Macrodactylus mexicanus Burmeister, 1855

García, Agustín Aragón- & Morón, Miguel Ángel, 2010, Description Of The Larvae Of Three Species Of Macrodactylus Dejean (Coleoptera: Scarabaeidae: Melolonthinae) From Mexico, With Notes On The Reproductive Behavior Of Macrodactylus Ocreatus Bates, The Coleopterists Bulletin 64 (3), pp. 193-200 : 195

Macrodactylus mexicanus Burmeister, 1855 ( Figs. 1–12 )

Description is based on seven third instars collected in Mexico: Puebla, Chignahuapan, San Antonio Matlacahuales (19°45′04″N, 98°05′46″W), 1,999 m, 24-I-2007, from soil in corn field, A. Aragón and A. N. Cortés (DAGAM).

Description. Head. Maximum head capsule width 2.45–2.50 mm; approximate dorsal body length 23–25 mm. Surface of cranium nearly smooth, light yellow. Frons ( Fig. 1 ) on each side with 1 exterior frontal seta, 2 posterior frontal setae, 1 anterior frontal setae, and 1 anterior angle frontal seta; remaining cranial surface with three dorsoepicranial setae, 1–2 epicranial setae, and seven paraocellar setae on each side. Clypeus trapezoidal, with 2 lateral setae on each side and 2 anterior setae. Labrum nearly symmetrical, rounded at sides, with 5 posterior setae, 2 central setae, and 5 lateral setae on each side. Epipharynx ( Fig. 2 ) with dark, elongate epizygum; haptomerum with 4–5 long stout heli; each acanthoparia with 9 curved, spine-like setae; acroparia with 6 long setae; corypha with 5 setae; each plegmatium with 10 short plegmata; right chaetoparia with mixture of many spine-like setae and slender setae; left chaetoparia mainly with long, slender setae; pedium narrowed; dexiophoba absent; laeophoba with 4–5 filaments; laeotorma short; pternotorma short; sclerotized plate large; sense cone rounded; crepis weakly indicated; haptolachus with few sensilla. Scissorial area of each mandible ( Figs. 4–5 ) with 2 scissorial teeth S1 and S2 fused, scissorial notch and S3 clearly defined; molar area with 3 lobes best defined in left mandible; mandibular stridulatory area absent. Mala with apical uncus of galea well developed, and 3 conical unci fused at their bases at apex of lacinia ( Fig. 3 ); maxillary stridulatory area with 9 small, sharply pointed teeth. Hypopharyngeal sclerome asymmetrical, produced on right side into a strong process ( Fig. 6 ). Last antennal segment with 1 ovate sensory spot on dorsal surface, 2 spots on ventral surface ( Figs. 8–9 ).

Thorax. Pronotum and mesonotum with transverse rows of scattered slender setae, but without spine-like setae ( Fig. 12 ). Thoracic spiracles light yellow, 0.25 mm long and 0.22 mm wide; lobes of respiratory plate curved, widely separated, directed posteriorly; spiracular bulla small, weakly convex ( Fig. 7 ). Tarsal claws similar in fore and middle legs, long with acute apex, each bearing 1 internal long seta and 1 external long seta ( Fig. 10 ); tarsal claw in hind legs slightly shorter than preceding, with rounded apex.

Abdomen. Dorsa of segments I-VII with mixture of few rows of long setae and many spine-like setae; dorsa of segments VIII-X without spine-like setae, but each with 16 long setae ( Fig. 12 ). Venter of abdominal segments I-VIII each with a transverse row of 6 long setae; venter of segment IX with 5 slender setae. Respiratory plates of segments I-VIII progressively shorter (0.17– 0.10 mm long; 0.25– 0.12 mm wide); lobes of respiratory plates separated, directed anteriorly. Spiracular bulla slightly convex, weakly prominent. Raster ( Fig. 11 ) with one pair of longitudinal short palidia (0.22 mm total length, 0.12 mm maximum width); each palidium with 5–6 curved, sharply pointed pali; tegilla formed by 15 stout hamate setae; campus with 4 stout, long setae; barbula formed by scattered slen- der setae. Lower anal lip deeply cleft on midline; anal slit Y-shaped.

Remarks. Larvae of M. mexicanus share similar characteristics with the larvae of M. nigripes , such as number of posterior, external and anterior frontal setae, and number of spine-like setae on the acanthoparia, but may be distinguished by the presence of 4–5 heli and 5–6 pali on each palidium.

Distribution and Habits. M a c ro d a c t y l u s mexicanus is recorded from many localities in Coahuila, Durango, Hidalgo, Jalisco, México, Michoacán, Morelos, Oaxaca, Puebla, Querétaro, Tlaxcala, Veracruz, Zacatecas, and Distrito Federal at elevations from 1,000 to 2,650 m. Males and females are commonly found in large number on leaves, flowers, and fruits of corn, apple and peach trees, wild grasses, and species of Senecio L., Baccharis L., and Tithonia Des.ex Juss. (Asteraceae) (Arce-Pérez and Morón 2000).

Figures

Figs. 1–11. Third instar of Macrodactylus mexicanus. 1) Head, frontal view; 2) Epipharynx; 3) Right maxilla, dorsal view; 4) Right mandible, ventral view; 5) Left mandible, ventral view; 6) Hypopharynx, dorsal view; 7) Thoracic spiracle; 8) Last antennal segment, ventral view; 9) Last antennal segment, dorsal view; 10) Tarsal claw, middle leg; 11) Raster. Scale bars = 1 mm, except in Figs. 7–10 where = 0.5 mm.

Fig. 12. Third instar of Macrodactylus mexicanus. Lateral view. Scale bar = 1 mm.