetocnema Lewisville Aquatic 33[degrees]04'45" N, Ecosystem Research 96[degrees]57'30" W Facility, Lewisville, Texas Lysathia United States Fish 29[degrees]50'22.29" N, ludoviciana and Wildlife Service 97[degrees]58'31.97" W; greenhouse, San 33[degrees]04'45" N, Marcos, Texas; 96[degrees]57'30" W; Lewisville Aquatic na (a); Ecosystem Research 32[degrees]18'22.71" N, Facility, Lewisville, 90[degrees]51'55.83" W Texas; Lake Seminole, Florida; United States Army Engineer Research and Development Center, Vicksburg, Mississippi Altica litigata Lewisville Aquatic 33[degrees]04'45"N, Ecosystem Research 96[degrees]57'30" W; Facility, Lewisville, na (a) Texas; Rio Grande, near Del Rio, Texas Auleutes 1 Fountain Grove na (a) Conservation Area, Missouri Auleutes 2 Residential canal in 25[degrees]52'46.9" N, Miami, Florida 080[degrees]20'23.1" W Perigaster Lewisville Aquatic 33[degrees]04 45 N, cretura Ecosystem Research 96[degrees]57'30" W; Facility, Lewisville, na (a); Texas; Fountain 38[degrees]25'24.28" N, Grove Conservation 95[degrees]53'6.68" W Area, Missouri; Lebo Lake, Kansas Tyloderma Lewisville Aquatic 33[degrees]04'45" N, sphaerocarpae Ecosystem Research 96[degrees]57'30" W Facility, Lewisville, Texas Eumorpha (b) Lewisville Aquatic 33[degrees]04'45" N, Ecosystem Research 96[degrees]57'30" W Facility, Lewisville, Texas Spilosoma (b) Lewisville Aquatic 33[degrees]04'45" N, Ecosystem Research 96[degrees]57'30" W Facility, Lewisville, Texas (a) Coordinates were not available. (b) Specimens that were observed only in the field and not collected.
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|Author:||Harms, Nathan E.; Grodowitz, Michael J.|
|Date:||Mar 1, 2012|
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