A principal praga de trigo armazenado, no Brasil, Rhyzopertha dominica (Fabricius), foi testada na Embrapa Trigo, em Passo Fundo-RS, em papel filtro impregnado com deltametrina nas concentrações letais CL5, CL25 e CL50 para verificar alterações no comportamento de deslocamento do inseto, as quais podem contribuir para o manejo da resistência de pragas em grãos armazenados. Foram testados insetos de quatro raças, duas resistentes, BR6 e BR12, e duas suscetíveis, BR4 e UK1, que foram coletadas em unidades armazenadoras no Rio Grande do Sul e criadas em laboratório. Espécimes da raça UK1 foram obtidos do laboratório do Imperial College of Science and Technology, Reino Unido. Os resultados mostraram diferenças no comportamento ambulatorial das raças durante o período de 24 horas. Os espécimes das raças resistentes reduziram sua locomoção sobre a superfície contaminada na tentativa de evitar o contato com o inseticida.

The most important pest of stored wheat in Brazil, Rhyzopertha dominica (Fabricius, 1792), was tested at Embrapa Trigo, in Passo Fundo-RS, on filter paper impregnated with LC5, LC25, and LC50 of deltamethrin to verify alterations in its walking behaviour that may contribute for pest resistance management in grain storage. Insects of four strains were used, two resistant, BR6 and BR12, and two susceptible, BR4 and UK1, which were collected in storage facilities in Rio Grande do Sul and reared in the laboratory. Insects of the UK1 strain were brought from the laboratory of the Imperial College of Science and Technology, United Kingdom. The results showed differences in the walking behaviour between individuals of strains during the 24 h of the assessment period. Insects of the resistant strains reduced their walking activities on contaminated surface, in an attempt to avoid the insecticide .

Resultados de bioesnsaios com pirimicarbe, associados aos níveis de esterases totais obtidos através de testes colorimétricos, foram utilizados nesta pesquisa para determinar concentrações diagnostica para a avaliação da resistência de populações de Myzus persicae a inseticidas em cultura de batata Coletas de M. persicae foram feitas ao acaso em plantas de batata de plantações comerciais, na região de Curitiba, Piraí do Sul e Contenda, no Paraná, e Ibicoara na Bahia, durante o período de 1994 a 1996. A CL50 foi estimada submetendo-se os afídeos a bioensaios com concentrações (g/100 ml) de 0.0125; 0.025; 0.05 e 0,1% foram congelados uma hora após o tratamento e submetidos à avaliação das esterases totais, através de ensaio colorimétrico. Na concentração de 0,0125%, a mortalidade foi muito baixa, enquanto que a 0,1% a mortalidade atingiu 100% da população, indicando que a concentração diagnostica encontra-se dentro desta faixa. A diferença foi significativa entre as mortalidades nas concentrações de 0,025 e 0.05% em cada população estudada, mas não entre as populações coletadas nas quatro regiões. A concentração de 0,05% de pirimicarbe causa a mortalidade de aproximadamente 50% dos indivíduos altamente resistentes (R2), 72% dos levemente resistentes (R1) e 89,7% dos suscetíveis (S), podendo ser utilizada para diagnosticar populações resistentes de M. persicae. A determinação desta concentração diagnóstica é importante nos programas de manejo da resistência da praga em cultivo de batata, pois os indivíduos podem ser avaliados quanto à resistência nesta única concentração e, assim, baixa freqüência de resistência podem ser detectadas.

Insecticide bioassays associated with colorimetric testes were used to determine the diagnostic concentrations of pirimicarb for insecticide resistance detection in Myzus persicae populations from potato crops. The aphids were randomly collected on potato plants of commercial crops in Curitiba, Piraí do Sul and Contenda, in Paraná State and Ibicoara in Bahia state, from 1994 to 1996. The LC50 was estimated by submitting the aphids to bioassay with increasing concentrations of pirimicarb. Dead and live aphids from the 0.0125; 0.025; 0.05 and 0.1% (g/100ml) insecticide treatments were frozen after one hour of the bioassay and submitted to the evaluation of total esterase by colorimetric assays. Mortality was low at 0.0125%, but at 0.1% it reached 100% of the populations; thus, indicating that the diagnostic concentration is within this range. A significant difference was found between mortality caused by 0.025 and 0.05% pirimicarb in the same population, but not between populations collected from different areas. The 0.05% primicarb concentrations caused mortality of nearly 50% of high resistant individuals (R2), 72.0%of the moderately resistant populations (R1) and 89.7% of susceptible ones (S). The determination of this diagnostic concentration is useful for M. persicae resistance management programs because all individuals can be tested at this single appropriate concentration and low resistance frequencies can be detected in the population.

Seventeen clones of Rhopalosiphum padi (Linnaeus, 1758), 14 of R. maidis (Fitch, 1856), and two of R. insertum (Walker, 1849), representing a wide range of host plants and geographic distribution, were examined electrophoretically to determine intra and interspecific variation. Twenty-one enzyme systems were tested using starch-gel techniques. The electromorph variation within species was low, as expected for parthenogenetic organisms. Frequency of heterozygotes was also relatively low for most populations. The percentage of polymorphic loci ranged from 0% to 27.3% in R. padi, but it was lower (0% to 18.2%) in the completely an holocyclic R. maidis. No consistent correlation between band patterns and host plant or geographic origin could be established for R. padi and R. maidis. The distinction between R. padi and R. insertum was made by Est-1, Lap-2, Pgm, Got-1,and α-gpdh.The enzymes Est-2, G-3pdh, Sdh, and Got-2 were useful to separate R. maidis from R. padi, while Est-1, Lap-2, Got-1, and α-gpdh, in addition to the first three mentioned above, separated R. maidis from R. insertum. However, many other loci shared only one electromorph and had another that was useful to partially distinguish the species. The utilization of starch-gel electrophoresis as a taxonomic tool in distinguishing populations and species of aphids and its combination with other taxonomic methods are briefly discussed.