Foraging Behavior of the Swarm-Founding Wasp

899 Foraging Behavior of the Swarm-founding Wasp Polybia (Trichothorax) sericea (Hymenoptera, Vespidae): Daily Resource Collection Activity and Flight Capacity by Carlos C. Bichara Filho1, Gilberto M. de M. Santos1, Alberto B. dos Santos Filho1, Vanessa P. Santana-Reis1, Jucelho D. da Cruz1 & Nivar Gobbi2 ABSTRACT A study on the flight capacity and daily activity ofPolybia (Trichothorax) sericea (Olivier, 1791) was conducted. The main foraging activity for resource collection in Polybia sericea, the collection of liquid food (glucidics) had an Efficiency Index (EI) of 59.11, followed by prey (EI = 13.40) and wood pulp (EI = 2.92) collection. We observed a circadian rhythm for resource foraging activities, with mean angle at 11:07 hours (Rayleigh r = 0.71; P<0.05). The logistic regression model using the quasi-Newton method provided ap- propriate description for flight capacity in Polybia sericea (X2 = 79.62; gl = 1; p < 0.001). According to the model, the flight capacity of Polybia sericea is low, occurs in short distances, and this species presents an effective flying distance of approximately 75m measured from their nest and radium of ac- tion (flying and return to the nest) of 37.5m that means a foraging area of approximately 4418m2. Key words: Ethology, social wasps, foraging, daily activity, flight capacity. INTRODUCTION Social wasps feed on several kinds of food resources and food intake de- pends on the wasp development stage. The diet of adult wasps is composed primarily of energetic food, such as nectar, fruits and honeydew, whereas larvae feed mainly on animal proteins gathered from small animals. Because wasp colonies need to be supplied with prey and vegetal food resources, social 1Laboratório de Entomologia, Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana ([email protected], [email protected], [email protected], vanesreis@ yahoo.com.br, [email protected]) 2 Centro de Estudos de Insetos Sociais, UNESP ([email protected]) 900 Sociobiology Vol. 55, No. 3, 2010 wasps can behave as flower-visiting insects (gathering nectar) or as predators, thus reducing herbivory and contributing to the control of herbivore population sizes in natural ecosystems and in crops (Marques 1996; Santos et al. 2006). Social wasps are opportunistic and generalist predators, and engage in a wide range of mechanisms to locate and collect or hunt for the resources they need. Social wasps are abundant in temperate and tropical climates, and perform important roles in natural and anthropic ecosystems by applying selective pressure to plant and animal populations. Several studies have shown wasps' potential to control natural pest populations in crops, but the wide behavioral and ecological variety found in social wasps requires that a large number of specific and technical management techniques must be studied and developed before these wasps can be used as pest control agents in crops (Ravaret-Richter 2000). The potential use of social wasps in Integrated Pest Management Programs has in fact led to research in crop management, on topics such as the selec- tivity of insecticides to these insects (Santos et al. 2003) and the biological aspects of social wasps: nesting habits (Santos & Gobbi 1998), diet (Prezoto et al.2006), daily activity (Andrade & Prezoto 2001; Resende et al. 2001; Cruz et al. 2006a), and flight capacity (Santoset al. 1994; Santos et al. 2000; Cruz et al. 2006b). In this work we studied the flight capacity and daily activities for resource collection of Polybia sericea, to gather the necessary information needed for future programs on social wasp management in crop ecosystems. MATERIAL & METHODS The studies were conducted at the Universidade Estadual de Feira de Santana, in the municipality of Feira de Santana, State of Bahia, Northeast of Brazil (12° 16' LS; 38° 58' LW). The climate in this region is Tropical Semi-arid with annual average rainfall of 867mm. Resource collection activities per worker of seven colonies of Polybia sericea were quantified from October 2000 to April 2001. Each colony was observed continuously for twelve hours, from 6:00 to 18:00 h. We recorded every time wasps left and returned to the nest and also the kinds of resources collected and brought to the nest (prey, nectar, or building material). Bichara Filho, C.C. et al. — Foraging Behavior of Swarm-founding Wasps 901 The material collected and transported was identified according to wasp behavior and visualization of the material, following the methodology used by Prezoto et al. (1994). Wasps carrying prey or solid building material were easily identified due to their slow flight and visible load. Transportation of liquid food (nectar or other glucidic foods) was identified every time foragers engaged in trophalaxy with nest mates when they returned to the nest. The analysis of the rhythmic frequencies of wasp activities when searching for resources was conducted using the Rayleigh test and the circular statis- tics method (Batschelet 1981). A resource-search efficiency index was also calculated as follows: Efficiency Index (EI) = number of wasps returning to nest with resource / number of wasps returning to nest x 100 (Giannotti et al. 1995). The capacity ofPolybia sericea workers to return to nests was tested using the mark-release method (Gobbi 1978; Santos et al. 1994, Santos et al. 2000). Workers captured in nests were marked and released at pre-determined distances (50, 100, 150, 200, 250, and 300m). One-hundred and seventy-four individuals of Polybia sericea from three colonies in the post-emergence stage were marked. Wasps were captured in their nests with plastic containers. The captured individuals were anesthetized at -10o C for 3 to 4 minutes until paralyzed (Santos et al. 1994; Santos et al. 2000). Wasps were then marked with nitrocellulose lacquer-based ink in different colors according to distance. After recovering from the anesthesia, wasps were released at predetermined distances. Release points were marked in straight lines, beginning at the departure nests. Two nights after wasps were released, all individuals in the nest were collected and the marked wasps that had returned to the colony were counted. The logistic regression method (Hosmer & Lemesshow 1989) was used to design the model that describes the relation between the proportion of wasps that returned to the nests and distance. The model tests the dependence of binary variables (here, the return of each wasp as given by presence or absence of the marked specimen) on a quantitative variable (distance). The statistical significance of the parameters was assessed by the chi-square test. The logistic model is described by the Equation: P(y=1)= ea+bx / 1+ ea+bx Where P = probability of wasp return; a, b are parameters of the equation; b represents the intensity of the effect of distance on probability of return; e represents the neperian algarism; and x the distance from the nest. 902 Sociobiology Vol. 55, No. 3, 2010 RESULTS & DISCUSSION The main resource-collection activity inPolybia sericea was the collection of glucidic food (carbohydrates) (Fig. 1), with an Efficiency Index (EI) of 59.11% of the wasps that returned to the nest, or 78.37% of all wasps that returned to the nest with some kind of identified load (prey, nectar or pulp). The second main item collected was prey, with EI of 13.40% of all wasps returning to the nest. Last, an EI= 2.92% was found for wasps that returned to the nest with wood pulp (cellulose). A 15.50% failure rate and 9.07% non-identified behavior rate also occurred. There is a clear decrease in the Polybia sericea nest return rate as the distances from the nest increase (Fig. 2). Return rates observed for Polybia sericea ranged from 89.3 % at 50 meters from the nest to 3.6 % at 300 meters from the nest. The predominance of nectar collection among foraging wasp workers has been widely reported for several social wasp species (Giannotti et al. 1995; Fig. 1. Daily activities to collect food resources and pulp for nest building by workers of Polybia sericea throughout the day. Bichara Filho, C.C. et al. — Foraging Behavior of Swarm-founding Wasps 903 Resende et al. 2001; Andrade & Prezoto 2001). The recurrence of nectar collection as main foraging activity among social wasps clearly shows the importance of energetic food for the colonies, both for adults and larvae (Andrade & Prezoto 2001). Several species of social wasps, including Polybia sericea store nectar as honey to be used in times of scarcity (Hunt et al. 1998, 2003). After an extensive literature review on the topic, Ravaret-Richter (2000) concluded that low availability of carbohydrates can limit the development of social wasp colonies, and effectively illustrates the importance of carbohydrates in determining the size of social wasp populations. The first foraging wasp of all seven colonies ofPolybia sericea started resource collection activities at 6:12h, the last one to return was at 18:00 hours, and activities concentrated around 12:00h (Fig. 1). Circular statistical analysis revealed a circadian rhythm for resource collection activities by Polybia sericea. The time for resource collection corresponding to the mean angle was 11:07h (Rayleigh r = 0.71; P<0.05). According to the circular statistical analysis, flights to collect materials to build the nest were concentrated in the mid-morning (with acrophase at 9:06h; Rayleigh r = 0.87; P<0.05), while flights to search for prey and to Fig. 2 – Probability for workers of Polybia sericea to return to colonies, Feira de Santana, Bahia, Brazil, June 2000. (Logistic Regression Method). d=distance. 904 Sociobiology Vol. 55, No. 3, 2010 collect nectar were both concentrated in late morning (hunting prey with acrophase at 11:21h; Rayleigh r = 0.77; P<0.05, and nectar collecting with acrophase at 11:27h, Rayleigh r = 0.68; P<0.05).

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