Seasonality of vespid species ( Hymenoptera : Vespidae ) in a central Brazilian cerrado

Foraging habitats as well as the tluctuations in vespid species' abundance in Mato Grosso State, Brazil, were deterrnined, through sampling effon per hour per collector in four cerrado sensu lato habitats, "campo úmido" (Cu), "campo sujo" (es), "cen'ado sensu stricto" (Css), and "gallery forest" (Mg), during four periods consisting of two dry (August 1988 and June 1989) and two wet (October and December 1988) season periods. For "campo úmido", sorne species seern to be highly seasonal, either in the dry or wet seasons, whereas very few species occur year-round. The abundance, species composition and richness varied between habitats types and between seasons.

There is much evidence suggesting that seasonal fluctuations in insect abundance are commonplace in the tropics.Previous studies in tropical regions have shown an increase in insect abundance from the dry season to the wet season (e. g.Wolda 1978,Tanaka&Tanaka 1982, Boinski & Scott 1988, Frith & Frith 1990).The major exceptions include sorne adult lepidopteran, bee, and Thysanoptera species (Owen & Chanter 1970, Heithaus 1979, Boinski & Scott 1988, Tanaka & Tanaka 1982).
TaxonomicaIly, the Vespidae of central Brazil are relati vely weIl known, mainly because of the works done by Fox in 1898 who described 10 species, and of Richards (1978) who registered most vespid species (85) of central Brazil.
However, their ecoJogy and life histories are still very límited (Henriques et al. 1992, Ramos & Diniz 1993, Diniz & Kitayama 1994).Species seasonal composition for any animal group ofthe cerrado are al so very poor known (Price et al.

RESULTS
Thirty six vespid species of the 50 sampled were collected in the four habitat types and used in the present work (Table 1).Polybia sericea (Olivier), P. ruficeps Schrotty, P. [iliacea (F), Synoeca surinama (L), Mischocyttarus drewseni de Saussure and Polistes subsericius de Saussure are the most abundant species in this region.
Po listes liliaciosus de Saussure, known as an amazonian wasp, was registered for the first time in this region (Table 1).
Thirteen species (35.2%) were restricted to one habitat type."Campo úmido" and gallery forest were the habitats where a ¡arger number of habitat-restricted species were encountered, but with a low number of individuals.Fifteen species (40.5%) were collected in two habitat types, 18.9% in three, and 5.4% in four habitats (Table 1 ).
Fluctuations in abundance and species richness between seasons was determined only forthose wasps collected in "campo úmido'?due to the constancy of sample collections during the four sample periods.Fourvespid species were collected only once, and during the wet season.Seven species were collected during both seasons, but the number of individuals collected was larger during the wet season than in the dry season (Table 2).At the end of dry season (August), 81.5% of the vespid species were collected in only one habitat, 7.5% in both two and three habitat types.
At the beginning of the wet season (October), 68.2% of the species were collected in one habitat, 18.2% in two, and 13.6% were small (Iess than 0.10).The highest similarity index was found between "cerrado sensu strieto" and "campo sujo" (0.530) at the beginning 01' wet season (October).

DISCUSSION
The 50 species represent an increase ol' 39 specíes i1' compared with Richards's (1978) numbers for this regíon (11 species).In spite of the poor sampling of gallery l'orest (only four hoursone collector) and the samplíng areas and restricted periods, the result may be considered very representative, since 43% of the known species of the whole state were collected.
The results shows that even for vespids, supposedly good flyers, a restriction in habitat occurs (Table 1).1).
The abundance and species ríchness in the dry season in "campo úmido" (64 individuals ol' 11 species) were much smaller than that l'ound during the wet season (132 individuals of 18 species) (Table 2).Similar results were obtained for other tropical regions (e. g.Tanaka & Tanaka 1982, Boinski & Scott 1988).
Gallery forest appears to be the most favorable habitat for wasps during the dry season, with larger numbers ol' species (63%) and individuals (70%).This result agrees with the argument that gallery forest "act as nueleus for re-colonization of deciduous habitat" (Forsyth 1980).Foraging habitats seem to vary between dry and wet seasons.Indeed, at least in "campo úmido", during the wet season, the number ol' species and specimens captured was as much as twice that which occurred during the dry season.
The results show evidence of the extreme importance of the moist habitats, 1'or the maintenance ol' vespid colonies during the long dry season in the "cerrado" area.Therefore, is it necessary to preserve all kinds of habitats in the cerrado, mainly due to [he faunal spatial and temporal variation, and especially because many species use only a specific habitat for nesting, usually which is more restricted than its foraging habital.
discusses the foraging habitats of vespid species and their seasonal actívity in the Brazilian central cerrado at Chapada dos Guimaraes, in Mato Grosso, during two dry and wet seasons.MATERIALS AND METHODS The work was carried out in Chapada dos Guimaraes (155°30' W; 14°52' S, -Mato Grosso State in central Brazil) in four habitat types of cerrado sensu lato vegetation.They included: a wet grassland (campo úmido -Cu), a scattered shrub area (campo sujo -Cs), a sparce shrubs and trees (cerrado sensu stricto -Css), and a gallery forest (Mata de galeria -Mg).AH these varieties of cerrado (savanna) habitats have been detailed elsewhere (e.g.Eiten 1972, Diniz & Kitayama 1994).The region of cerrado is characterized by a wet season of five to seven months, with an average precipitation 01' around 200 mm/month, and a long dry season 01' about five months, from May to September, with a mean monthly precipitation of les s than 30 mm.Vespids were collected during four series of collecting trips; the first three occurred in 1988, in August (end ofdry season), in October (beginning 01' wet season), and in December (middle of wet season).The last one occurred in June 1989 (beginning 01' dry season).In each habitat type a small area was selectcd of one to three ha in size for collecting wasps using an insect neL Each sampling period consisted of four hours of collection per collector, between seven to 11 a. m.The total sample size for each habitat type was variable, with four hr in gallery forest, 12 hr in "campo sujo" and 16 hr in both "cerrado sensu stricto" and "campo úmido".Voucher vespid species are deposited in the Entomology Collection of the Zoology Department of the University of Brasília.
species were captured in all three habitats: M. matogrossoensis, Polistes subsericius and Polybia serieea.At the middle of the wet season 73.7% ofthe species were captured in one habitat, 15.8% in two, and two species, Polistes eanadensis andPolístes subsericius, were collected in all three habitats.At the beginning of the dry season (June), only "campo úmido" and "cerrado sensu strieto" were sampled.Seventeen species (89.5%) were collected in one kind of habitat: of these, 63.2% in cerrado sensu strieto and 26.3% in "campo úmido".Two species were collected in both: Po listes subsericius andPolybia rLrfieeps.P. subsericius occurs in all habitattypes while foraging, during all seasons, but its nesting habitat is 'campo úmido' where it constructs its nest at the base of the grass (pers.obs.).Comparing the Shannon diversity índex among habitattypes andsampling períods, "cerrado sensu strieto" presented the highest diversity index during the dry season CH' = 1.004 in August 1988) and (H' = 1.035 in June 1989) while "campo úmido" at the beginning ol' the wet season (H' = 1.080 in October 1988), and "campo sujo" at the middle 01' the wet season (H = 0.849 in December 1988).The gallery forest presented in the dry season (August) the highest number of species but also the highest abundance what reflected in the diversity index (H' =0.058).Most ol' the coeft1cients of similarity (Bray & Curtís) Few species that nest in one habitat may hunt their preys or seek water in other habítats.Such exceptíons inelude Mischocyttarus mattog rossoensis Zikán, Po listes canadensis (L), and P. subserieius which nest in "campo úmido" (Diniz & Kitayama 1994) and forage in cerrado sensu strieto<Índ "campo sujo"; Polybia serieea, which nestsin cerrado sensu strieto, and Synoeea surinama .. which nests in gal!ery forest, and were found foraging in al! four habitats studied.Indeed, these Jast two wasp species are ¡arge and robust, therefore they can t1y a longer distance 1'rom their nests.Misehocyttarus drewseni was captured only in its nesting habitat (Table

TABLE 2
Species (!r vespid col/ected in campo úmido during fiJur sample periods, and species abundance and richness fúr each habitar type in Mato Grosso state (Brazil).