Lab 9: Coleoptera (Coleoptera: beetles)




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Lab 9: Coleoptera
(Coleoptera: beetles)

Coleoptera are commonly known as the beetles. It is believed that rather than having one evolutionary entrance into the aquatic world, that instead, beetles have made multiple transitions into aquatic systems over time. Because of these multiple entrances into the water, the life history strategies employed by each of the groups of aquatic beetles are often quite different from other beetles in terms of respiration, habitat preference, feeding, etc. For this same reason, aquatic stages (egg, larvae, pupa, adult) in life history can be comprised of almost any combination.


The suborders and evolutionary relationships of Coleoptera are as follows:
Archostemata

Adephaga
Myxophaga


Polyphaga

There are four major respiratory strategies used by aquatic Coleoptera: (1) reliance of self-contained air reserves (e.g. Dytiscidae, Hydrophilidae, Hydraenidae); (2) transcuticular respiration, with or without tracheal gills (larvae of most families); (3) plastron respiration (adult Dryopidae, Elmidae, etc.); and (4) piercers of plant tissues (e.g. larval Crysomelidae).


Immatures

Head well-developed with ocelli and chewing mouthparts. Three pairs of thoracic legs; no abdominal prolegs. Body form: Campodeiform -- Slender, active crawlers; Scarabaeiform -- Grub-like, fleshy, c-shaped body; Elateriform -- Wireworms; elongate, cylindrical, with a hard exoskeleton and tiny legs.


Adults

Chewing mouthparts (sometimes located at the tip of a beak or snout). Front wings (elytra) are hard and serve as covers for the flight (hind) wings; meet in a line down the middle of the back. Hind wings large, membranous, folded beneath the elytra. Tarsi 2- to 5-segmented.


Morphological things to know:
Tarsal formulas

Tarsal formulas are characters used in a key for splitting groups of beetles apart from each other. Tarsal formulas are determined by counting the tarsal segments of the foreleg, middle leg, and hindleg. So, a beetle with a tarsal formula of 5-5-4 would mean that the foreleg has 5 tarsal segments, the middle leg has 5 tarsal segments, and the hindleg has 4 tarsal segments. However, at times, individual tarsal segments will be especially small and difficult to see without high power magnification. Some keys will report that the tarsal formula is apparently 5-4-4, meaning that the tarsal formula only looks like 5-4-4, while it may actually be 5-5-4, where one of the tarsal segments is much smaller and may be difficult to see without high-power magnification.



Polyphaga and Adephaga

The morphological division between the two major suborders of Coleoptera (Polyphaga and Adephaga) is determined by the division of the first abdominal sternite by the hind coxae.





Hind coxae dividing the 1st abdominal sternite into lateral sclerites. (Adephaga)

Hind coxae NOT dividing the 1st abdominal sternite into lateral sclerites. (Polyphaga)




Antennal types

Beetles have a very diverse assortment of antennal types. (See antennae handout.) Additionally, when viewed from above, the palps of the adult beetle may be confused with the antennae. You will need to look closely, under the eye of the beetle to check the antennal type.


Terms to know:

urogomphi

ventral keel

operculum



Families to know:

Larvae & Adults Aquatic

HaliplidaeA (crawling water beetles)

DytiscidaeA (predaceous diving beetles)

GyrinidaeA (whirligig beetles)

HydrophilidaeP(water scavenger beetles)

ElmidaeP (riffle beetles)

NoteridaeA * (burrowing water beetles)

AmphizoidaeA (trout stream beetles)


Larvae Aquatic / Adults Terrestrial

PsephenidaeP (water pennies)

ScirtidaeP (marsh beetles)

CrysomelidaeP * (leaf beetles)

PtilodactylidaeP * (toed-winged beetles)

LimnichidaeP * (marsh-loving beetles)



Larvae Terrestrial / Adults Aquatic

DryopidaeP (long-toed water beetles)

HydraenidaeP * (moss beetles)

Curculionidae P *(weevils)


Other Aquatic (or Semi-aquatic) Families

StaphylinidaeP * (rove beetles)

CarabidaeA * (ground beetles)

HydroscaphidaeM * (skiff beetles)


* not in the teaching collection
A Adephaga

P Polyphaga

M Myxophaga




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