Myrmecologische Nachrichten 6 67 - 76 Wien, Dezember 2004 Novel blend of life history traits in an inquiline ant, Temnothorax minutissimus, with description of the male (Hymenoptera: Formicidae) Alfred BUSCHINGER & Timothy A. LINKSVAYER Abstract Forty-five colonies of Temnothorax curvispinosus (MAYR, 1866) containing the rare inquiline ant T. minu- tissimus (SMITH, 1942) have been collected near Bloomington, Indiana, USA. The colonies were censused and some were kept in laboratory culture. Dealate and alate females of T. curvispinosus and T. minutis- simus were dissected. The parasite females have a total of six ovarioles. Both, T. minutissimus and the host species, are facultatively polygynous, and the parasite is host-queen tolerant. Alate males were found in August and September. High numbers of alate and dealate, mated but not yet reproductive, young females of T. minutissimus were present in colonies collected in early spring, a feature which had been known as "Intranidal Mated Offspring Hibernation" (IMOH). Mated young queens of T. minutissimus seem to dis- perse in spring to invade host colonies. Apparently they are accepted quite easily by host colonies. Rearing of colonies collected in the early spring, or hibernated in the laboratory, yielded first a brood of sexuals of T. curvispinosus, and subsequently considerable numbers of gyne pupae of T. minutissimus appeared. Only very few males were produced (sex ratio about 0.1 ♂/♀). Intranidal mating attempts were observed, and newly mated young females were detected in colonies having reared gynes and males of T. minutissimus. Life history of the species thus is a novel combination of traits found in different other parasitic ant species: Intranidal mating and IMOH as in a few European "degenerate slavemakers" of the genus Myrmoxenus, but the parasite is host-queen tolerant, as is the case in two of the three European inquiline species of Lepto- thorax (former Doronomyrmex). The development of the parasites after the host species sexuals is a novel trait. The male of T. minutissimus is described. It is characterized by a reduced number of antennomeres (9-11 instead of 12), and a certain "morphological feminization". Key words: Temnothorax minutissimus, Temnothorax curvispinosus, inquilinism, intranidal mating, female-biased sex ratio, IMOH, morphological feminization of male Prof. Dr. Alfred Buschinger, Rossbergring 18, D-64354 Reinheim, Germany. E-mail: hormigaleon.buschinger@t-online.de (contact author) Timothy A. Linksvayer, Department of Biology, Indiana University, Bloomington, IN 47405, USA. Introduction "Social parasitism" occurs when a parasitic social in- sect species depends on another, usually closely re- lated social insect species for at least one stage in colony development. A parasite-host relationship be- tween two closely related species may frequently originate through intraspecific parasitism (e.g., BU- SCHINGER 1990, BOURKE & FRANKS 1991, SAVO- LAINEN & VEPSÄLÄINEN 2003). However, social para- sitism in the broad sense also includes the "guest ants" that live together with only distantly related host species (e.g., the myrmicine genus Formicoxenus with the other myrmicine genera Myrmica and Manica or with the formicine genus Formica, respectively). Sev- eral major types of social parasitism in the strict sense have been described, including temporary so- cial parasitism, dulosis, and inquilinism. In temporary social parasitism, a young parasite queen penetrates a host nest, replaces the host queen, and rears her first brood with the aid of the remain- ing host workers. Later, after the natural death of the host workers, such colonies have numerous wor- kers of the parasitic species, living similarly to in- dependent species. A second group of social para- sites practice dulosis, and are the slavemakers. Again, the young queen replaces the host colony queen(s), usually by force, and in some species the queen also kills or ejects all host workers, taking over only the host colony brood from which her first "slaves" emerge. Slavemaker workers also develop, but they are specialized on slave raiding and cannot forage or rear the slavemaker's broods. Instead, they attack neighboring nests of the host species from where