Márcio da Silva Araújo

Impacto da queima controlada da palhada da cana-de-açúcar sobre a comunidade de insetos locais

The previous burning of sugarcane straw before harvest causes a series of inconvenients to the environment, specially to the tillage-associated insects. Fire is used to control pests and diseases in the agriculture, however its effect on insect populations is not well understood or documented, mainly on invertebrate groups responsible for nutrient recycling and energy flow. Our objective was to evaluate the effect of controlled burning sugarcane straw on the local insect community. The insects were collected in different dates before and after burning. The species selected for the analysis were affected by fire. Among the 35 taxa collected, 17 were considered more relevant to explain the observed variation in the frequency of species captured through time. In the first sampling after burning, there was a decrease in abundance of five species [Nitidulidae (species 2; Coleoptera), Lutosa brasiliensis (Brunner von Watternwyl) (Orthoptera: Gryllacrididae), Phoridae e Drosophilidae (Diptera) e Labia minor L. (Dermaptera: Labiidae)], among the 17 species selected for analysis. The canonical variate analysis for different sampling dates indicated significant difference between treatments, considering the composition and the species abundance. Despite the different composition of the insect community observed before and after burning, there is a tendency of community recovery to the observed pattern before burning.

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.

Impacto da queima controlada da cana-de-açúcar na nidificação e estabelecimento de colônias de Atta bisphaerica Forel (Hymenoptera: Formicidae)

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.

Levantamento de Attini (Hymenoptera, Formicidae) em povoamento de Eucalyptus na região de Paraopeba, Minas Gerais, Brasil

This Work was conducted in Eucalyptus stands at the Itapoa farm of the Mannesmann Fi-El Florestal Ltda. in Paraopeba, MG. The species of fungus growing-ants and leaf-cutting ants found in regrowth areas and in harvesting phase plantings were: Acromyrmex balzani Emery, 1890; Acromyrmex laticeps nigrosetosus Forel 1908; Acromyrmex subterraneus subterraneus Forel, 1893; Atta laevigala (F. Smith, 1858); Alta sexdens rubropilosa Forel, 1908; Mycocepurus goeldii Forel, 1893; Sericomyrmex sp.; Trachymyrmex fuscus Emery, 1894 and three morphospecies of Trachymyrmex Forel, 1893. Taxa belonging to the genus Atta Fabricius, 1804 represented 39.14 and 41.22% of the total number of nests found in the regrowth area and in the harvesting phase plantings, respectively. For Acromyrmex Mayr, 1865 these values were 14.34 and 13.16%; for Trachymyrmex, 40.59 and 30.89%; for Mycocepurus Forel, 1893, 5.34 and 12.50% and Sericomyrmex Mayr, 1865, 0.59 and 2.23% in the regrowth area and in the harvesting phase plantations, respectively.

Caracterização de ninhos e atividade forrageadora de Trachymyrmex fuscus Emery (Hymenoptera, Formicidae) em plantio de eucalipto

Seven nests of T. fuscus Emery, 1834 have been studied for their structure. These nests, which opened at the soil surface, had two to four chambers located one above the other. Externally all of these nests presented a heap of brownish-yellow debris that was constituted basically by remains of vegetable material. The total nest population was, on average, 1,048 individuais. The diel pattern of foraging of this species was studied for four consecuti ve months on two nests. This activity occurred predominantly in the night period, and the workers transported, mainly, dry vegetation to the nest.

Resistance of rice varieties to Sitophilus oryzae (Coleoptera: Curculionidae)

Abstract Rice, Oryza sativa L. (Poaceae), is one of the worlds most important food crops. Among the insects that damage rice grains, the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), is the most important species. The objective of this study was to identify rice varieties with resistance to S. oryzae as measured by grain feeding damage and S. oryzae reproduction. The rice varieties evaluated were obtained from the germplasm bank of the National Center of Research Rice and Beans, Embrapa, Brazil. The experimental design was completely randomized with 3 replications and 22 treatments (varieties). The varieties Bonança, Esmeralda, and Rio Verde had the antibiosis and/or antixenosis type of resistance, providing high rates of mortality, low rates of adult emergence, and low rates of grain consumption by S. oryzae. The varieties Pepita and Progresso were susceptible, with a high rate of S. oryzae adult emergence and grain consumption. The presence or absence of a fissure in the grain was a major morphological characteristic determining susceptibility or resistance to S. oryzae in rice varieties.

Toxicity of Andira paniculata (Fabaceae) Extracts to Helicoverpa armigera (Lepidoptera: Noctuidae)

Helicoverpa armigera is one of the most important pests of soybean crop in Brazil. The purpose of this work was to evaluate the effect of organic Andira paniculata extracts on its biology, feeding and the attractiveness of soybean plants to H. armigera . Hexane, dichloromethane, ethyl acetate and hydroalcoholic fractions at concentrations of 0.01, 0.1, 0.5 and 1% were evaluated. For the biological parameters the period and viability of larval stage, caterpillar weight at ten days, period, viability and pupal weight at 24 hours, total longevity, LC 50 and deterrence were evaluated. The non-preference for feeding and attractiveness, the number of caterpillars and the dry matter consumed in each fraction of the extracts were evaluated. The extract of A. paniculata in hexane (0.01%) resulted up to 85% mortality of H. armigera . The A. paniculata extract did not affect the larval period, weight, pupal period and mortality or the consumption of H. armigera . The hydroalcoholic extracts obtained the better results for deterrence. The A. paniculata extract in dichloromethane fraction had the lowest LC 50 . The A. paniculata extracts in the hexane fractions (0.1%), ethyl acetate (0.01 and 0.5%) and hydroalcoholic (0.01 and 0.5%) were fagodeterrents for H. armigera . Thus, A. paniculata extract in hexane fraction is the most promising for use in the control of H. armigera in soybean.

Antibiosis in Soybean Cultivars to Heliothis virescens (Lepidoptera: Noctuidae)

Abstract The tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), damages soybean crops by feeding on the leaves, pods, and terminal buds. The purpose of this study was to evaluate antibiosis resistance to H. virescens by different soybean cultivars. Soybean cultivars evaluated were P 98Y30 RR, NA 7337 RR, SYN 1163 RR, NK 7059 RR, ANTA 82 RR, M 7110 IPRO, BRS 8160 RR, BRSGO Jataí, and IAC 100. The variables analyzed were duration of the larval stage, percentage of larval survival, larval weight at 10 d, duration of the prepupal stage, percentage of prepupae survival, duration of the pupal stage, percentage of pupal survival, pupal weight at 24 h, total duration of the life cycle, overall survival, and adult longevity. The cultivars BRS 8160 RR, BRSGO Jataí, and P 98Y30 RR were highly susceptible to tobacco budworm, whereas IAC 100 and M 7110 IPRO showed antibiosis resistance to H. virescens.

Post-fire effect of savannah vegetation on the establishment of new colonies of Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Abstract Establishing their initial colony is probably the most critical moment in the life of leaf-cutting ants. The non-establishment is connected to abiotic and biotic factors, and the high mortality rates of initial colonies are possibly associated with entomopathogenic or antagonistic microorganisms to the symbiotic fungus present in the soil, hosted by these ants. Fire in the vegetation, depending on the intensity, is known to cause significant changes to the soil physical, chemical, and microbiological properties. The impact of a fire in savannah vegetation (Cerrado) on the establishment of early colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) was evaluated. For this end, two areas were selected, one where there had been an accidental fire, and a contiguous one with the same size and vegetation characteristics without burning. In these areas and in soil collected in the same areas and stored in the laboratory, females recently fertilized in the nuptial flight were placed to excavate the soil and establish their colonies. Post-fire changes in the soil chemical and microbiological properties were quantified and correlated successfully in the establishment of new colonies of this leaf-cutting ant. Under field conditions, the females of A. sexdens rubropilosa did not show preference for which areas to excavate: the ones that had been burned or the ones that were unburned; under this condition, no colony survived according to the evaluation performed 120 d after the nuptial flight. Under laboratory conditions, the majority of the females excavated the soil, whether it had been burned or not. However, the establishment of initial colonies was significantly higher in soils collected far from the surface and in areas that had not directly been affected by the fire, showing a negative effect of fire on colony establishment under laboratory conditions.