Jamilton P. Santos

Insecticidal activity of monoterpenes against Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst)

Secondary metabolites play an important role in plant resistance to insects. The monocyclic monoterpenes 1,8-cineole (eucalyptol) and R-(+)-limonene have been considered economically important in this context. Cineole is a component of different species of Eucalyptus spp. and limonene is a constituent of Citrus spp. essential oils. These substances were bioassayed to determine possible fumigant, contact, and ingestion activity against Rhyzopertha dominica (F.), lesser grain borer, and Tribolium castaneum (Herbst), red flour beetle, which are important pests of stored grain. It was possible to show that both compounds are insecticidal against the two insects, mainly in the contact and/or ingestion action.

Resistance to DDT and pyrethroids in Brazilian populations of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae)

Abstract Control failures of deltamethrin used against Sitophilus zeamais Motsch. in Brazil led to the investigation of the possible resistance of this pest to DDT, pirimiphos-methyl and the pyrethroids deltamethrin, cypermethrin and pemethrin, synergized or not with piperonyl butoxide. DDT is not now approved for use in Brazil, but was widely used in the past against this pest. Pirimiphos-methyl and synergized deltamethrin are recommended for S. zeamais control, and cypermethrin and permethrin are not used despite their efficiency against this pest. Bioassay tests were carried out using the insecticide-impregnated filter paper method recommended by FAO, and the discriminating concentrations were established based in the LC 99.9 of each compound, synergized or not, for the standard susceptible population. With these tests, a cross-resistant spectrum to DDT and pyrethroids was verified in six populations of S. zeamais . One population showed resistance only to DDT and deltamethrin, while three other populations showed resistance only to DDT.

Inheritance of Deltamethrin resistance in a Brazilian strain of maize weevil (Sitophilus zeamais mots.)

Abstract Insecticide‐impregnated paper assays were used to analyse the inheritance of Deltamethrin resistance (2634X) in a DDT‐pyrethroid cross‐resistant strain of maize weevil, Sitophilus zeamais Mots., from Brazil. At the KD50 the responses of the F1hybrid reciprocal crosses were very different and χ2 analyses of the observed responses of F2 and F1‐backcross progenies provided evidence that a single gene was responsible for resistance. Deltamethrin resistance seems to be controlled by a single recessive sex‐linked gene.

Controle de Rhyzopertha dominica pela atmosfera controlada com CO2, em trigo

Controlled atmosphere with inert gases offers an alternative to phosphine use to control stored grain pests. The objective of this research was to test a controlled atmosphere with CO2 to control Rhyzoperta dominica, (Fabr.) (Coleoptera: Bostrichidae), an important pest of stored wheat grain. This test consisted of five CO2 concentrations ( 0, 30, 40, 50 and 60%; completed with N2), fumigation periods of 5, 10 and 15 days; insect populations collected from Campo Mourao, PR, Sete Lagoas, MG and Santa Rosa, RS, in Brazil and seven developing stages (egg, larva of 1st, 2nd, 3rd and 4th instar, pupa and adult), in three replications. All the different life stages of the insect were kept as individual samples in a small voile cloth bag and put inside a 200 liter fumigation chamber with 75% of this volume full of grain with the metal lid sealed at the edge with silicone rubber to guarantee hermetic conditions. The different CO2 concentrations were then added inside the chambers. The results showed that all CO2 concentrations tested caused 100% mortality to all adult stage of the three insect populations in all fumigation periods tested. The mortality of the pupa stage of the three insect population was 100% when the 60% CO2 concentration was used in the 15 days fumigation period; however, all CO2 concentrations in 15 days fumigation period caused 100% mortality in pupa of insects collected in Santa Rosa. For adequate control of all larval stages it requires 50% CO2 or above this concentration. During the 10 and 15 days fumigation periods all CO2 concentrations controlled 100% of the eggs from the three populations studied.

Nível de dano econômico de Sitophilus zeamais (M.) em trigo armazenado

Calcular o nivel de dano economico (NDE) para o principal inseto-praga Sitophilus zeamais (Motschulsky, 1895) do trigo armazenado, foi o objetivo deste trabalho. Para o calculo do NDE relacionaram-se o grau de infestacao e as perdas qualitativa e quantitativa dos graos, depois de tres meses de armazenamento. Utilizaram-se potes de vidro transparente de 2,5 L, com 1,5 kg de graos de trigo tipo durum, da safra de setembro/97, com teor de umidade de 12,5%. Os potes foram infestados com densidades populacionais de 0, 2, 10, 20, 30, 50, 100, 200 e 300 insetos da especie S. zeamais, em tres repeticoes, e entao armazenados por um periodo de 90 d, em câmaras tipo BOD, com temperatura de 27 oC e 65 ± 5% de umidade relativa. Logo depois do periodo de armazenamento tomava-se a temperatura da massa de graos e, em seguida, contava-se o numero de insetos adultos vivos e mortos. Os graos foram analisados quanto a perda de peso e a perda de qualidade (peso hectolitrico e teor de umidade). Tanto a massa final quanto o peso hectolitrico (PH) para cada nivel de infestacao, foram corrigidos para o teor de umidade inicial dos graos. Utilizando-se os dados do valor de mercado do grao de trigo importado e nacional, do custo de controle para fumigacao e do valor obtido pela inclinacao das curvas de regressao entre perda de peso (g) e PH (g 250 mL-1) em relacao a infestacao final de S. zeamais, calculou-se o NDE. Com base na reducao do peso da massa de graos, no peso hectolitrico e no valor de mercado do trigo, encontrou-se um NDE de 0,18 inseto kg-1 de grao.

Aspectos da biologia da cigarrinha-do-milho, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae)

Na cultura do milho, a cigarrinha, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) e vetora de tres patogenos: Spiroplasma kunkelii (corn stunt spiroplasma), o fitoplasma do milho (maize bushy stunt phytoplasma) e o virus da risca do milho (maize rayado fino virus). Os prejuizos causados por essas doencas podem variar de nove a 90 %, dependendo da susceptibilidade das cultivares e dos patogenos envolvidos. O objetivo deste trabalho foi estudar aspectos da biologia de D. maidis, sob condicoes controladas e utilizando-se insetos e cultivares de milho e sorgo adaptados as condicoes brasileiras. Plântulas de milho e de sorgo foram cultivadas em vasos plasticos, cobertas com gaiolas de plastico e infestadas com 10 adultos por planta. Sempre utilizando-se 10 plântulas por tratamento, foram conduzidos dois ensaios independentes. No 1°, estudou-se o periodo de incubacao nas temperaturas constantes de 17, 20, 23, 26, 29 e 32oC ± 1oC e fotofase de 12 h. No 2°, estudou-se o desenvolvimento de ninfas a temperatura constante de 26,5 ± 2oC e mesma fotofase. O periodo de incubacao foi mais curto nas temperaturas de 26 e 29oC, nas quais cerca de 70% das ninfas levaram nove dias para a eclosao. Foram observados ate cinco instares, embora cerca de 76% da populacao tenha completado o desenvolvimento passando por apenas quatro instares. A duracao media de cada instar foi de 3,14 dias. Os adultos viveram em media 51,4 dias e o ciclo medio de ovo a adulto foi de 26,3 dias. Portanto, para a manutencao de colonias de insetos ou no desenvolvimento de estudos com essa especie e importante observar os limites maximos e minimos de temperatura.