Corixidae - Water Boatmen

Introduction

This key to the Corixidae of Michigan is mostly based on information from Hungerford's masterful tome on the Corixidae of the Western Hemisphere (1948), with a chapter from Reece Sailer for Trichocorixa, and Bill Hilsenhoff's (1984) work in Wisconsin published in the Great Lakes Entomologist. Future work will include information from specimen collections, incorporating photographs and drawings, and developing a key to final instar nymphs, but for now this provisional key will have to suffice.

Key to the Genera of Corixidae of Michigan

Adults (after Hilsenhoff 1984 and Hungerford 1948)

1a	a. Rostrum without transverse grooves	Cymatia americana Hussey
	b. Pronotum without transverse dark bands
	c. Length 6.5-8.2 mm
1b	a. Rostrum with transverse grooves	2
	b. Pronotum with transverse bands, although sometimes indistinct or faint
2a(1b)	a. Entire hemelytral pattern effaced	Ramphocorixa acuminata (Uhler)
	b. Palar claw serrate at base
	c. Vertex of male acuminate
	d. Length 5.3-6.0 mm
2b	a. Hemelytral pattern distinct, although limited areas may be effaced	3
	b. Palar claw not serrate
	c. Vertex of male not acuminate, but rounded in outline
3a(2b)	a. Apex of clavus (posterior point) scarecely exceeding a line drawn through the costal margins at the nodal furrows	Trichocorixa Kirkaldy
	b. In apperance, small and shining
	c. In dorsal view, abdomen of male with sinistral asymmetry
	d. Pala of male short, triangular, with the tibia produced apically over it
3b	a. Apex of clavus clearly exceeding a line drawn throught he costal margins at the nodal furrows	4
	b. In dorsal view, abdomen of male with dextral asymmetry
	c. Pala of male longer, with tibia not produced apically over it
4a(3b)	a. Markings on clavus transverse, those on corium transvers, longitudinal, or reticulate	5
	b. Hemelytra with dark areas predominating
4b	a. Markings on clavus and corium narrow and broken, usually open reticulate with many interconnections	7
	b. Hemelytra with light areas predominating or light and dark areas about equal in prominance
5a(4a)	a. Pruinose area at base of claval suture short and broadly rounded at apex, about 2/3x long as postnodal pruinose area	Hesperocorixa Kirkaldy
	b. Prothoracic lobe truncate
5b	a. Pruinose area at base of claval suture narrowly rounded, or pointed at apex and subequal in length to postnodal pruinose area	6
	b. Prothoracic lobe rounded
6a(5b)	a. Corial pattern transverse with little contrast between dark and light markings	Callicorixa White
	b. Male strigil absent
	c. Mesoepimeron slightly wider than prothoracic lobe, and with scent gland osteole near tip
	d. Metaxyphus slightly longer than wide
	e. Length 6.5-8.1mm
6b	a. Corial pattern longitudinal, reticulate, or transverse, with light and dark markings usually contrasting	Sigara Fabricius
	b. Male strigil present
7a(4b)	a. Rear margin of head sharply curved, embraching an unusually short pronotum	Palmacorixa
	b. Interocular space much narrower than width of an eye
	c. Males with dorsal median lobe of Ab7bearing a hook-like projection
7b	a. Rear margin of head gently curved, with the pronotum longer	8
	b. Interocular space about equal to width of an eye
	c. Males without a hook-like structure on dorsal medial lobe of Ab7
8a(7b)	a. Prothoracic lobe tapering to a naroowly rounded apex	Corisella Lundblad
	b. Dark marks on anterior of clavius very narrow, often obscure
8b	a. Prothoracic lobe truncate at apex	9
	b. Dark marks on anterior of clavis distinct
9a(8b)	a. Postocular space broader than antenna	Dasycorixa hybrida (Hungerford)
	b. Anterior distal angle of prothoracic lobe produced and turned inward
	c. Length about 7.6-9.2mm
9b	a. Postocular space narrower than antenna	Cenocorixa
	b. Apex of prothoracic lobe squarely truncate
	c. Length <8.3mm

Callicorixa (after Hungerford 1948)

Adults (after Hilsenhoff 1984 and Hungerford 1948)

1a	a. First tarsal segment of hind leg concolorous throughout	Callicorixa audeni Hungerford
	b. In lateral view, distal portion of right clasper of male genital capsule broadly curved, not angulate
1b	a. First tarsal segment of hind leg infuscated on distal third	Callicorixa alaskensis Hungerford
	b. In lateral view, distal portion of right clasper of male genital capsule forming almost a right angle

Cenocorixa

Adults (after Hilsenhoff 1984 and Hungerford 1948)

1a	a. Last metatarsal seegment black or dark brown	Cenocorixa dakotensis (Hungerford)
	b. Metafemur pubescent for about 1/3 its length
	c. Body length about 7.5-8.0 mm
8b	a. Last metatarsal segment pale	2
	b. Metafemur pubescent for at least 2/5 its length
2a(1b)	a. Length of shining costal area just anterior to nodal furrow longer than the length of the mesotarsus	Cenocorixa bifida (Hungerford)
	b. Peg row of male pala divided
	c. Body length about 6.8-8.0 mm
2b	a. Length of shining costal area just anterior to nodal furrow about equal to the length of the mesotarsis	Cenocorixa utahensis (Hungerford)
	b. Peg row of male pala entire
	c. Body length about 6.8-8.3 mm

Corisella (after Hilsenhoff 1984 and Hungerford 1948)

Adults (after Hilsenhoff 1984 and Hungerford 1948)

1a	a. Both segments of metatarsus brown	Corisella tarsalis (Fieber)
	b. Pronotum with a slight carina on anterior third
	c. In lateral view, male genital capsule (Ab9 which is envaginated in body) with a large dorsal and ventral projection, the former ending sharply acuminate, the later somewhat triangular, both separated by a notch that appears rectangulate
	d. Smaller, body length < 7.0 mm
1b	a. Both segments of metatarsus pale	2
	b. Pronotum rugulose but without a carina on anterior third
	c. In lateral view, male gential capsule with a large dorsal projection ending more triangulate, the ventral with an undulating dorsal margin, both separated by notch that appears rounded, not rectangulate
	d. Larger, body length usually > 7.0 mm
2a(1b)	a. Dark markings of hemelytra usually in a definite longitudinal series	Corisella edulis (Champion)
	b. Male pala not broader than the tibia, or at least the dorsal part not projecting above the tibia
	c. Vertex of male plainly produced
	d. Pruinose area on corial side of claval suture long
	e. Rear margin of last ventral abdominal segment of female nearly straight
2b	a. Dark markings of hemelytra usually not in a definite longitudinal series	Corisella inscripta (Uhler)
	b. Male pala broader than the tibia, its dorsal margin projecting above the tibia
	c. Male vertex not plainly produced
	d. Pruniose area on corial side of claval suture short
	e. Rear margin of last ventral abdominal segment of female broadly medially produced

Hesperocorixa

Adults (adapted from Dunn 1979)

1a	Mesoepimeron, at the level of the scent gland osteole, as wide as, or wider than the lateral lobe of the pronotum	2
1b	Mesoepimeron, at the level of the scent gland osteole, narrower than the lateral lobe of the pronotum	6
2a(1a)	Metaxyphus wider than longer	Hesperocorixa kennicottii (Uhler)
	also: Clavus and corium with solid black or pale transverse bands, never with spots; Hemelytra slightly rastrate
2b	Metaxyphus not wider than long	3
3a(2b)	a. Mesoepimeron, at the level of the scent gland osteole, as wide as the lateral lobe of the pronotum	Hesperocorixa atapodonata (Hungerford)
	b. Distal peg in peg row on pala of male offset from rest of row
3b	a. Mesoepimeron, at the level of the scent gland osteole, distinctly wider than the lateral lobe of the pronotum	4
	b. Distal peg in peg row on pala of male in line with the rest of row
4a(3b)	Dorsal surface of hind femur with no more than three stout spines	Hesperocorixa minorella (Hungerford)
4b	Dorsal surface of hind femur with many spines	5
5a(4b)	Corial pattern of transverse band	Hesperocorixa michiganensis (Hungerford)
5b	Corial pattern of longitudinal series of flavous patches	Hesperocorixa semilucida (Walley)
6a(1b)	Color pattern effaced on corium	Hesperocorixa lucida (Abbott)
6b	Color pattern on corium with transverse lines which extend to the lateral margin	7
7a(6b)	Pronotum wider than long, width-to-length ratio >2.0x	Hesperocorixa scabricula (Walley)
7b	Pronotum not as wide, width-to-length ratio <2.0x	8
8a(7b)	Hemlytral pattern reticulate; pronotum nonrastrate	Hesperocorixa laevigata (Uhler)
8b	Hemelytral pattern not reticulate; pronotum rastrate	9
9a(8b)	Pale bands of corium beyond hemlytral suture forming a narrow transverse series, and corium and membrane not separated by a flavous line	Hesperocorixa vulgaris (Hungerford)
	also: Tip of Ab9 of male bifid
9b	Pale bands of corium beyond hemlytral suture not forming a narrow transverse series, or if forming a narrow transverse series, then the corium and membrane separated by a flavous line	10
10a(9b)	Hind femur with a row of about ten spines on the disto-ventral portion of rear margin	Hesperocorixa nitida (Fieber)
10b	Hind femur with a row of about six spines on the disto-ventral portion of rear margin	11
11a(10b)	a. Corium and membrane not separated by a flavous line	Hesperocorixa obliqua (Hungerford)
	b. Upper, distal angle of male pala obliquely produced
11b	a. Corium and membrane separated by a flavous line	12
	b. Upper, distal angle of male pala not obliquely produced
12a(11b)	Metaxyphus as long as broad; in dorsal view, interocular space nearly equal to width of eye	Hesperocorixa lobata (Hungerford)
12b	Metaxyphus longer than broad; in dorsal view, interocular space narrower than width of eye	Hesperocorixa interrupta (Say)

Palmacorixa Abbott

Adults (after Hilsenhoff 1984 and Hungerford 1948)

1a	a. Pala of male a very broad, flattened plate, length roughly 1.5x or less that of its width	Palmacorixa gillettei Abbott
	b. Male pala with a cluster of poorly defined pegs near its base
	c. Pronotal disk of both sexes with well-marked anterolateral depressions
1b	a. Pala of male elongate, not a broad, flattened plate, with length about 2.0x or more of its width	2
	b. Palar pegs of male in an arching row, often crowded into a double row of longer pegs distally
	c. Pronotal disk of both sexes with anterolateral depressions weak or absent
2a(1b)	a. Mesofemur of male with a longitudinal row of pegs on its ventral surface	Palmacorixa nana Walley
	b .Female < 5.2 mm in length
2b	a. Mesofemur of male without a longitudinal row of pegs on its ventral surface	Palmacorixa buenoi Abbott
	b. Female > 5.4 mm in length

Sigara

Adults (after Hilsenhoff 1984 and Hungerford 1948; length data from Hilsenhoff 1984)

1a	Pronotal disk with median longitudinal pale line	2
1b	Pronotal disk with transverse lines unbroken by pale longitudinal median lin	7
2a(1a)	Tip of the mesoepimeron as close, or closer, to scent gland osteole than to the mesosternum (seen in ventral view, mesoepimeron extends from lateral margin posterolaterally to the prothoracic lobe, and extends posteromedially)	3
2b	Scent gland osteole remote from tip of mesoepimeron, farther than distance from tip to mesosternum	5
3a(2a)	a. Hemelytra nearly black with somewhat wide but obscure longitudinal pale markings	Sigara variabilis (Hungerford)
	b. Dorsal edge of male pala thickened, with a prominent keel on the outside
	c. Body length about 5.7-6.6 mm
3b	a. Hemelytral markings not as above	4
	b. Male pala not as above
4a(3b)	a. Male pala with a single row of pegs	Sigara johnstoni Hungerford
	b. Female abdomen with anal lobes not notched on inner margin
	c. Body length about 6.3-7.2 mm
4b	a. Male pala with two rows of pegs	Sigara knighti Hungerford
	b. Female abdomen with anal lobes notched on inner ventral margin
	c. Body length about 5.4-6.5 mm
5a(2b)	a. Pronotum and hemelytra (including membrane) boldly cross-barred	Sigara transfigurata (Walley)
	b. Vertex in both sexes conically produced beyond eye-curve
	c. Body length about 5.5-5.8 mm
5b	a. Pronotum and hemelytra not so cross-barred, less striking	6
	b. Vertex not noticeably produced
6a	a. Pattern of membrane effaced or indistinct	Sigara compressoidea (Hungerford)
	b. Pale figures on corium and distal half of clavis transverse
	c. Male strigil small and round
	d. Body length about 5.2-5.8 mm
6b	a. Pattern of membrane usually distinct	Sigara mackinacensis (Hungerford)
	b. Pale figures on corium and distal half of clavis arranged more or less longitudinally
	c. Male strigil elongate
	d. Body length about 5.0-6.3 mm
7a(1b)	Body length of males >6.8 mm, females >7.3 mm	8
7b	Body length of males <6.7 mm, females <7.2 mm	11
8a(7a)	a. Metaxyphus broad, truncated or notched at tip	Sigara decorata (Abbott)
	b. Claw of pala serrate at base in both sexes
	c. Body length about 8.1-9.5 mm
8b	a. Metaxyphus pointed apically	9
9a(8b)	a. Pala of both sexes with 14-16 lower palmar hairs	Sigara decoratella (Hungerford)
	b. Pale marks on corium distinctly transverse
	a. Body length about 6.9-8.2 mm
9b	a. Pala of both sexes with 18-22 lower palmar hairs	10
	b. Pale marks on corium never distinctly transverse, but at least somewhat longitudinal
10a(9b)	a. Interocular space plainly narrower than width of an eye	Sigara penniensis (Hungerford)
	b. Pale marks on corium and distal half of clavus arranged in a definite longitudinal series
	c. Male pala with peg row near palm
	d. Body length about 6.9-7.9 mm
10b	Interocular space equal to the width of an eye	Sigara conocephala (Hungerford)
	Pale marks on clavus and some on corium transverse
	Male pala not as above
	Body length 7.3-8.5 mm
11a(7b)	a. Two black longitudinal stripes on corium	Sigara lineata (Forster)
	b. Body length <4.6 mm (about 3.8-4.6 mm)
11b	a. Body length >4.6 mm; if body length <5.0 mm, corium without longitudinal stripes
12a(11b)	Metaxyphus much longer than wide (measured from widest point to tip)	13
12b	Metaxyphus short, at most as long as wide	16
13a(12a)	a. Clavus with pale lines in a wavy longitudinal series	Sigara douglasensis (Hungerford)
	b. Hypo-ocular suture ending laterad of the middle line of the eyes
	c. Body length about 5.2-5.9 mm
13b	a. Markings on clavus and corium not in a wavy longitudinal series	14
14a(13b)	a. Mesoepimeron, at level of scent gland osteole, about equal in width to the prothoracic lobe	Sigara dolabra Hungerford and Sailer
	b. Male with stridular area on front femor
	c. Female pala depressed dorsally near apex
	d. Body length about 6.0-6.8 mm
14b	a. Mesoepimeron, at level of scent gland osteole, much broader than the width of the prothoraci	15
15a(14b)	a. Hemelytral pattern dark, with little contrast between light and dark marks	Sigara signata (Fieber)
	b. Pale bands on corium more or less broken and confused
	c. Dorsal surface of metafemur with 2 or 3 rows of pegs
	d. Female pala depressed dorsally near apex
	e. Body length about 4.5-5.3 mm
15b	a. Hemelytral pattern bold	Sigara solensis (Hungerford)
	b. Pale bands on base of clavus entire, bands on corium plainly transverse
	c. Dorsal surface of metafemur with only 3 or 4 pegs
	d. Female pala normal, not as above
	e. Body length 4.8-5.8 mm
16a(12b)	Scent gland osteole nearer the base of the mesoepimeron than the tip	17
16b	Scent gland osteole nearer the tip of the mesoepimeron than the base	20
17a(16a)	a. Corium with 3 dark longitudinal stripes	Sigara trilineata (Provancher)
	b. Body length 5.1-6.0 mm
17b	a. Corium without without dark longitudinal stripes	18
18a(17b)	a. Head with a median longitudinal brown line	Sigara mathesoni Hungerford
	b. Mesoepimeron with a deep incision at or near the lateral bend
	c. Body length 4.8-5.6 mm
18b	a. Head without such a longitudinal line	19
	b. Mesoepimeron without a deep incision near the lateral bend
19a(18b)	a. Osteole almost in the lateral bend of the mesoepimeron, at least 4/5th the distance from the tip	Sigara grossolineata Hungerford
	b. Tip of metaxyphus truncated
	c. Body length about 4.8-5.9 mm
19b	a. Osteole not so close to the lateral bend, about 1/2-3/5 the distance from the tip	Sigara modesta (Abbott)
	b. Tip of metaxyphus rounded
20a(16b)	a. Corium with 3 bold, uninterrupted, longitudinal black stripes	Sigara mullettensis (Hungerford)
	b. Male pala with 2 rows of pegs
	c. Anal lobes of female only very slightly notched on inner margin
	d. Body length about 5.5-6.8 mm
20b	a. Corial pattern transverse or indistinctly longitudinal	21
	b. Male pala with one row of pegs
	c. If corial pattern is somewhat longitudinal, anal lobes of female distinctly notched on inner margin
21a(20a)	a. Pattern of membrane, and usually also the inner basal angle of clavus, effaced or obscure	Sigara hubbelli (Hungerford)
	b. 4-6 pegs on dorsal surface of hind femur
	c. Body length 4.6-5.6 mm
21b	a. Pattern of membrane and clavus distinct	22
	b. Body length >5.2 mm
22a(21b)	a. Pronotum crossed by 5 or 6 dark bands	Sigara macropala (Hungerford)
	b. Body length about 5.2-5.9 mm
22b	a. Pronotum crossed by 8 or 9 dark bands	23
23a(22b)	a. Corium with 3 or more or less distinct dark longitudinal bands	Sigara defecta Hungerford
	b. Pale of male with pegs becoming widely separated distally
	c. Anal lobes of female notched on inner margin
	d. Body length about 5.4-6.8 mm
23b	a. Corium without 3 dark longtiduinal band	24
	b. Pegs of male pala evenly spaced
	c. Anal lobes of female not notched on inner margin
24a(23b)	Metaxyphus short, plainly broader than long, and margins at right angle to a rounded tip	Sigara bicoloripennis (Walley
24b	Metaxyphus about as broad as long, and margins forming less than a right angle to a pointed tip	25
25a(24b)	a. Mesoepimeron of equal width from osteole to the lateral bend	Sigara alternata (Say)
	b. Osteole posterior to the disto-lateral angle of the mesosternum
	c. Body length about 5.9-7.2 mm
25b	a. Mesoepimeron broader at the lateral bend than at the level of the scent gland osteole	Sigara zimmermanni (Fieber)
	b. Osteole on a level with the disto-lateral angle of the mesosternum
	c. Body length <5.0 mm
	also: Hind femur pubescent ventrally for 2/3 its length and with only 2-3 spines or none on the dorsal surface

Trichocorixa

Adults (after Hilsenhoff 1984 and Sailer 1948)

1a	Male strigil ovoid, round, < 18 combs (under high magnification)	2
	Nodal furrow in females at apex of pruinose area of embolar groove
1b	Male strigil elongate, cruved, > 18 combs	3
	Nodal furrow in females dividing embolium
2a(1a)	Pronotal disk wide, its median length about 1/4x its width, and with 2 or 3 narrow black transverse lines	Trichocorixa macroceps (Kirkaldy)
	Costal margin of female only slightly emarginate just anterior to nodal furrow
	Very small, length <3.3 mm
2b	Pronotal disk longer, its median length about 1/3x its width, and with about 6 transverse bands on pronotum	Trichocorixa sexcincta (Champion)
	Costal margin of female hemelytron deeply emarginate just anterior to nodal furrow
	Larger, length >3.3 mm
3a(1b)	In dorsal view, male strigil noticeably widened (to about the width of the mesotarsus) in medial half of abdomen	Trichocorixa borealis Sailer
	Length of apical area of embolar groove (pruniose area) exceeding the length of mesotarsus
3b	In dorsal view, male strigil not noticeably widened in medial half of abdomen, and distinctly narrower than mesotarsus	4
	Length of apical area of embolar groove less than length of mesotarsus
4a(3b)	Male strigil appearing as little more than a heavy dark line along the lateral margin of the left tergal lobe of Ab6, usually curved abruptly upward at the median apex	Trichocorixa calva (Say)
	Female with sternum of Ab7 with only a fine pubescence on right side
4b	Male strigilappearing normal, showing definite transverse comblike rows of teeth, about 8-10x long as wide	Trichocorixa kanza Sailer
	Female with sternum of Ab7 with 2-3 patches of bristle-like setae

References

Dunn CE. 1979. A revision and phylognetic study of the genus Hesperocorixa Kirkaldy (Hemiptera: Corixidae). Proceedings of the Academy of Natural Science Philadelphia 131:158-190.
Hungerford HB. 1948. The Corixidae of the Western Hemisphere (Hemiptera). Reprint of The University of Kansas Science Bulletin 32:1-827, reprinted (1977) by Entomological Reprint Specialists: Los Angeles, California.
Hilsenhoff WL. 1984. Aquatic Hemiptera of Wisconsin. The Great Lakes Entomologist 17(1):29-50.
Sailer RI. 1948. The genus Trichocorixa (Corixidae, Hemiptera), p. 289-407 in Hungerford HB. The Corixidae of the Western Hemisphere (Hemiptera). Reprint of The University of Kansas Science Bulletin 32:1-827, reprinted (1977) by Entomological Reprint Specialists: Los Angeles, California.

Page created: September 19, 2003 (EB) - Last updated: September 23, 2006 (EB)