Megasoma sleeperi Hardy (1972)

Van Dam, Matthew, Van Dam, Alex & Wilcox, Michael D., 2006, Description of the Third-instar Larva and Adult Male of Megasoma sleeperi Hardy (Scarabaeidae: Dynastinae), The Coleopterists Bulletin 60 (1), pp. 59-67 : 59-60

Megasoma sleeperi Hardy (1972)

is the northernmost species of Megasoma Kirby. This species is associated with sandy washes and dune habitat bordering the Imperial Valley of Southern California, and is strongly associated with palo verde trees ( Cercidium floridum A. Gray ). The larvae of M. sleeperi feed on the rotting wood of this tree in captivity, as observed by Richard Cunningham, pers. comm. and Ted Rado, pers. comm. The larvae in the wild presumably feed on rotting Palo Verde, and other detritus they find buried in the sand. The previously undescribed third instar larva of M. sleeperi is described in this article. Three adult males were collected in the same locality as the larvae. Though pictures of the male of M. sleeperi have been taken Lachaume (1985), no thorough description has been written for the male.

Methods

The following description is based upon three third-instar larvae of Megasoma sleeperi that were hatched in captivity from eggs obtained from adult females. The females were collected in drainages dominated by Palo Verde trees in the vicinity of Glamis, Imperial Co., California USA. The adults were attracted to mercury vapor and blacklights between dusk, and approximately 11:00 pm. The larvae were raised using mulch of leaves of Coast Live Oak, a non-native plant species to the area. Characters used to describe the larvae can be found in Ritcher (1966). The comparisons of M. sleeperi and M. occidentalis Bolivar y Pieltain et al. (1963) and Megasoma cedrosa

Hardy (1972) are included in hopes to aid the recognition of phylogenetically important characters. The specimens are deposited in LACM and the UCR Entomology Museum.

Description of Larva

Head ( Fig. 7 ). Head capsule width 6.5 mm. Epicranium surface pitted, irregularly dark red brown color; setae present on sides of epicranium around occiput. Frons same color and texture as epicranium. Clypeus with same punctation as cranium. Clypeus with four long setae on pleural margins and two setae medially. Labrum subtrapezoidal. Labrum with four central setae and 12 lateral setae; finer setae scattered on surface. Two distinctive setae on the center come out of large pits. Epipharynx ( Fig. 1 ) with fused zygum and epizygum forming moderately raised, longitudinal, sclerotized tubercle on haptomerum; chaetoparia left side broader containing 38 spinelike setae; right side with 34, setae blending into the gymnoparia; acanthoparia on left side with 11 setae; right acanthoparia have ten; pedium broad semicircular; acroparia and corypha merged, left with 14 curved setae right with 21. Heli and plegmatia absent. Sense cone produced into rounded lobe. Dexiotorma narrow. Sclerotized plate on immediate lower right of dexiotorma. Laeotorma elongate, pternotorma present as rounded lobe. Crepis present only as strong sulcus. Right mandible with five well-marked teeth, notches present between S 1 þ 2 and S3 and between S4 and S5, S4 a sharp bump protruding out of the blade; two molar lobes. Left mandible with four teeth; notch present between S 1 þ 2 and S3, S4 produced as small bump that is more significant in younger specimens, S4 broad rounded tooth; two molar lobes. First molar lobe greatly produced rounded; stridulatory area well marked on ventral surface ( Fig. 4 ). Left mandible’s dorsal surface ( Fig. 3 ) with row 8–12 setae near molar area; dorsal surface with two distinct crater-like depressions each producing large setae; brustia with one row of stout setae. Labium with galea well-developed, conical uncus. Mala with apical uncus of galea welldeveloped and three conical unci fused at bases at apex of lacinia; maxillary stridulatory file containing eight trapezoidal files, one wide truncate anterior tubercle. Labium cylindrical. Glossa with weakly sclerotized area. Hypopharynx with hypopharyngeal sclerome strongly developed; left lobe hypopharyngeal area with central row of long fine setae; right hypopharyngeal lobe with row of long fine setae ( Fig. 5 ). Dorsal surface of terminal antennal segment with four to five plate-like sensillae.

Thorax. Densely covered long red brown setae not arranged in rows. Lateral sclerite covered with setae. Thorax lacking spinelike setae. Claws with two exterior and two interior long flattened setae. Prothoracic claw much more pointed than other two ( Fig. 6 ).

Abdomen. Segment I with same seta pattern as thorax. Segment II; first annulet with four rows of long setae and with very few spinelike setae on dorsal surface; second annulet with two rows of long setae; dorsal surface with five to six rows of spinelike setae; third annulet of segment II with two rows of long setae, and with two rows of spinelike setae. Segment III; first annulet with two rows long setae and three rows spinelike setae; second annulet with one row long setae and 5–6 rows spinelike setae; third annulet with two rows long setae and 2–3 spinelike setae. Segments IV–VI same as segment III. Segment VII with first row of long setae at anterior followed by second row of long setae at posterior and a further row 1/2 as long behind posterior row, spinelike setae start at anterior of first row of long setae and stop at first posterior row of setae. Segments VIII–IX same as VII. Dorsum of segment X covered in spinelike setae with long setae near tip. Venter of segment X posterior to anal slit covered in long fine setae, also with many spinelike setae. With 3–4 rows of long setae anterior to the anal slit; also present are spinelike setae ( Fig. 8 ). Spiracles progressively smaller from segments II–VIII ( Fig. 2 ). First abdominal spiracle about 1 mm, second 1.5 mm and then progressively smaller to the 8 th which is 1 mm in diameter. Spiracular bulla rounded, convex and prominent. Lobes separated by distance slightly shorter than bulla; respiratory plate with approximately 50 holes across longest diameter. Body length of mature larva 5.5 cm.

Figures

Figs. 5–8. Megasoma sleeperi, third instar. 5) labium; 6) protarsis; 7) head capsule; 8) ventral view abdomen.

Figs. 1–4. Megasoma sleeperi, third instar. 1) epipharynx; 2) abdominal spiracle; 3) dorsal rt., lt. mandible; 4) ventral lt., rt. mandible.