Alberto S. Corrêa

Distribution of the related weevil species Sitophilus oryzae and S. zeamais in Brazil.

The genus Sitophilus (Coleoptera: Curculionidae) encompasses species of great economic importance as stored grain pests worldwide. Among these species, the maize and the rice weevils (Sitophilus zeamais and Sitophilus oryzae, respectively) are particularly important in warmer climates. These two weevils exhibit closely morphological and ecological resemblance making difficult their proper identification and recognition of their distribution in grain‐producing regions. Both species are recorded in South America and particularly in Brazil, but their respective distribution and prevalence were not yet assessed in the region. Therefore, several insect samples throughout Brazil were collected and subjected to morphological identification using male genitalia and also using molecular identification with species‐specific primers designed for clear recognition of both the species. The primers were designed for the specific amplification of a gene fragment of the cytochrome oxidase subunit I, which exhibited high specificity during our preliminary experiments with insects from six populations of known species (either S. zeamais or S. oryzae). Both identification strategies provided the same results indicating prevalence of the maize weevil S. zeamais throughout the country. Two hypotheses may explain such prevalence: (i) the likely host preference of S. zeamais for maize because this is the most cultivated cereal in Brazil, and (ii) the prevalence of S. zeamais in tropical regions as compared with S. oryzae, which is more disseminated in subtropical and temperate regions.

Resistência vs susceptibilidade a piretróides em Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae): há vencedor?

Studies on insecticide resistance evolution usually associate the phenomenon with an adaptative cost to the individual carrying this trait. Our objective was to verify if insecticide resistance in a population of Sitophilus zeamais Motschulsky incurs in fitness cost under an insecticide-free environment. Two populations of the species (a susceptible and a pyrethroid resistant population) were submitted to competition against each other for two consecutive generations in the absence of insecticide. A factorial bivariated derivated from an additive series was used in the experimental design with two initial density levels (lower, with 50 individuals of one population and a crescent series of individuals from 0 to 50 from the other population; and higher, with 100 individuals of a population and a crescent series of individuals from 0 to 100 from the other). The total number of adult insects, mortality by deltamethrin and insect body mass for each treatment were recorded. Adaptative disadvantage was not found on the resistant population compared with the susceptible population in an insecticide-free environment since both populations showed similar growth rate. This finding brings about practical complications for insecticide resistance management in this species because management strategies based on the interruption of pyrethroid use aiming their future reintroduction may not achieve the desired effects. This may take place because even after a long period without insecticide use, the resistant populations may still maintain themselves as such since there is no perceptible adaptative disadvantage associated with this trait.

High frequency of CYP337B3 gene associated with control failures of Helicoverpa armigera with pyrethroid insecticides in Brazil

Control failures with the use of pyrethroid insecticides have been reported frequently for populations of Helicoverpa armigera (Hübner) in Brazil, since its detection in 2013. Here, we confirmed and investigated the metabolic mechanisms of pyrethroid resistance in H. armigera populations from Brazil. Mortality of H. armigera populations was lower than 50% at the highest dose (10μg a.i./3rd instar larva) of the pyrethroids deltamethrin and fenvalerate in dose-response bioassays. Very low mortality (10 to 40%) was obtained at a diagnostic dose of 10μg a.i./larva for each pyrethroid in H. armigera populations collected from different agricultural regions in Brazil, from 2013 to 2016. In synergist bioassays, when larvae were treated with PBO synergist, the mortality of all populations tested was 100%. The frequency of the cytochrome P450 CYP337B3 gene was above 0.95 in all populations of H. armigera. We found only fourteen heterozygous H. armigera out of 497 individuals tested for this gene subfamily. Our results indicated that H. armigera populations from Brazil have different degrees of susceptibility to deltamethrin and fenvalerate, but all populations can be considered tolerant to pyrethroid insecticides. The chimeric P450 CYP337B3 enzyme is one of the main mechanisms of pyrethroid resistance in Brazilian H. armigera populations.

The Invasive Liriomyza huidobrensis (Diptera: Agromyzidae): Understanding Its Pest Status and Management Globally

Liriomyza huidobrensis (Blanchard) is native to South America but has expanded its range and invaded many regions of the world, primarily on flowers and to a lesser extent on horticultural product shipments. As a result of initial invasion into an area, damage caused is usually significant but not necessarily sustained. Currently, it is an economic pest in selected native and invaded regions of the world. Adults cause damage by puncturing abaxial and adaxial leaf surfaces for feeding and egg laying sites. Larvae mine the leaf parenchyma tissues which can lead to leaves drying and wilting. We have recorded 365 host plant species from 49 families and more than 106 parasitoid species. In a subset of the Argentinian data, we found that parasitoid community composition attacking L. huidobrensis differs significantly in cultivated and uncultivated plants. No such effect was found at the world level, probably due to differences in collection methods in the different references. We review the existing knowledge as a means of setting the context for new and unpublished data. The main objective is to provide an update of widely dispersed and until now unpublished data, evaluate dispersion of the leafminer and management strategies in different regions of the world, and highlight the need to consider the possible effects of climate change on further regional invasions or expansions.

The reunion of two lineages of the Neotropical brown stink bug on soybean lands in the heart of Brazil

The rapid pace of conversion of natural areas to agricultural systems is highly concerning, and the consequences for conservation and pest management are not yet fully understood. We examined mitochondrial (COI and Cytb) and nuclear (ITS1) gene regions of 21 populations of the stink bug Euschistus heros, to investigate the genetic diversity, genetic structure, and demographic history of this emerging soybean pest in South America. Two deep lineages that diverged in the Pliocene (4.5 Myr) occur over wide areas of Brazil. Historical changes during the Plio-Pleistocene led to significant genetic differences between E. heros populations, which differentiated further in several biomes. The northern lineage is older, more diverse, and prevalent in the Amazon and Caatinga, while the southern lineage is younger, less diverse, and prevalent in the Atlantic Forest and Chaco biomes. Euschistus heros populations are expanding in size and range but at different rates, strongly affected by environmental variables. Secondary contact between the main lineages is now occurring, mainly in areas of intensive farming and particularly in the Cerrado, an important agricultural frontier. Individuals adapted to different environmental conditions and to large monocultures might currently be combining into a panmictic and hard-to-control pest population.

Effects of glyphosate on the non-target leaf beetle Cerotoma arcuata (Coleoptera: Chrysomelidae) in field and laboratory conditions

ABSTRACT This study aimed to assess the glyphosate application effects on the Cerotoma arcuata Oliver (Coleoptera: Chrysomelidae) population in glyphosate-resistant soybean crops. Field studies were conducted with glyphosate and the insecticide endosulfan to observe the effects of these pesticides on C. arcuata, on its damages in the crop and on the populations of natural enemies in glyphosate-resistant soybean crops. Moreover, the lethal and behavioral sublethal response of C. arcuata to glyphosate and endosulfan was conducted in the laboratory. The results of the field and laboratory experiments showed that glyphosate caused moderate toxicity and high irritability in C. arcuata and that endosulfan caused high toxicity and irritability. Therefore, the direct effect of glyphosate on C. arcuata was negative and does not explain the population increases of this pest in glyphosate-resistant soybean. However, the glyphosate also decreased the density of predators. Thus, the negative effect of glyphosate on the predators may be related to population increases of C. arcuata in glyphosate-resistant soybean crops, however, more studies are needed to better evidence this relationship. This study suggests that glyphosate can impact other non-target organisms, such as herbivorous insects and natural enemies and that the use of this herbicide will need to be carefully stewarded to prevent potential disturbances in beneficial insect communities in agricultural systems.

Comparative cytogenetics and derived phylogenic relationship among Sitophilus grain weevils (Coleoptera, Curculionidae, Dryophthorinae)

Abstract Cytogenetic characteristics and genome size are powerful tools for species characterization and identification of cryptic species, providing critical insights into phylogenetic and evolutionary relationships. Sitophilus Linnaeus, 1758 grain weevils can benefit from such tools as key pest species of stored products and also as sources of archeological information on human history and past urban environments. Moreover, the phylogenetic relationship among these weevil species remains controversial and is largely based on single DNA fragment analyses. Therefore, cytogenetic analyses and genome size determinations were performed for four Sitophilus grain weevil species, namely the granary weevil Sitophilus granarius (Linnaeus, 1758), the tamarind weevil S. linearis (Herbst, 1797), the rice weevil S. oryzae (Linnaeus, 1763), and the maize weevil S. zeamais Motschulsky, 1855. Both maize and rice weevils exhibited the same chromosome number (2n=22; 10 A + Xyp). In contrast, the granary and tamarind weevils exhibited higher chromosome number (2n=24; 11 A + Xyp and 11 A + neo-XY, respectively). The nuclear DNA content of these species was not proportionally related to either chromosome number or heterochromatin amount. Maize and rice weevils exhibited similar and larger genome sizes (0.730±0.003 pg and 0.786±0.003 pg, respectively), followed by the granary weevil (0.553±0.003 pg), and the tamarind weevil (0.440±0.001 pg). Parsimony phylogenetic analysis of the insect karyotypes indicate that S. zeamais and S. oryzae were phylogenetically closer than S. granarius and S. linearis, which were more closely related and share a more recent ancestral relationship.