J. HYM.RES. Vol. 17(1), 2008, pp. 110-115 Nest Structure, Seasonality, and Host Plants of Thygater aethiops (Hymenoptera: Apidae, Eucerini) in the Andes (VHG) Department of Ecology and Evolutionary Biology, Haworth Hall, 1200 Sunnyside Avenue, University of Kansas, Lawrence, Kansas 66045-7523, USA; email: [email protected] (MO) Instituto de Investigacidn de Recursos Bioldgicos Alexander von Humboldt, Villa de Leyva, Boyacii, Colombia; email: [email protected] Abstract.-Thygatw is a Neotropical genus of 30 species of solitary bees occurring from Mexico to Argentina. Information on the nesting biology is only available for a single species, T. analis, from southern Brazil. We studied the nest architecture, seasonality, and host plants of T. aethiops in two localities in the Eastern Andes of Colombia (- 2700-2900 m). Bees nested singly or forming aggregations in flat ground or sloping surfaces. Nests were deep (39-59 cm) and consisted of an unlined but smooth long main tunnel meandering downward from the surface. Nests had three to seven nearly vertical cells, which were located singly at the ends of short vertical tunnels that descended from the main tunnel. The older brood was located closer to the nest entrance, indicating a progressive nest development. Monthly sampling and appraisal of museum specimens showed that, although females were more commonly collected than males, both sexes were present year- round. We present a list of 32 plant species (27 genera in 18 families), including exotic, native, and cultivated plants used by T. aethiops in Colombia. The most noticeable differences from T. analis are in the pattern of nest development and seasonality. Thygatw aethiops builds nests in a progressive manner and it is likely to be multivoltine, whereas T. analis has a regressive nest development (i.e., older brood located far from the entrance) and a single generation per year. Long-term studies on different populations are required to determine if T, aethiops has continuous brood production or if larval diapause occurs at some point during the year. The purpose of this paper is to provide common species of the genus. Nests of this information on the nest architecture, sea- species are frequently found in grazing sonality and host plants of Thygater aethiops pastures, city parks, gardens, and along (Smith) at higher elevations in the Colom- sidewalks in towns and densely populated bian Andes. Thygater Holmberg is a Neo- cities such as BogotA (Gonzalez and Engel tropical genus of 30 species of solitary bees 2004, Gonzalez et al. 2005). occurring from Mexico to Argentina (Ur- We studied the nesting biology of T. ban 1967, 1999). The biology of Thygater is aethiops in two localities in the Eastern still poorly known. Information on the Andes of Colombia (- 2700-2900 m), and nesting biology is only available for a compared it with that of T. analis. We single species, T. analis (Lepeletier), from describe the nest and, based on monthly southern Brazil (Michener and Lange 1958, samplings and examination of museum Rozen 1974). Thygater aethiops is widely specimens, we show that both sexes of T. distributed in the Neotropical region, aethiops are present year-round, visiting occurring from Costa Rica to Argentina, flowers of exotic, native, and cultivated and is largely sympatric with T. analis in plants. The nesting biologies of both most of its range (Urban 1967). In Colom- species are very similar, except for the bia, T. aethiops is found between 1400 and pattern of nest development and seasonal- 3500 m of elevation and is the most ity. Thygater aethiops builds nests in a 300 Males 0Females 250 -Rainfall Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Fig. 1. Seasonal collections of Thygater aethiops at high altitudes (2700-2900 m) in the Andes of Colombia. Monthly surveys were done in 1999 in La Calera (Departamento of Cundinamarca), except in January, April, May, June and December. To complete the seasonal cycle, we used the number of museum specimens collected in La Calera and contiguous areas during those months. Females were more commonly collected than males (X2.001[221 = 534.1, P < 0.001) every month, and the female/male ratios were not homogeneous among months (X2,O5,111 = 28.9, P < 0.001). The total number of individuals is indicated at the top of each column. progressive manner (i.e., older brood lo- Mondofiedo is a semiarid area highly cated near the entrance, thus first to be disturbed by cattle ranching, gravel extrac- completed), and is likely to be multivoltine, tion, and waste dumping whose soils are whereas T. analis has regressive nest very compacted, shallow, and strongly development and a single generation per eroded (details in Gonzalez and Chiivez year. However, long-term studies on dif- 2004). The soils in La Calera are looser and ferent populations are required to deter- less eroded than in Mondofiedo, and mine if T. aethiops has continuous brood primarily used to grow potato, corn, beans, production or if larval diapause occurs at and wheat (IGAC 1996). Annual rainfall in some point during the year, and to detect La Calera is bimodal (Fig. I), with higher any variation in nest development depend- monthly precipitation than in Mondofiedo. ing on soil conditions. We excavated the nests using a geologcal pick, hand shovel, wood chisels and a MATERIAL AND METHODS pocketknife. Prior to excavation, and in order to trace the nest structure, we used a syringe Study sites and nest excavations to inject into the tunnel a slurry of plaster-of- The nesting biology of T. aethiops was Paris and water, which was allowed to studied by VG during December 2004 harden for about 2-5 minutes; we then in Mondofiedo (2720 m, 4"39'52.9"N, excavated the nests. We measured nest 74"17'2"W), whereas the seasonality and features in the field using a caliper. Maxi- host plants were studied in 1999 by MO in mum nest depth was measured from the nest La Calera (2900 m, 4"43'22"N, 73"5B118"W). entrance to the bottom of the deepest cell. Seasonality Table 1. Measurements (cm) of some structures of eight nests of Thygater aethiops. f: mean value, 2 : We collected bees on flowers and exam- standard error, R : range, N : sample size. Samples ined museum specimens to determine the varied in number because, to increase variation, we seasonal cycle of T. aethiops in La Calera. measured remains of nest structures (e.g., cells, Bees were collected when they appeared to tunnels) that we found during excavations. - - - be more active, frequently between 8:00 Nest structure .f + R N and 11:OO am, and from one to three days - - - Nest density (nests/m2) each month depending on weather condi- Inter-nest distance tions. Once we identified and sexed them, Maximum nest depth bees were released. Thygateu aethiops is the Tumulus only species of the genus occurring in La Length Calera. However, we decided to capture Width Nest entrance them because sometimes it was difficult for Main tunnel us to distinguish T. aethiops females from Length small, black workers of the bumble bee Diameter Bombus atratus Franklin (Apidae, Bombini). Laterals Males and females of T. aethiops were easy Length Diameter to distinguish in the field because, as in Cell depth other eucerines, males have longer anten- Number of cells per nest nae that surpass the base of the abdomen. Cell dimensions The monthly surveys in La Calera were Length Diameter done during the year of 1999, except in January, April, May, June, and December. To complete the seasonal cycle, we used the number of museum specimens collect- boldt (IAvH), Villa de Leyva, Boyaca, and ed in La Calera and contiguous areas the Museo Entomol6gico Francisco Luis during those months. We used a G-test Gallego, Universidad Nacional de Colom- (Sokal and Rohlf 2000) to compare percent- bia in Medellin (MEFLG). ages of males and females of T. aethiops, RESULTS and to determine if female/male (F/M) ratios were homogeneous among months. Nest architecture Host plants Nest measurements are given in Table 1. Nests were found singly or forming aggre- We recorded the plants visited by T. gations in flat ground or sloping surfaces. aethiops in La Calera, and also extracted The nest sites were either barren or sparsely floral records from data from specimen covered with grasses in areas frequently labels. We examined about 300 specimens well exposed to the sun (Figs 2, 3). Nest of T. aethiops deposited in the Snow entrances were circular and when nests Entomological Museum, University of were active, irregular tumuli extended Kansas, USA (SEM), National Museum of downward from the nest entrances. Nests Natural History, Washington, D.C. were deep, and consisted of an unlined but (USNM), and the following Colombian smooth long main tunnel meandering institutions: Laboratorio de Investigaciones downward from the surface (Fig. 4). Cells en Abejas, Departamento de Biologia (LA- were nearly vertical and placed singly at the BUN), and the Museo de Historia Natural, ends of short laterals, or vertical tunnels that Instituto de Ciencias Naturales (ICN) in descended from the main tunnel. Once the BogotA, Instituto de Investigaci6n de Re- cells were completed, these vertical tunnels cursos Biol6gicos Alexander von Hum- were filled with loose, coarse soil (Fig. 5). Figs 2-5. Nests of Thygatev aethiops. 2, single nest in flat ground; note the tumulus around nest entrance. 3, cluster of nests in a barren, sloping surface; all nest entrances are encircled and one of them is indicated by an arrow. 4, an excavated nest showing the meandering main tunnel, indicated by a white solid line. 5, detailed view of a cell in saggital section; A, main tunnel; B, short laterals filled with loose soil after cell completion; C, whitish spidenveb- like layer, likely a mass of mold hyphae, found in most of excavated cells (nest measurements in Table 1).