Immune Defense Strategies of Queens of the Social Parasite Ant Acromyrmex ameliae and Queens of Its Natural Hosts.

Social parasitism is well known in ants, but many aspects of this social phenomenon remain mysterious and unexplored. In some cases, parasite queens, who are able to mate very rarely end up producing brood and, thus, depend virtually on the labor of host ants. In this work, we sought to test the occurrence of grooming by host workers of Acromyrmex subterraneus subterraneus Forel, to their own queens and queens of the parasite Acromyrmex ameliae De Souza, Soares and Della Lucia and to compare the immune defense responses of parasite queens and queens of A. subterraneus subterraneus and Acromyrmex subterraneus brunneus Forel, the natural hosts. Duration and frequency of behavioral acts were recorded. The relative size of the bulla and the encapsulation response to a standardized antigen were analyzed. Regarding behavioral acts, self-grooming (duration and frequency) and allogrooming (duration) were statistically different between the species; the first is more frequent and lasted longer in parasite queens, while the second act lasted longer in host ants than in parasite ants. The bulla of A. ameliae was approximately 50% wider than those of its hosts. Parasite queens exhibited a stronger immune response than host queens. The results of this work contribute to elucidate potential mechanisms involved in the parasitism capacity of A. ameliae queens such as their strategies of immune defense.

Deleterious action of azadirachtin against the mutualistic fungus of leaf-cutting ants.

Leaf-cutting ants have a beneficial and obligatory relationship with the fungus that they grow. This mutualism allowed the evolutionary success of these ants. The great defoliation capacity of these insects, which often exceeds the level of tolerable economic damage, includes them as severe pests in many cultures. However, given the close relationship between these two agents of mutualism, it is expected that an impact on the fungus will reflect on the performance of the colony as a whole. Therefore, the effect of azadirachtin on the development, and the macronutrient composition of Leucoagaricus gongylophorus was evaluated. Azadirachtin reduced the final fungal mass at the end of treatment at all concentrations tested, but did not reduce the final growth area. A reduction in the amount of hyphae produced with increasing azadirachtin concentration was also observed. Regarding macronutrients, the compound did not affect their total amount in the fungus. Thus, it is observed that azadirachtin did not alter the composition of L. gongylophorus macronutrients, but inhibited its growth by reducing the number of hyphae produced. This reduction reflects directly on the amount of nutrients offered to the workers and the queen and may improve the management of these insects.

Disentangling the ecotoxicological selectivity of clove essential oil against aphids and non-target ladybeetles.

The plant-based biopesticides have been proposed as insect pest control tools that seem to be safer for the environment and human health when compared to synthetic conventional molecules. However, such assumptions are generally made without considering the absence of detrimental effects on sublethally-exposed non-target organisms or showing the physiological basis of the selective action of such botanical products. Thus, by using in silico-based and in vivo toxicological approaches, the present investigation aimed to disentangle the ecotoxicological selectivity of clove, Syzygium aromaticum, essential oil against the aphid Rhopalosiphum maidis and the non-target ladybeetle, Coleomegilla maculata. We also investigated whether the sublethal exposure to clove essential oil would affect the locomotory and predatory abilities of C. maculata. We found that the clove essential oil concentration estimated to kill 95% (LC95: 0.17 µL/cm2) of the aphids was lethal to <18% of C. maculata. Indeed, our in silico results reinforced such differential susceptibility, as it predicted that eugenol and ß-caryophyllene (i.e., the clove essential oil major components) bound to three potential molecular targets (i.e., transient receptor potential (TRP) channels, octopamine, and gamma-aminobutyric acid (GABA) receptors) of the aphids but only to the octopamine receptors of the ladybeetles. Additionally, the ladybeetles that were exposure to the clove essential oil exhibited unaffected abilities to locomote and to prey upon R. maidis aphids when compared to unexposed ladybeetles. Thus, by displaying lower toxicity against the ladybeetles, the clove essential oil represents a safer alternative tool to be integrated into programs aiming to manage aphid infestations.

Effect of azadirachtin on mortality and immune response of leaf-cutting ants.

Leaf-cutting ants are difficult pests to control because they have numerous defense strategies and are highly selective in their plant harvesting choices. The search for effective pest control methods that have minimal negative effects on the environment has been continuous. Azadirachtin, a compound extracted from the neem tree (Azadirachta indica), is a promising alternative for the control of various pests, as it is toxic to some insects but readily degrades in the environment. In this study, we evaluated the effects of azadirachtin on the mortality, through topical exposure to the compound, and immune response, by introducing an artificial antigen into leaf-cutting ants Atta sexdens and Acromyrmex subterraneus subterraneus. Azadirachtin caused death to minor and major workers of both species in a concentration-dependent manner. Topical application of the compound did not diminish the immune response of ants in a microfilament encapsulation assay. Azadirachtin showed no effect on the immune response of workers but increased worker mortality, which indicates its potential as an ant control agent.

Managing leaf-cutting ants: peculiarities, trends and challenges.

Leaf-cutting ants are generally recognized as important pest species in Neotropical America. They are eusocial insects that exhibit social organization, foraging, fungus-cultivation, hygiene and a complex nest structure, which render their management notoriously difficult. A lack of economic thresholds and sampling plans focused on the main pest species preclude the management of leaf-cutting ants; such management would facilitate their control and lessen insecticide overuse, particularly the use of insecticidal baits. Recent restrictions on the use of synthetic compounds for such purposes impose additional challenges for the management of leaf-cutting ants. Considerable effort has been exerted regarding these challenges, which are addressed herein, but which also remain challenges that are yet to be conquered.

Comparative reproductive biology of the social parasite Acromyrmex ameliae de Souza, Soares & Della Lucia and of its host Acromyrmex subterraneus subterraneus Forel (Hymenoptera: Formicidae).

Social parasites exhibit several characteristics that allow them to exploit their host species efficiently. The smaller size of parasite species is a trait commonly found in ants. In this work, we investigated several aspects of the reproductive biology of Acromyrmex ameliae De Souza, Soares & Della Lucia, a recently discovered parasite of Acromyrmex subterraneus subterraneus Forel. Sexuals of A. ameliae are substantially smaller than those from host species. Parasite queens laid significantly less worker eggs than host queens and inhibit sexual production of the host. The sex ratio of parasite species is highly female biased. Interestingly, we have observed parasite coupling on the laboratory, inside the nests and in the ground, opening the possibility to use controlled mating to study genetic approaches of parasitism in the ants.

Comparative reproductive biology of the social parasite Acromyrmex ameliae de Souza, Soares & Della Lucia and of its host Acromyrmex subterraneus subterraneus Forel (Hymenoptera: Formicidae)

Social parasites exhibit several characteristics that allow them to exploit their host species efficiently. The smaller size of parasite species is a trait commonly found in ants. In this work, we investigated several aspects of the reproductive biology of Acromyrmex ameliae De Souza, Soares & Della Lucia, a recently discovered parasite of Acromyrmex subterraneus subterraneus Forel. Sexuals of A. ameliae are substantially smaller than those from host species. Parasite queens laid significantly less worker eggs than host queens and inhibit sexual production of the host. The sex ratio of parasite species is highly female biased. Interestingly, we have observed parasite coupling on the laboratory, inside the nests and in the ground, opening the possibility to use controlled mating to study genetic approaches of parasitism in the ants.

Sampling plan for Diaphania spp. (Lepidoptera: Pyralidae) and for hymenopteran parasitoids on cucumber.

The objective of this work was to determine the best technique, sampling unit, and the number of samples to compose a conventional sampling plan for the cucurbit borers, Diaphania spp. (Lepidoptera: Pyralidae), and for hymenopteran parasitoids on cucumber. This research was carried out in 10 commercial cucumber crops fields from July to December 2000 in Tocantins, Minas Gerais State, Brazil (21 degrees 11' 15" S; 42 degrees 03' 45" W; altitude 363 m). The sampling methods studied were beating on a tray, direct counting of insects on the lower leaf surface, and whole leaf collection. Three sampling units also were studied: leaves from a branch located in the apical, median, or basal third of the canopy. The best sampling systems, which included the best technique and sampling unit, were determined based on the relative variance and the economic precision of the sampling. Once the best sampling systems were established, the numbers of samples to compose the conventional sampling plans were determined. The more suitable sampling system for the larvae of Diaphania spp. in cucumber plants was beating a leaf of the median third of the canopy on a plastic tray. One leaf must be sampled for every 50 plants in a crop. The more suitable sampling system for hymenopteran parasitoids in cucumber plants was to directly count the adults on one leaf of the median third of the canopy. One leaf must be sampled for every 74 plants in a crop.

Queen adoption in colonies of the leaf-cutting ant Acromyrmex subterraneus molestans (Hymenoptera: Formicidae).

Bioassays were conducted in both laboratory and the field to determine if monogynous colonies of Acromyrmex subterraneus molestans (Myrmicinae, Attini) adopt queens from other colonies of the same subspecies. The results suggest that the adoption of fertilized queens is a possible mechanism to explain the occurrence of colonies with multiple queens in this subspecies. Only minor workers were able to discriminate queens from other colonies and were aggressive toward them. Therefore, queen recognition differs among subcastes.

Impacto da queima controlada da cana-de-açúcar na nidificação e estabelecimento de colônias de Atta bisphaerica Forel (Hymenoptera: Formicidae) / Impact of sugar cane foliage burning on the nesting and establishment of Atta bisphaerica Forel colonies (Hymenoptera: Formicidae)

Queimadas de baixas intensidades podem promover sensíveis alterações nas propriedades físicas, químicas e microbiológicas do solo, na profundidade onde se estabelecem os sauveiros iniciais de Atta Fabricius. Considerando que o estabelecimento da nova colônia é o período mais crucial da vida da colônia, investigaram-se neste trabalho as implicações pós-fogo de uma queima controlada de palhiço de cana-de-açúcar de intensidade igual a 615 kJ. m-1.s-1 na escolha de locais para escavação dos ninhos e estabelecimento inicial de colônias de Atta bisphaerica Forel. A queima eliminou matéria orgânica superficial da área, o que implicou em aumento significativo de densidade até a profundidade de 15 cm. Da mesma forma, a eliminação da vegetação pelo fogo promoveu maior resistência do solo à penetração. Essas alterações nas propriedades físicas não afetaram significativamente a escavação dos ninhos iniciais por fêmeas de A. bisphaerica e nem tampouco influenciaram a profundidade de construção de suas câmaras iniciais em condições de laboratório. A queima alterou a constituição química do solo e promoveu alterações na atividade microbiológica do mesmo. Em condições de campo, as fêmeas de A. biphaerica apresentaram maior taxa de estabelecimento em locais queimados. Em condições de laboratório, colônias cujas fêmeas estabeleceram-se em solos provenientes de áreas queimadas apresentaram maior mortalidade do que aquelas estabelecidas em solos de áreas não queimadas.

Even low intensity fires may often modify the chemical, physical and microbiological properties of the soil, in the depth where leaf-cutting ants Atta Fabricius establish their nests. Considering that nest foundation and establishment are the most crucial steps in a colony life cycle, this research investigated the implication that a controlled 615 kJ.m-1s-1 fire intensity of sugar cane dry foliage have on the nesting of Atta bisphaerica Forel. Burning eliminated organic matter from the soil surface; this resulted in a significant increase on its density down to a depth of 15 cm. The elimination of vegetation by fire also increased soil resistance to penetration. These alterations on physical properties had no significant effect on the depth of initial A. bisphaerica chambers under field and laboratory conditions. Burnings did affect soil chemical and microbiological properties. A. bisphaerica females looked for sites which had been burned to establish their colonies in the field. Under laboratory conditions, the mortality of colonies was higher in soil originating from burned areas than unburned ones.

Desenvolvimento de iscas granuladas com atraentes alternativos para Atta bisphaerica Forel, (Hymenoptera: Formicidae) e sua aceitação pelas operárias / Development of granulated baits with alternative attractants to Atta bisphaerica Forel (Hymenoptera: Formicidae) and their acceptance by workers

This research aimed to develop a methodology to prepare granular baits with alternative attractants for the workers of the leaf-cutting ant Atta bisphaerica Forel, and to compare these baits attractiveness with that of the citrus pulp. Granule pick ups of hand made baits of jaraguá grass (Hyparhenia rufa); sugar cane leaves and stalks and of wheat flour were compared to that of commercial baits without active ingredient in six nests located in Viçosa, MG. The bait of jaraguá grass was the most attractive to the ant workers, followed by the bait of sugar cane leaves. Commercial granulated baits had both mass and diameter inadequate for picking up by the ants, besides having the leastattractiveness.

Este trabalho teve como objetivos desenvolver uma metodologia para confecção de iscas granuladas a base de atraentes alternativos para as operárias de Atta bisphaerica Forel, e comparar aatratividade destas iscas com a de polpa cítrica. Os carregamentos de grânulos das iscas artesanais de folhas de capim jaraguá e cana-de-açúcar, de colmo de cana-de-açúcar, e de farinha de trigo foram comparados com o da isca comercial sem princípio ativo, em seis formigueiros localizados no municípiode Viçosa, MG. Concluiu-se que a isca de capim jaraguá foi a preferida pelas operárias de A. bisphaerica, seguida pela isca a base de folhas de cana-de-açúcar. Além da baixa atratividade, verificou-se que as iscas granuladas comerciais apresentaram massa e diâmetro inadequados para o carregamento por essa espécie, dificultando o seu transporte pelas operárias forrageadoras.

First record of Phorid Parasitoids (Diptera: Phoridae) of the leaf-cutting ant Atta bisphaerica Forel (Hymenoptera: Formicidae) / Primeiro registro de Forídeos Parasitóides (Diptera: Phoridae) da saúva Atta bisphaerica Forel (Hymenoptera: Formicidae)

Phoridae flies parasitize several ant species, including many Atta leaf-cutting ants. In this note, the attacks of three coexisting phorid species (Myrmosicarius grandicornis Borgmeier, Apocephalus attophilus Borgmeier and Neodorhniphora bragancai Brown) against Atta bisphaerica Forel workers in a pasture located in Viçosa County, Minas Gerais State, Brazil, are reported. The first two species of phorids are known to parasitize other leaf-cutting ants. N. bragancai, however, has been found only around A. bisphaerica nests. Each of these phorid species selects ants engaged in different tasks and oviposits in specific sites of the ant body.

Moscas da família Phoridae parasitam várias espécies de formigas, inclusive diversas saúvas (Atta spp.). Nesta nota são relatados ataques de três espécies de forídeos (Myrmosicarius grandicornis Borgmeier, Apocephalus attophilusBorgmeier e Neodohrniphora bragancai Brown) contra operárias de Atta bisphaerica Forel em uma área de pastagem localizada em Viçosa, Minas Gerais. As duas primeiras espécies já são conhecidas como parasitóides de outras saúvas, mas N. bragancai foi recentemente descrita e encontrada somente ao redor de ninhos de A. bisphaerica. Cada uma dessas espécies de forídeos seleciona operárias que realizam diferentes tarefas e oviposita em partes específicas do corpo do hospedeiro.

Efeito de Secreções da Glândula Mandibular de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) Sobre a Germinação de Conídios de Botrytis cinerea Pers. Fr. / Inhibition of the Germination of Botrytis cinerea Pers. Fr. Conidia by Extracts of the Mandibular Gland of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae)

This research investigated the effect of mandibular gland secretions of Atta sexdens rubropilosa Forel on the germination of Botrytis cinerea Pers. Fr. conidia. This fungus attacks several species of cultivated plants of economic importance. From 20 mandibular glands of workers of the leaf-cutting ant (3.60-4.30 mm head capsule width) we obtained 9.4 mg of acetone soluble secretion. To this mass, sterile water and the dispersing agent Tween 20 were added to prepare four doses which composed the treatments of 0.94 mg/ml, 4.70 mg/ml, 9.40 mg/ml and 37.60 mg/ml. We also used a negative control (water), a solvent control (acetone) and a positive control (the Mancozeb fungicide at 1600 ppm). Five microliters of B. cinerea conidia suspension were added to excavated plates maintained at 20°C in the dark. Therefore the solution concentrations of the treatments were reduced to half, that is 0.47 mg/ml, 2.35 mg/ml, 4.70 mg/ml and 18.80 mg/ml. A total of 12 replicates were performed for each of four treatments. The percentage of conidia germination was obtained 8h after treatments. Results by Probit analysis of data indicated that higher gland concentrations led to higher inhibition of conidia germination. The concentration of 18.80 mg/ml had an inhibitory effect (94.2 percent) similar to that of Mancozeb (95.3 percent).

Estudou-se o efeito de secreções da glândula mandibular de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) sobre a germinação de conídios de Botrytis cinerea Pers. Fr., fungo fitopatogênico de várias plantas de importância econômica. De 20 glândulas mandibulares de operárias dessa formiga cortadeira, com cápsula cefálica entre 3,60 e 4,30 mm, obtiveram-se 9,40 mg de secreção, aos quais adicionaram-se 0,25 ml de água esterilizada, resultando em uma solução de concentração 37,60 mg/ml. Essa mistura foi utilizada para o preparo de soluções com diferentes concentrações de secreção (0,94 mg/ml, 4,70 mg/ml e 9,40 mg/ml). Foram também preparadas uma testemunha negativa (água), uma testemunha de acetona e outra positiva, o fungicida Mancozeb a 1600 ppm. A cada 5 ml de solução dos tratamentos, foram adicionados 5 ml de suspensão de conídios de B. cinerea em lâminas escavadas, as quais foram mantidas a 20°C, no escuro. Portanto as concentrações das soluções dos tratamentos foram reduzidas à metade, ou seja, 0,47 mg/ml, 2,35 mg/ml, 4,70 mg/ml e 18,80 mg/ml. Após 8h, determinou-se a porcentagem de germinação de conídios desse fungo. Os experimentos foram realizados em 12 repetições. A análise de Probit indicou que quanto maior a concentração das soluções, maior foi o efeito inibitório sobre a germinação de conídios de B. cinerea. A solução de concentração 18,80 mg/ml mostrou efeito inibitório de (94,2 por cento) semelhante ao do fungicida Mancozeb (95,3 por cento).