Open access journal: http://periodicos.uefs.br/ojs/index.php/sociobiology ISSN: 0361-6525 Sociobiology 60(1): 96-100 (2013) Effect of Habitat Disturbance on Colony Productivity of the Social Wasp Mischocyttarus consimilis Zikán (Hymenoptera, Vespidae) KB Michelutti1, TS Montagna2, WF Antonialli-Junior1,2 Introduction Anthropogenic disturbance of natural habitats is one of the main factors that contribute to reduction of the bio- diversity in tropical environments (reviewed in Samways, 2005; 2007). The effect of habitat on the colony dynamics of social insects has been examined in several studies (Santos & Gobbi, 1998; Inagawa et al., 2001; Gamboa et al., 2005). However, few studies have evaluated the effect of habitat modification by humans on the development of colonies in a tropical environment (Penna et al., 2007; Montagna et al., 2010). Evidence that human presence alters habitat qual- ity has been reviewed recently by Raupp et al. (2010) and Schowalter (2012). The modification of natural habitats is due mainly to the progress of agriculture and livestock rais- ing, as well as to urbanization (Abensperg-Traun & Smith, 2000; reviewed in New, 2005; reviewed in Raupp et al., 2010). Abstract Social wasps are important elements of the fauna in a variety of environments, including human-modified environments. Evidence indicates that habitat quality affects the growth of colonies of social wasps in urban environments. This study investigated whether the colony productivity of the social wasp Mischocyttarus consimilis Zikán is affected by loss of habitat quality in a human-occupied envi- ronment. Nests of M. consimilis were collected in forest and urban environments between January 2010 and June 2011. Only nests that reached the declining stage were sampled. As productivity parameters, we measured the total number of cells constructed, the total number of adults produced and dry mass of the nests. Pro- ductivity was significantly lower in urban than in forest environments for all pa- rameters analyzed. Habitat quality is probably the principal factor that contributed to the lower productivity in the urban environments. In this type of environment, particularly where the study was conducted, the vegetation adjacent to the nest- ing sites was composed predominantly of grasses. Such habitats may have limited available resources, especially those used by wasps for feeding the larvae, such as immatures of other insects. This result suggests that human degradation of habi- tats negatively affects the final productivity of colonies of social wasps. Sociobiology An international journal on social insects 1 - Universidade Estadual de Mato Grosso do Sul, Dourados-MS, Brazil 2 - Universidade Federal da Grande Dourados, Dourados-MS, Brazil RESEARCH ARTIClE - WASPS Article History Edited by: Sergio R. Andena, UEFS, Brazil. Received 25 October 2012 Initial acceptance 21 November 2012 Final acceptance 13 February 2013 Keywords Social wasp, synanthropism, independent foundation, functional ecology, conservation biology Corresponding author Kamylla B. Michelutti Programa de Pós-graduação em Recursos Naturais Univ. Estadual de Mato Grosso do Sul Dourados-MS, Brazil, 79804-970 E-Mail: kamylla_michelutti@yahoo.com.br Social wasps are important elements of the fauna in many environments and important predators of other arthro- pods in tropical regions (Gould & Jeanne, 1984; Gobbi & Machado, 1986; Prezoto et al., 2005). In the tropics, many social wasps are facultatively synanthropic, occurring abun- dantly in both forest and urban environments (Fowler, 1983; Curtis & Stamp, 2006; De Oliveira et al., 2010). A recent approach suggests that nesting behavior in social insects is influenced by several ecological variables, including compe- tition, foraging efficiency, microclimate, nest deterioration, nest quality, parasitism, predation, seasonality, and colony growth (reviewed in McGlynn, 2012). The wide range of nesting sites on human constructions and low interspecies competition may partly explain the facultative occurrence of some social wasp species in urban environments (Giannotti & Mansur, 1993; Prezoto et al., 2007; De Oliveira et al., 2010). However, synanthropic colonies of social wasps are directly exposed to the effects of human interference in the Sociobiology 60(1): 96-100 (2013) 97 habitat (Curtis & Stamp, 2006). Habitat quality is one of the principal factors that in- fluence the colony dynamics of social wasps (Inagawa et al., 2001; Gamboa et al., 2005; D’Adamo & Lozada, 2007). It has been suggested that habitat quality is reduced drastically with increased urbanization (reviewed in Raupp et al., 2010; reviewed in Schowalter, 2012). Therefore, it is expected that the low habitat quality in urban environments negatively af- fects the development of the social insect colonies. In the urban environment, as a direct consequence of the human- caused habitat degradation, the foraging areas surrounding the colony consist mainly of grasses, suggesting that this type of habitat offers less resources compared to sites where the original vegetation is preserved (Gould & Jeanne, 1984). For example, Naug and Wenzel (2006) demonstrated that the supply of resources in the surroundings of the nests was the main limiting factor on colony growth in Ropalidia margi- nata (Lepeletier). Similarly, Mead and Pratte (2002) demon- strated that differences in local resource availability among populations of the social wasp Polistes dominula (Christ) resulted in considerable differences in terms of nest growth and production of offspring. Mischocyttarus consimilis Zikán is a Neotropical so- cial wasp with a distribution restricted to Paraguay and the southern region of the state of Mato Grosso do Sul (Rich- ards, 1978; Montagna et al., 2009). Colonies of M. consimi- lis are usually established by a single female, and the nests are composed of a single, uncovered comb that is attached to the substratum by a single, central petiole (Montagna et al., 2010). Colonies of this species found and abandon their colonies throughout the year (Torres et al., 2011). This spe- cies can be considered facultatively synanthropic, since it is abundant in locations affected by intense movement of people, as well as in forest environments (Montagna et al., 2010). This study investigated the effect of habitat distur- bance on colony productivity of the social wasp M. consimi- lis. Material and Methods Data collection and field procedures To evaluate the effects of the human-caused habitat disturbance on colony development, we compared the final productivity of colonies of M. consimilis located in a for- est environment (conserved habitat) and an urban environ- ment (disturbed habitat), in the municipality of Dourados (22º13’16’’S; 54º48’20’’W) in the state of Mato Grosso do Sul. We collected 11 abandoned nests in each environment during January 2010 to June 2011. Colonies in the selected areas were monitored weekly to determine the end of the colony cycle. Only nests that reached the declining stage (widespread presence of empty cells in the comb and nest abandonment), as defined by Jeanne (1972), were used in the sample. As productivity parameters we measured the num- ber of constructed cells, number of adults produced, and dry mass of the nest. The number of adults produced was es- timated by counting the number of layers of meconium in each cell of the comb. The meconium layer is formed on the floor of the productive cells as a result of the elimination of feces by the last-instar larva, just before pupation (Gobbi & Zucchi, 1985; Giannotti, 1999). The meconium layer was removed in the laboratory with the aid of tweezers, section- ing each cell of the comb. For analysis of the nest dry mass, the nest was placed in a separate Petri dish, and then dried in a vacuum chamber for 24 h and immediately weighed on a precision balance. Study sites The forest environment selected in this study belongs to an environmental preservation area known as the “Reser- va do Coqueiro”, located 10 Km from the urban perimeter of the city of Dourados. The Reserva do Coqueiro is composed predominantly by a preserved forest, traversed by a road that leads to approximately a dozen camp-houses adjacent to the forest. The camp-houses are used mainly for recreational events and remain closed most of the year. Human traffic in that area is sparse. All the nests collected in the reserve were located on the edges of the camp-houses. The contrasting urban environment is in a residential area known as the “Cidade Universitária”, near the campus of the Universidade Federal da Grande Dourados. This area is undergoing rapid development, with extensive new con- struction in progress. The areas adjacent to the buildings are predominantly grassed or covered by sidewalks or asphalt, and human traffic is intense year-round. All the nests col- lected in this environment were located on the edges of oc- cupied houses and university buildings. Statistical analysis The t-test for two independent samples was used to evaluate possible differences in colony productivity param- eters between the two wasp populations. We performed a correlation analysis between the number of individuals pro- duced and the number of cells constructed, to evaluate pos- sible differences in strategies of comb use between the two populations. For all analyses, the variable was considered when the resulting regression coefficient was significant at the 0.05 level. Results For nests in the forest environment, the mean values (± SE; n=11) were: number of adults produced, 250.6 ± 6.62; number of constructed cells, 215 ± 22.8; nest dry mass, 1.11 ± 5.66 g; proportion of productive cells, 67.4 ± 39.6%; pro- KB Michelutti, TS Montagna, WF Antonialli-Junior - Effect of Habitat Disturbance on Social Wasp Colony Productivity98 portion of reused cells, 37.3 ± 6.85%; and number of adults produced per cell, 1.09 ± 0.13 (Table 1). In this environment we found a significant positive correlation between the num- ber of cells constructed and the number of adults produced (r=0.84; p<0.01; n=11) (Fig. 1). For nests in the urban environment, the mean val- ues (± SE; n=11) were: number of adults produced, 131.9 ± 4.69; number of constructed cells, 142.2 ± 13.4; nest dry mass, 0.59 ± 5.70 g; proportion of productive cells, 56.2 ± 20.2%; proportion of reused cells, 39.3 ± 5.91%; and num- ber of adults produced per cell, 0.98 ± 0.09 (Table 1). In this environment, the correlation analysis was significantly posi- tive between the number of constructed cells and the number of adults produced (r=0.64; p=0.03; n=11) (Fig. 1). Productivity in the urban environment was signifi- cantly lower than in the forest environment with respect to the number of adults produced (t=-2.35; df=13.69; p<0.05), number of cells constructed (t=-3.08; df=17.80; p<0.01), and dry mass of nests (t=-3.51; df=15.16; p<0.01) (Table 1). In contrast, the proportion of productive cells (t=-1.59; df=19.73; p=0.12), proportion of reused cells (t=0.25; df=19.93; p=0.8), and number of adults produced per cell (t=-1.04; df=17.68; p=0.3) did not show significant differ- ences between the two environments (Table 1). Discussion Colony productivity for M. consimilis was determined by the size of the nest in both environments, with larger nests being more productive. However, nests collected in the urban environment were less productive than nests collected in the forest environment, as estimated by the number of cells con- structed, number of adults produced, and dry mass of nests. Montagna et al. (2010), studying colonies of M. consimilis in an urban environment, found a mean productivity of 72.9 ± 10.5 and 40.7 ± 14.0, for the number of cells constructed and adults produced, respectively. The productivity found by Montagna and coworkers is lower than in our study; how- ever, the authors evaluated only colonies in the post-emer- gence stage. Our results and those of Montagna and cowork- ers suggest that colony productivity in tropical social wasps is affected by the habitat quality, and an increase in urban- ization negatively influences the development of the colo- nies. Particularly in the study locale, the vegetation adjacent to the nesting sites was composed predominantly of grasses. Studies demonstrate that habitats with those characteristics have low availability of resources, especially prey used by Figure 1. Correlation between the number of cells constructed and adults produced per colony of the social wasp Mischocyttarus con- similis nesting in conserved and disturbed habitat. Table 1. Comparison of the colony productivity of the social wasp Mischocyttarus consimilis nesting in conserved and disturbed habitat. Parameter Conserved habitat Disturbed habitat T P N Mean SE N Mean SE Built cells 11 215 22.8 11 142.2 13.4 -3.08 0.006 Produced adults 11 250.6 6.62 11 131.9 4.69 -2.35 0.03 Nests dry mass (g) 11 1.11 5.66 11 0.59 5.7 -3.51 0.003 Productive cells (%) 11 67.4 39.6 11 56.2 20.2 -1.59 0.12 Reused cells (%) 11 37.3 6.85 11 39.3 5.91 0.25 0.8 Adults produced/cell 11 1.09 0.13 11 0.98 0.09 -1.04 0.3 n = nest number; SE = standard error. Sociobiology 60(1): 96-100 (2013) 99 social wasps to feed the larvae (Gould & Jeanne, 1984; Raw, 1998; Nadeau & Stamp, 2003). Mead and Pratte (2002) sug- gested that the low availability of prey in a disturbed habitat negatively affects the food allocation rates for the colony, leading to deficient feeding of the larvae. Poorly fed larvae have longer development periods, thus reducing the capacity to reuse the comb to produce more adults. A reduction of the colony cycle in wasp nesting in an urban environment is another factor that may have con- tributed to the lower productivity in this environment. Al- though it was not possible to quantify this parameter, field observations during the study period indicated that colonies in the urban environment generally had shorter cycles than colonies in forest environments. Torres et al. (2011) noted that the colony cycle of M. consimilis in a urban environ- ment lasts approximately eight months, but can exceed one year in forest environments. The various human effects on the habitat can cause disturbances that could, on average, shorten the colony cycle. This appears to be a likely reason for the shortening of the colony cycle in M. consimilis, since in tropical regions, wasp colonies can ordinarily remain ac- tive year-round because climatic variables do not impose re- strictions on the colony’s activities (Gobbi & Zucchi, 1980; Giannotti, 1997; Torres et al., 2011). There was no evidence that the different wasp popu- lations use different strategies with respect to the use of the comb. The number of adults produced per cell as well as the proportions of reused and productive cells did not differ between the two populations. This result eliminates a pos- sible strategy of a difference in use of the comb between the two wasp populations. Montagna et al. (2010), studying this same species, demonstrated that old cells in the comb were more often used to produce adults. Similarly, Inagawa et al. (2001) observed an association between the proportion of productive cells and adult production, and did not find evidence for differentiated use of the comb among different populations of the social wasp Polistes snelleni (Saussure). Despite the considerable reduction in the colony pro- ductivity, the social wasp M. consimilis usually nested in urban environments. 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