Vilmar Machado

Identification and Comparison of Fall Armyworm (Lepidoptera: Noctuidae) Host Strains in Brazil, Texas, and Florida

Abstract Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major economic pest throughout the Western Hemisphere. Studies of populations in the southern United States and the Caribbean demonstrated the existence of two morphologically identical but genetically distinct host strains. These races can be distinguished by using polymorphisms in the mitochondrial cytochrome oxidase I gene that define two distinct maternal lineages that correlate with strain-specific behaviors in Florida populations. Although there is evidence of different biotypes in Brazil, it has not been demonstrated that these biotypes are equivalent to the U.S. strains. Sampling from Brazil indicates that its fall armyworm populations consist of the two strain-specific haplotypes found in Florida and also display the expected biases in plant host distribution. The same genetic markers also were present in samples from Texas, a major source of migrating fall armyworm in North America. These results indicate that the biology and behaviors of Brazilian fall armyworm populations are similar to those found in North America.

Molecular Characterization of Host Strains of Spodoptera frugiperda (Lepidoptera: Noctuidae) in Southern Brazil

Abstract Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a Neotropical species found from Argentina to the United States of America. In its distribution area, two genetically distinct strains are found that differ in their plant host distribution. The strains are morphologically identical, and they can only be reliably distinguished by molecular markers. In this study, we characterized caterpillars collected in corn, Zea mays L., and rice, Oryza sativa L., plantations in the state of Rio Grande do Sul, Brazil. The mitochondrial haplotype typical of the rice strain was found in 100% of the caterpillars collected from that crop, whereas 83% of the caterpillars obtained from corn were of the corn strain haplotype. A sex-linked tandem repeat element called FR was previously shown to have a strain-biased distribution in North American populations. We demonstrated that the same element is found in Brazilian fall armyworm and that it also organized in large tandem repeat clusters that are most frequently observed in caterpillars collected from rice and that display the rice strain mitochondrial haplotype. These results indicate that the Brazilian and North American fall armyworm populations are virtually indistinguishable with respect to the known genetic markers that are diagnostic of strain identity. Furthermore the data are consistent with other studies suggesting substantial gene flow between these widely separated populations. The strain-biased distribution of the FR element makes it a potentially useful marker to estimate interstrain hybridization frequencies of this species in Brazil.

Phylogenetic relationships and the evolution of mimicry in the Chauliognathus yellow-black species complex (Coleoptera: Cantharidae) inferred from mitochondrial COI sequences

The phylogenetic relationships of twelve species of Chauliognathus were investigated by studying the mitochondrial cytochrome oxidase I gene. A 678 bp fragment of the COI gene was sequenced to test the hypothesis that the Mullerian mimicry species of the “yellow-black” complex make up a monophyletic clade, separated from species with other colour patterns. The data set was analysed by neighbour-joining, maximum parsimony and maximum likelihood procedures. The results support a single origin of the yellow-black colour pattern during the evolution of the genus, with one main clade formed by Chauliognathus lineatus, C. tetrapunctatus, C. riograndensis, C. flavipes, C. octomaculatus, C. fallax, and another one formed by two species, C. expansus and C sp 1, plus an orange-black-coloured species. The nucleotide divergences found between C. sp 3 (black) and the other species studied fall within the level expected for species from different genera. The similarity of colour patterns of the yellow-black species has been considered an example of Mullerian mimicry by conservation of the ancestral state with some minor modifications.

Elytra colour polymorphism and randomness of matings in Chauliognathus fallax Germar 1824 from southern Brazil (Coleoptera, Cantharidae)

Beetles of the species Chauliognathus fallax Germar 1824 are polymorphic for elytron colouration with six morphs distinguished on the basis of black pigmentation on a yellow background. We investigated samples of C. fallax taken in eight consecutive weeks aiming to determine the frequency of the morphs which were grouped, for statistical analysis, into three classes according to elytra pigmentation as well as the possible occurrence of assortative mating. Our results showed a variation in the frequency of the classes throughout the season, both in males and females, with the maximum frequency of each class at the fourth and fifth week. The three classes (A, B, C) showed the same pattern of variation, and class B was always the more frequent. To test randomness of matings two approaches were taken: in the first, we compared the frequency of each class in copulating and non-copulating insects. In the second, the frequency of each class in the whole sample was taken as the probability of occurrence of the respective class; then, using the criterion of the probability of independent events we calculated the expected proportion of copulating insects for each pair of events. Both methods gave non-significant differences, suggesting that the matings were random.

Impact of lambdacyhalothrin on arthropod natural enemy populations in irrigated rice fields in southern Brazil

The present study aimed to determine the selectivity of the pyrethroid lambdacyhalothrin on arthropod natural enemy populations in irrigated rice fields in Rio Grande do Sul, Brazil. The study was conducted at three sites: districts of Cachoeira do Sul, Eldorado do Sul and Capivari do Sul during the crop years of 2007/2008 and 2008/ 2009. Each site consisted of two subareas divided into four plots. One of the subareas received a spray application of 150 ml/ha of lambdacyhalothrin CS 50, while the other subarea was untreated. Arthropods were collected at 2, 15, 30 and 45 days after the application of the insecticide to assess its impact on natural enemy populations. The results indicated consistent differences in natural enemy populations between the treated and untreated areas, especially within the first 2 weeks after the application of the insecticide. Principal components analysis together with χ2 analysis revealed differences in the populations of Tetragnathidae, Anyphaenidae, Araneidae, Coccinellidae, Phytoseiidae and Coenagrionidae between the treated and untreated areas. This study indicated the existence of a great diversity of arthropod natural enemies in irrigated rice fields in a subtropical environment similar to that reported previously from rice fields in tropical environments. In addition, lambdacyhalothrin was shown to be a rapid acting insecticide, with a significant initial decrease in natural enemy populations followed by a rapid recovery beginning at 2 weeks after the application of the insecticide. Especially disconcerting is the severe impact of the insecticide on Phytoseiidae and Araneidae, which are considered key natural enemies for the management of rice pests in southern Brazil.

The aggregation of Chauliognathus species (Coleoptera, Cantharidae) and its possible role for coexistence and mimicry

The relative population sizes of a species complex of Chauliognathus are reported, as well as their spatial distribution associated with different patches of food plants. Field work was done at Fazenda Santa Isabel, municipality of Guaiba, State of Rio Grande do Sul, Brazil. The results suggest that two mechanisms account for the reduction in food competition among the species involved: one is asynchrony in the appearance of the species in the area, and the other is aggregation in different patches of food plants. Since the species here reported show a similar colour pattern (yellow-black) the possibility of the occurrence of serial mimicry in this complex of species is dicussed.

Diversity of culturable Gram-negative bacteria isolated from irrigation water of two rice crop regions in Southern Brazil

In this study, we assessed the diversity of Gram-negative bacteria found in water used for irrigation of rice crops in two growing areas of southern Brazil. Samples were collected from the main irrigation channel and field drain area. Twenty-two bacterial species were found in Cachoeirinha and 28 in Camaquã. In both areas, the most frequent bacterial families were Enterobacteriaceae and Aeromonadaceae. Differences in microbial diversity were observed in both study areas. Thirty-five Gram-negative species were identified; however, only 15 were common in both locations. In addition, there were found pathogenic and drug-resistant species, such as Acinetobacter sp., Brucella spp., and Chryseobacterium meningosepticum. This study demonstrates the existence of a number of pathogenic species in aquatic ecosystems analyzed in three consecutive crop years, especially water used for rice production.

Bacillus thuringiensis Characterization: Morphology, Physiology, Biochemistry, Pathotype, Cellular, and Molecular Aspects

In this publication, “Bacillus thuringiensis and Lysinibacillus sphaericus – characterization and use in the field of biocontrol,” this chapter can be seen as a brief general and historical introduction to the central theme of the book, where data on the cellular physiology, biochemical, genetic, molecular, and toxicological aspects of the bacterium, B. thuringiensis (Bt), are reported. This predominant entomopathogenic prokaryote was discovered and denominated Bt around a century ago, between 1902 and 1911. From the microbiological point of view, this bacterium is ubiquitous, Gram-positive, produces ellipsoidal but predominantely cilindrical endospores (central to paracentral) and contains a parasporal inclusion body called crystal or δ-endotoxin. The crystal is constituted of Cry proteins with molecular weight between 30 kDa and 140 kDa, which are coded by cry genes. On the other hand, this bacterial species synthesizes several enzymes and toxins that give them a wide adaptation to natural habitats. Bt strains have been studied and, over time, characterized and described as toxic and specific for Lepidoptera, Diptera, Coleoptera, Nematoda, Protozoa, Trematoda, Acari, Hymenoptera, Hemiptera, Orthoptera, Isoptera, Mallophaga, and among other target pests. Globally, 82 Bt serovars sometimes called subspecies were described until 1999, which currently correspond to more than 700 cry genes distributed in about 70 classes. The nomenclature review of cry genes, which encode Bt Cry proteins, has been published by Crickmore et al. and has been constantly updated on the website: http://www.lifesci.sussex.ac.uk/home/Neil_Crickmore/Bt/.

Microbial, physical and chemical properties of irrigation water in rice fields of Southern Brazil

This paper presents the results of the statistical analysis of microbiological, physical and chemical parameters related to the quality of the water used in rice fields in Southern Brazil. Data were collected during three consecutive crop years, within structure of a comprehensive monitoring program. The indicators used were: potential hydrogen, electrical conductivity, turbidity, nitrogen, phosphorus, potassium, calcium, total and fecal coliforms. Principal Component and Discriminant Analysis showed consistent differences between the water irrigation and drainage, as the temporal variation demonstrated a clear reduction in the concentration of most of the variables analyzed. The pattern of this reduction is not the same in the two regions - that is, the importance of each of the different variables in the observed differentiation is modified in two locations. These results suggested that the variations in the water quality utilized for rice irrigation was influenced by certain specific aspects of each rice region in South Brazilian - such as anthropic action or soil/climate conditions in each hydrographic basin.