Impact of herbicides on a predator ant guild

O impacto provocado pelos herbicidas alachlor, metolachlor, dimethenamid e diuron em uma guilda de formigas predadoras, foi avaliado em Dourados, MS (22°13'16"S e 54°48'20"W). Duas áreas testemunhas, com e sem capina, foram utilizadas neste estudo. As formigas foram amostradas através de duas iscas de sardinha por parcela, com quatro repetições por tratamento. Solenopsis sp. foi a espécie mais abundante e freqüente em relação às cinco espécies encontradas nas iscas. Houve um decréscimo no número de formigas nas parcelas pulverizadas e nas testemunhas por um período de 40 dias, não tendo sido encontrada diferença significativa entre as parcelas com e sem herbicidas.The effects of alachor, metolachlor, dimethenamid and diuron herbicides on a predator ant guild were evaluated in Dourados, MS (22°13'16"S and 54°48'20"W). Two control areas, with and without weeds, were used in the study. The ants were sampled using two sardine baits per plot with four replications per treatment. Solenopsis sp. was the most abundant ant species among the five sampled species. There was a decrease in the number of ants in the treatment and control plots afier 40 days. No significant differences were found between the herbicide and control plots.

Nest Architecture, Colony Productivity, and Duration of Immature Stages in a Social Wasp, Mischocyttarus consimilis

This study examined the nest architecture, colony productivity, and duration of the immature stages of the social wasp Mischocyttarus consimilis Zikáán (Hymenoptera: Vespidae). The study was carried out under field conditions. Nests of M. consimilis consist of a single uncovered comb, which is attached to the substratum by a single petiole. The data for the nest architecture showed a positive and significant correlation between the size of the comb and the diameter of the petiole, and also between the height and diameter of the cells. The nests were constructed on horizontal, vertical, and sloping substrata with no apparent preference for a specific orientation. The colonies produced 72.9 cells and 40.7 adults on average. The mean frequency of productive cells was 33.3%, and 19.4% of the cells were reused. The mean duration of the immature stages combined was 69.7 days and the egg, larval, and pupal stages had mean durations of 14.9, 36.0, and 18.8 days, respectively. The duration of each immature stage was significantly shorter in the warmhumid season, and the larval and pupal stages were shorter during the colony pre-emergence stage

Comunidade de Carabidae (Coleoptera) em manchas florestais no Pantanal, Mato Grosso do Sul, Brasil

Neste trabalho foi estudado o efeito do tamanho, susceptibilidade à inundação e complexidade vegetacional na estrutura de comunidade de Carabidae (Coleoptera) em ilhas de vegetação arbórea (capões de mata) no Pantanal sul-mato-grossense, sub-regiões Miranda e Abobral. Os dados foram obtidos no período de outubro de 1998 a outubro de 1999 em seis capões de mata, através de 30 armadilhas de queda ("pitfall traps") instaladas por seis dias, mensalmente, no interior dos capões. Foram capturados 2.071 indivíduos, distribuídos em 64 espécies. Negrea scutellaris (Dejean, 1831) e uma espécie não-identificada de Lebiini foram as espécies mais abundantes (com 472 e 464 indivíduos, respectivamente). A distribuição gregária e o elevado número de espécies pouco abundantes encontrados pode refletir o padrão de disponibilidade de recursos das regiões tropicais. Entre as variáveis estudadas, apenas a complexidade vegetacional explicou a variação da riqueza de espécies nos capões de mata. A composição das espécies não foi explicada por nenhuma das variáveis avaliadas. Possivelmente a variação em tamanho e em complexidade vegetacional dos capões não seja tão evidente para demonstrar estas relações e a composição das espécies esteja variando mais em escala regional do que em escala local

Nest structure and occurrence of three species of Azteca (Hymenoptera, Formicidae) in Cecropia pachystachya (Urticaceae) in non-floodable and floodable pantanal areas

Thirty Cecropia pachystachya trees were examined in non-floodable and floodable areas to investigate the association between C. pachystachya and Azteca ants in the Pantanal of Mato Grosso do Sul, Brazil. The species Azteca ovaticeps, Azteca isthmica, and Azteca alfari were found nesting inside domatia of C. pachystachya. A. ovaticeps was the most frequent species in the trees in the floodable area, while A. isthmica and A. alfari, in the non-floodable area. A. ovaticeps and A. isthmica maintained more entrance/exit holes in comparison to A. alfari. All Azteca species maintained entrance/exit holes in the closest domatia to the apical area of the branch, due to proximity to Müllerian and pearl bodies, suggesting that these species of Azteca were influenced by their environment during evolution and became specialized. All internodal septa of each examined branch were perforated by ants, indicating the branches were inhabited by a single colony

Colony cycle of the social wasp Mischocyttarus consimilis Zik\ue1n (Hymenoptera, Vespidae)

Colony cycle of the social wasp Mischocyttarus consimilis Zikán (Hymenoptera, Vespidae). This study describes some aspects of the colony cycle of the Neotropical social wasp Mischocyttarus consimilis, from data obtained under field conditions. Our results showed that the colony cycle in M. consimilis is annual and asynchronous in relation to the months of the year. The colonies remained active for approximately eight months. Most of the abandonments were associated with natural causes, and were most frequent in the pre-emergence stage. The nests were constructed preferentially in man-made structures, especially in sites protected from direct sunlight and rain. Colony foundation was either by haplometrosis or pleometrosis, being the first form predominant

Description of the Immature and Adult Stages of Ectatomma vizottoi (Formicidae: Ectatomminae)

We estimated the number of larval instars of the ant Ectatomma vizottoi (Ectatomminae), by measuring the maximum width of the head capsules of 208 larvae and the morphology of the immature stages (eggs, larvae and pupae) and adults. There are three larval instars during the post-embryonic development. The reproductive eggs are dark brown. Hairs are present beginning with the first instar, are uniformly distributed over the larval body, and do not vary in length in the three instars. Pupae are protected by a light-brown silk cocoon. Adults of the worker and queen castes can be differentiated by size

Ant community in natural fragments of the Brazilian wetland: species–area relation and isolation

Biogeographic theory has been given much attention for its potential application to biodiversity conservation in areas fragmented through anthropic action. The objective of this study was to determine whether ant community structure established in natural woodland fragments immersed in a matrix of natural grasslands could be explained by this theory. We therefore investigated whether the relationship between species richness and both area and isolation that have previously been found in anthropogenically formed forest fragments are applicable to naturally formed forest fragments. The sampling consisted of eight natural woodland fragments with varying areas and degrees of isolation. Sampling was undertaken proportionally to the fragment size, and each sampling point was spaced at least 10 m apart. Ants were collected from each point through arboreal and epigeic “pitfall” traps. In addition, five epigeic traps were placed 100 m from each sampled fragment in the adjacent grassland. A total of 81 ant species were sampled. Total and epigaeic species richness increased with size of area and fragment isolation. However, arboreal ants responded positively only with respect to increasing area, but not with isolation. Moreover, specialist and generalist species richness had a positive relationship with area, but not with isolation. Biogeographic Theory can only be applied to some of the patterns found in the natural fragments in the present study. This positive relationship of ant richness and isolation suggests that these environments bear unique characteristics and therefore, must be regarded as conservation targets. The results obtained in this study suggest the need for further studies, to reinforce the importance of biodiversity conservation of this characteristic habitat in the Pantanal