Susana Padín

Grain loss caused by Tribolium castaneum, Sitophilus oryzae and Acanthoscelides obtectus in stored durum wheat and beans treated with Beauveria bassiana

The effect of the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete) on the losses caused to durum wheat and beans by storage insects was investigated. Grains were infested with Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Acanthoscelides obtectus (Say). Beauveria bassiana was produced in inoculated autoclaved rice. The spore formulation (ground rice and B. bassiana) was applied to grain (wheat or bean) and shaken to evenly cover the grain. Adults of T. castaneum or S. oryzae were added to wheat and adults of A. obtectus to bean. Five replicates were set up for each treatment and controls (milled rice but no conidia). The insecticidal effect of B. bassiana was tested by measuring the fresh weight and weight loss of grains after four months of storage. Wheat grains infested with S. oryzae without the conidia was significantly more damaged by weevils than grains treated with B. bassiana. The mean fresh weight of grains with the conidia was significantly greater (18.4%) than the corresponding mean without the fungus when S. oryzae were present. Percentage weight loss decreased by 81.5% and was significantly smaller than the loss from the untreated grain. Significant differences were not found in the fresh weight of seed infested with T. castaneum or A. obtectus in treated or untreated grain nor in the percentage weight loss of grains infested with these insects, with and without B. bassiana.

Laboratory evaluation of chemical-biological control of the rice weevil (Sitophilus oryzae L.) in stored grains.

The virulence of ten different fungal isolates of: Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii and Paecilomyces farinosus to the rice weevil Sitophilus oryzae was tested. A fungal mix of the most efficient isolates, B. bassiana ARSEF 5500+M. anisopliae ARSEF 2974, which caused the highest mortality, was assayed in combination with fenitrothion at a concentration lower (3 ppm) than the normal 6 ppm. Fungal inoculation of insects was done by spraying conidial suspensions of each fungus on wheat. Insecticide formulations were added by spraying wheat. Treated and untreated insects were incubated on durum wheat. Insects were kept in a climatized chamber for 30 days. Observations were performed at 7, 14 and 30 days to record insect mortality. Highly significant differences were demonstrated for B. bassiana 5500 and 5501 and for M. anisopliae 2974. The level of mortality produced by treatments was: 6 ppm insecticide=97.50%, B. bassiana ARSEF 5500+M. anisopliae ARSEF 2974+3 ppm insecticide=74.17%, B. bassiana ARSEF 5500+M.anisopliae ARSEF 2974=50% and 3 ppm insecticide=37.50%. There was a statistically significant difference (p<0.05) among treatments.

Increased mortality of Acanthoscelides obtectus by alkane-grown Beauveria bassiana

The effect of alkane-growth induction of theentomopathogenic fungus Beauveria bassiana(Balsamo) Vuillemin (Deuteromycotina:Hyphomycetes), on the ability to kill the beanweevil Acanthoscelides obtectus Say(Coleoptera: Bruchidae), was tested. Adultinsects were sprayed with an 0.01% Tween 20aqueous suspension of 4 × 106 conidia/ml.The performance of fungi grown in complete agarmedium containing glucose as carbon source(FS0) was compared to that of alkane-grownfungi (FS1) with n-hexadecane as the onlycarbon source. Mortality increased (p< 0.05) from 22 ± 4.5% to 44 ±11.4% at day 7, and from 26 ± 5.5% to 60± 7.1% 14 days after treatment withFS0 or FS1 respectively. The insectepicuticular hydrocarbons were analysed bycapillary gas chromatography (CGC); majorcomponents were saturated hydrocarbons, 27 to29 carbons in length. A variety ofmethyl-branched isomers of C27 were theprevailing structures, and nC27 was the majorstraight chain component. Whole insecthydrocarbons were qualitatively identical tothose of the epicuticular surface. Oleic,linoleic and palmitic acids accounted foralmost 88% of the fungal fatty acids,irrespective of the carbon source used forgrowth; however, the unsaturated/saturatedratio diminished markedly from 4.32(FS0) to 2.47 (FS1). These resultsindicate that alkane supplementation of culturemedia might be a tool to improve the virulenceof some mycoinsecticides.

Pathogenicity of Beauveria bassiana for adults of Tribolium castaneum (Col.: Tenebrionidae) in stored grains

Conidia ofBeauveria bassiana were evaluated for activity against adults ofTribolium castaneum, under laboratory conditions closely resembling the stored-grain conditions.Three doses of the fungus were applied in the treatments: 0.1 g, 0.5 g and 1 g per 20 insects/dose/flask. Treated insects and untreated were incubated in broken wheat. There were 5 replications for each test.A total of 1600 treated and control insects used were kept in a climatic chamber (70±5% and 27±2°C) for 45 days. Observations were performed daily and the recording of infected cadavers began when the percentage of mortality exceeded 50%. The evaluation of the efficiency of each dose ofB. bassiana was made 14, 21, 28 and 45 days after inoculation.Mortality of adults that were exposed to the beetles treated with 0.5 g and 1 g of conidia ofB. bassiana / 20 adults was 87 and 85% respectively, within 21 days of exposure. Onset of mortality was further delayed at lower dosage of the fungus; 55% after 21 days. After 28 days there were no difference in mortality between the 0.5 g and 1 g dosages ofB. bassiana. The most efficient treatment was 0.5 g/20 insects, which resulted in a control higher than 50% 14 days post treatment.RésuméL’activité des conidies deB. bassiana vis-à-vis d’adultes deTribolium castaneum a été évaluée dans des conditions de laboratoire similaires à celles existant dans des grains stockés.Les traitements ont consisté en une application de trois doses de champignon: 0,1 g, 0,5 g et 1 g dans des flacons contenant 20 insectes par dose, avec du blé concassé pour les témoins comme pour les individus traités. Les insectes utilisés (au nombre de 1600) ont été placés dans une chambre climatisée (70±5% et 27±2°C) pendant 45 jours. Des observations quotidiennes ont été faites et le contrôle des individus morts infectés a commencé quand le pourcentage de mortalité a dépassé les 50%. L’évaluation de l’efficacité de chaque dose deB. bassiana a été faite 14, 21, 28 et 45 jours après l’inoculation. La mortalité des adultes traités avec 0,5 g et 1 g de conidies deB. bassiana/20 adultes a été respectivement de 87 et 85%, dans les 21 premiers jours d’exposition. Le début de la mortalité a été retardé avec des doses plus faibles du champignon: seulement 55% après 21 jours d’exposition. A partir de 28 jours, il n’y a pas de différence de mortalité observée entre les doses de 0,5 g et de 1 g deB. bassiana. Le traitement le plus efficace a été obtenu avec une dose de 0,5 g / 20 insectes et a produit une mortalité supérieure à 50% après 14 jours.

Biocontrol of Acanthoscelides obtectus and Sitophilus oryzae with diatomaceous earth and Beauveria bassiana on stored grains

Abstract Combined treatment with Beauveria bassiana, and diatomaceous earth (DE) was evaluated against the bean weevil Acanthoscelides obtectus and rice weevil Sitophilus oryzae. DE from Argentina was screened both alone or in combination with water or dry fungal formulations. DE killed 100% of A. obtectus and 68% of S. oryzae showing a significantly higher insecticidal effect than the fungal dust. For A. obtectus, median lethal time (MLT) with the DE–dry fungus was significantly lower than with a fungal aqueous-suspension. In S. oryzae, powder formulations with either of B. bassiana or DE showed a MLT significantly higher than the wet treatments.

Interaction of fungicides with the entomopathogenic fungus Isaria fumosorosea

Abstract The effects of eight commonly used fungicides: propamocarb, fenarimol, triadimefon, procimidone, azoxystrobin, carbendazim, cooper oxychloride and Trichoderma harzianum on germination, mycelial growth and virulence of Isaria fumosorosea (Wize) Brown & Smith (Ascomycota: Hypocreales) was studied. The greatest effect on germination was observed by azoxystrobin, followed by carbendazim, triadimefon and procimidone. Propamocarb, fenarimol, cooper oxychloride and T. harzianum did not affect conidial germination with germinations of 95, 93, 79 and 84%, respectively. Virulence was evaluated against early fourth instar nymphs of Trialeurodes vaporariorum (Hemiptera: Aleyrodidae). The mix containing fungal conidial suspensions plus cooper oxychloride or fenarimol presented a significant reduction in the mortality in comparison with spore suspension itself. This study suggests that the most appropriate fungicides for use in Integrated Pest Management Programs against T. vaporariorum in combination with I. fumosorosea are propamocarb and T. harzianum.

Utilización de Aceite Esencial de Lemongrass (Cymbopogon citratus Stapf) Como Repelente de Diuraphis noxia Kurdj. (Hemiptera: Aphididae) en Trigo

Una herramienta alternativa para el manejo integrado de plagas, es la utilizacion de productos naturales, como aceites esenciales y extractos vegetales. El objetivo del trabajo fue evaluar la actividad repelente del aceite esencial de lemongrass (Cymbopogon citratus Stapf) sobre el pulgon ruso (Diuraphis noxia Kurdj.) en trigo (Triticum aestivum L.). El aceite esencial se formulo en solucion acuosa empleando como emulsionantes propilenglicol al 5% y lecitina de soja al 0,5%. Las concentraciones evaluadas fueron 0,5; 1; 2; 3 y 4% y testigos en blanco, con cinco repeticiones por tratamiento. Se utilizaron dos tecnicas de aplicacion: impregnacion de papeles y pulverizacion directa, cuando las plantas de trigo se encontraban al estado de dos hojas completamente desarrolladas. Luego de la aplicacion, se colocaron 10 pulgones adultos por maceta y se realizo el recuento a las 6 h. Los resultados obtenidos se transformaron en porcentaje de repelencia y se analizaron por ANDEVA y test de Tukey (P = 0,05). Para las tecnicas de aplicacion, se obtuvo un porcentaje de repelencia de 66,07 y 74,33% para pulverizacion e impregnacion de papeles, respectivamente. Al evaluar las formulaciones con los dos emulsionantes, lecitina de soja y propilenglicol, el porcentaje de repelencia fue de 64,78 y 75,63%, respectivamente. Para las concentraciones de lemongrass, el porcentaje de repelencia oscilo entre 65 y 89%. Se concluye que los volatiles de C. citratus demostraron poseer actividad repelente sobre D. noxia.

Insecticidal efficacy of beauveria bassiana, diatomaceous earth and fenitrothion against rhyzopertha dominica and tribolium castaneum on stored wheat

ABSTRACT Bioassays were conducted in stored grains to evaluate the combined use of the entomopathogenic fungus Beauveria bassiana, diatomaceous earth (DE) and fenitrothion against adults of Rhyzopertha dominica and Tribolium castaneum. The insecticide agents were applied to wheat as follows: the fungus at 1 × 108 conidia/kg of wheat, DE at 3 g/kg of wheat and fenitrothion at a rate of 0.15 ml/kg of wheat (25% of field dose rate). Surviving insects and progeny production were monitored at thirty-day intervals until four months. For both insect species, significantly less progeny was produced on wheat treated with fenitrothion and DE + B. bassiana formulations in comparison with controls. The effect of insecticides on the grain damage, germination power of wheat and bulk density was also evaluated. After four months, B. bassiana mixed with DE reduced the damaged insect grains by 50% in comparison with both fenitrothion and control treatments. Trials using DE caused a reduction in bulk density while there were no significant differences for germination testing between treatments.