Different trophic groups of arboreal ants show differential responses to resource supplementation in a neotropical savanna.

Resource-ratio theory predicts that consumers should achieve optimal ratios of complementary nutrients. Accordingly, different trophic groups are expected to vary in their N-limitation depending on the extent to which they feed primarily on carbohydrate (CHO) or protein. Among arboreal ants, N-limitation ranges from high (for trophobiont tenders), intermediate (leaf foragers) and low (predators). We report results from a manipulative field experiment in a Brazilian savanna that tests the differential attractiveness of nitrogen and CHO to arboreal ants, as well as experimentally examines changes in broader ant foraging patterns in response to protein and CHO supplementation. Every tree within 32 20 × 20 m plots were supplemented with either protein, CHO; protein + CHO or a water control (n = 8 in each case) for a 7-day period in each of the wet and dry seasons. As predicted, different trophic groups responded differentially to supplementation treatment according to the extent of their N-limitation. The richness and abundance of the most N-limited group (trophobiont tenders) was highest at protein supplements, whereas less N-limited trophic groups showed highest species richness (leaf foragers) or abundance (predators) at CHO supplements. Protein supplementation markedly increased the general foraging abundance of trophobiont tenders, but decreased the abundance of leaf foragers. We attribute the latter to increased competition from behaviorally dominant trophobiont tenders. Our study provides experimental evidence that nutrient availability is a major factor influencing arboreal ant communities, both directly through the provision of different resources, and indirectly through increased competitive pressure.

Similar alpha and beta diversity changes in tropical ant communities, comparing savannas and rainforests in Brazil and Indonesia.

Local biodiversity can be expected to be similar worldwide if environmental conditions are similar. Here, we hypothesize that tropical ant communities with different types of regional species pools but at similar habitat types in Brazil and Indonesia show similar diversity patterns at multiple spatial scales, when comparing (1) the relative contribution of alpha and beta diversity to gamma diversity; (2) the number of distinct communities (community differentiation); and (3) the drivers of ß-diversity (species replacement or species loss/gain) at each spatial scale. In both countries, rainforests and savannas (biome scale) were represented by three landscapes (landscape scale), each with four transects (site scale) and each transect with 10 pitfall traps (local scale). At the local scale, α-diversity was higher and ß-diversity lower than expected from null models. Hence, we observed a high coexistence of species across biomes. The replacement of species seemed the most important factor for ß-diversity among sites and among landscapes across biomes. Species sorting, landscape-moderated species distribution and neutral drift are potential mechanisms for the high ß-diversity among sites within landscapes. At the biome scale, different evolutionary histories produced great differences in ant community composition, so the replacement of species is, at this scale, the most important driver of beta diversity. According to these key findings, we conclude that distinct regional ant species pools from similar tropical habitat types are similarly constrained across several spatial scales, regardless of the continent considered.

Fire in the Amazon: impact of experimental fuel addition on responses of ants and their interactions with myrmecochorous seeds.

The widespread clearing of tropical forests causes lower tree cover, drier microclimate, and higher and drier fuel loads of forest edges, increasing the risk of fire occurrence and its intensity. We used a manipulative field experiment to investigate the influence of fire and fuel loads on ant communities and their interactions with myrmecochorous seeds in the southern Amazon, a region currently undergoing extreme land-use intensification. Experimental fires and fuel addition were applied to 40 × 40-m plots in six replicated blocks, and ants were sampled between 15 and 30 days after fires in four strata: subterranean, litter, epigaeic, and arboreal. Fire had extensive negative effects on ant communities. Highly specialized cryptobiotic and predator species of the litter layer and epigaeic specialist predators were among the most sensitive, but we did not find evidence of overall biotic homogenization following fire. Fire reduced rates of location and transport of myrmecochorous seeds, and therefore the effectiveness of a key ecosystem service provided by ants, which we attribute to lower ant abundance and increased thermal stress. Experimental fuel addition had only minor effects on attributes of fire severity, and limited effects on ant responses to fire. Our findings indicate that enhanced fuel loads will not decrease ant diversity and ecosystem services through increased fire severity, at least in wetter years. However, higher fuel loads can still have a significant effect on ants from Amazonian rainforests because they increase the risk of fire occurrence, which has a detrimental impact on ant communities and a key ecosystem service they provide.

Are all ant mosaics caused by competition?

In this paper we tested the hypothesis that ant mosaics are generated and maintained by stochastic processes, against the general idea that deterministic processes, such as competition, are the main forces that structure these communities. We analysed 14 published ant mosaics, described for crops and natural forests, transforming their data in presence/absence matrices. These matrices were submitted to species co-occurrence analysis, using software that generates null models. The observed species co-occurrence index was then statistically compared to the null matrices, to test whether there is evidence for biological processes structuring the ant communities. From the 14 mosaics analysed, seven had less and one had more co-occurrence than expected by chance. In six mosaics, species co-occurrence was within the 95% limits of frequency distribution of randomized matrices. Even though the observation of ant spatial distribution, together with association indices between species pairs, have usually been interpreted as a result of negative interactions, our results show that in only 50% of the studied mosaics there is evidence for this explanation. Furthermore, there are alternative hypotheses to explain the result of less co-occurrence than expected by chance, besides the competition hypothesis. Association of ant species with resources and conditions may also explain the observed pattern, although these hypotheses are rarely exploited. In conclusion, competition may be an important process when studying assembly rules in ant communities, although it is certainly not the only process involved. The importance of other biological processes and of stochastic events has to be taken into account to explain the species distribution patterns.

[Do Capsicum spp. trichomes influence the biological aspects of the broad mite, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)?]. / Os tricomas de Capsicum spp. interferem nos aspectos biológicos do ácaro-branco, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)?

Plant morphology traits can affect the feeding preference, oviposition choice and the vulnerability of herbivores to natural enemies. At long term, these plant variations may influence herbivore population dynamics due to the interference on their development, survival and reproduction. In this paper, the development of the broad mite Polyphagotarsonemus latus (Banks) was evaluated on five species of Capsicum with different density of trichomes. We tested the hypothesis that P. latus population growth has a negative relationship with the increase trichome density on leaves. It was assessed a decrease in the intrinsic growth rate (r m) of P. latus with the increase of trichome density on the leaves tested. The lower r m was measured in leaves of C. praetermissum (r m = 0.46), which has the highest trichome density among the assessed Capsicum species. The highest values of r m were observed on Capsicum species with intermediate densities of trichomes on leaves such as Capsicum frutescens (r m = 0.77) and Capsicum chinense (r m = 0.76). Capsicum spp. trichomes acted as a limiting plant trait for the development of P. latus when they were in higher densities and better distributed on the leaf surface. We also discuss the role of morphologic and chemical plant defenses on P. latus development.

Suitability of leguminous cover crop pollens as food source for the green lacewing Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae).

Diversification of crops with species that provide suitable pollen for predators may reduce pest population on crops by enhancing predator effectiveness. In this paper we evaluated the suitability of leguminous cover crop pollens to the predatory green lacewing Chrysoperla externa (Hagen). The predator is commonly found in coffee agroecosystems and the plant species tested were pigeon pea and sunn hemp, which are used in organic coffee systems. Newly emerged females and males of C. externa were reared on diets containing pollen of pigeon pea, sunn hemp, or castor bean, used as a control. The reproductive success of C. externa was evaluated when females fed the pollen species and when honey was added to the diets, to verify the predator need for an extra carbohydrate source. Similar intrinsic growth rates were found for females fed on pigeon pea pollen and on sunn hemp pollen but these rates increased significantly when honey was added to the diets. Females fed with pigeon pea pollen plus honey and with sunn hemp pollen plus honey had higher intrinsic growth rates than those fed with castor bean pollen plus honey. Females fed on castor bean pollen only or on honey only, did not oviposit. Leguminous pollen species were equally suitable for C. externa especially when they were complemented with honey. The results suggest that to successfully enhance predator effectiveness, organic coffee plantation should be diversified with plant providing pollen in combination with plant providing nectar.

Os tricomas de Capsicum spp. interferem nos aspectos biológicos do ácaro-branco, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)? / Do Capsicum spp. trichomes Influence the biological aspects of the broad mite, Polyphagotarsonemus latus Banks (Acari: Tarsonemidae)?

Variações nas características morfológicas das plantas podem ter efeito imediato sobre a preferência alimentar, escolha de sítios de oviposição e vulnerabilidade de herbívoros a inimigos naturais. A longo prazo, podem ter consequências sobre a dinâmica populacional desses organismos, já que atuam sobre seu desenvolvimento, sobrevivência e reprodução. Neste trabalho, avaliou-se o desenvolvimento de Polyphagotarsonemus latus (Banks) em cinco espécies de Capsicum com diferentes densidades de tricomas. Testou-se a hipótese de que o crescimento populacional de P. latus nessas plantas apresenta relação negativa com o aumento da densidade de tricomas nas folhas. Observou-se um padrão decrescente na taxa intrínseca de crescimento (r m) de P. latus com o aumento da densidade de tricomas nas folhas. O menor r m foi obtido em folhas de C. praetermissum (r m = 0,46), que apresenta a maior densidade de tricomas entre as espécies de Capsicum avaliadas. Os maiores valores de r m foram observados em espécies de Capsicum com densidade intermediária de tricomas nas folhas, Capsicum frutescens (r m = 0,77) e Capsicum chinense (r m = 0,76). Os tricomas de Capsicum spp. atuaram como fator limitante ao desenvolvimento de P. latus à medida que se apresentaram em maiores densidades e mais bem distribuídos na superfície foliar. Foi discutido ainda o papel da defesa morfológica e química de plantas de Capsicum sobre o desenvolvimento de P. latus.

Plant morphology traits can affect the feeding preference, oviposition choice and the vulnerability of herbivores to natural enemies. At long term, these plant variations may influence herbivore population dynamics due to the interference on their development, survival and reproduction. In this paper, the development of the broad mite Polyphagotarsonemus latus (Banks) was evaluated on five species of Capsicum with different density of trichomes. We tested the hypothesis that P. latus population growth has a negative relationship with the increase trichome density on leaves. It was assessed a decrease in the intrinsic growth rate (r m) of P. latus with the increase of trichome density on the leaves tested. The lower r m was measured in leaves of C. praetermissum (r m = 0.46), which has the highest trichome density among the assessed Capsicum species. The highest values of r m were observed on Capsicum species with intermediate densities of trichomes on leaves such as Capsicum frutescens (r m = 0.77) and Capsicum chinense (r m = 0.76). Capsicum spp. trichomes acted as a limiting plant trait for the development of P. latus when they were in higher densities and better distributed on the leaf surface. We also discuss the role of morphologic and chemical plant defenses on P. latus development.

Suitability of leguminous cover crop pollens as food source for the green lacewing Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae)

Diversification of crops with species that provide suitable pollen for predators may reduce pest population on crops by enhancing predator effectiveness. In this paper we evaluated the suitability of leguminous cover crop pollens to the predatory green lacewing Chrysoperla externa (Hagen). The predator is commonly found in coffee agroecosystems and the plant species tested were pigeon pea and sunn hemp, which are used in organic coffee systems. Newly emerged females and males of C. externa were reared on diets containing pollen of pigeon pea, sunn hemp, or castor bean, used as a control. The reproductive success of C. externa was evaluated when females fed the pollen species and when honey was added to the diets, to verify the predator need for an extra carbohydrate source. Similar intrinsic growth rates were found for females fed on pigeon pea pollen and on sunn hemp pollen but these rates increased significantly when honey was added to the diets. Females fed with pigeon pea pollen plus honey and with sunn hemp pollen plus honey had higher intrinsic growth rates than those fed with castor bean pollen plus honey. Females fed on castor bean pollen only or on honey only, did not oviposit. Leguminous pollen species were equally suitable for C. externa especially when they were complemented with honey. The results suggest that to successfully enhance predator effectiveness, organic coffee plantation should be diversified with plant providing pollen in combination with plant providing nectar.

A diversificação das culturas com plantas que forneçam pólen nutricionalmente adequado para predadores pode reduzir a população de pragas pelo aumento da efetividade dos predadores. Neste trabalho, avaliou-se a viabilidade nutricional de polens de leguminosas utilizadas como adubação verde, para o crisopídeo Chrysoperla externa (Hagen), comumente encontrado em agroecossistemas cafeeiros. Os adubos verdes testados foram guandu e crotalária, leguminosas utilizadas em sistemas orgânicos de café. Adultos de C. externa recém-emergidos foram criados em dietas contendo pólen de guandu, de crotalária e de mamona (controle). O sucesso reprodutivo de C. externa foi avaliado nas dietas de pólen e quando mel foi adicionado ao pólen, para se verificar a necessidade do predador por fonte extra de carboidratos. A taxa de crescimento populacional do predador foi semelhante nas dietas de pólen de guandu e de crotalária. No entanto, a taxa aumentou significativamente quando mel foi adicionado às dietas. Fêmeas alimentadas com pólen de guandu e mel e com pólen de crotalária e mel tiveram crescimento superior ao das alimentadas com pólen de mamona e mel. Fêmeas alimentadas somente com pólen de mamona ou somente com mel não ovipositaram. Os polens de guandu e de crotalária foram igualmente adequados para C. externa, especialmente quando foram complementados com mel. Os resultados sugerem que para aumentar a efetividade dos predadores, os sistemas orgânicos de café deveriam ser diversificados com plantas que forneçam pólen em combinação com plantas que forneçam néctar.

Performance of an oligophagous insect in relation to the age of the host plant / Performance de um inseto oligófago em relação à idade da planta hospedeira

The performance of monophagous and oligophagous herbivore insects should be negatively influenced by the ageing of their host plants. Plutella xylostella L. (Lepidoptera: Yponomeutidae), a specialist in Cruciferae, was reared in the laboratory on detached cabbage leaves (Brassica oleraceae var. capitata). We used fourth expanded leaves from differently aged plants, and leaves from three strata of the mature plant. Plant ageing increased pre-imaginal mortality and reduced larval developing rate, pupae weight, and fecundity. The insect net reproductive rate (Ro) and intrinsic rate of population growth (r) decreased as plant aged. No leaf category of mature plants was qualitatively superior to leaves from younger plants. If there exist a positive correlation between oviposition preference and offspring performance, in field conditions, a decreasing temporal trend in the intensity of attack along the host plant development can be expected.

A performance de insetos folívoros monófagos e oligófagos deveria ser afetada negativamente pelo envelhecimento das suas plantas hospedeiras. Plutella xylostella L. (Lepidoptera: Yponomeutidae), uma especialista em Cruciferae, foi criada em laboratório com folhas destacadas de repolho (Brassica oleraceae var. capitata). Foram utilizadas a quarta folha expandida de plantas de diferentes idades mais as folhas dos três estratos da planta madura. O envelhecimento da planta aumentou a mortalidade pre-imaginal e reduziu a taxa de desenvolvimento das larvas, o peso das pupas e a fecundidade dos adultos. A taxa reprodutiva líquida (Ro) e a taxa intrínseca de crescimento populacional (r) diminuíram com o envelhecimento da planta. Nenhuma das categorias de folhas da planta madura mostrou-se qualitativamente superior às folhas de plantas mais jovens. Se em condições de campo existir uma correlação positiva entre preferencia de oviposição e performance da prole, espera-se uma tendência temporal decrescente na intensidade de ataque de larvas ao longo do desenvolvimento da planta.

Occurrence of Atta robusta Borgmeier (Hymenoptera: Formicidae) in the north of Espírito Santo State, Brazil / Ocorrência de Atta robusta Borgmeier (Hymenoptera: Formicidae) no norte do Espírito Santo

Atta robusta Borgmeier has been described as an endemic species from the lowlands of Rio de Janeiro State. However, the scarce studies carried out with species disagree in relation to its geographic distribution. In this note we describe the occurrence of A. robusta in the "restingas" of Guriri Island, north of Espírito Santo State. This occurrence makes clear that A. robusta is not endemic from Rio de Janeiro State, being distributed at least in "restingas" in Rio de Janeiro and Espírito Santo states

Atta robusta Borgmeier foi descrita como endêmica da Baixada Fluminense, Rio de Janeiro. No entanto, os poucos estudos sobre a espécie não são concordantes quanto a sua distribuição geográfica. A presente nota comunica a ocorrência de A. robusta nas restingas da Ilha de Guriri, norte do Espírito Santo. Esse novo dado permite afirmar que A. robusta não é endêmica da Baixada Fluminense, estando distribuída pelo menos nas restingas dos estados do Rio de Janeiro e Espírito Santo

Flora visitada pelas abelhas eussociais (Hymenoptera, Apidae) na Serra da Capivara, em caatinga do Sul do Piauí / Flora visited by the eusocial bees (Hymenoptera, Apidae) in a Savanna of the South of Piauí, Brazil

Estudou-se a flora explorada por Apis mellifera L. (abelhas africanizadas) e meliponíneos, em vegetação de caatinga, no Parque Nacional da Serra da Capivara, PI. Durante um ano foram feitas amostragens mensais em dois locais, utilizando-se redes entomológicas para a coleta das abelhas eussociais em visita às plantas. Coletaram-se 69 espécies de angiopermas de 28 famílias nos dois locais amostrados. Leguminosae foi a família com maior número de espécies florais e de maior visitação pelas abelhas eussociais, como ocorreu com outras localidades de caatinga, mas há poucas espécies melitófilas em comum. As plantas coletadas foram visitadas por 12 espécies de meliponíneos e, ou pelas abelhas africanizadas. A. mellifera visitou 32 espécies florais e os meliponíneos 58 espécies, destes destacou-se Trigona spinipes Fabr. com maior espectro de plantas visitadas. O comportamento oportunista foi aparente em A. mellifera, mas não foi observado em todas as espécies de meliponíneos coletadas. A fenologia da flora e da fauna de abelhas foi similar à relatada em outros estudos regionais de mesma formação florística: abundância e heterogeneidade floral durante a estação chuvosa, favorecendo o forrageamento das abelhas, e escassez de recursos florais durante a seca, quando a ocorrência das abelhas se reduz.

This study presents the flora explored by Apis mellifera L. (Africanized honey bee) and stingless bees, and their seasonal phenology, in a caatinga vegetation, located in the Parque Nacional Serra da Capivara, Piauí State, tropical Brazil. During one year, bees were monthly collected with entomological nets, while visiting flowers. Sampling took place in two places. Eusocial bees, A. mellifera and 12 stingless bees species, were collected visiting 69 angiopermas species. Like reported in other studies on caatinga, a plant family heavily foraged was Leguminosae, but there were a few melittophilic species in common. A. mellifera visited 32 floral species and the stingless bees visited 58 species; among them Trigona spinipes Fabr. had the largest spectrum of plant species visited. A. mellifera showed the opportunistic behavior, but this was not observed with the majority of the stingless bee species. Regarding the seasonal phenology, the picture is like others studies conducted in the caatinga: abundance and floral heterogeneity during the rainy station, when the sampling was most effective, and shortage of floral resources during the dry season, when the occurrence of the eusocial bee species was reduced.

Geographic distribution of Atta robusta Borgmeier (Hymenoptera: Formicidae) / Distribuição geográfica de Atta robusta Borgmeier (Hymenoptera: Formicidae)

The available information regarding the geographic distribution of Atta robusta Borgmeier is confused and raised the necessity of revision of both its distribution and its endemic status. This paper ascertained the occurrence of A. robusta in restingas of Espírito Santo and Rio de Janeiro states, Brazil, through fieldwork, museum visits and bibliographical revision. No reference mentioned its occurrence out of restinga vegetation, as well as in states located south of Rio de Janeiro. We confirmed that A. robusta is endemic of restinga vegetation and it is restricted to the strip of the denominated Moist Oriental Tertiary Brazilian Coast. Such a distribution is possibly due to geographical and ecological barriers that obstruct its dispersion to other environments.

Dúvidas geradas pelas informações disponíveis na literatura levaram à necessidade de uma revisão na distribuição geográfica de Atta robusta Borgmeier e seu status de endemicidade. Por meio de coletas em campo, exame de coleções entomológicas e revisão bibliográfica, verificou-se que A. robusta ocorre em todos os ambientes de restingas dos estados do Espírito Santo e Rio de Janeiro. Nenhuma referência foi encontrada sobre sua ocorrência fora dos ambientes de restingas, bem como para os estados localizados ao sul do Rio de Janeiro. Sugere-se que A. robusta é endêmica das restingas e está restrita à faixa do litoral brasileiro denominado de Terciário Oriental Umido, devido às barreiras geográficas e ecológicas que impedem sua dispersão.