Entomological Science (2004) 7, 359–368 Correspondence: Fuki Saito, Natural History Laboratory, Faculty of Science, Ibaraki University, Mito, 310-8512 Japan. Email: jkrte@mx.ibaraki.ac.jp. Received 9 February 2004; accepted 17 March 2004. ORIGINAL ARTICLE Cryptically dimorphic caste differences in a Neotropical, swarm-founding paper wasp genus, Parachartergus (Hymenoptera: Vespidae) Fuki SAITO, 1 Takahiro MURAKAMI 2 and Jun-ichi KOJIMA 1 1 Natural History Laboratory, Faculty of Science, Ibaraki University, Mito and 2 Evolutionary Regeneration Group, Center for Developmental Biology, RIKEN, Kobe, Japan Abstract Morphological differences in body shape between females of different reproductive conditions (in terms of insemination and ovarian development) were examined in two species of the Neotropical polistine genus Parachartergus: P. smithii and P. fraternus. The present study shows, for the first time, that non-size-based morphological divergence between queens and workers occurs in Parachartergus, an epiponine genus once believed to have little or no morphological caste differences. In the P. smithii colony examined, queens were significantly larger than workers in five of the eight body parts measured (head width, eye width, genal width, mesosomal length, wing length, first metasomal tergum width, and width and length of the second tergum), but the mean values of wing length and first and second tergum widths were not significantly different between them. The queen : worker size ratios tended to be greater anteriorly and smaller posteriorly, although the size ratio was greatest in second tergum length. Analysis of covariance ( ANCOVA) with mesosomal length as covariate showed that queens had proportionally wider heads and narrower first terga than did workers. In the P. fraternus colony, size differences between queens and workers were not significant, and there was little or no difference in shape, but queens had significantly proportionally wider first terga than did workers. Key words: allometric growth, Epiponini, ovary condition, Parachartergus fraternus, Parachartergus smithii, Polistinae. INTRODUCTION Approximately 200 species of the New World polistine tribe Epiponini are arranged in 20 genera (Wenzel & Carpenter 1994; Carpenter et al. 1996, 2000), and all of them found colonies with a swarm of workers (non- reproductive females) associated with one to many queens (reproductive females) (swarm founders; Jeanne 1980, 1991). Swarm founding is considered to be a more advanced mode of colony foundation than inde- pendent founding, in which a colony is founded by one to several inseminated females. Phylogenetic relation- ships among polistine genera (Carpenter 1991; Wenzel & Carpenter 1994) indicate that swarm founding evolved at least three times in the Polistinae; namely, it evolved independently in Epiponini and two genera (Ropalidia and Polybioides) of the Old World tribe Ropalidiini. Female dimorphism in accordance with physiological reproductive conditions (inseminated or un- inseminated, and ovary condition) in swarm-founding polistines have increasingly been documented in all of the three groups (e.g. Epiponini: Shima et al. 1994, 1996a,b, 1998; Noll et al. 1996, 1997; Sakagami et al. 1996; Noll & Zucchi 2002; Ropalidia: Kojima & Kojima 1994; Shima et al. 2000; Fukuda et al. 2003; Polybioides: Turillazzi et al. 1994). Jeanne et al. (1995) concluded that occurrence of non-size-based (or non-allometric) morphological caste differences in Apoica (basal clade in the Epiponini: Wen-