Eliane Dias Quintela

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.

Compatibility of conventional agrochemicals used in rice crops with the entomopathogenic fungus Metarhizium anisopliae

The toxicological impact of chemical pesticides on fungal entomopathogens and their use in tank-mixing can be directly measured through in vitro compatibility tests. This study reports the in vitro toxicity of eight insecticides, four fungicides and five herbicides in the conidial germination, vegetative growth and conidiation of Metarhizium anisopliae (strain CG 168). A conidial suspension containing the pesticide at recommended field dosage was subjected to constant agitation in a rotary shaker for 3h to simulate a tank mixing. Then, aliquots of each suspension were used to determine conidial germination, vegetative growth and conidiation on potato dextrose agar (PDA). The fungicides difenoconazole (69 mL ha-1), propiconazole (75 mL ha-1), trifloxystrobin (313 g ha-1) and azoxystrobin (56 mL ha-1) were the most harmful products to all biological stages of M. anisopliae and they should not be applied together with this fungus in tank mixing. The insecticides exhibited the least degree of toxicity to this fungal pathogen, whereas the herbicides had the greatest impact on mycelial growth. The agrochemicals compatible with M. anisopliae were the insecticides methyl parathion (240 mL ha-1), thiamethoxam (31 g ha-1), and lambda-cyhalothrin (6.3 mL ha-1) and the herbicides glyphosate (1560 mL ha-1), bentazon (720 mL ha-1), and imazapic+ imazapyr (84 g ha-1). The compatible pesticides could be simultaneously used with this bio-control agent for integrated pest management in rice production systems.

Toxicity of neem oil to Bemisia tabaci biotype B nymphs reared on dry bean.

O objetivo deste trabalho foi determinar o estagio ninfal de Bemisia tabaci biotipo B mais suscetivel ao oleo de nim (Azadirachta indica A. Juss.) aplicado em feijoeiro (Phaseolus vulgaris L.), em casa telada. Foram avaliados o tempo letal (TL) e concentracao letal (CL) do oleo comercial de sementes de nim Dalneem. Para CL, concentracoes de 0, 0,1, 0,25, 0,5, 1 e 2% do produto foram pulverizadas diretamente sobre as ninfas em cada instar. Para TL, o produto foi avaliado a 0, 0,5 e 1% de oleo de nim em cada instar. Ninfas vivas e mortas foram contadas cinco dias apos a pulverizacao para CL e diariamente para TL durante seis dias. Para o quarto instar, a CL50 foi de 0,56% de oleo de nim. Considerando todos os instares, CL50 e CL95 foram estimadas em 0,32 e 2,78% de oleo de nim, respectivamente. Os TL50 para 1% de nim foram estimados em 2,46, 4,45, 3,02 e 6,98 dias para o primeiro, segundo, terceiro e quarto instares, respectivamente. Os TL50 estimados para 0,5 e 1% de oleo de nim foram de cinco e quatro dias, respectivamente, considerando todos os instares. No sexto dia, foi observada mortalidade superior a 80% para o primeiro, segundo e terceiro instares a 1% de oleo de nim. Os tres primeiros instares foram mais suscetiveis ao oleo de nim que o quarto instar.

Unveiling chemical defense in the rice stalk stink bug against the entomopathogenic fungus Metarhizium anisopliae

Eggs, nymphs (1st-5th instar) and adults of Tibraca limbativentris were challenged by conidial suspensions of its major fungal pathogen Metarhizium anisopliae in order to assess their susceptibility. The role of chemical defensive compounds from exocrine secretions produced by both nymphs and adults were examined for their participation on M. anisopliae infection. Although insect susceptibility to M. anisopliae followed a dose-dependent manner, adults followed by older nymphs displayed the highest resistance. Eggs were highly susceptible showing >96% fungal infection. Crude extracts isolated from metathoracic scent gland and dorsal abdominal glands of adults and nymphs, respectively, showed fungistatic effects by impairing spore germination, vegetative growth and sporulation. Gas chromatography-mass spectrometry analysis of these extracts revealed that the major components were short-chain hydrocarbons (C10-13) and unsaturated aldehydes. In vitro tests with the corresponding synthetic standards indicated compounds with greater antifungal activity including (E)-2-hexenal, (E)-2-octenal, and (E)-2-decenal, with the latter being the most deleterious to fungal fitness. We demonstrated that differential susceptibility of the rice stalk stink bug to M. anisopliae infection is age-specific and partly mediated by fungistatic properties of aldehydes, which are produced by scent glands of both nymphs and adults.

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.

NEEM OIL ANTIFEEDANT AND INSECTICIDAL EFFECTS ON Oebalus poecilus (HEMIPTERA: PENTATOMIDAE) MALES AND FEMALES 1

The antifeedant and insecticidal effects of two commercial neem ( Azadirachta indica ) oil formulations (Dalneem and Nim-I-Go) to Oebalus poecilus were evaluated on irrigated rice. To evaluate the antifeedant effect, both formulations were tested at 1% and 2% (v/v) concentration levels. The insecticidal effect was evaluated at 0.5%, 1%, 2%, and 4% (v/v) concentrations of Dalneem, by ingestion. Both experiments were conducted with four replications by treatment, containing one panicle and adult insects segregated by gender (two insects per plot for the antifeedant effect and five for the insecticidal effect). Both products were efficient, reducing the damage caused by insects. Insects fed less on the panicles treated with neem oil, causing lower number of feeding sheaths per panicle and lower percentage of damaged grains than the control. Spikelets weight was higher in panicles treated with neem oils. Females caused significantly higher damage than males in controls, for numbers of feeding sheaths and for the feeding deterrence index. Only at the 4% (v/v) concentration level, Dalneem caused adult mortality higher than in the control. Results showed that neem oil formulations, at >= 1% (v/v) concentration, can be used to reduce the quantitative and qualitative damages caused by O. poecilus in lowland rice. KEY-WORDS: Small rice stink bug; Azadirachta indica ; qualitative damages; Oryza sativa ; botanical extract.

First record of epizootics in the ocola skipper, Panoquina ocola (Lepidopera: Hesperiidae), caused by Isaria tenuipes in flooded rice fields of Central Brazil

We report the first occurrence of an epizootic of the ascomycete fungus, Isaria tenuipes (teleomorph Cordyceps takaomontana), on the ocola skipper Panoquina ocola (Lepidoptera: Hesperiidae), an insect pest affecting rice in Brazil.

Populational survey of arthropods on transgenic common bean expressing the rep gene from Bean golden mosaic virus

Genetically modified (GM) crops is considered the fastest adopted crop technology in the history of modern agriculture. However, possible undesirable and unintended effects must be considered during the research steps toward development of a commercial product. In this report we evaluated effects of a common bean virus resistant line on arthropod populations, considered as non-target organisms. This GM bean line (named M1/4) was modified for resistance against Bean golden mosaic virus (BGMV) by expressing a mutated REP protein, which is essential for virus replication. Biosafety studies were performed for a period of three years under field conditions. The abundance of some species was significantly higher in specific treatments in a particular year, but not consistently different in other years. A regular pattern was not observed in the distribution of insects between genetically modified and conventional treatments. Data analyses showed that minor differences observed can be attributed to random variation and were not consistent enough to conclude that the treatments were different. Therefore the present study indicates that the relative abundance of species are similar in transgenic and non-transgenic fields.

Phenotype responses to abiotic stresses, asexual reproduction and virulence among isolates of the entomopathogenic fungus Cordyceps javanica (Hypocreales: Cordycipitaceae)

Selecting entomopathogenic fungal isolates with resilience to environmental stresses, optimal mass production characteristics, and with high virulence to target pests favors the development of mycopesticides. A case in point, Cordyceps (= Isaria) javanica has been extensively investigated for non-chemical control of whiteflies worldwide. We phylogenetically characterized 11 native C. javanica isolates from Northeastern and Central Brazil. These isolates were screened for tolerance to heat-shock, UV-B radiation, osmotic and oxidative stresses, as well as conidial production on cereal grain and insecticidal activity against the whitefly Bemisia tabaci (MEAM 1) in the laboratory. All isolates were pathogenic to whiteflies and significant (3-fold) differences in median lethal concentration were observed among isolates. Furthermore, pronounced differences among isolates were found for stress factors and conidial production. Using principal component analysis, our results highlighted three major clusters formed by isolates (i) resistant to osmotic and oxidative stress, (ii) resilient to UV-B, and (iii) with high virulence, conidial production and heat tolerance. Overall, isolate CG1228 performed best based on multi-stress resistance, mass production and virulence attributes in the laboratory. This study highlights the importance of exploring natural variation in entomopathogenic fungi for selection of appropriate isolates for effective biocontrol of insect pests coupled with mass production characteristics and abiotic stress tolerances.

Enhanced mortality of Bemisia tabaci nymphs by Isaria javanica combined with sublethal doses of chemical insecticides

The aim of this current study was to evaluate the mortality of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) nymphs by the combination between the entomopathogenic fungus Isaria javanica (Friedrichs & Bally) Samson & Hywel‐Jones and synthetic chemical insecticides. The bioefficacy of I. javanica and the insect growth regulators named spiromesifen and buprofezin was tested alone and in combination against B. tabaci nymphs under screenhouse conditions. The in vitro compatibility between these two control agents was previously assessed under laboratory conditions. The sublethal concentration (LC25) of these insecticides towards second‐instar nymphs was determined and then mixed with the fungal treatments to investigate the type of interaction. All I. javanica isolates at 5 × 107 conidia/ml inflicted nymphal mortality by up to 62.4%. The insecticides did not influence the germination and mycelial growth of the selected I. javanica isolate CG1282. In general, the insecticide–fungus combinations increased nymphal mortalities in comparison with their single counterparts. Combinations with the fungus and buprofezin or spiromesifen augmented nymphal mortality by 10% and 24%, respectively, in comparison with the fungus alone. Additive interaction was found with the combination of the I. javanica CG1282 at 1 × 106 conidia/ml and spiromesifen at 1.56 ppm, and additive and synergistic interactions were achieved with the fungus at 5 × 106 conidia/ml and spiromesifen at 3.12, 6.25 and 12.5 ppm. Additive interactions were also observed from mixtures of fungus at 5 × 106 and buprofezin at 3.12 and 6.25 ppm. Only combinations of I. javanica with spiromesifen reduced to some extent the mycosis on dead nymphs. The joint action of I. javanica with sublethal doses of these insecticides may be a promising tool to assist in the integrated management system for B. tabaci.