Würzburg, University, Diss., 2002.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Leafcutter ants (Atta spp.) are Neotropical herbivores that play important ecological roles, but are also notorious pests, causing millions of dollars in annual damage to agriculture across their range. Three species, A. cephalotes, A. sexdens, and A. laevigata, stand out as the most widespread and economically important. Two studies were conducted using these three species to better understand their biogeography and evolutionary history. First, using a maximum entropy niche-based modeling approach, locality information for these three species was used to (1) accurately describe the current geographic range of each species, (2) determine what factors limit their respective ranges, and (3) identify areas where each species is capable of becoming established. By comparing the model's predictions with published records and targeted surveys, a more accurate picture of the current ranges of each species was obtained. Areas in which a species does not currently occur, but that are predicted to be suitable, may reveal the ecological factors limiting the spread of these species. Such areas may also represent potential sites for invasion by these ants, with potentially devastating results. Second, these species were used to test the leading biogeographic hypotheses on the origins of high Amazonian diversity, an issue that remains unresolved despite much research. The hypotheses are the riverine barrier, Pleistocene refugia, and marine incursion hypotheses, each of which has been tested almost exclusively on vertebrates. A comparative, molecular phylogeographic approach was combined for the first time with paleodistribution modeling for the last glacial maximum to test these hypotheses on an insect. All analyses rejected the predictions of the riverine barrier hypothesis for each species. Tests of gene tree topology could not reject the refugia hypothesis for A. sexdens, while population-genetic and historical demography analyses failed to reject both the refugia and marine incursion hypotheses for all three species. However, coalescent-based estimates of population divergences for each species suggest that current population structure formed recently, suggesting that Miocene marine incursions have not promoted diversification in these species. Therefore, of the hypotheses examined, only the Pleistocene refugia hypothesis can explain the current population structure of Amazonian leafcutter ants.

As formigas cortadeiras (Hymenoptera-Formicidae) estão distribuídas desde o sul dos Estados Unidos até a Argentina. São herbívoros comuns de florestas que coletam material vegetal para cultivar um fungo mutualista específico. São conhecidas pelo seu papel ecológico na aeração do solo, na infiltração da água e na ciclagem de nutrientes. Atividades humanas, como o desmatamento e a agricultura, afetam o ambiente, alterando também o comportamento das saúvas, que acabam atacando os espécimes cultivados. Devido aos prejuízos causados à agricultura, novos inseticidas específicos são necessários. Muitos trabalhos têm sido desenvolvidos usando metabólitos secundários para essa finalidade. Este trabalho tem como objetivo avaliar o efeito da cafeína na mortalidade de Atta sexdens rubropilosa (Forel, 1908) e no crescimento in vitro de seu fungo mutualístico Leucoagaricus gongylophorus (Möller) Singer (Leucocoprineae: Agaricaceae), obtidos de sauveiros mantidos em laboratório. Foram utilizadas quatro concentrações de cafeína, 0,01%, 0,05%, 0,10% e 0,50%. Mortalidade das formigas foi avaliada pelo ensaio de ingestão, acrescentando a cafeína a dietas artificiais sólidas. A cafeína foi incorporada ao meio de cultura para medir a sua influência no crescimento in vitro. Independente das concentrações de cafeína, esse metabólito parece atuar como repelente para a saúvas. A respeito do fungo, quanto maior a concentração de cafeína, menor o crescimento in vitro. Inibição do crescimento foi observada em 0,10% e 0,50% e morte do fungo foi observada em algumas amostras Em conclusão, os resultados sugerem que a cafeína pode ser usada como fungicida, sendo adicionada a iscas que serão coletadas pelas formigas e carregada aos ninhos, causando a redução do fungo e/ou a morte e consequentemente, a morte das formigas. / The leaf-cutting ants (Hymenoptera-Formicidae) are found from south of United States to Argentina. They are common florest herbivorous which collect plant material to feed a specific mutualist fungus. These insects are known by their ecological role at soil aeration, water permeation and nutrient cycling. Human activities, like deforestation and agriculture, affect the environment, affecting the behavior of leaf-cutting ants, which start to attack the crops. Due to crops lost, new specific pesticides are needed. Several researches have been developed using secondary metabolites for this purpose. The present work aimed to evaluate the effect of caffeine at Atta sexdens rubropilosa (Forel, 1908) mortality, and at in vitro growth of the mutualist fungus Leucoagaricus gongylophorus (Möller) Singer (Leucocoprineae: Agaricaceae), collected from laboratory nests. Four caffeine concentrations were tested: 0.01%, 0.05%, 0.10% and 0.50%. Ant\'s mortality was evaluated by ingestion assay, adding caffeine to artificial diets. Caffeine was added to culture medium, to measure its influence on in vitro fungus growth. Despite caffeine concentrations, this compound seems to act as repellent to ants. Concerning to the fungus, the higher the caffeine concentration, the lower the in vitro fungus growth. Growth inhibition was observed at both 0.10% and 0.50% concentrations and death of fungus was observed in some samples. In conclusion, the results suggest that caffeine could be used as fungicide, being added to baits which could be collected by ants and carried to the nests, causing fungus reduction and/or death and consequently, the death of the nests.

A agricultura é uma das atividades mais importante que exercemos e, no decorrer do tempo vem sofrendo mudanças sustentáveis, aquelas que amenizam os impactos ambientais dessa atividade. As saúvas são os principais insetos-praga dos cultivos florestais, uma vez que causam severos danos às plantas. Essas formigas podem causar a desfolha total, tanto de mudas como de plantas adultas, levando as plantas à morte, o ataque pode variar de acordo com a idade das plantas e os prejuízos causados também. Novos estudos estão sendo realizados para o uso de plantas com propriedades inseticidas no controle de formigas-cortadeiras e a espécie Azadirachta indica é uma das espécies mais estudadas da família Meliaceae, sendo que seus efeitos inseticidas foram comprovados em cerca de 400 espécies de insetos. Diversos métodos alternativos no controle de insetos-praga estão sendo avaliados, dentre eles, alguns agentes biológicos como o fungo entomopatogênico Metarhizium anisopliae. O reconhecimento da presença de um organismo invasor é fundamental para o sistema imunológico de qualquer individuo por isso após a invasão de algum patógeno, os hemócitos que circulam livremente na hemolinfa migram para o local da infecção, fagocitam e destroem os invasores. Baseando-se nesses princípios da imunologia das formigas-cortadeiras e no fato de que algumas plantas possuem compostos secundários com ação toxica contra alguns insetos, buscou-se estudar as propriedades do óleo de nim contra formigas-cortadeiras e avaliar a patogenicidade do fungo Metarhizium anisopliae quando aplicado juntamente com óleo de nim. Na metodologia utilizada, foi aplicado de óleo de nim ou 1 μl de óleo de soja, dependendo do tratamento, no dorso mais 1μl no aparelho bucal de cada formiga operária das espécies Atta sexdens e Atta laevigata, com exceção do controle onde nada foi aplicado. Em seguida, foram aplicados 2 μl de uma suspensão de Metarhizium anisopliae na concentração de 107 conídios mL-1. O óleo de nim provocou mortalidade significativa de operárias de Atta laevigata. No entanto, a sua associação com um fungo entomopatogênico não influenciou os resultados, pois a mortalidade desse tratamento não diferiu estatisticamente do tratamento realizado apenas com óleo de soja. Em Atta sexdens a associação com o fungo foi necessária para que o resultado fosse estatisticamente diferente do grupo controle, isto é, o tratamento com óleo de nim puro mais o fungo apresentou diferença estatística significativa comparado aos demais tratamentos. A substância azadiractina, presente no óleo de nim, deve ser melhor estudada a fim de se verificar seus efeitos imunossupressores em outras espécies de formigas-cortadeiras, sua ação fungicida, bem como sua influência em outros aspectos fisiológicos desses insetos pragas. / Agriculture is one of the most important human activities and it has undergone sustainable changes over time. Recently, measures have been taken in order to mitigate the environmental impacts of this activity. Leaf-cutting ants are the main insect pests of forest crops, since they cause severe damage to plants. These ants can cause total defoliation, both in seedlings and in adult plants, causing death of the plants. Damages vary according to the age of the plants. Studies are being conducted to use insecticides derived of plants in leaf-cutting ant’s control. Azadirachta indica is one of the most studied species of Meliaceae family and its insecticides properties have been demonstrated in about 400 species of insects of different orders. Furthermore, several alternative methods to control insect are being evaluated, including some biological agents such as entomopathogenic fungi. In this sense, Metarhizium anisopliae is one of the most promising species. Recognition of the presence of an invading organism is critical to the immune system of any individual. So, after pathogen invasion, hemocytes freely circulating in the hemolymph migrate to the site of infection, phagocyte and destroy invaders. Here, it was applied neem 1 ul of oil or soybean oil, depending on the treatment, on the back and 1μl in the mouthparts of each ant, with the exception of control where nothing was applied. Subsequently, it was prepared a fungal suspension of Metarhizium anisopliae at a concentration of 107 conidia ml-1, which was applied to the dorsum of each worker (2 μl). Neem oil caused significant mortality of Atta laevigata worker; its association with entomopathogenic fungus did not influence the results because the treatments with only oil produced the same results. In Atta sexdens, the association of neem oil with M. anisopliae, produced significant mortality when compared to other treatments. The effects of neem oil vary according to insect species. Azadirachtin should be further studied in order to verify their immunosuppressive effects in other species of leaf-cutting ants, their fungicidal action and their influence on other physiological processes of these insect pests.

As formigas cortadeiras (Hymenoptera-Formicidae) estão distribuídas desde o sul dos Estados Unidos até a Argentina. São herbívoros comuns de florestas que coletam material vegetal para cultivar um fungo mutualista específico. São conhecidas pelo seu papel ecológico na aeração do solo, na infiltração da água e na ciclagem de nutrientes. Atividades humanas, como o desmatamento e a agricultura, afetam o ambiente, alterando também o comportamento das saúvas, que acabam atacando os espécimes cultivados. Devido aos prejuízos causados à agricultura, novos inseticidas específicos são necessários. Muitos trabalhos têm sido desenvolvidos usando metabólitos secundários para essa finalidade. Este trabalho tem como objetivo avaliar o efeito da cafeína na mortalidade de Atta sexdens rubropilosa (Forel, 1908) e no crescimento in vitro de seu fungo mutualístico Leucoagaricus gongylophorus (Möller) Singer (Leucocoprineae: Agaricaceae), obtidos de sauveiros mantidos em laboratório. Foram utilizadas quatro concentrações de cafeína, 0,01%, 0,05%, 0,10% e 0,50%. Mortalidade das formigas foi avaliada pelo ensaio de ingestão, acrescentando a cafeína a dietas artificiais sólidas. A cafeína foi incorporada ao meio de cultura para medir a sua influência no crescimento in vitro. Independente das concentrações de cafeína, esse metabólito parece atuar como repelente para a saúvas. A respeito do fungo, quanto maior a concentração de cafeína, menor o crescimento in vitro. Inibição do crescimento foi observada em 0,10% e 0,50% e morte do fungo foi observada em algumas amostras Em conclusão, os resultados sugerem que a cafeína pode ser usada como fungicida, sendo adicionada a iscas que serão coletadas pelas formigas e carregada aos ninhos, causando a redução do fungo e/ou a morte e consequentemente, a morte das formigas. / The leaf-cutting ants (Hymenoptera-Formicidae) are found from south of United States to Argentina. They are common florest herbivorous which collect plant material to feed a specific mutualist fungus. These insects are known by their ecological role at soil aeration, water permeation and nutrient cycling. Human activities, like deforestation and agriculture, affect the environment, affecting the behavior of leaf-cutting ants, which start to attack the crops. Due to crops lost, new specific pesticides are needed. Several researches have been developed using secondary metabolites for this purpose. The present work aimed to evaluate the effect of caffeine at Atta sexdens rubropilosa (Forel, 1908) mortality, and at in vitro growth of the mutualist fungus Leucoagaricus gongylophorus (Möller) Singer (Leucocoprineae: Agaricaceae), collected from laboratory nests. Four caffeine concentrations were tested: 0.01%, 0.05%, 0.10% and 0.50%. Ant\'s mortality was evaluated by ingestion assay, adding caffeine to artificial diets. Caffeine was added to culture medium, to measure its influence on in vitro fungus growth. Despite caffeine concentrations, this compound seems to act as repellent to ants. Concerning to the fungus, the higher the caffeine concentration, the lower the in vitro fungus growth. Growth inhibition was observed at both 0.10% and 0.50% concentrations and death of fungus was observed in some samples. In conclusion, the results suggest that caffeine could be used as fungicide, being added to baits which could be collected by ants and carried to the nests, causing fungus reduction and/or death and consequently, the death of the nests.

This study investigates the foraging behaviour of grass-cutting ants, Atta vollenweideri, with specific consideration of the following issues: (a) cutting behaviour and the determination of fragment size, (b) the effect of load size on transport economics, (c) division of labour and task-partitioning. Grass-cutting ants, Atta vollenweideri, harvest grass fragments that serve as substrate for the cultivation of a symbiotic fungus. Foragers were observed to cut grass fragments across the blade, thus resulting in longish, rectangular-shaped fragments in contrast to the semicircular fragments of leaf-cutting ants. Cutting was very time-consuming: In tough grasses like the typical grassland species Paspallum intermedium and Cyperus entrerrianus, cutting times lasted up to more than 20 minutes per fragment and roughly half of all initiated cutting attempts were given up by the ants. Foragers harvesting the softer grass Leersia hexandra were smaller than those foraging on the hard grasses. Fragment size determination and the extent of size-matching between ant body size and fragment size was investigated regarding possible effects of tissue toughness on decision-making and as a function of the distance from the nest. Tissue toughness affected decision-making such that fragment width correlated with ant body mass for the hard grass but not for the soft one, suggesting that when cutting is difficult, larger ants tend to select wider grasses to initiate cutting. The length of the fragments cut out of the two grass species differed statistically, but showed a large overlap in their distribution. Distance from the nest affected load size as well as the extent of size-matching: Fragments collected directly after cutting were significantly larger than those carried on the trail. This indicates that fragments were cut once again on their way to the nest. Size-matching depended on the trail sector considered, and was stronger in ants sampled closer to the nest, suggesting that carriers either cut fragments in sizes corresponding to their body mass prior transport, or transferred them to nestmates of different size after a short carrying distance. During transport, a worker takes a fragment with its mandibles at one end and carries it in a more or less vertical position. Thus, load length might particularly affect maneuverability, because of the marked displacement of the gravitational center. Conversely, based on the energetic of cutting, workers might maximise their individual harvesting rate by cutting long grass fragments, since the longer a grass fragment, the larger is the amount of material harvested per unit cutting effort. I therefore investigated the economics of load transport by focusing on the effects of load size (mass and length) on gross material transport rate to the nest. When controlling for fragment mass, both running speed of foragers and gross material transport rate was observed to be higher for short fragments. In contrast, if fragment mass was doubled and length maintained, running speed differed according to the mass of the loads, with the heavier fragments being transported at the lower pace. For the sizes tested, heavy fragments yielded a higher transport rate in spite of the lower speed of transport, as they did not slow down foragers so much that it counterbalanced the positive effects of fragment mass on material transport rate. The sizes of the fragments cut by grass-cutting ants under natural conditions therefore may represent the outcome of an evolutionary trade-off between maximising harvesting rate at the cutting site and minimising the effects of fragment size on material transport rates. I investigated division of labour and task partitioning during foraging by recording the behaviour of marked ants while cutting, and by monitoring the transport of fragments from the cutting until they reached the nest. A. vollenweideri foragers showed division of labour between cutting and carrying, with larger workers cutting the fragments, and smaller ones transporting them. This division was absent for food sources very close to the nest, when no physical trail was present. Along the trail, the transport of fragment was a partitioned task, i.e., workers formed bucket brigades composed of 2 to 5 carriers. This sequential load transport occurred more often on long than on short trails. The first carriers of a bucket brigade covered only short distances before dropping their fragments, turned back and continued foraging at the same food source. The last carriers covered the longest distance. There was no particular location on the trail for load dropping , i.e., fragments were not cached. I tested the predictions of two hypotheses about the causes of bucket brigades: First, bucket brigades might occur because of load-carriage effects: A load that is too big for an ant to be carried is dropped and carried further by nestmates. Second, fragments carried by bucket brigades might reach the nest quicker than if they are transported by a single carrier. Third, bucket brigades might enhance information flow among foragers: By transferring the load a worker may return earlier back to the foraging site and be able to reinforce the chemical trail, thus recruitment. In addition, the dropped fragment itself may contain information for unladen foragers about currently harvested sources and may enable them to choose between sources of different quality. I investigated load-carriage effects and possible time-saving by presenting ants with fragments of different but defined sizes. Load size did not affect frequency of load dropping nor the distance the first carrier covered before dropping, and transport time by bucket brigades was significantly longer than by single carriers. In order to study the information transfer hypothesis, I presented ants with fragments of different attractivity but constant size. Ants carrying high-quality fragments would be expected to drop them more often than workers transporting low-quality fragments, thus increasing the frequency of bucket brigades. My results show that increasing load quality increased the frequency of bucket brigades as well as it decreased the carrying distance of the first carrier. In other words, more attractive loads were dropped more frequently and after a shorter distance than less attractive ones with the first carriers returning to the foraging site to continue foraging. Summing up, neither load-carriage effects nor time-saving caused the occurrence of bucket brigades. Rather, the benefit might be found at colony level in an enhanced information flow. / Die vorliegende Dissertation untersucht das Sammelverhalten der grasschneidenden Ameise Atta vollenweideri, unter besonderer Berücksichtigung der folgenden Themen: (a) das Schneideverhalten und die Wahl der Fragmentgröße, (b) der Effekt der Fragmentgröße auf den Transport und (c) die Arbeitsteilung während des Sammelns. Die Grasschneiderameise Atta vollenweideri sammelt Grasfragmente, die im Nest zerkleinert werden, um darauf einen symbiotischen Pilz zu züchten. Die Sammlerinnen schnitten ihre Fragmente quer über die Halmbreite, so dass längliche, rechteckige Fragmente entstehen, im Gegensatz zu den halbkreisförmigen Fragmenten der Blattschneiderameisen. Das Schneiden war ein sehr zeitaufwendiger Prozess: Bei harten Gräsern wie die für die Savanne typischen Paspallum intermedium und Cyperus entrerrianus betrug die Schneidezeit pro Fragment bis zu 20 Minuten oder länger. Etwa die Hälfte aller begonnenen Schnitte wurde von den Ameisen aufgegeben. Sammlerinnen, die das weichere Gras Leersia hexandra ernteten, waren kleiner als diejenigen, die die harten Gräser schnitten. Ich untersuchte, inwiefern die Härte des geschnittenen Materials und die Entfernung vom Nest einen Einfluss auf die Wahl der Fragmentgröße und auf die Stärke der Korrelation zwischen Ameisen- und Fragmentgröße hat. Die Länge „harter“ und „weicher“ Fragmente unterschied sich zwar statistisch, zeigte aber eine starke Überlappung. Die Korrelation zwischen Ameisen- und Fragmentgröße existierte bei dem harten Gras, nicht jedoch bei dem weichen Gras. Das heißt, dann wenn das Schneiden schwierig wird, suchen sich größere Tiere breitere Halme zum Schneiden (bzw. kleinere Tiere schmalere Halme). Sowohl Fragmentgröße als auch die Stärke der Korrelation zwischen Fragment- und Ameisengewicht hing von der Entfernung zum Nest ab: Fragmente, die ich direkt nach dem Schneiden sammelte, waren signifikant größer als solche, die ich auf dem Trail sammelte. Dies bedeutet, dass die Fragmente auf ihrem Weg zum Nest ein zweites Mal geschnitten wurden. Die Korrelation zwischen Fragment- und Ameisengewicht war um so stärker, je näher am Nest die Tiere gesammelt wurden, was bedeutet, dass die Trägerinnen entweder die Fragmente vor dem Transport entsprechend ihrer eigenen Körpergröße geschnitten hatten, oder aber dass die Fragmente nach einer kurzen Strecke an Nestgenossinnen anderer Körpergröße übergeben wurden. Um ein Fragment zu transportieren, packen A. vollenweideri-Arbeiterinnen das Fragment mit den Mandibeln an einem Ende und halten es mehr oder weniger senkrecht. Daher ist zu vermuten, dass lange Fragmente schwieriger zu manövrieren sind, da sich der Schwerpunkt mit zunehmender Länge nach oben verschiebt. Lange Fragmente haben jedoch den Vorteil, dass die Menge an geerntetem Material pro Schneideversuch größer ist als bei kurzen; Arbeiterinnen könnten also ihre Sammelrate jedoch dadurch maximieren, dass sie möglichst lange Fragmente schneiden. Im Hinblick auf die Schneidekosten wären dann also lange Fragmente vorteilhaft, im Hinblick auf den Transport hingegen kurze. Ich untersuchte daher den Effekt der Fragmentgröße (Länge und Gewicht) auf den Transport. Waren die Fragmente gleich schwer aber unterschiedlich lang, war die Laufgeschwindigkeit der Arbeiterinnen und damit auch die Eintragsrate bei den kurzen Fragmenten höher. Wenn hingegen das Fragmentgewicht verdoppelt und die Länge konstant gehalten wurde, unterschied sich die Laufgeschwindigkeit entsprechend dem Gewicht der Fragmente: Schwere Fragmente wurden langsamer getragen als leichte. Die Transportrate hingegen war für die schwereren Fragmente höher, da der höhere Eintrag aufgrund des zusätzlichen Gewichts die langsamere Laufgeschwindigkeit aufwog. Die Fragmentgrößen, die Grasschneiderameisen unter natürlichen Bedingungen schneiden, könnten daher im Laufe der Evolution aufgrund des Kompromisses entstanden sein, einerseits die Ernterate am Schneideort zu maximieren und andrerseits die negativen Effekten der Fragmentgröße auf den Transport möglichst gering zu halten. Ich untersuchte die Arbeitsteilung während des Sammelns, indem ich das Verhalten schneidender Tiere beobachtete und indem ich den Fragmenttransport vom Schneideplatz bis zum Nest verfolgte. Schneiden und Tragen von Fragmenten wurde von unterschiedlichen Arbeiterinnengruppen durchgeführt, wobei größere Sammlerinnen die Fragmente schnitten und kleinere sie transportierten. Diese Arbeitsteilung existierte nicht, wenn die Futterquelle sehr nah war, wenn also kein sichtbarer Trail vorhanden war. Der Transport selbst war ebenfalls unterteilt: Die Trägerinnen bildeten Arbeitsketten, die aus zwei bis fünf Trägerinnen bestanden. Diese Arbeitsketten kamen häufiger auf langen als auf kurzen Trails vor. Die ersten Trägerinnen einer solchen Arbeitskette legten nur eine kurze Strecke zurück, bevor sie das Fragment ablegten oder an eine Nestgenossin abgaben. Sie kehrten dann zur gleichen Futterquelle zurück und sammelten weiter. Die letzten Trägerinnen einer Arbeitskette transportierten die Fragmente über die größte Strecke. Es gab keine speziellen Orte auf dem Trail, an denen die Fragmente abgelegt wurden. Ich testete die Voraussagen zweier Hypothesen über den Entstehungsgrund von Arbeitsketten: Nach der ersten Hypothese könnten Arbeitsketten aufgrund von Transporteffekten entstehen, wenn z. B. ein Fragment für eine Ameise zu groß ist, daher abgelegt und von Nestgenossinnen weitergetragen wird. Fragmente könnten auch durch Arbeitsketten schneller transportiert werden, als wenn ein Tier die ganze Strecke bis zum Nest läuft. Nach der zweiten Hypothese könnten Arbeitsketten den Informationsfluss unter den Sammlerinnen erhöhen: Indem sie ein Fragment abgibt, kann eine Sammlerin früher zum Ernteort zurückkehren, sie kann so die Trailmarkierung verstärken und Nestgenossinnen rekrutieren. Zudem könnten unbeladene Arbeiterinnen durch das abgelegte Fragment selbst darüber informiert werden, was gerade geerntet wird. Dies könnte den Sammlerinnen die Möglichkeit geben, zwischen Futterquellen unterschiedlicher Attraktivität zu wählen. Ich untersuchte die Transporteffekte und die mögliche Zeitersparnis, indem ich Ameisen Fragmente unterschiedlicher, jedoch definierter Größe sammeln ließ. Die Fragmentgröße hatte weder einen Einfluss auf die Wahrscheinlichkeit, dass ein Fragment abgegeben wurde, noch auf die Strecke, die es vor der Abgabe getragen wurde. Die Transportzeiten waren höher für Fragmente, die durch Arbeitsketten transportiert wurden, als für solche, die ein Tier die ganze Strecke trug. Um die Informationsfluss-Hypothese zu untersuchen, ließ ich die Ameisen Fragmente sammeln, die gleich groß jedoch unterschiedlicher Attraktivität waren. Nach dieser Hypothese würde man erwarten, dass Ameisen ihre Fragmente eher ablegen, wenn sie attraktiv sind, um dann an den Ernteort zurückzukehren, so dass Arbeitsketten häufiger bei attraktiven Fragmenten auftreten sollten als bei weniger attraktiven. Meine Ergebnisse zeigen, dass ein Anstieg in der Attraktivität der Fragmente die Häufigkeit der Arbeitsketten erhöhte und dass die Strecke, die die erste Trägerin zurücklegte, kürzer war als bei weniger attraktiven Fragmenten. Anders ausgedrückt, attraktivere Fragmente wurden häufiger und nach kürzeren Strecken abgelegt als weniger attraktive. Das bedeutet also, dass die Ursache für das Vorkommen von Arbeitsketten weder in Transporteffekten noch in einer Zeitersparnis beim Transport zu suchen ist. Es scheint vielmehr, dass der Vorteil auf Kolonieebene liegt, indem der Informationsfluss unter den Sammlerinnen erhöht wird.

Made available in DSpace on 2016-04-28T20:17:23Z (GMT). No. of bitstreams: 1 mestrado-Alzimiro Marcelo Conteiro Castilho.pdf: 399125 bytes, checksum: f42c772f226470430fe65c4d260420dd (MD5) Previous issue date: 2005-07-29 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / This survey was carried out under laboratory and field conditions for evaluating the efficiency of entomopathogenic fungi to control the ants Atta sexdens rubropilosa and Atta bisphaerica. The isolates from Agronomy National school (Escola Nacional de Agronomia) ENA1, ENA2, ENA3 and ENA4 of Metarhizium anisopliae as well as the isolates ENA6, ENA7, ENA13 and ENA14 of Beauveria bassiana were tested and inoculated on soldiers ants. After to have been collected, the soldiers were separated by groups of 10 individuals and wetted on a conidia suspension of 1.0 x 106 to 1.0 x 1011 conidia/ml .Each ants group was placed on a wet chamber and kept under no feeding condition at 27 ? 1 0C. Both fungi were pathogenic , although the isolates ENA 4 of Metarhizium anisopliale and ENA 6 and ENA 13 of Beauveria bassiana were considered the most virulent ones for A. bisphaerica, and for A. sexdens rubropilosa the isolates ENA 4 of Metarhizium anisopliae and ENA 14, ENA 13 and ENA 6 of Beauveria bassiana among the tested ones as well .The greatest mortality percentage was performed by these isolates with Lethal time (LT50) of 1.15 days for the isolate ENA 4, 1.39 days for ENA 6 and 1.44 days for ENA 13 ,for A. bisphaerica soldiers. For A. sexdens rubropilosa the Lethal time (LT50) was 1.37 days for the isolate ENA 4, 1.68 days for ENA 14, 1.95 days for ENA 13 and 2.14 days for ENA 6. In regard to the mortality index, the percentage of dead soldiers at the tested concentrations ranged from 45% to 71,67% . The isolates ENA 4, ENA 14, ENA 13, and ENA 6 caused the greater soldiers mortality averages in a shorter time period. The isolates ENA 4 and ENA 14 were applied by pulverization and spraying over plus 3 years old adult ants nests and 30 days after the entomopathogenic fungi application there still was some activity on the underground galleries. / Este trabalho foi conduzido em condi??es de laborat?rio e campo para se observar a efici?ncia de fungos entomopatog?nicos no controle de Atta sexdens rubropilosa e Atta bisphaerica. Foram utilizados os isolados ENA 1 (Escola Nacional de Agronomia) ENA 2, ENA 3 e ENA 4 de Metarhizium anisopliae e Beauveria bassiana, ENA 6, ENA 7, ENA 13 e ENA 14, inoculados em soldados. Ap?s coleta, exemplares de soldados foram separados em grupos de 10 indiv?duos e banhados em suspens?es de con?dios de 1,0 x 106 a 1,0 x 1011 con?dios.mL-1. Cada grupo de formiga foi transferido para c?mara ?mida e mantido sob regime de fome a 27 ? 1? C. Os dois fungos foram patog?nicos, embora os isolados ENA 4 de M. anisopliae e ENA 6 e ENA 13 de B. bassiana tenham sido os mais virulentos para A. bisphaerica e para A. sexdens rubropilosa dentre os testado. Esses isolados foram aqueles que apresentaram maior porcentagem de mortalidade confirmada, com TL50 de 1,15 dias para o isolado ENA 4, 1,39 dias para o ENA 6 e 1,44 dias para o ENA 13, para soldados de A. bisphaerica. Para A. sexdens rubropilosa a TL50 foi de 1,37 dias para o isolado ENA 4, 1,68 dias para o isolado ENA 14, 1,95 dias para o ENA 13 e 2,14 dias para o ENA 6. Quanto ao par?metro mortalidade, as concentra??es testadas proporcionaram a porcentagem de soldados mortos que variou de 45,0 a 71,67 %. Os isolados ENA 4, ENA14, ENA 13 e ENA 6 causaram as maiores m?dias de mortalidade de soldados em menor espa?o de tempo. Os isolados ENA 4 e ENA 14 foram aplicados na forma de pulveriza??o e polvilhamento, em formigueiros adultos com mais de tr?s anos de idade, e ap?s 30 dias da aplica??o dos fungos entomopatog?nicos, os olheiros ainda apresentavam ativos.

Orientador: Maurício Bacci Júnior / Resumo: A formiga saúva-da-mata, Atta cephalotes, tem como área de ocorrência a Mata Atlântica e a Floresta Amazônica, pois não consegue viver em regiões quentes e secas como o Cerrado e Caatinga. Como os demais atineos, corta folhas e flores que servem de substrato para o fungo que cultivam, sendo considerada, na Bahia, uma importante espécie que ataca as plantações de cacau na mata cabrucada. Sua classificação taxonômica sempre foi controversa e dificil devido à dificuldade de separar as subespécies através de caracteres morfológicos, que são polimórficos e pouco informativos, fazendo com todas as subespécies fossem sinonimizadas como Atta cephalotes. O presente estudo teve como objetivo caracterizar os Ioci mitocondriais CDI, IGS, Leu-tRNA e CDII de populações de Atta cephalotes e estabelecer uma relação filogenética entre essas populações. Procedeu-se a extração de DNA genômico total, seguida de amplificação com iniciadores específicos e purificação dos amplicons. O produto purificado foi seqüenciado no sentido direto e reverso e consenso das seqüências foi submetido ao alinhamento múltiplo, análise de máxima parcimônia, análise de haplótipos e divergência genética. Os resultados mostraram que existem duas populações geneticamente distintas de Atta cephalotes, uma predominantemente de ocorrência amazônica e outra de Mata Atlântica, contrariando a classificação atual. Foram encontradas no Pará e Amapá dois grupos de populações: um se agrupa com o grupo de espécimes de Mata Atlântica (Bahia e Pernambuco) e o outro com os espécimes da Amazônia, sugerindo a existência de populações simpátricas nesses estados. Talvez o uso de outros marcadores, associados a estudos ecológicos e comportamentais, esclareça se nesses dois estados suas populações estão isoladas reprodutivamente. Possivelmente o grupo da Bahia deve ser classificado como uma espécie diferente do grupo da região Norte. / Abstract: Not available. / Mestre

Em 1998 iniciou-se no campus da USP de Ribeirão Preto, SP, um projeto recuperação florestal entitulado "Floresta da USP", com o propósito de recompor,numa área de 75 ha, a floresta estacional semidecidual, um dos tipos de vegetação nativa da região. O presente estudo teve como objetivo avaliar as principais modificações que se processam neste novo habitat nos primeiros anos seguidos ao plantio, utilizando a comunidade de artrópodos e as relações de herbivoria como bioindicadores. Inicialmente, foram avaliados alguns parâmetros da estrutura do habitat em quatro sub-áreas com idades diferentes, comparando-as com um remanescente de floresta nativa existente nas proximidades. Entre estes mesmos locais, foi comparada a comunidade de artrópodos epígeos através de análise multivariada, buscando relacioná-las com variáveis ambientais. Além disso, numa das áreas foi acompanhada a dinâmica da comunidade de artrópodos associada à seis espécies vegetais (três pioneiras e três tardias), por dois anos consecutivos. Nas mesmas espécies vegetais utilizadas para a amostragem de artrópodos, foram avaliados os níveis de herbivoria e algumas características vegetais que poderiam influenciar na preferência por insetos herbívoros. Ficou demonstrado que as maiores transformações do habitat recomposto ocorrem nos dois primeiros anos seguidos ao plantio. As principais variáveis do habitat relacionadas com a fauna de artrópodos epígeos foram a altura da vegetação, presença de gramíneas invasoras e presença de um terceiro estrato arbóreo, exclusivo da mata nativa. Apesar de muito dissimilares da comunidade da mata, as comunidades das sub-áreas da Floresta da USP mostram uma tendência de se aproximarem da existente na mata de acordo com o tempo transcorrido após o plantio. Em relação à fauna de dossel, embora não se tenha observado diferença na riqueza, abundância e diversidade geral entre os dois anos seguidos ao plantio, foi detectada uma grande dissimilaridade de espécies e uma profunda reestruturação da abundância de organismos dentro das guildas. As formigas, tanto por sua abundância como riqueza, tiveram grande participação dentro das diversas variáveis da comunidade analisadas e, entre elas, as formigas cortadeiras foram também responsáveis por uma grande elevação nos níveis de herbivoria do primeiro para o segundo ano de acompanhamento, tanto em espécies iniciais quanto tardias. / In 1998 a recomposition project named "Floresta da USP" was started at the USP campus in Ribeirão Preto, SP, aiming at recovering a 75 ha area with the regional native vegetation, the seasonal semideciduous forest. This study evaluated the main changes that ocurried in this new habitat during the first years after planting, considering the arthropod community and the herbivory relationships as bioindicators. We measured some habitat structure parameters at four sites of different ages, contrasting them to the same parameters measured at a local forest patch. The epigeous arthropod community was compared among sites using multivariate analysis, including several environmental variables. We also monitored the community dynamics of arthropods, herbivory levels and leaf physical chemical caracteristics of six plant species (3 pioneers and 3 late successional) at one of the sites during two years as well as the main leaf variables that could have some effect on the herbivore preferences. Results indicated great chances in the first years of recomposition. Vegetation height, presence of alien grasses, and presence of a third stratum at the forest patch were the principal habitat features related to the epigeous arthropod community. Despite the high dissimilarity, arthropod community of recomposed sites had a tendency of reducing this dissimilarity over time in relation to the forest. Richness, abundance, and diversity of canopy arthropod community were not different between the two years. However, a high species dissimilarity was detected and a strong guild rearrangement concerning abundance from one year to another. There was a high number of species and individuals. Leaf-cutting ants were important to the ecosystem dynamics due to the high levels of herbivory imposed to several plant species.