Pachyrhinus Schönherr 1823

Benzel, Joseph & Bright, Donald E., 2021, A revision of the genus Pachyrhinus Schӧnherr 1823 (Coleoptera: Curculionidae Entiminae) in the Nearctic Region, Zootaxa 4999 (6), pp. 501-533 : 503-508

Pachyrhinus Schönherr 1823

Pachyrhinus Schönherr 1823: 40 ; Fall 1901: 308; O’Brien & Wibmer 1982, 43.

Scythropus Schönherr 1826 , O’Brien & Wibmer, 1982, 43.

Carpomanes Gistel 1856 , Alonso-Zarazaga & Lyal 1999.

Parisodrosus Voss 1936 , Alonso-Zarazaga et al. 2017

Type species: Curculio mustela Herbst, 1797 = Curculio squamulosus Herbst, 1795 . Gender, masculine.

Diagnosis. Members of Pachyrhinus are medium sized (4–10 mm) entimine weevils without post ocular lobes or vibrissae, and with elytra bearing well developed humeri ( Fig. 1 ). The genus belongs to the Polydrusini , sharing with Polydrusus laterally oriented antennae ( Fig. 2 ) and connate tarsal claws ( Fig. 3 ). It can be distinguished from Polydrusus by its thick blunt rostrum bearing a large glabrous callosity and carina on the epistoma ( Figs. 4 and 5 ) and by its elongate scales with only thin, poorly developed ribs ( Figs. 6–8 ) as opposed to the large, pronounced ribs of Polydrusus ( Fig. 9 ).

Description (male). Length: 4.0–8.0 mm, average 6.5 mm ( Fig. 1 ), 2.0× as long as wide in dorsal view, widest portion of elytra at apical 2/3; shape elongate, subrectangular; dorsal outline in lateral view subplanar to weakly convex; color black, red or orange, lighter on legs, antennae red to orange; vestiture composed of elongate, appressed, contiguous, mostly nonoverlapping scales and both short, recurved and long, erect setae sparsely arranged over body, scales 2.0 to 4.0× as long as wide ( Figs. 6–9 ), ribbed, with ribs extending out into spines at terminal end of scale, variably colored ( Figs. 10–15 ), color iridescent green or blue ( Fig. 10 ) to orange brown ( Fig. 11 ) or ash white ( Fig. 12 ), scales lighter to pearlescent on underside, sides and elytral sulcus Head in dorsal view rounded ( Fig. 4 ); eyes small, ⅓ length of head in lateral view, produced ⅔ from base of head, projected outward, in lateral view round ( Fig. 2 ),, separated from anterior margin of prothorax by diameter of eye; eye facets uniformly well defined; frons subrectangular ( Fig. 4 ), shortest distance located between eyes ¾ greatest width of pronotum, bearing shallow impression at apical point where it meets rostrum; ventral surface scaled, bearing sparse pearlescent setae; gular suture clearly visible, rostrum stout ( Fig. 4 ), subquadrate, subequal to size of head, in dorsal view ¾ length of head, as long as wide; sides parallel to slightly diverging; medial region slightly impressed; epistomal area large, nearly semicircular, bearing prominent glabrous carina on edge, separated from nasal plate by shallow groove bearing three to five long setae at apical edge; nasal plate expanded into large glabrous callosity; rostrum in lateral view curved downward, length ½ basal width; mandibles large ( Fig. 16 ), shiny, bearing 3–5 long laterally positioned setae; mandibular scar prominent, medially situated, deciduous process large ( Fig. 17 ), prominent, talon shaped, about length of rostrum, red or orange in color, maxillae rarely visible ( Fig. 18 ), hidden by small projections of the head capsule at ventrolateral angles of oral cavity; cardo stout, as wide as long; maxillary palps three segmented, 2.0× as long as wide, I and II bearing single setae on buccal side, labium not covered by prementum ( Fig. 18 ), subquadrate, as long as wide, external surface smooth; labial palps three segmented, inserted at apex of labium; palpomeres gradually reduced in size toward apex, bearing short fine setae on apical margin. Antennae ( Fig. 19 ) 11-segmented, color black to orange; insertion at apical edge of rostrum ( Fig. 2 ). Scrobe curved downwards 20–30°, deep at initiation in apicodorsal region, poorly defined through most of length, ending in basolateral region ventrad of apical margin of eye, separated from eye by width of scrobe, scape clavate with bulbous region extending from of length to apex, otherwise slender; antennae directed ventrad of eye in resting position, length reaching apical margin of prothorax, passing just below eye, bearing elongate setae; funicle (including peduncle) seven-segmented, as long as scape, densely pilose with hairlike setae; funicular antennomeres I and II clavate, 2.0× as long as other antennomeres; antennomeres III to VII conical, either subequal in length or decreasing in size to antennomer V, then increasing in size; club three-segmented, ⅓ length of scrobe, 3.0–4.0× as long as wide, covered in dense setae, club segments decreasing in length and width apically. Pronotum transverse ( Fig. 1 ), greatest width about ⅔ from anterior mar- gin; dorsal surface densely punctate, each puncture bearing a scale or seta; sides with lateral margins subparallel, rounded near midpoint; posterior margin straight to gently sinuate, as wide as anterior margin; in lateral view dorsal outline flattened about 1.5× long as ventral outline, anterior margin straight. Scutellum conspicuous ( Fig. 20 ), triangular, covered in scales. Thorax with mesepisternum triangular, densely covered with scales; metepisternum trapezoidal, suture concealed by dense scales, of greatest width at anterior edge, diminishing to parallel-sided band along metepisternal suture; metepimeron not visible, entirely covered by elytron. Abdominal ventrites with dense coating of pearlescent scales ( Fig. 26 ); ventrites I–II connate, III–V separate; II shorter than I, subequal to III; III longer than IV; V subequal in length to I, subtriangular, covered with dense hair like setae; anterior margin of I and suture between II and III bisinuate, other margins straight. Procoxae contiguous, close to anterior margin of prothorax. Legs subequal in length ( Fig. 21 ), front legs appear shorter as protibia arcuate, uniformly covered with pearlescent white, elongate setiform scales; femora stout, unarmed, approximately 1.5× length of pronotum, about 4.0× long as wide, proximal ¾ gradually widening then abruptly narrowing at tibial condyle; tibia arcuate, ventral margin flared, bearing row of spiniform setae increasing in length ventrally; mucro ⅓ size of tarsal claw; corbel open, surface glabrous; tarsi ventrally with dense cover of setae; tarsomeres I and II subtriangular, I larger than II, III deeply bilobed, 2.0× wide as II, IV miniscule, ⅜ size of II, concealed by III, V elongate, lacking setae pad, as long as I and II combined; claws connate, otherwise simple. Elytra length in dorsal view 2.0× greatest width, 2.0× width of pronotum ( Fig. 22 ); anterior margins straight; humeri prominent, roundly angulate, 1.5× width of posterior margin of pronotum; lateral margins parallel anteriorly, gently diverging in middle ⅓, converging to point at apical ⅓; apex pointed; declivity gradual, convex with 10 complete striae; stria separated by width of tibia; interstrial punc- tures shallow ( Fig. 23 ), hidden by scales, separated longitudinally by diameter of puncture, bearing single, small, recumbent setae just before anterior side of puncture ( Fig. 23 ); stria covered in scales ( Fig. 24 ). Scale color pattern variable by species and individual; straight, erect setae or more elongate scales arranged in rows along mid region of stria, longitudinally placed at every third interstrial puncture; interval X produced along apical ⅓ of elytra. Wings fully developed ( Fig. 25 ), 2.0X length of elytra, in repose folded inward at middle of anterior edge by sclerotized elbow, poorly veined. Genitalia with spiculum gastrale apodeme longer than pedon and aedeagus ( Fig. 27 ), thin with hooked anterior end; hook turning 90°, reaching ⅓ length of pedon; laminae on apical ⅛ of pedon, abruptly widen- ing out from apex, bearing single blunt sclerotized projection on each side near tip; tegmen apodeme shorter than those of aedeagus ( Fig. 28 ), blunt-tipped; posterior ring thin, unarmed; aedeagus pedon length to width ratio 6:1; anteroventral margin weakly sclerotized, mesally curved; lateral margins curved ending in lengthened point covered by long fine setae; ostium elongate, ovate, highly arcuate, laterally emarginated, terminating in abrupt narrow point with slight ventral curvature; apodemes subequal pedon, partially embedded in lateral folds of pedon, sclerotized throughout, forming into wide paddles anteriorly.

Female.Generally similar to male except length 5.0–10.0 mm, average 6.9 mm, same proportions as male except where noted below; protibia straight with gentle sloping arch extending from ⅔ along tibia to outer apical angle, otherwise same as male; abdominal ventrite II expanded to length of ventrites III and IV combined ( Fig. 30 ), other features identical; sternum VIII with spiculum ventral long ( Fig. 31 ), elongate; lamina triangular, arms entire, weakly sclerotized. Anterior margin significantly curved; lateral margins elongate, converging into blunt point at posterior; apical point and lateral margins bearing relatively long fine setae; ovipositor with coxites heavily sclerotized throughout ( Fig. 32 ), only marginally longer than wide, bearing sparse fine setae along edge; two; bearing small styli near end of distal coxites; spermatheca variable in size, comma or C shaped, apically sclerotized with small projection perpendicular to ramus; ramus subconical; cornu short, tightly to loosely recurved, subcylindrical.

Distribution. Pachyrhinus species are common in pine forests in the temperate Palearctic and Nearctic regions. In the Nearctic they are distributed from New Brunswick west to British Columbia south to Baja California and Arizona in the west. In the east their range reaches as far south as Indiana and Pennsylvania ( Bright & Bouchard 2008). No species are present in the southeastern United States. In the Palearctic, Pachyrhinus species are found as far north as southern Poland and from England to Japan ( Yunakov 2013, Kono & Morimoto 1960). They are most diverse in the Western Mediterranean, reaching as far south as the Atlas Mountains in Morocco, Algeria, and Tunisia (Hustache 1946, Hoffman 1961). Nearctic species are associated with species of pines but may also be found on Douglas fir ( Bright & Bouchard 2008).

Biology. Despite being a potential pest on economically important hosts, the biology of Pachyrhinus remains little studied. The damage they cause the host plant is apparently not permanent ( Furniss & Carolin 1977). Jensen & Koehler (1969) reported that adult P. californicus in Alameda Co. California first appear in late February and can be found until early May. Maximum numbers are reached around late February to early March. The adult beetles feed on the needles of Pinus spp. ; specifically, P. californicus feeds on Monterey pine, P. radiata D. Don. Adult feeding results in intermittent notches along the needle’s length and causes death of the needle beyond the damaged area ( Burke 1937). Severely affected trees have a brownish appearance until the damaged needles fall off before winter. The weevils show no preference for feeding location on the tree ( Jensen & Koehler 1969).

Female P. californicus begin to produce eggs in February and continue production until the females die off ( Jensen & Koehler 1969). Males have a shorter life span than the females resulting in a one to four male to female ratio by the time of the breeding season. The females may live to August and September in captivity and continue producing fertile eggs until death, even after all the males have died. Eggs are laid in an oviposition chamber constructed from three adjacent needles glued together in a bundle by a sticky exudate produced by the female. Females produce an average of 1,200 eggs distributed among an average of 36 egg clusters ( Jensen & Koehler 1969). Once the larvae hatch, they drop to the ground where they burrow into and feed on the tree’s rootlets. From laboratory reared specimens, pupation has been determined to occur in early September with adults emerging later in the month. Jensen and Koenher (1969) speculate that pupation occurs in the soil and that the weevils overwinter as adults, suggesting a two-year life cycle.

The feeding habits of adult Pachyrhinus do not directly seem to cause lasting harm to the tree ( Furniss & Carolin 1977). The attacked needles simply fall off the tree in autumn. However, larval feeding on the roots may cause more extensive damage. No studies are available that have determined the extent of the root damage caused by Pachyrhinus larvae.

Figures

FIGURES 1–5. 1. Pachyrhinus squamulosus, dorsal view. 2. Pachyrhinus head, lateral view. 3. Pachyrhinus tarsus showing connate tarsal claws. 4. Pachyrhinus head, frontal view. 5. Polydrusus sericeus (Schaller) head, frontal view.

FIGURES 6–9. Elytral Scales. 6. Pachyrhinus elegans. 7. Pachyrhinus californicus. 8. Pachyrhinus cinereus scale. 9. Polydrusus impressifrons Gyllenhall 1834.

FIGURES 10–15. Elytral Vestiture. 10. Pachyrhinus elegans. 11. Pachyrhinus californicus. 12. Pachyrhinus cinereus. 13. Pachyrhinus squamulosus. 14. Pachyrhinus lethierryi. 15. Polydrusus sericeus.

FIGURES 16–19. 16. Mandibles showing scars at deciduous process attachment point. 17. Mandibles with deciduous process. 18. Oral cavity with maxillae and labium. 19. Antennae, lateral view.

FIGURES 20–21. 20. Scutellum. 21. Male protibia.

FIGURES 26–28. 26. Abdominal ventrites. 27. Spiculum gastrale. 28. Tegmen.

FIGURES 22–25. 22. Elytra. 23. Puncture in elytral interstria. 24. Scales on elytral stria. 25. Wing.

FIGURES 29–32. 29. Female protibia. 30. Female abdominal ventrites. 31. Eighth sternite. 32. Ovipositor.