Sociobiology 60(2): 214-216 (2013) DOI: 10.13102/sociobiology.v60i2.214-216 Age Polyethism in the Swarm-founding Wasp Metapolybia miltoni (Andena & Carpenter) (Hymenoptera: Vespidae; Polistinae, Epiponini) L Chavarría1; FB Noll1,2 Introduction Division of labor characterizes insect societies. Work- ers allocate tasks responding to internal and external condi- tions, and to individual workers decisions (Sendova-Franks & Franks, 1999). There are two general patterns: worker age polyethism (task allocation correlated with age) and morpho- logical polymorphisms (changes in size or shape related to task performance) (Beshers & Fewell, 2001). Organization of labor in wasps of the tribe Epiponini seems not to be re- lated with morphological polymorphism because there is no morphological specialization or subcastes. Division of labor could be associated with worker’s age, or with individual task specialization (Jeanne, 1996; Karsai & Wenzel, 2000). According to Jeanne (1991) epiponines have the most evident worker age polyethism of social Vespidae. Previous studies in Polybia (Lepeletier), Protopolybia (Ducke) and Agelaia (Ducke) (Simões, 1977; Forsyth, 1978; Jeanne et al., 1988; Jeanne et al., 1992) found that young and middle aged workers perform nest tasks (building, brood care, nest main- Abstract In Epiponini division of labor is associated with age polyethism and individual task spe- cialization. We observed worker activities in three colonies of Metapoybia miltoni in Brazil. We analyzed differences of task allocation among age groups. Old workers tend to forage more than young, but age polyethism was less evident in other tasks. Age composition of population could be a determinant factor in task allocation. Workers are probably allocating to perform tasks according to colony needs, and not to individual’s age. Considering age population in studies of division of labor could help to understand how colonies respond to different situations. Sociobiology An international journal on social insects 1 - Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil 2 - Universidade Estadual Paulista Júlio de Mesquita Filho, São José do Rio Preto, São Paulo, Brazil SHORT NOTE Article History Edited by: Sergio R. Andena, UEFS - Brazil Received 22 December 2012 Initial acceptance 18 March 2113 Final acceptance 01 April 2013 Keywords Social wasps, workers, division of labor Corresponding author Laura Chavarría FFCLRP-USP Av. Bandeirantes 3900 Bloco 9 Ribeirão Preto, São Paulo, Brazil 14040-901 E-Mail: laurachp@usp.br tenance, defense), while old workers forage. Nevertheless, the presence of workers specialized in a particular task is rare in most of social Hymenoptera (Robinson, 1992; Sendova- Franks & Franks, 1999; O’ Donnell, 1998; Karsai & Wenzel, 2000; Beshers & Fewell, 2001; Johnson, 2003). Within Epi- ponini, Karsai and Wenzel (2000) did not find specialization in colonies of Metapolybia aztecoides (Richards) and M. me- soamericana (Smethurst & Carpenter). Because organization and regulation of work is com- plex, conventional patterns are insufficient to explain the di- vision of labor of several insect societies (Beshers & Fewell, 2001). For these reasons, we studied task allocation according to age in three colonies of Metapolybia miltoni (Andena & Carpenter) in Maranhão, Brazil. We observed colonies for three days in 2008: colonies N-1 and N-2 on February, in Reserva Merck (S 02° 39' 7.8" and W 44° 09' 04.0"); and colony N-3 on March, in Reserva das Paineiras (S 03° 14' 35.4" W 43° 25' 28.7"). Nest enve- lope was removed in order to perform video recordings (Sony Handycam DCR-SR42). We took a random sample of work- Sociobiology 60(2): 214-216 (2013) 215 ers to perform individual observations (N=15 for N-1, N=11 for N-2 and N=18 for N-3). All individuals were marked with quick-drying paint. Video recordings included 197, 194 and 370 minutes for N-1, N-2 and N-3, respectively. We observed allocation of work in three tasks: cell inspection, construc- tion (envelope and cells) and forage. In these cases, forager’s activities were directly observed due to difficulties to follow them in video. Females were classified according to age, based on three categories for the coloration of the transverse apodeme (Richards, 1971): light for younger, brown for middle age, and black for older females. To verify if the amount of work- ers that performs a determinate task varied according to age, and within colonies N-1 and N-3 (all observed workers of N-2 were young) a Chi-square test was applied. Our results indicate that colony cycle stage did not af- fect workers frequency performing tasks among colonies (cell inspection x2=0,854 df= 2 p>0.5; construction x2=0,381 df= 2 p>0.5; foraging x2=3,641 df= 2 p>0.5). Colony N-1 was in a mature stage of colony cycle (eggs, larvae, pupae and low queen proportion), and most of workers were young (old= 1% middle= 8% young= 90%). Colony N-2 was also in a mature stage, but in male production and most of the workers were young (young= 90% middle= 10%). Colony N-3 was in a pre- emergence phase (only eggs and higher queen proportion), and most of workers were old (middle= 17% old= 83%). We observed a similar number of old and young work- ers perfoming nest tasks (cell inspection and construction) and foraging (young x2= 4.588 df= 2 p>0.05; middle x2= 1.333 df= 2 p>0.5; old x2= 0.839 df= 2 p>0.5). Nevertheless, it is clear that young workers tended to forage less than olders (Fig 1 colonies N-1, N-3), even in colony N-2 young workers tended to forage less. Also, the amount of workers that perform tasks across different ages inside colonies N-1 and N-3 was similar (N-1 x2= 2,798 df= 2 p>0.1; N-3 x2= 0,802 df= 2 p>0.5). As mencioned before, previous studies of division of labor in the Epiponini found that as workers get old they switch to perform tasks less related with brood care (Jeanne, 1991). Similarly, we observed that old workers tend to forage more than young individuals (Fig 1). We did not find signifi- cant differences probably because of the small sample of for- agers (N=24). Nevertheless, even when old workers tend to forage more, young workers can also forage (Fig 1). Age polyethism was less evident in the other tasks: old workers as young ones can build and inspect cells (Fig 1). Age composition of worker population within colonies may be a determinant factor in task allocation. The observed colonies did not include individuals of different ages; work- ers of colonies N-1 and N-2 were mostly young, and workers of colony N-3 were mostly old. Because colonies population has little variation in terms of age, workers must be allocated to perform tasks according to colony needs and not to indi- vidual’s age. On the other hand, in colonies with differently aged workers, polyethism could be more important to delimit tasks, as demonstrated in previous studies (Jeanne et al., 1988; Jeanne et al., 1992). As observed by Karsai and Wenzel (2000), we also found flexibility in activities performed by workers; young, middle and old individuals perform different tasks. Workers of all insect societies retain some behavioral flexibility that helps to respond to changing conditions (Robinson, 1992). Caste flexibility is decisive for colony survival in swarm wasps because it allows colonies to respond efficiently to dif- ferent situations that may arise. Fig 1. Percentage of workers of different age (LY= light yellow for younger, B= brown for middle age, BL= black for older females) that perform a task (IC= cell inspection, Const= construction, Forrg= foraging) throught the studied colonies of Metapolybia miltoni. Workers decisions are dependent of colony context, and workers would be allocated to perform certain tasks when necessary (Karsai & Wenzel, 2000). In conclusion, considering age composition of popu- lation and studying colonies exposed to different situations would help to understand how colonies allocate tasks. The division of labor of swarm wasps is more complex than pre- viously thought; colonies do not organize labor in the same manner. In fact, as evidenced by Noll & Wenzel (2008), caste dimorphism may have evolved at least eight times and social organization probably derived directly from an ancestor with incipient caste dimorphism in most taxa. For this reason gen- eral patterns are not enough to understand different strategies across the tribe. Acknowledgments We especially thank to Organization of America States (OAS), the Incentive Commission of Ministerio de Ciencia y Tecnología (MICIT) and Consejo Nacional para Investi- gaciones Científicas y Tecnológicas (CONICIT) from Costa Rica, for financial support to do this investigation. To Con- L Chavarría, FB Noll - Age polyethism in Metapolybia miltoni216 Jeanne, RL. (1996). Regulation of nest construction beha- vior in Polybia occidentalis. An. Behav. 52: 473-488. DOI: 10.1006/anbe.1996.0191 Johnson, BR. (2003). Organization of work in the honeybee: a compromise between division of labor and behavioral fle- xibility. Proc. R. Soc. Lond. 270: 147-152. DOI: 10.1098/ rspb.2002.2207 Karsai, I. & Wenzel, JW. (2000). Organization and Regulation of Nest Construction behaviour in Metapolybia wasp. J. Insect Behav. 13(1): 111-140. 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