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_Dytiscus fasciventris_; functional dimorphism

Dytiscus fasciventris Say, (unstriped diving beetle) is a relatively large (22-28 mm) predaceous diving beetle (Dytiscidae) found across Canada and in adjacent United States in permanent ponds and marshes with sedges present. They’re often found on or among the aquatic vegetation, where they prey upon various aquatic animals, including the larvae of other insects and small fish, and appear to feed primarily upon mosquito larvae in the spring. Dytiscus fasciventris is active in the spring through fall, basically, if it’s warm enough for liquid water, they’re around (slight exaggeration!). Despite the long active season, D. fasciventris only produces a single generation per year with mating occuring in the spring or fall, and individuals overwintering as adults.
Many dytiscids are strong swimmers, and Dytiscidae in general have hind legs modified into paddles for swimming. The legs move together like oars to propel the beetle through the water; this differs from some other aquatic beetle families, like Hydrophilidae, in which the legs move opposite one another, like they do in most land-dwelling taxa.

Dytiscus fasciventris is sexually dimorphic. While both sexes have the same basic colouration, dark brown/greenish/black with a broad pale lateral stripe on the pronotum and basal half of the elytra, some females have longitudinal sulca (ridges running the length) elytra (the hardened forewing), while the elytra of males and some females are smooth. In male D. fasciventris, the first three protarsal (the tarsi of the front legs, or prolegs) segments are expanded into a large pad, covered in various bristles and suction cups, which are absent in the female. These pads are used to grasp the smooth areas of the female’s pronotum and basal section of the elytra during copulation, the initial stages of which can be fairly intense. It is unknown what the exact function of the sulca, with hypotheses that they both aid in males copulating with the females, and that they may hinder males gripping the female, giving her greater choice in when mating is initiated. Miller (2003) suggests that the sculpture in some females is the result of mating conflict, rather than to assist the males.

Class: Insecta
- Order: Coleoptera
— Suborder: Adephaga
—- Family: Dytiscidae
—— Subfamily: Dytiscinae
——- Tribe: Dytiscini
——— Genus: Dytiscus

* Miller, K.B. 2003. The phylogeny of diving beetles (Coleoptera: Dytiscidae) and the evolution of sexual conflict. Biological Journal of the Linnean Society 79: 359-388.

1 blog comments below


I hate bugs.

Note to self: stay away from ponds and marshes and nearby aquatic vegetation.
TheGremlyn on Sun Jan 13, 2013 8:58 pm

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