The third instar larvae of Megasoma pachecoi Cartwright, M. punctulatus Hardy, M. thersites LeConte, M. vogti Cartwright, M. cedrosa Hardy, M. elephas (F.), M. actaeon (L.), and M. occidentalis Bolívar y Pieltain, Jiménez-Asúa, and Martínez are described. Preliminary diagnosis for the larvae of Megasoma species from North and Central America and a key to eight species are presented. Comparative, brief descriptions of first and second instar larvae of M. elephas, M. thersites, M. pachecoi, and

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... cedrosa, and a detailed description of the male pupa of M. elephas, are also included. Diagnostic structures of immatures are illustrated. Notes on the habits, biology, and distribution of the eight species are reviewed. Resumen Se describen las larvas de tercer estadio de Megasoma pachecoi Cartwright, M. punctulatus Hardy, M. thersites LeConte, M. vogti Cartwright, M. cedrosa Hardy, M. elephas (F.), M. actaeon (L.), y M. occidentalis Bolívar y Pieltain, Jiménez-Asua y Martínez. Se presenta una diagnosis preliminar para las especies de Megasoma en Norte y Centroamérica, incluyendo una clave para separar las larvas de las ocho especies mencionadas. Se agregan breves descripciones comparativas del primero y segundo estadio larvario de M. elephas, M. thersites, M. pachecoi y M. cedrosa, y también una descripción detallada de la pupa de un macho de M. elephas. Se ilustran las estructuras diagnósticas de éstos estadios inmaduros, y se incorporan notas y comentarios sobre los hábitos, biología, y distribución de las ocho especies citadas. The genus Megasoma Kirby consists of 14 species of moderately-sized to very large beetles in the tribe Dynastini. They are collectively known as "elephant beetles" because the size of several species in Central and South America are very large, ca. 10 cm. Species in the genus are found from the southwestern United States to northern Argentina. Four species are found only in South America, seven species are found in northern Mexico and the southwestern United States, and the remaining three species occur in southern Mexico and Central and South America. The Mexican Megasoma 91 The Coleopterists Bulletin, 59(1):91-126. 2005. occidentalis Bolívar y Pieltain, Jiménez-Asúa, and Martínez was recently elevated to species status by Morón and Gòmez-Anaya (2002). Adults of Megasoma are recognized by their moderate to large size, broadly truncate to emarginate clypeal apex with acute or toothed anterior angles, mandibles with two or three acute teeth, short prosternal process, and tridentate anterior tibia. Males all have a variably developed, bifurcate head horn, and the pronotum is either armed or not. Hardy (1972) reviewed the North and Central American species, Endrödi (1977 Endrödi ( , 1985 provided a synopsis of all the species, and Lachaume (1985) illustrated (life-size) all the species as part of the Sciences Nat Beetles of the World series. The immature stages, biology, and life cycle of the species of Megasoma species are poorly known. Some comments and photographs about collecting larvae of M. actaeon (L.) inside the standing trunk of the "matamatá" tree, Lecythis chartacea Berg, (Myrtaceae), in the Brazilian Amazon were published by Zahl (1959) . Gibson (1964) published some data on the habits and larval development of M. pachecoi Cartwright that were reared from eggs laid by captive females that were collected on the branches of "palo brea," Cercidium torreyanum (Wats.) Sarg. (Caesalpinaceae). Möhres-Reitter (1966) provided a short note and picture of the larva of M. gyas (Herbst) in Brazil, and he indicated Cordia gerascanthus L. (Boraginaceae; "palo de rosa") was the rotting tree in which the larvae were found. William Warner (pers. comm., to BCR) indicated that adult females of M. sleeperi Hardy occasionally come to lights (males rarely so), and that males can be found on the trunks of blue palo verde, Cercidium floridum Benth. (Caesalpinaceae), at night or on small branches feeding from dawn to ca. 0900 h. Adults have also been observed emerging from the sand beneath palo verde trees at dusk. Morón (1977) provided a description of the third-stage larva of M. occidentalis that was found in the rotten stem of a coconut palm, Cocos nucifera L. (Arecaceae). Life cycle notes and illustrations of immature stages of M. elephas (F.) reared in captivity were provided by Morón (1984) , Morón et al. (1997), and Deloya (2001) . Fourteen species of Megasoma are distributed from the southwestern United States to northern Argentina (Endrödi 1985) . One of us (BCR) was able to obtain over the last five years the larvae of six species of Megasoma from the southwestern United States, northwestern Mexico, and South America that provided the foundation for this work. MAM obtained the larvae of two additional species. In this paper we describe for the first time the third-instar larvae of M. pachecoi Cartwright, M. punctulatus Hardy, M. thersites LeConte., M. vogti Cartwright, M. cedrosa Hardy, M. actaeon (L.), and M. elephas (F.), as well as a redescription of the third-instar larva of M. occidentalis Bolívar y Pieltain, Jiménez-Asúa and Martínez. We also have notes on the first and second instars of M. elephas and describe the pupa. Megasoma species for which the immature stages have not been discovered and/or described are M. gyas (Herbst), M. mars (Reiche), M. anubis (Chevrolat), M. joergenseni (Bruch) (all South American), M. sleeperi Hardy (SW United States), and M. lecontei Hardy (Baja California Sur, Mexico). Terms and characters used in the descriptions are those of