Megasoma occidentalis, Bolivar, Pieltain, Jimenez-Asua & Martinez, 1963

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 : 116

with M. occidentalis and M. pachecoi . Shared characters are: number of epicranial setae;

8 maxillary stridulatory teeth; 8–10 dorsal sensory spots on the last antennal segment; 8– 9 setae on each acanthoparia; dorsum of abdominal segment II with short, spine-like setae; abdominal spiracles progressively larger toward segment VIII; lobes of respiratory plate of spiracles contiguous, and bulla of spiracles convex, rounded, and scarcely prominent. Megasoma elephas is easily distinguished from M. occidentalis by the presence of 70–80 anterior frontal setae (4 in M. occidentalis ), 4 posterior frontal setae on each side (2 in M. occidentalis ), dorsum of abdominal segment I without short, spine-like setae (with these setae in M. occidentalis ), and only 4–6 setae on the campus (20–27 in M. occidentalis ). Megasoma elephas differs from M. pachecoi in the number of posterior frontal seta, anterior angular frontal setae, and epicranial setae, dorsum of abdominal segment I with spine-like setae, bulla of spiracles raised and acute, and the larger head and body size.

Distribution and Habits. Adults of M. elephas ( Figs. 79–80) have been collected in a wide number of localities ranging from southeastern México to Venezuela. On the slopes bordering the Gulf of Mexico, they have been reported from Plan de las Hayas, Veracruz (19 8 40 9 N) to the northern Yucatan peninsula, and along the Caribbean slopes from Quintana Roo and Belize to Colombia and Venezuela. On the slopes of Pacific Ocean, they have been collected from the Soconusco area in Chiapas, México to the Canal Zone in Panama (Ratcliffe and Morón 1997; Morón and Gómez-Anaya 2002). The habitat for M. elephas is tropical evergreen forests, tropical deciduous forests, tropical plantations, and some small remnants of tropical forests located between sea level and 1,000 meters in elevation.

Males and females are active from September to January and are commonly attracted to lights between 2100–2300 h. They fly primarily during the night when the relative humidity nears 98–100 % and the temperature is 20.5–22 8 C ( Morón 1979). Numerous adults have been observed in January feeding during daylight hours on twigs and flowers of ‘‘machiche’’ ( Lonchocarpus castilloi Standl. , Fabaceae ) near Xpujil, Calakmul, Campeche, México (P. Reyes, pers. comm., to MAM) and on the flowering tree Lonchocarpus sp. (?) in Guanacaste, Costa Rica (A. Solís and F. Chacón, pers. comm., to MAM). Near Mercedes de Guasimo, Limón, Costa Rica, this species is abundant, and adults have been observed feeding on the sap flows of recently cut twigs of ‘‘tangerine’’ ( Citrus nobilis Lour. , Rutaceae ). During the night, they cut a twig with the aid of both foretibiae crossed as a scissors and turn around many times so that the twig is broken (B. Kohlmann, pers. comm., to MAM).

Larvae have been found inside unidentified rotten stumps in coffee-cacao plantations near Cacaohatan, Chiapas (J. Valenzuela, pers. comm., to MAM); under bark of ‘‘jobo’’ ( Spondias mombin L., Anacardiaceae ) rotten log placed in tropical rain forest near Yaxchilán, Chiapas (E. Fuentes, pers. comm., to MAM); and inside a hollow near the top of standing trunk of Cedrela mexicana Roem. (Meliaceae) growing near Escárcega, Campeche (D. Cibrián, pers. comm., to MAM). Nine larvae were reared from eggs laid by a female collected at lights in Carrillo Puerto, Quintana Roo, that coupled in captivity with males obtained at the same locality. Two of these larvae (a male and female) completed their development after 630 and 900 days respectively, while feeding on a mixture of milled wood, dry cow dung, and forest soil. Third instar larva of 190 mm in dorsal length may reach a live weight of 86 g (Morón and Deloya 2001).

It is also interesting to note that, notwithstanding that adults of M. elephas are frequently attracted to lights in high numbers in some Mexican localities, systematic searching in rotten logs and stumps rarely revealed larvae of this species. Inasmuch as adults possibly remain in the canopy and upper branches of trees, it is entirely possible that adult females search for hollows in the upper parts of live trees or dead, standing, large trunks in which to oviposit. Such hollows are formed or enlarged by nesting birds strikes that break the top of a trunk or large branches. These hollows are abundant at heights of 8 or more meters from the forest floor. The hollows are progressively filled with organic debris, thus forming a rich organic soil or compost that is an excellent rearing medium for many scarab beetles and other arthropods. It is highly possible that females of M. elephas lay eggs in these natural cavities that provide food, stable microclimate, and protection for developing larvae. Second and third instar larvae may also eat the rotten walls of the wood cavity, enlarging the cavity and adding an abundant quantity of fecal pellets that then provide more nitrogenous nutrients to the compost for a subsequent generation of beetles. Pupation would also occur in such hollows, and emerging adults could live in the canopy without need to visit the forest floor. This way of life could explain why we find only occasional M. elephas larvae in rotten logs on the forest floor that were perhaps in recently fallen trunks or branches occupied by these larvae during the previous 2–3 years when the trunk was standing. We have some evidence to support the idea that females do not lay eggs in fallen tree trunks on the forest floor. One of us (MAM) and other colleagues have sampled numerous rotten logs in areas where adults are known to be abundant, but we never found eggs, larvae, pupae, or fresh remains of adult females.