ABSTRACT

Mature larvae of Hydroporus signatus Sharp collected from a small eutrophic habitat served as substrates for Peritrichida (Ciliophora). The rate of infestation was 60% and there were indications of body site specificity for the colonies with most found attached to the cranium

Key Words: Protozoa; Peritrichida, beetle larva; southeastern United States.

**********

Dytiscid larvae identified by distribution (1) and available descriptions (2) as Hydroporus signatus Sharp were collected between 23 January and 19 March 2007 from a small eutrophic habitat in Baldwin County, central Georgia (USA). An examination of 10 mature larvae selected randomly from a laboratory cohort of 40 larvae revealed that 60 % of the larvae had protozoan colonies (Peritrichida, probably Epistylis) attached to sclerotized areas. Steffan's (3) review of ectosymbiosis of aquatic insects includes reports of Peritrichida infestations of Ephemeroptera, Odonata, Hemiptera, Diptera, Trichoptera, and Coleoptera. Reported coleopteran infestations include dytiscid species; however, dytiscid larvae are difficult to identify. The level of infestation of larvae of H. signatus is comparable to that reported by Evans et al. (4) for a crustacean, Mysis sp. (55-85%). Peritrich colonies (Fig. 1A & B) with a maximum of five or six branches were observed attached to the venter of the extended nasale (Fig. 1A), on the mouthparts, ventrally at the union of the cranium and prothorax, and on the seventh abdominal segment. A single larva had one colony on the dorsum of the seventh abdominal segment. Epibiont colonies were observed on or near the cranium of the remaining infested larvae, suggesting a degree of body site specificity for successful colonization of the dytiscid larvae. Indications of site specificity have also been reported for epibionts on other arthropods (5, 6, 7).

[FIGURE 1 OMITTED]

This peritrich-dytiscid interaction may be at least moderately detrimental to the dytiscid larvae, although the peritrichs may derive some advantages (5) from the association. The prey of Hydroporus signatus includes highly mobile ostracods (Fig. C) and other small invertebrates. Detection of potential prey (as well as predators) and their subsequent capture are probably due, at least in part, to sensory functions of the numerous sensilla that originate on the cranium and its appendages. The presence of detrital and/or biotic material, including peritrich colonies, on the cranium and its appendages may interfere with sensory functions of those sensilla, diminishing larval ability to detect suitable prey. Nilsson (8) described structural modifications of he protarsi of Cybister and Coptotomus and hypothesized that these modifications were employed to aid in removal of detrital and/or biotic material from the cranium and cranial appendages. A more complex "cleaning" system has also been described for Hydaticus bimarginatus (9). Although comparable "cleaning" structures and behaviors have not been observed for H. signatus, selection for structures dedicated to removal of extraneous materials in other taxa provides indirect evidence of the importance to dytiscid larval survival of maintaining relatively pristine cranial and cranial appendage surfaces. Thus, it seems probable that the presence of peritrich colonies on the cranium of these hydroporine larvae will diminish sensory functions and possibly interfere with biomechanical efficiency, resulting in at least a limited reduction in predator effectiveness of infested larvae.

ACKNOWLEDGEMENTS

This is Aquatic Coleoptera Laboratory Contribution No. 70. This project was supported in part by a Faculty Research Grant awarded by the Office of Research Services, Georgia College & State University. We thank Drs. Dennis Parmley and Kalina Manoylov of this University, Ms. T. Shepley-James of Georgia Military College, and the anonymous reviewers for their valuable assistance.

REFERENCES

1. Turnbow R and CL Smith: An annotated checklist of the Hydradephaga (Coleoptera) of Georgia. J Ga Entomol Soc 18: 429-443, 1983.

2. Alarie Y: Description of larvae of 17 Nearctic species of Hydroporus Clairville (Coleoptera: Dytiscidae: Hydroporinae) with an analysis of their phylogenetic relationships. Can Entomol 123: 627-704, 1991.

3. Steffan AW: Ectosymbiosis in aquatic insects. In Henry SM, ed., Symbiosis. Vol. 2. Academic Press, Inc, New York, pp. 207-289, 1967.

4. Evans MS, DW Sell, and AM Beeton: Tokophrya quadripartita and Tokophrya sp. (Suctoria) associations with crustacean zooplankton in the Great Lakes Region. Trans Am Micros Soc 100: 384-391, 1981.

5. Baldock BM: Peritrich ciliates epizoic on larvae of Brachycentrus subnubilus (Trichoptera): importance in relation to the total protozoan population in streams. Hydrobiologia 132: 125-131, 1986.

6. Henebry MS and BT Ridgeway: Epizoic ciliated protozoa of planktonic copepods and cladocerans and their possible use as indicators of organic water pollution. Trans Amer Micros Soc 98: 495-508, 1979.

7. Evans MS, LM Sicko-Goad, and M Omair. Seasonal occurrence of Tokophrya quadripartita (Suctoria) as epibionts on adult Limnocalanus macrurus (Copepoda: Calanoida) in southeastern Lake Michigan. Trans Am Micros Soc 98:102-109, 1979.

8. Nilsson AN: A review of primary setae and pores on legs of larval Dytiscidae (Coleoptera). Can J Zool 66: 2283-2294, 1988.

9. Jackson R, EH Barman, BP White, and GW Wolfe: A description of the third instar of Hydaticus bimarginatus (Say) (Coleoptera: Dytiscidae). Ga J Sci. 65: 182-192, 2007.

E. H. Barman

Jessica L. Rackett

W. P. Wall

Department of Biological & Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

Address Correspondence To:

E. H. Barman

Department of Biological & Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

e.barman@gcsu.edu