Cricotopus diversus Boesel, 1983:85

Cuppen, Hub, Gresens, Susan E. & Tempelman, David, 2020, DESCRIPTION OF THE LARVAE OF CRICOTOPUS FESTIVELLUS (KIEFFER 1906) AND CRICOTOPUS DIVERSUS (BOESEL 1983) WITH KEYS TO DISCRIMINATION OF LARVAL, PUPAL AND ADULT STAGES (DIPTERA: CHIRONOMIDAE) Abstract, CHIRONOMUS Journal of Chironomidae Research 33 (33), pp. 4-16 : 8-9

Cricotopus diversus Boesel, 1983:85 .

nec LeSage and Harrison 1980:94, C. (s.s.) festivellus

Description of larval C. diversus : based on 4 th instar larval exuviae (n = 5) with total length 3.5-4 mm. Measurements of bilaterally symmetric structures are reported as mean values from both sides of specimen. Head capsule light golden, head capsule width = 369 µm (n = 4). Bifid S1 setae with branches of similar size; S2 seta simple. Antennae 5 segmented, Lauterborn organs well-developed and extending 2/3 the length of antennal segment 3. Antennal blade extends to last segment, accessory blade half that length. Antennal ratio (AR = basal segment/distal segments) 1.3-1.6, mean 1.41 (n = 4). Pecten epipharyngis composed of 3 subequal scales. Mandible with 3 inner teeth, color brown extending to molar area with wide pale base. Outer margin of mandible smooth. Seta subdentalis grey, ca. 2 times long as wide with a notched asymmetric tip with one half blunt and the other half produced to a sharp point. Seta interna with 6 branches. Premandible simple. Galea of maxilla with no more than 2 rows of pectinate lamellae along the base of the scale-like marginal lamellae. Mentum with 6 brown lateral teeth; median tooth strongly projecting forward and at least 3 times wider than first lateral tooth MR (width of median tooth/width first lateral tooth ranges from 3.0- 3.8, mean 3.53 (n = 5). The median tooth, first and second lateral teeth are slightly grey compared to the brown lateral teeth. VM-plate reaches only 2nd lateral tooth. Submental setae located at the level of the basal corners of the mentum.

Large claws of the anterior parapods with robust inner teeth at least three quarters as long as apical tooth ( Fig. 6A ). Abdominal segments 1 - 6 bear posterolateral setal tufts of 10-26 filaments. Length of tufts from 108 – 200 µm, up to half the length of a segment. Setal tufts on segments I and VI bear fewer and shorter setae. Procercus wider than long, bearing a sclerotized scale and 5-6 apical setae plus 2 fine lateral setae.

Pupal exuviae of C. diversus : Measurements are mean values (n = 10) unless stated otherwise. Length 3.5-4 mm, general color yellowish, tergites darker, sternites colorless. Frontal warts absent. Frontal setae fine, located on prefrons, 64 µm. Thoracic horn (TH, Fig. 4 ) length 106 µm, L/ W 9.9. Two median antepronotal setae: 153 and 130 µm long. Three precorneal setae: 160, 143, 124 µm, distinctly longer than TH. Notum weakly granular along eclosion line.

Abdomen with Pedes spurii B on segment II, but absent on segment III. Pedes spurii A on sternites 4-6. Hooklet row on tergite 2 with 37-58 hooklets, mean = 47; hooklet row covers 0.42 of width of segment (580 µm). Armament of abdominal tergites (T) as follows: TI bare, TII may bear a very small number of fine points immediately anterior to hooklet row, or points absent. TIII with 2 patches of strong spinules: distinct median and posteromedian patches may merge around a central oval clear area. TIV and TV similar: more extensive median and posteromedian spinule patches are clearly merged, or with small median clear oval ( Fig. 8A ). TVI spinule patch less extensive; may appear as 2 distinct patches. TVII and TVIII similar: 2 anterolateral patches of fine spinules, less extensive on TVIII. Lateral setae distributed as follows: one seta on segment 1 and 3 on segments 2-7. Segment 8 bears 4 L setae, with L4 no larger than L3. Sternites SI and SII without fine spinules. SIII and SIV with very fine spinules primarily on lateral areas of sternite. SV and SVI with 2 anterolateral patches of fine spinules and a posteromedian patch. SVII with 2 anterolateral patches of small spinules whereas SVIII bears fine spinules only in lateral areas. Anal lobe slightly wider than long: mean length 199 µm, width 223 (n = 7). The three anal lobe macrosetae of equivalent length, 172 µm (n = 11).

Re-description of adult C. diversus , based on holotype, paratypes and MD specimens:

Male: Head and antennae brown, Antennal ratio (AR) 1.4 ( Boesel 1983) to 1.49 (MD, n = 3). Thorax brown with lighter humeri; vittae, and notum darker brown to black. Scutellum dark brown with an irregular row of fine bristles. Leg ratio (foretarsal segment 1/fore-tibia) = 0.62 ( Boesel 1983), LR = 0.61 (MD). Foreleg brown, except for tibia: basal 15% brown, medial white ring and distal 30% brown. Mid and hind legs with brown femur, mid-tibia may have an indistinct light ring, otherwise as hind tibia: light brown darkened distally, tarsi light brown. Wing light brown, halteres yellow. Abdominal TI white/bright yellow. TII highly variable among both the paratypes and MD specimens, ranging from yellow to black, often yellow-white with a brown band covering roughly the middle third of TII. The incisures between TII-TIII and TIII-TIV narrowly light; TIII brown; TIV light on posterior 70-75% length of tergite, anterior brown; TV anterior 30- 40% white with posterior brown. TVI, TVII, TVIII brown with incisures slightly lighter. Hypopygium white. Holotype and most of the slide-mounted paratypes are mounted intact in lateral view, largely obscuring details of the genitalia. Based on three paratypes, the inferior volsella is broad basally, apically bluntly rounded and bending posterior. In two specimens a small triangular spur is present at base of inferior volsella. In MD specimens, the inferior volsella tapers gradually from a broad base to a more conical rounded tip, also bending posterior ( Figs 11B, 11C , 12 ). Gonostylus with strong crista dorsalis.

Female: (based on allotype, paratypes and MD specimens): Antennae with preapical bristle; terminal flagellomere slightly longer than the 3 preceding flagellomeres (i.e., AR = 1.12, n = 4). Thorax brown to dark brown, humeri lighter; vittae, notum darker brown. Scutellum brown with 1 row of fine bristles. Femurs apically brown to black, lighter at base. Fore-tibia brown with median white ring covering half of segment; fore-tarsi brown; LR = 0.58 ( Boesel 1983), LR = 0.57 (MD). Mid and hind legs with light tibiae slightly darker distally mid tibia may bear an indistinct light ring; tarsi light brown. Typically, TI, TV and TVI are light yellow/white but may be brownish in dark specimens. Tergite 5 is most consistently light, although it may be brownish in dark specimens ( Fig. 10B ). Sternites yellow, SIV-SVIII with medial spine patches. Spermathecae oval with ducts posterior; ducts with anterior “S” bend otherwise straight.

Specimens examined: Peabody Museum of Yale University , M. Boesel collection: holotype ♂ + paratype ♂, allotype ♀ and 3 additional ♂ paratypes Put in Bay, Ohio, USA, 21 June 1946; paratype ♀ Oxford, Ohio, USA, 4 June 1978, ♂ paratype - hypopygium mounted separately, Put in Bay, Ohio, USA, 30 June 1924; pinned paratypes 68 ♂♂ and 37 ♀♀ dates span 1925-1976, locations include OH, Michigan, New York, Delaware and Pelee Is. Canada (details in Boesel 1983) .

Canadian National Collection of Insects , Ottawa : DRO 32.4-50 1 ♂ + pex Green Creek Ontario 19 June 1967 ; Towson University Entomology Museum (Barcode Specimen IDs): SEG 46 ♀, SEG 47♀, SEG 48♂, SEG 49♀, SEG 50♀, SEG 51♂, SEG 52♂ Baismans Run , Oregon Ridge Park, Baltimore, USA, 11. Sept. 2010; CHIM830 3 pex Chimney Branch , 1 July 2002 .

Figures

Figure 4. Cricotopus diversus; respiratory organ and precorneal setae (400x). Oregon Ridge Park, Baismans Run, 11 September 2010.

Figure 6. A) Middle sized claws of anterior parapods of Cricotopus diversus. Oregon Ridge Park, Baismans Run, 11 September 2010. B) Middle claws of anterior parapods of Cricotopus festivellus. Veluwerandmeer, 5 October 2016.

Figure 8. A) Cricotopus diversus exuviae segment 4. Oregon Ridge Park, Baismans Run, 11 September 2010. B) Cricotopus festivellus exuviae segment 4. Sprangcapelle Waalwijk, 4 August 1992.

Figure 10. A) Cricotopus festivellus male. Målsjøen, Klaebu, 30 May 2011. B) Cricotopus festivellus female. Blomstertjønna, Bymarka, Trondheim, 31 July 2011.

Figure 11. A) Cricotopus festivellus hypopygium. “b”: gonocoxite; pond, Ringve Botanical Garden, Trondheim, 24 July 2011. B) Cricotopus diversus male hypopygium; Oregon Ridge Park, Baismans Run, 11 September 2010. C) Cricotopus diversus male hypopygium; arrow: inferior volsella of gonocoxite. Same specimen as in B.

Figure 12. Comparison of inferior volsellae of C. diversus (left) and C. festivellus (right). Same individuals as Fig. 11.