Megasoma punctulatus Cartwright

Ratcliffe, Brett C. & Morón, Miguel-Angel, 2005, Larval Descriptions Of Eight Species Of Megasoma Kirby (Coleoptera: Scarabaeidae: Dynastinae) With A Key For Identification And Notes On Biology, The Coleopterists Bulletin 59 (1), pp. 91-126 : 96-99

Megasoma punctulatus Cartwright , 3rd instar ( Figs. 16–28 )

Description based on two third instar larvae reared from eggs laid by female collected in U.S.A., Arizona, Santa Cruz Co. 6.5 mi E Hwy 82 on Duquesne Rd., 4-VIII-1997, preserved last week of VIII-1998, W.B. Warner (UNSM, IEXA).

Description. Head. Maximum width of head capsule 7.6 mm. Surface of cranium densely punctate, dark brown. Frons ( Fig. 16 ) on each side with 6–7 posterior frontal setae, anterior frontal setae absent, 7–8 exterior frontal setae, and 3–5 anterior angle frontal setae; remaining cranial surface with 2–3 dorsoepicranial setae, 40–46 epicranial setae, and 6–7 paraocellar setae on each side. Clypeus with 3 lateral setae on each side. Labrum slightly asymmetrical, ovate, with 4–5 posterior setae,2 central setae, and 2–3 lateral setae.Ocelli not evident.Epipharynx ( Fig.17 ) with fused zygum and epizygum forming oblique, raised, subconical, well-sclerotized tubercle on haptomerum; heli and plegmatia absent; right chaetoparia with 46–48 spine-like setae and 18–20 sensillae toward gymnoparia; left chaetoparia with 80–88 spine-like setae and 8–10 sensillae; acroparia with 10–11 straight, long, thick setae toward right side and 12–15 straight, long, thick setae toward left side; right acanthoparia with 8 short, curved, spine-like setae; left acanthoparia with 9 short, curved, spine-like setae; pedium wide, epitorma vague; dexiotorma long, narrowed toward left nesium, with rounded inner side;laeotorma narrowed,diffuse,with wide,rounded pternotorma;dexiophoba sparse,formed by 7–8 setae; laeophoba sparse with 7–10 setae between haptolachus and inner side of laeotorma; sclerotized plate or right nesium large, subtriangular; sense cone on left nesium represented by large, wide,longitudinal, well-sclerotized plate;crepis partially defined at right side and vaguely marked on left side. Scissorial area of right mandible ( Figs. 18, 20 ) slightly abraded, with 3 large, wide teeth, well-separated by notches,and 1 basal, small tooth; molar area with 3 lobes, brustia sparse.Scissorial area of left mandible ( Figs. 19, 21 ) not abraded, with 2 well-marked, large teeth and 1 subtriangular, pre-incisor tooth; molar area with 2 wide lobes, sparse brustia and long, acute acia. Stridulatory area of each mandible well-marked by 23–25 fine striae. Mala ( Fig. 22 ) with apical uncus of galea welldeveloped,and 3 conical unci fused at their bases at apex of lacinia; maxillary stridulatory area with 7 small, subtrapezoidal, rounded teeth and wide, truncate anterior process. Labium with numerous long, strong setae located near sides and short, spine-like setae at middle; hypopharynx with right anterior lateral process of hypopharyngeal sclerome strongly developed, raised and curved, heavily sclerotized; left hypopharyngeal lateral lobe with patch of 20–22 posterior lateral short setae and a line of minute, thin setae ( Fig. 22 ). Last antennal segment on dorsal surface ( Fig. 23 ) with 5–6 sensory spots; ventral surface with 5–6 spots ( Fig.24 ). Thorax. Pronotum with wide, irregular,nearly pentagonal, reddish brown, lateral scleromes and many long, slender setae not arranged in rows. Meso- and metanotum each with many long, slender setae not arranged in rows. Thoracic spiracles 0.69 mm long and 0.80 mm wide; lobes of respiratory plate nearly contiguous, directed posteriorly. Spiracular bulla rounded, convex, scarcely prominent.Tarsal claws ( Fig. 25 ) similar on all legs, with acute apex, each bearing 2 internal, long, thick, basal setae and 2 external, long,thick,preapical setae. Abdomen. Dorsum of segment I with many long, slender setae not arranged in rows. Dorsa of segments II–VII ( Fig. 27 ) each with mixture of long and short, spine-like setae, not arranged in rows, 98 THE COLEOPTERISTS BULLETIN 59(1), 2005

with short setae predominant on anterior half of each annulet and long ones predominant on posterior half of each annulet.Dorsa of segments VIII–IX with scattered, spine-like setae and long setae mainly near sides and posterior border. Dorsum of segment X with numerous, short, spine-like setae on anterior 2/3 and long setae on posterior third. Venter of abdominal segments I–IX each with median transverse tuft of long setae. Raster without pallidia and septula, with 28–30 long, slender setae on campus, teges formed by 42–46 slender setae; cuticle slightly rugose. Lower anal lip with 44–48 short,spine-like setae and 32–35 medium size, erect setae.Upper anal lip with 46–54 short,spine-like setae and50–56 long, slender setae, mainly near sides.Spiracles of segments I–V progressively larger (0.60–0.80 mm long); spiracles of segments V–VIII progressively smaller (0.80– 0.61 mm long); lobes of respiratory plate contiguous ( Fig. 26 ), directed forward. Spiracular bulla convex, rounded, scarcely prominent; respiratory plate with 37–42 irregularly shaped holes across any diameter. Approximate dorsal body length 64 mm.

Remarks. Shared characters of the larvae of M. punctulatus and M. thersites are: absence of anterior frontal setae, 2–3 dorsoepicranial setae, 40–46 epicranial setae, 45–50 setae on right chaetoparia, 7 maxillary stridulatory teeth, spine-like setae on abdominal segment II, and bulla rounded, scarcely prominent. Similarities with the larvae of M. vogti consists of: 5–7 posterior frontal setae, 3–5 anterior angular frontal setae, 7 maxillary stridulatory teeth, 5–6 dorsal sensory spots on last antennal segment, 5–9 setae on acanthoparia, lobes of respiratory plates of spiracles contiguous, spine-like setae on abdominal segment II, and bulla rounded, scarcely prominent. The abundance of setae on the clypeus, labrum, and campus, absence of spine-like setae on the first abdominal segment, and an increase in the size of the abdominal spiracles toward segment V, serves to distinguish the larvae of M. punctulatus .

Distribution and Habits. Adults of M. punctulatus ( Fig. 28 ) have been collected in a limited number of localities of Arizona desert having a shrub cover of mesquite with occasional Quercus sp. , Acacia spp. , Mimosa sp. , sycamore, hackberry, Condalia sp. , Lycium sp. , Agave and Opuntia species in the Santa Rita Range Reserve (Pima Co.), Patagonia, Rio Rico, and Duquesne (Santa Cruz Co.), and the Baboquivari Mts. of Arizona, between 1,300 –1,350 m elevation. Males and females are attracted to lights but are also found on the trunks or branches of ‘‘catclaw’’ ( Acacia greggi A. Gray , Mimosaceae ). Adults are active during July and August ( Cartwright 1952; Hardy 1972).

Figures

Figs. 16–26. Megasoma punctulatus, third instar. 16) Head, frontal view; 17) epipharynx; 18–19) mandibles, ventral view, 18) right and 19) left; 20–21) mandibles, dorsal view, 20) left and 21) right; 22) left maxilla and hypopharynx, dorsal view; 23–24) distal segment of antenna, 23) dorsal view and 24) ventral view; 25) left posterior tarsal claw, external view; 26) second right abdominal spiracle. Figs. 16–22, bar ¼ 1 mm. Fig. 26, bar ¼ 0.5 mm.

Fig. 27. Megasoma punctulatus, third instar, lateral view. Bar ¼ 5 mm. Setal pattern simplified.

Fig. 28. Megasoma punctulatus on mesquite, Prosopis juliflora (Swartz). Photo by Barney Streit.