Checklist of Insects Associated with Salvinia minima Baker in Louisiana , USA

This study presents a list of adult insects (excluding Diptera and Lepidoptera) collected from an infestation of an invasive aquatic weed, common salvinia ( Salvinia minima Baker), in southern Louisiana, USA. Insects were sampled from May – November of 2009 and 2010 using floating pitfall traps. A total of 7,933 specimens were collected, representing seven orders, 70 families, and 235 species. Species of note include three currently undescribed species of Coleoptera, one previously undescribed braconid wasp, two new state records of Curculionidae, a new state generic record for the family Limnichidae, and a new record for the United States.


Introduction
Aquatic macrophytes contribute to the structure and function of wetlands in a variety of ways, including positively affecting diversity among associated groups and providing shelter from predation (Brown 1998, Olson et al. 1994, Batzer 1998).Many species of invertebrates show distinct preferences for aquatic plants based on their physical structure (Dvorak and Best 1982, Cyr and Downing 1988, Dvorak 1996).However, invasive plants threaten wetland community structure and integrity by forming monotypic stands, changing available habitat, altering diversity, and modifying food webs (Zedler and Kercher 2004).As more non-native plants such as Salvinia species invade waterways, the ecosystem functions that macrophytes provide are likely to change (Luken and Thieret 1997).
Older studies examining insects associated with Salvinia species focused on identifying potential biological control agents for S. molesta Mitchell by examining the S. auriculata complex (S.auriculata Aubl., S. molesta, S. herzogii de la Sota, and S. biloba Raddi) (Bennett 1966, Forno andBourne 1984).Several recent studies have examined macroinvertebrates associated with Salvinia from a conservation standpoint within its native range (Herrera et al. 2000, Albertoni and Palma-Silva 2006, Poi de Neiff and Neiff 2006).Studies sampling insect diversity associated with Salvinia species have returned results ranging from 10 insect species (with S. biloba; Forno and Bourne 1984) to 113 insect species (with S. molesta; Pelli and Barbosa 1998).
No investigations have been carried out to document diversity of invertebrates associated with either S. minima or S. molesta in the United States.Pelli and Barbosa (1998) suggested that a rich fauna associated with Salvinia in Brazil is possibly a side effect of a rich endemic aquatic fauna that uses Salvinia incidentally.Unfortunately, while the habitat is commonly found in the southeastern United States, few studies that compared invertebrates from swamps and flooded woodlands to other wetland Abstract: This study presents a list of adult insects (excluding Diptera and Lepidoptera) collected from an infestation of an invasive aquatic weed, common salvinia (Salvinia minima Baker), in southern Louisiana, USA.Insects were sampled from May -November of 2009 and 2010 using floating pitfall traps.A total of 7,933 specimens were collected, representing seven orders, 70 families, and 235 species.Species of note include three currently undescribed species of Coleoptera, one previously undescribed braconid wasp, two new state records of Curculionidae, a new state generic record for the family Limnichidae, and a new record for the United States.Arnett et al. 2002, Epler 2006, Merritt et al. 2008, Epler 2010).Voucher specimens of all species listed in (Hymenoptera: Ichneumonidae).As these specimens were not collected in protected geographic areas or exported outside the USA, no permits or licenses were required to collect them.
Infrequently collected species (<5 individuals) made up 64.7% of our identified species (151/235) with the majority of those that were rare being singletons (105/152).While singletons made up 44.7% of the richness observed, they only accounted for 1.3% of our total abundance.This situation is commonly observed in arthropod surveys; on average 32% of specimens collected in tropical areas are singletons (Coddington et al. 2009).Many hypotheses have been presented in the literature to account for rare species including insufficient sampling efforts, genuinely low populations, edge effects, and tourist species (Novotny andBasset 2000, Coddington et al. 2009).
As part of this research we collected three currently undescribed species of Coleoptera (located in the families Staphylinidae, Scirtidae, and Ptiliidae) and one previously undescribed braconid wasp.An unidentified genus (near Nephanes) in the family Ptiliidae has been observed from dung and fermenting organic material across the eastern coast of the United States and does not currently match any established name (M.Sörensson, pers.com.).The undescribed staphylinid, which belongs to Hoplandria (Genosema), is known from only one specimen; the other Nearctic species of this subgenus (H.pulchra Kraatz) is collected from feces and organic material (J.-S. Park pers.com.).The undescribed species of Cyphon (Scirtidae) is conspecific with Epler's (2010) "C.sp.2."Its range encompasses much of the Atlantic and Gulf coasts (Tetrault unpublished dissertation 1967, Epler 2010).The braconid wasp was described as Neothlipsis parysae Sharkey in conjunction with researchers at the Hymenoptera Institute at the University of Kentucky (Sharkey et al. 2011).Other species of note included two new Louisiana state records of Curculionidae (Bagous hydrillae O'Brien, [see Center et al. 2013] and Onychylis texanus Burke), a new state generic record for the family Limnichidae (Limnichites punctatus (LeConte)), and a new country record for Pyramica epinotalis (Weber) (see Chen et al. 2012).
Evaluating β-diversity and comparing our results with other studies associating invertebrates with Salvinia species has been difficult due to differences in native fauna between study locations, taxonomic resolution, and sampling strategies.Several of the studies only identified invertebrates to family level (Pelli and Barbosa 1998, Albertoni and Palma-Silva 2006, Mfundisi et al. 2008).Junk (1977) identified specimens only to order, and Gopalan and Nair (1975) only identified invertebrates to class.Of the papers that provide taxonomic resolution, Bennett (1966) and Forno and Bourne (1984) both focus solely on herbivorous insects, eliminating some of the larger taxonomic groups we sampled.
Several other Salvinia invertebrate association studies also report Coleoptera as their most species-rich and/or abundant group (Pelli and Barbosa 1998, Herrera et al. 2000, Poi de Neiff and Neiff 2006).Coleoptera represent one of the largest "aquatic" groups in the world (Jäch and Balke 2008).Both Mfundisi et al. (2008) and Albertoni and Palma-Silva (2006) reported larval Chironomidae as the most abundant macroinvertebrates, but we did not collect these due to our sampling design.Differences in taxa collected across these studies are almost certainly a result of differences in sampling method (Meyer et al. 2011).Our sampling effort for associated insects was much more intensive (2600 samples over two years) than other published studies and focused solely on adult insects.Sklar's (1983) unpublished dissertation provided one of two inventories available for macroinvertebrates associated with floating vegetation in Louisiana (Lemna species, prior to Salvinia invasion).His list contains 48 taxa of insects (mostly identified to genus, though some to the species level).Ziser (1978) evaluated wetlands adjacent to our field site and collected 55 taxa of insects (mostly larvae and nymphs).Our study shows much higher levels of richness than Sklar's (1983Sklar's ( , 1985) ) or Ziser's (1978) works.
While Pelli and Barbosa's (1998) hypothesis that invertebrates that already exist in a habitat will use invasive vegetation incidentally would account for some increase in richness and abundance, we would expect values to be similar to other studies in similar habitats.We observed over triple the number of taxa documented in Sklar (1983) or Ziser (1978), including many predaceous terrestrial Coleoptera and parasitic Hymenoptera.Either these groups are collected preferentially by a floating pitfall trap as opposed to removing whole plant samples, or the mat of S. minima may be supporting a community of arthropods exploring a formerly unavailable habitat.
To examine these ideas more closely, we consulted relevant literature for taxa collected during our study (Arnett and Thomas 2000, Arnett et al. 2002, Epler 2006, Jäch and Balke 2008, Epler 2010).Habitat associations and lifestyles for the taxa for which information was available are presented in Table 1.For the Coleoptera, Jäch (1998) defined six ecological groups based on familial associations with water: True Water Beetles (1), False Water Beetles (2), Phytophilous Water Beetles (3), Parasitic Water Beetles (4), Facultative Water Beetles (5), and Shore Beetles (6).These classifications are roughly associated with the amount of time spent in contact with the water and presented in the habitat column of Table 1 as "A1-6."Out of the 169 species of Coleoptera we collected, 89 were listed as hygrophilic or riparian in one of the references (Jäch 1998, Arnett and Thomas 2000, Arnett et al. 2002).Intriguingly, many of them were also noted as being crepuscular or nocturnal which could also explain their absence from lists created from other (diurnal-only) collection methods.Most of the Hemiptera collected were aquatic in nature or known to feed on aquatic plants (Epler 2006).While many parasitic Hymenoptera are semiaquatic in nature, we refrained from indicating habitat associations in our taxa list without genus-or specieslevel identifications.The exception is Anoplius depressipes Banks which is known to hunt the semi-aquatic spiders of the genus Dolomedes (Roble 1985).A number of the listed species are hypogenic and are likely exploiting previously unavailable habitats (Parys and Johnson 2012).
Despite gaps in our knowledge of the identity and natural history of some of our sampled taxa, we conclude that most taxa collected in our study are either hydro-or hygrophilous through examination of relevant literature.This suggested that most species that occured in the list were already present in the broader habitat prior to invasion by S. minima and are likely using the mat to exploit new, adjacent microhabitats.Utilizing new collection methods resulted in different taxa collected than expected (Meyer et al. 2011) and the use of a long term non-destructive collection method produced crepuscular and nocturnal insects that are not collected by traditional collecting methods.
Parys et al. | Insects associated with Salvinia minima 2000, Table 1 are deposited at LSAM.Additional specimens are deposited with: CWOB -the personal collection of Charles W. O'Brien, Green Valley, Arizona (Coleoptera:

Table 1 .
Jäch (1998)lected from a mat of Salvinia minima (excluding Diptera and Lepidoptera) between 15 May and 02 November 2009, and between 07 May and 08 November 2010.Lifestyle/food associations are as follows: D= detritus, F= fungus, C= carnivorous/predaceous, H= herbivorous, and P= Parasitic.Habitat associations are as follows: T=terrestrial, A= aquatic.Habitat associations for Coleoptera followJäch (1998), representing a range of 6 ecological affiliations with water: A1 (completely aquatic) -A6 (riparian).Voucher refers to a representative specimen deposited at LSAM, the number presented is the LSAM specimen number.