José Francisco da Silva Martins

Eficiência de Metarhizium anisopliae no controle do Percevejo-do-Colmo Tibraca limbativentris (Heteroptera: Pentatomidae) em lavoura de arroz irrigado

The rice stem bug, Tibraca limbativentris Stal, 1860 (Heteroptera: Pentatomidae), is an important pest of rice (Oryza sativa L.) in Brazil, mainly in flooded system of cultivation. The effect of two ways of application (conidia in aqueous suspension and on rice grain) of Metarhizium anisopliae strain 172 for the control of the rice stem bug, was evaluated in three experiments conducted in 1991, 1992 and 1994 in commercial irrigated rice. In 1991, the spraying of conidia suspension and manual distribution of rice grain covered with fungal material at dose of 7.2 x 1013 conidia.ha-1, on soil and among rice stems, where the bugs were located, reduced significantly the insect natural population with control efficiencies of 52.6 and 61.8%, respectively. Studies about establishment and persistence of fungal conidia in soil, using the colony forming unity (CFU) counts, indicated that the fungus persisted in the soil between two rice crop seasons, up to 216 days after application, when new rice crops were established. The number of CFU was greater in the plots treated with rice grain covered with fungal material. The linear growth of CFU in the control plots showed that the fungus spread to the untreated areas of the rice field. Significant control efficiency was obtained in 1993 for grain and aqueous fungus treatment with 48.2% and 51.8%, respectively. In 1994, the conidial suspension at dose of 5x1013 conidia.ha-1 resulted in control efficiency of 39.5%. The level of insect mycosis, however, was low in both 1993 and 1994, reaching a maximum of 20% mycosis in 1993. The low numbers of insect with mycosis compared with the level of mortality, may probably reduce the rate of fungal dissemination in rice fields and, consequently, be detrimental to the occurrence of epizootics.

Preferência alimentar e biologia de Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) em arroz e capim-arroz

Lagartas de Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) foram criadas em laboratorio, alimentadas com folhas de arroz (Oryza sativa) e capim-arroz (Echinocloa sp.) a 25±2 oC; 70±10% RH e fotofase de 14 h. Maiores diferencas foram observadas quanto a duracao da fase larval (22,0 dias em arroz e 18,6 dias em capim-arroz), viabilidade de lagartas (78% em arroz e 83,0% em capim-arroz) e pupas (71,4% em arroz e 87,8% em capim-arroz) bem como na fecundidade (773 e 1017 ovos/femea provenientes de lagartas alimentadas em arroz e capim-arroz, respectivamente). Insetos criados em capim-arroz desenvolveram-se mais rapidamente, apresentando maior viabilidade e fecundidade. O capim-arroz foi preferido pelas lagartas de S. frugiperda.

Eficácia de diferentes inseticidas e de volumes de calda no controle de Spodoptera frugiperda nas culturas do milho e sorgo cultivados em várzea

The fall armyworm Spodoptera frugiperda (J. E. Smith, 1797) has caused significant damage, mainly, in corn and sorghum growing in low land areas. A trial was carried out at Embrapa Clima Temperado de Pelotas, Estacao Experimental de Terras Baixas, Capao do Leao, RS. The objective was to study the efficacy of S. frugiperda control based upon yield response of the corn cv Pioneer 30F33 and sorghum cv Aventis BRS 305. The experimental design was a random block with split plot. The insecticides and rate were Match CE (lufenurom), 300mL p.c. ha-1; Rimom 100 CE (novalurom), 150mL p.c. ha-1; Tracer SC (spinosad), 50mL p.c. ha-1; Lorsbam 480 BR (chlorpyrifos), 500mL p.c. ha-1 and Karate 50 Zeon (lambda-cyhalothrin), 150mL p.c. ha-1. Evaluations were done at 5, 10, 15, 20, and 25 days after application. The volumes of 0, 150, 200, 250 e 300L ha-1 were sprayed, respectively, for each treatment. The best control of S. frugiperda was obtained with lufenurom, novalurom, spinosad, chlorpyrifos and lambda-cyhalothrin sprayed with 150, 200, 250 e 300L ha-1, respectively, implying that treatment efficacy was independent of volume application. However, treatment efficacy was dependent oN corn and sorghum growth stage and timing of spray. Yield variation was not related to volume application for both, corn and sorghum.

Diversidade genética de Tibraca limbativentris Stål (Hemiptera: Pentatomidae) de Santa Catarina e do Rio Grande do Sul, usando marcadores RAPD

The work was carried out to test DNA extraction protocols and to characterize populations of Tibraca limbativentris Stål, an important rice insect-pest. Insects were collected in Joinville, Rio do Oeste and Turvo, in Santa Catarina State, and Agudo, Uruguaiana, Pelotas and Palmares do Sul, in Rio Grande do Sul State, and six literature-referenced protocols, besides a new one, were tested. DNA from ten individuals of each population was extracted using the best protocol and RAPD reactions were carried out with ten initiators. The new protocol showed the best results and was used in the PCR reactions, that generated 151 polymorphic bands, allowing to access genetic differences among all the populations; no individuals from one population were clustered with individuals from another. The largest intrapopulacional similarity was found in Uruguaiana (22%), and the smallest in Palmares do Sul (50%), which was also the most divergent population in relation to the others. The Gst was 0.5215, and the Nm was 0.4588; these values reflect the low similarity between the populations. The smallest genic flow was obtained when Palmares do Sul and Pelotas were included in the comparisons, in accordance with the largest divergence of these two populations in relation to the others. There was no significant relation between geographic distance and genetic similarity, which can reflect unknown model of dispersion of T. limbativentris. New studies exploring the species dispersion strategies may help to understand the insect distribution and to unveil the main factors linked to the genetic variability within and between populations.

Resistência de genótipos de milho para cultivo em várzeas subtropicais à lagarta-do-cartucho Spodoptera frugiperda

Spodoptera frugiperda e uma das pragas com elevado potencial para causar perdas economicas na cultura do milho, no ecossistema de varzeas subtropicais. Com o objetivo de identificar fontes de resistencia, foi avaliado, em laboratorio, o desenvolvimento de S. frugiperda em nove genotipos de milho. Cem lagartas recem-eclodidas foram individualizadas em tubos de vidro, contendo porcoes de folhas de milho, mantidos a temperatura de 25±1°C, umidade relativa de 70±10% e fotofase de 14h. Avaliaram-se a duracao e a viabilidade das fases de larva e pupa, o peso de larvas e de pupas e a mortalidade larval. Dentre os genotipos avaliados, destacaram-se o BRS Missoes-B e o BR 111 VI Sel. Dent C, os quais afetaram, respectivamente, o desenvolvimento da fase de larva e de pupa.

Seletividade de agrotóxicos utilizados na cultura do arroz irrigado ao fungo Metarhizium anisopliae, agente de controle microbiano de Tibraca limbativentris

Searching for integrated control strategies for the insect-pest Tibraca limbativentris, the in vitro compatibility between isolated CG 891 of Metarhizium anisopliae and several pesticides used in the culture of irrigated rice was evaluated. The followings parameters were studied: vegetative growth, sporulation and the germination viability in pre- and post-contact of the fungus for two concentrations of fipronil, thiametoxan, fenitrothion, carbofuran, pyrazosulfuron-ethyl, bentazon, clomazone, glyfosate and quinclorac and one concentration of tricyclazole and azoxystrobin. Significant reductions in the vegetative growth and sporulation of M. anisopliae were observed for fenitrothion, carbofuran and azoxystrobin. The germination in pre-contact was affected by azoxystrobin. The percentage of germination changed the classification of pesticides in relation to its selectivity on the fungus. However, the results show that in vitro, the pesticides fenitrothion, carbofuran, glyfosate and azoxystrobin are harmful to isolated CG 891 of M. anisopliae.

Relação entre flutuação populacional de Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) e período de perfilhamento de cultivares de arroz irrigado

The synchronism between infestation period of Oryzophagus oryzae (Costa Lima) larvae and tillering period, was evaluated in four cultivars of irrigated rice (Bluebelle, BR-IRGA 410, BR-IRGA 414 e Dawn), which differ on degree of resistance to the insect and duration of development cycle. The experiments were carried out in the field, during 1994 and 1995 rice seasons. The number of larvae and tillers were registered weekly from 10 to 85 days after rice plants inundation (DAI). The first larvae were found 10 DAI, while the peak of larval population occurred 31 DAI, regardless the cultivars. The cultivars BR-IRGA 414 and Bluebelle (early cycle) produced tillers up to 45 DAI, while the cultivars BR-IRGA 410 and Dawn (medium cycle) produced tillers up to 68 DAI. The tillering period of early and semi-early cultivars lasted respectively 14 and 37 days, after the populational peak of larvae occurred. Medium cycle cultivars have shown higher capacity of recovering damaged roots after larval attack, thus becoming potentially more tolerant to insect damage.

Efeito de isolados de Metarhizium anisopliae (Metsch.) Sorok. e Beauveria bassiana (Bals.) Vuill. sobre o percevejo-do-colmo do arroz, Tibraca limbativentris Stal

The rice stem bug, Tibraca limbativentris Stal (Heteroptera: Pentatomidae), is an important pest of irrigated rice (Oryza sativa) crop in Brazil. The effect of isolates (CP) of the entomopathogenic fungi, Beauveria bassiana (Bals.) Vuill. (Bb) and Metarhizium anisopliae (Metsch.) Sorok. (Ma) was evaluated in the field using cages. In the 1st and 2nd experiments, conidial suspensions at dosages equivalents to 1013 conidia/ha, were sprayed on the soil and on rice plant stems, where the bugs were concentrated. Significant mortality (M) was caused by isolates CPBb164, CPMa171 and, mainly, by CPMa172 (46,5% < M < 88,7%). In the 3rd experiment, conidial sprays and broadcast of fungus on inoculated grain rice at 1013 conidia/ha were evaluated.. Both applications were effective (42,7% < M < 70,8%) in controlling the insect.

Associação entre teor de nitrogênio em cultivares de arroz e ataque de Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae)

The rice water weevil Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) is one of the most important pests in irrigated rice culture due to the damage caused by the larvae in the roots. The association between the nitrogen content and the O. oryzae damage was evaluated on BR IRGA 410, BRS Firmeza, Dawn and BRS Atalanta cultivars differentiated by the phenological development cycle and the insect resistance degree. The experiments were conducted under field conditions, with and without chance of host plant choice, at Embrapa Clima Temperado, Pelotas, RS. The following parameters were evaluated: number of damaged leaves, number and weight of larvae. The nitrogen content in the leaves and roots were evaluated at three different rice growth stages. The adult feeding of O. oryzae were stimulated by the content of nitrogen in the foliage of the plant. The cultivar Dawn was the only one to revover the nitrogen content, due to the presence of the smallest number of larvae and the largest development cycle in compare to other cultivars. The root damage caused by O. oryzae larvae decreased the nitrogen content, and consequently reduced the rice yield.

Occurrence of Euphoria lurida (Fabricius) (Coleoptera: Scarabaeidae) in the corn cultivated in Lowland at Rio Grande do Sul State

Euphoria lurida adults (Fabricius) is registered as pests of some fruits and flowers. However, this is the first record of this insect in maize fields. In march, 2006 adults attacked about 15% of maize plants in an area with almost 1 ha. The damage occurred in plants in the reproductive stage. Transversal and longitudinal holes were found in the stalks just above the ear insertion. The attack to the ear occurred more intensively in the upper part of the plant, where the insect fed on the silk and the filling grains.