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| Distinguishing Characteristics |
- Ventral and dorsal surfaces are convex
- Legs: long, slender, and adapted for swimming
- Mandibles: falcate, without enlarged molar portions
- Fore and middle tarsi with 4 segments or with segment 4 very small, concealed between lobes of segment 3
- Scutellum concealed (except in celina)
- Hind tarsi with single claw; if 2 claws, scutellum exposed
- Larval Features
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| Ecology |
Life History
Mating occurs from spring to autumn, most species lay eggs above water in moist soil (1).
Other species (Agabus, Coptotomus, Cybister, Dytiscus, Hydaticus, Iiybius, Laccophilus, and Thermonectus) use a cutting ovipositor to pierce into plants and inert a large egg mass (1).
Inserting eggs into the stem of plants could help survival rates as plants typically dry out much later than the surface soils.
Feeding Ecology
Both adults and larvae are important predators in streams and ponds. In Sub-Antarctic, South Georgia, Lancetes angusticollis are voracious predators, feeding primarily on the copepod Boeckella poppei and benthic ostracods (3).
Species of Dytiscidae are aquatic predators and may play an important role in controlling mosquitoes. Their actual importance is not yet understood, but at least some attention is nowadays paid to the problem (4).
Habitat
Dytiscidae is found to burrow into the stream substratum during seasonal droughts, typically to depths of 70-90 cm (4). This burrowing behavior could help explain their high survival rates after a drought.
Behavior
Some species in the Dytiscidae family are able to detect chemical cues released by predators. Acilius sulcatus has developed specific chemoreceptors that distinguish between kairomones released by hungry and satiated perch (2). Knowing the level of predatory danger in the environment increases the chance of survival as well as lowering unnecessary high energy retreats. Although kairomones play a large role in predator stimuli, visibility is also a determining factor in prey activity (2).
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| Bibliography |
(1) Cummings, K.W., Merritt, R.W. (1996). An Introduction to the Aquatic Insects of North America. Kendall and Hunt Publishing company
(2) Abjornsson, K., Wagner, B.M.A., Axelsson, A., Bjerselius, R., Olsen, K.H. (1997). Responses of Acilius sulcatus (Coleoptera: Dytiscidae) to chemical cues from perch (Perca fluviatilis). Oecologia, 111:166 - 171
(3) Arnold, R.J., Convey, P. (1998). The life history of the diving beetle, Lancetes angusticollis (Coleoptera: Dytiscidae), on sub-Antarctic South Georgia. Polar Biol 20: 153-160
(4) Fenoglio, S., Bo, T., and Bosi, G. (2006). Deep interstitial habitat as a refuge for Agabus Paludosus (Fabricius) (Coleoptera: Dytisicidae) during summer droughts. The Coleopterists Bulletin, 60(01): 37-41
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