Daniel Ricardo Sosa-Gómez

Neotropical brown stink bug (Euschistus heros) resistance to methamidophos in Paraná, Brazil

The objective of this work was to evaluate the soybean neotropical brown stink bug (Euschistus heros) resistance to methamidophos through laboratory bioassays. Bioassays were carried out using populations of adults and nymphs of Euschistus heros in the last instar collected in soybean crops in Parana State. Highest frequencies of genotypes resistant to methamidophos were observed in Alvorada do Sul, Toledo and Nova Santa Rosa, PR. Populations from Bela Vista do Paraiso, Araruna, Campo Mourao, Mariluz, Cascavel, Sao Joao do Ivai, and Mambore were more susceptible to methamidophos. However, an increase on resistant genotypes in this locations cannot be discarded.

The impact of fungicides on Nomuraea rileyi (Farlow) Samson epizootics and on populations of Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae), on soybean

The fungus Nomuraea rileyi (Farlow) Samson is one of the most important natural enemies of soybean caterpillars, mainly under humid weather conditions. Outbreaks of the fungus Microsphaera diffusa Cooke & Peck have demanded fungicide applications on soybeans, which could result in outbreaks of noctuid populations by reduction of the natural inocula of N. rileyi. The recommended fungicides have shown to be detrimental to beneficial fungi, reducing infection, delaying epizootics, and resulting in increased host population densities. In laboratory assays, benomyl, difenoconazole, sulphur and carbendazim affected conidial germination of N. rileyi, being the latter less deleterious. To assess the impact of fungicides used to control M. diffusa, on N. rileyi, two tests were carried on, spraying difenoconazole (75 g a.i./ha) and benomyl (262.5 g a.i./ha) on soybean plots. In the 1997/98 trial, fungicide was sprayed once on soybean plants at R1-R2 developmental stages. In the 1998/99 test, two applications were made, when plants were at V5 and V7 developmental stages, respectively. The number of VBC larvae was significantly higher in the fungicide treated plots than in the control plots. In the 1997/98 test, benomyl treated plots resulted in higher populations of VBC than in the control or in the difenoconazole plots. In the 1998/99 test, VBC population was higher from 7 to 12 days after the first application, and remained high until 19 days after the second application. In general, fungicide treatments delayed the begining of N. rileyi epizootics from 2 to 14 days.

Insecticide resistance to endosulfan, monocrotophos and metamidophos in the neotropical brown stink bug, Euschistus heros (F.)

The Neotropical brown stink bug, Euschistus heros (F.), is usually controlled by organophosphate (OP) and cyclodiene (endosulfan) insecticides. Some unsuccessful control cases lead us to search for resistance to these insecticides in E. heros, the most common stink bug in the soybean growing regions of Parana State, Sao Paulo State and Central Region of Brazil. Bioassays were performed with endosulfan, monocrotophos and metamidophos against adults. The most susceptible population was found in Londrina. Populations from Pedrinhas Paulista (SP) showed the highest resistance ratio (RR) to endosulfan (RR= 8.7) and metamidophos (RR=2.7); resistance to monocrotophos was detected on bugs from Centenario do Sul (PR) (RR= 3.1). Stink bugs collected from Toledo (PR), showed susceptibility to metamidophos comparable to those from Londrina.

Use of Viruses Against Soybean Caterpillars in Brazil

Among the lepidopterous insects associated with soybeans in Brazil, the velvetbean caterpillar, Anticarsia gemmatalis, is the most important and widespread defoliator, seconded by species of Plusiinae, such as Pseudoplusia includens and Rachiplusia nu, which are of lesser importance but usually occur associated with populations of A. gemmatalis. Research with a nuclear polyhedrosis virus of A. gemmatalis (AgNPV) has led to a wide-scale use of the pathogen at farmer level, estimated in ca. 1,000,000 hectares annually. Most of its production has been carried out by estate organizations and farmer cooperatives, but at present four private companies are commercializing the AgNPV as a biological pesticide. NPVs of the Plusiinae complex are also being developed as a microbial insecticide, through a cooperative effort between Brazilian, Argentinian, and Uruguaian researchers. Research developments with the AgNPV, progress in its use at farmer level, and the work being carried out with baculoviruses of other soybean insects are discussed.

An Overview of Arthropod-Associated Fungi from Argentina and Brazil

Arthropod pests in forest and agricultural systems are affected by many pathogenic organisms. Among them, entomopathogenic fungi are the one most common control agents that regulate their populations. This review compiles the information available from Argentina and Brazil about the entomopathogenic fungi occurring in agricultural and natural environments. The scientific names of the fungi are listed according to the latest phylogenetically based classification of fungi. We present an updated list of arthropod-pathogenic fungi occurring in 15 of the 23 provinces of Argentina and 20 of the 27 states of Brazil based on published literature and our personal observations. The list includes a total of 114 fungal species from 53 genera: of Blastocladiomycetes (2 genera), Entomophthorales (8 genera), Harpellales (13 genera), and a diverse assortment of ascomycetes (primarily from Hypocreales) in 22 anamorphic and 5 teleomorphic genera. In the both countries, molecular studies on arthropod-pathogenic fungi are still in their early stages and have focused primarily on intraspecific variability and adequate generic assignment. This listing seeks to encourage more active collection and characterization of these fungi by both traditional and molecular approaches from the obviously rich but underexplored flora of fungi affecting arthropods throughout this large region of South America.

Intraspecific variation and population structure of the Velvetbean Caterpillar, Anticarsia gemmatalis Hübner, 1818 (Insecta: Lepidoptera: Noctuidae)

The velvetbean caterpillar (VBC), Anticarsia gemmatalis Hubner, 1818 (Insecta: Lepidoptera: Noctuidae), is one of the most important New World soybean agro-ecosystems pests, occurring from 40° N in the USA to 39° S in Argentina. Information on the migration patterns of the VBC moth may be important for managing the resistance of VBC populations to insecticides or plants carrying the Bacillus thuringiensis insecticide genes, especially since sedentary populations have a higher potential to became resistant than migratory populations. We studied intraspecific variations of geographically distinct VBC populations in order to determine the genetic distance between them and to assess the variability of VBC populations from near the city of Londrina (Parana (PR) state, Brazil). Samples of the VBC were obtained from sites near the following towns or cities: Marianna and Quincy (Florida, USA); La Virginia (Tucuman province, Argentina); Londrina (PR), Passo Fundo (Rio Grande do Sul, Brazil) and Planaltina (Goias, Brazil). The VBC samples were used to construct a genetic similarity matrix based on random amplified polymorphic DNA (RAPD) allele frequencies, the cotton leafworm, Alabama argillacea, Hubner 1823 (Insecta: Lepidoptera: Noctuidae), being used as an outgroup. Interestingly, despite the great distance (about 6,500 km) between Planaltina and Quincy some of the specimens from the Quincy population clustered in a group genetically close to the Planaltina populations. Larvae collected on peanuts in Marianna and on soybean in Quincy, 70 km apart, appeared genetically similar. The population from Planaltina was the most heterogeneous (polymorphism = 85.6%; heterozygosity = 0.1505). The Argentinean VBC population was entirely different from the Brazilian populations. The genetic similarities found between individuals from geographically distant populations and effective migration rate values (2.0566 > Nm < 15.2618) indicate that migration occurs.

Susceptibility of Alphitobius diaperinus (Panzer) (Coleoptera, Tenebrionidae) to cypermethrin, dichlorvos and triflumuron in southern Brazil

Susceptibility of Alphitobius diaperinus (Panzer) (Coleoptera, Tenebrionidae) to cypermethrin, dichlorvos and triflumuron in southern Brazil. The lesser mealworm, Alphitobius diaperinus (Panzer), is an important insect pest in poultry houses in Brazil. Susceptibility of the lesser mealworm collected from eight poultry houses in Parana state, southern Brazil, was evaluated for cypermethrin, dichlorvos and triflumuron. Adult A. diaperinus were tested in bioassays with cypermethrin and dichlorvos. Larvae were fed rabbit feed wetted with a triflumuron-water solution. Concentration-mortality regressions were estimated using Probit analysis and resistance ratios were calculated based on the susceptible population. Among the field populations evaluated, cypermethrin LC50 values for adults, ranged from 68.1 to 6,263 ng (AI)/cm2. LC50 values for adults challenged with dichlorvos ranged from 10.3 to 1,385 ng (AI)/cm2. One population from Pato Branco showed reduced susceptibility to triflumuron (LC50 = 272 µg (AI)/ml of solution) when compared to the most susceptible population (LC50 = 109.8 µg (AI)/ml). Application of cypermethrin and dichlorvos analogues should be managed with caution to minimize insecticide resistance problems.

Molecular characterization of Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) isolates

ITS and RAPD analyses were used to investigate molecular variations within samples of Paecilomyces isolates and to resolve five morphologically atypical isolates resembling P. fumosorosus, obtained from whitefly in Northern Parana State. The ITS4-ITS5 amplicon was 700 base pairs (bp) long in all isolates. The five isolates of Paecilomyces not assigned to species produced restriction profiles identical to all the reference strains of P. fumosoroseus. The extent of fingerprint variability observed by RAPD was sufficient to discriminate all the isolates. The genetic similarity among unidentified isolates and strains of P. fumosoroseus was even higher than that observed among reference strains of this species, allowing us to conclude that isolates CNPso-P77, CNPso-P78, CNPso-P80, CNPso-P85 and CNPso-P91 are P. fumosoroseus.

Insecticide Susceptibility of Euschistus heros (Heteroptera: Pentatomidae) in Brazil

ABSTRACT Euschistus heros (F.) (Heteroptera: Pentatomidae) is the most prevalent stink bug pest in Brazil, and populations can be difficult to manage using organophosphates or endosulfan. Because E. heros is difficult to rear in the laboratory, no baseline insecticide susceptibility data have been published. Therefore, we conducted dose-mortality studies using field-collected insects, and, using the results from the dose-mortality studies, we surveyed susceptibility to acephate, methamidophos, and endosulfan in populations from southern and central Brazil. In addition, esterase activity was evaluated among populations as these enzymes have been related to organophosphate resistance. Finally, newer chemistries were evaluated for E. heros population management in small-plot field studies. In the dose-mortality bioassays, variation in susceptibility to methamidophos and endosulfan among populations was significant, but the variation in susceptibility to acephate was not. The population from Londrina (at the Embrapa Soybean Research Station, northern Parana state) was among the most susceptible, whereas the population from Pedrinhas Paulista (southwestern Sao Paulo state) was among the least susceptible. Significant variation among populations was observed in esterase activity with the population from Pedrinhas Paulista having the highest esterase levels and the population from Londrina having among the lowest levels. To survey populations, we used the dose-mortality data for the Londrina population (because it was, consistently, one of the most susceptible populations) to estimate the insecticide concentration that killed 99% of the population (LC99). The corresponding doses were 5.9 µg (AI) of acephate adult-1, 0.7 µg (AI) methamidophos adult-1, and 1,600 µg (AI) endosulfan adult-1. The survey data confirmed the data from the dose-mortality bioassays in that the population from Pedrinhas Paulista was identified as one of the least susceptible and the population from Londrina was one of the most susceptible. The field tests confirmed that older chemistries provided minimal control (<50% control), whereas the products containing mixtures of pyrethroids and neonicotinoids provided better control (>60%).

First Records of Entomopathogenic Diseases in the Paraguay Tea Agroecosystem in Argentina

The northeastern region of Argentina leads that country in the production of Paraguay tea ( Ilex paraguariensis Saint Hilarie) with 170 metric tons per year. The most important pests of tea in this region are: a psyllid Metaphalara spegazziniana (Lizer)(Homoptera: Psyllidae), the “paraguay tea hornworm” Pengonia lusca ilus Bsd. (Lepidoptera: Sphingidae), and the gall bud mite Dichopelnus notus Keifer (Acarina: Eriophyid)]. M. spegazziniana is usually controlled by foliar sprays with dimethoate