Terezinha Maria Castro Della Lucia

Eye size and behaviour of day- and night-flying leafcutting ant alates

The morphology of insect eyes often seems to be shaped by evolution to match their behaviour and lifestyle. Here the relationship between the nuptial flight behaviour of 10 Atta species (Hymenoptera: Formicidae) and the eye size of male and female alates, including the compound eyes, ommatidia facets, and ocelli were examined. These species can be divided into two distinct groups by nuptial flight behaviour: those that initiate the nuptial flight during the day and those that initiate it at night. The most striking difference between day- vs night-flying alates was in ocellus area, which was almost 50% larger in night-flying species. Night-flying species also had significantly larger ommatidia facets than day-flying species. A scaling relationship was also found between compound eye area, facet diameter, and ocellus area vs overall body size. Detailed observations are also presented on the nuptial flight behaviour of a night- vs day-flying species, A. texana and A. sexdens , respectively. The pattern in A. texana is for a single large and precisely timed nuptial flight before dawn, while flights of A. sexdens last for several hours, beginning at midday. Further observations suggest that the timing of the nuptial flight in A. texana is easily disrupted by light pollution.

CONTROLE INTEGRADO DE SPODOPTERA FRUGIPERDA (SMITH & ABBOTT) UTILIZANDO-SE O PARASITÓIDE TELENOMUS REMUS NIXON

Este estudo foi conduzido em 1996 e 1997 para avaliar a eficiencia da liberacao de Telenomus remus Nixon (cerca de 200.000 adultos/ha), sozinho ou integrado ao virus de poliedrose nuclear de Spodoptera frugiperda (VPNSf) ou a um inseticida quimico seletivo, para o controle de Spodoptera frugiperda (Smith & Abbott). Os experimentos foram conduzidos em delineamento experimental de blocos ao acaso, com seis tratamentos e quatro repeticoes. Foram avaliados os danos provocados pela praga as folhas (escala de 0 a 5) e o rendimento de espigas. De maneira geral, os danos provocados pela praga foram significativamente superiores nas parcelas testemunhas (nota media de 2,94). Nao houve diferenca significativa entre os demais tratamentos (media 1,04). De maneira semelhante, houve diferenca significativa no rendimento de espiga entre testemunha (7.165 kg/ha) e demais tratamentos (9.084 kg/ha). Nao houve efeito dos tratamentos no comprimento da espiga e no dano as espigas.

Colonial recognition of fungus in the fungus-growing ant Acromyrmex subterraneus subterraneus (Hymenoptera: Formicidae)

Summary. Leaf cutting ants live in symbiosis with a basidiomycete fungus that is exploited as a source of nutrients for the ant larvae. Tests of fungus transport demonstrated that Acromyrmex subterraneus subterraneus workers discriminate concolonial fungus from alien fungus, and rejected the latter. Larvae and pupae of the ant were used as controls. Chemical analysis of the fungus revealed a great similarity between its hydrocarbon profile and that found on the ant brood. Experiments with lures showed that chemical extracts from the fungus are responsible for this discrimination process. Moreover, the presence of brood inside the fungus seemed to be important for discrimination of the fungus by workers. Resident workers accepted concolonial broodless fungus less than concolonial fungus inoculated with brood odor. Fungus seems to acquire colonial odor passively, simply by contact with the brood. The impact of fungus volume present in the nest on closure of the colony is discussed. We show here for the first time the importance of a symbiotic vegetal organism in colonial recognition in social insects.

Variation with caste of the mandibular gland secretion in the leaf-cutting antAtta sexdens rubropilosa.

InAtta sexdens rubropilosa, a strongly polyethic and polymorphic species of myrmicine ant, the contents of the mandibular gland vary with caste. Small workers of head width 0.5–1.8 mm, those generally engaged in duties inside the nest, contain chiefly 4-methyl-3-heptanone. Larger workers, those chiefly engaged in foraging, and the soldier caste contain a mixture dominated by neral and geranial, with very little of the ketone of the smaller workers. The soldiers have massive glands containing milligram amounts of neral and geranial. Virgin and mated females contain essentially only 4-methyl-3-heptanone, the amount increasing after mating, while virgin males have 4-methyl-3-heptanone and 4-methyl-3-heptanol in approximately equal proportions. Mated males have less secretion and lose the 4-methyl-3-heptanol.

Weevil x Insecticide: Does ‘Personality’ Matter?

An insect’s behavior is the expression of its integrated physiology in response to external and internal stimuli, turning insect behavior into a potential determinant of insecticide exposure. Behavioral traits may therefore influence insecticide efficacy against insects, compromising the validity of standard bioassays of insecticide activity, which are fundamentally based on lethality alone. By extension, insect ‘personality’ (i.e., an individual’s integrated set of behavioral tendencies that is inferred from multiple empirical measures) may also be an important determinant of insecticide exposure and activity. This has yet to be considered because the behavioral studies involving insects and insecticides focus on populations rather than on individuals. Even among studies of animal ‘personality’, the relative contributions of individual and population variation are usually neglected. Here, we assessed behavioral traits (within the categories: activity, boldness/shyness, and exploration/avoidance) of individuals from 15 populations of the maize weevil (Sitophilus zeamais), an important stored-grain pest with serious problems of insecticide resistance, and correlated the behavioral responses with the activity of the insecticide deltamethrin. This analysis was performed at both the population and individual levels. There was significant variation in weevil ‘personality’ among individuals and populations, but variation among individuals within populations accounted for most of the observed variation (92.57%). This result emphasizes the importance of individual variation in behavioral and ‘personality’ studies. When the behavioral traits assessed were correlated with median lethal time (LT50) at the population level and with the survival time under insecticide exposure, activity traits, particularly the distance walked, significantly increased survival time. Therefore, behavioral traits are important components of insecticide efficacy, and individual variation should be considered in such studies. This is so because population differences provided only crude approximation of the individual personality in a restrained experimental setting likely to restrict individual behavior favoring the transposition of the individual variation to the population.

Efeito de Secreções da Glândula Mandibular de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) Sobre a Germinação de Conídios de Botrytis cinerea Pers. Fr.

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%) similar to that of Mancozeb (95.3%).

Diversity of Fungi Associated with Atta bisphaerica (Hymenoptera: Formicidae): The Activity of Aspergillus ochraceus and Beauveria bassiana

The grass-cutting ant Atta bisphaerica is one of the most serious pests in several pastures and crops in Brazil. Fungal diseases are a constant threat to these large societies composed of millions of closely related individuals. We investigated the occurrence of filamentous fungi associated with the ant A. bisphaerica in a pasture area of Vicosa, Minas Gerais State, Brazil. Several fungi species were isolated from forager ants, and two of them, known as entomopathogenic, Beauveria bassiana and Aspergillus ochraceus, were tested against worker ants in the laboratory. The two species were highly virulent, achieving 50 percent worker mortality within 4-5 days. It is the first time A. ochraceus, a commonly found fungal species, is reported to infect Atta species at a high prevalence. Possible uses for the fungus within biological control are discussed.

A FAUNA DE FORMIGAS EM POVOAMENTOS DE EUCALIPTO E MATA NATIVA NO ESTADO DO AMAPÁ

This survey of the ant fauna in a native forest and in three plantations of Eucalyptus of 6, 20 and 106 months of age was conducted in August 1992. Sampling consisted of two 100 m transects per area along which 10 pitfall traps were placed for 7 days, after which they were replaced for traps baits with sardines, crackers and sugar laid during one hour per day. In addition hand collecting was performed on soil, litter, trees and shrubs for five non consecutive hours in each area. A total of 121 species belonging to 5 subfamilies and 50 genera was collected. The calculated Hill indices have indicated that in the native area there was a lower dominance and a higher species diversity. In the eucalipt there was a tendency towards reduced dominance and increased diversity as the stands grew older.

Natural mortality factors of Leucoptera coffeella (Lepidoptera: Lyonetiidae) on Coffea arabica

Abstract The natural mortality of the coffee leafminer, Leucoptera coffeella (Guérin-Méneville) was investigated in three strata of coffee plant canopy for three seasons through construction and analysis of ecological life tables. Mortality of the leafminer was similar on all thirds of the canopy. Total mortality of immature stages was 95%, with 38.5, 43.8 and 12.7% occurring during egg, larval, and pupal stages. Rainfall killed 39.3% of eggs and larvae, and together with egg inviability (16.3%) and Vespidae (11.3%), were the highest mortality factors. Six wasp parasitoids caused 8% of larval mortality. Egg and larva were the critical stages. Variation in mortality was primarily associated with egg inviability, rainfall, and parasitism by Horismenus sp. (Hymenoptera: Eulophidae). Physiological disturbances during molting and metamorphosis also contributed for fluctuations in mortality of the leafminer. Tactics of integrated pest management to enhance natural mortality of the leafminer while conserving or augmenting the action of natural enemies are discussed.

Espécies de formigas que interagem com as sementes de Mabea fistulifera Mart. (Euphorbiaceae)

As formigas, quando atraidas por um apendice nutritivo, produzido na semente de certas plantas, podem exercer o papel de agente predador ou dispersor das sementes. No processo de dispersao, grande numero desses insetos pode interagir com sementes de determinada planta. O objetivo deste trabalho foi identificar as especies de formigas em contato com sementes de Mabea fistulifera Mart. - uma especie arborea e colonizadora em areas antropicas no Brasil - e o tipo de interacao desses insetos com as sementes, bem como determinar as especies dispersoras. Foram realizadas coletas manuais de formigas em fragmentos de vegetacao com alta densidade de M. fistulifera, no municipio de Vicosa, MG, no momento de sua visitacao as sementes. As formigas capturadas foram triadas e identificadas por especie. Alem disso, durante as coletas foram feitas observacoes quanto ao tipo de comportamento das formigas que se associaram as sementes e ao calculo da taxa de remocao destas, verificando-se que 16 especies tiveram contato com estas. Acromyrmex subterraneus subterraneus, Atta sexdens rubropilosa, Ectatomma edentatum, Pachycondyla sp.1 e Pheidole sp. 2 foram, de fato, dispersoras, ja que transportaram efetivamente as sementes. Ac. subterraneus subterraneus, Camponotus rufipes, Ectatomma permagnum, Megalomyrmex sp.1, Pachycondyla sp. 1, Pachycondyla sp. 2, Pheidole sp. 4, Pheidole sp. 5 e Pogonomyrmex sp. sao, pela primeira vez, relatadas interagindo com sementes. A taxa de remocao das sementes de M. fistulifera pelas formigas foi de 85 a 97%.