Differential response to the South American rice water weevil (Coleoptera: Curculionidae) damage of rice cultivars with contrasting levels of resistance: implications for field management.

BACKGROUND: Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) is a major pest of flooded rice paddies throughout South America, and species with very similar life histories are present in many rice-producing regions of the world (collectively rice water weevils, RWWs). The damage caused by RWW larvae on rice cultivars with contrasting levels of resistance ('BRS Pampa CL'= 'Pamp': susceptible, 'BRS Atalanta' = 'Atal': resistant-antibiosis) was evaluated in two consecutive years in the field under seven infestation levels: 0, 2, 4, 6, 8, 10 and 20 adult couples per cage with plants. RESULTS: Higher densities of adults increased the number of leaf-feeding scars and larvae on roots, respectively, at the rate ≤2.14 and 2.75 in Pamp and 2.23 and 2.48 in Atal, with the total number of larvae generated being lower in Atal. Grain yield was negatively impacted with increasing larval density on the roots, mainly by decreasing root volume and the number of grains per panicle. Root injury intensity and yield loss showed a nonlinear relationship. It was found that significant yield losses occurred with 8.37 larvae per plant in Pamp and 9.80 larvae per plant in Atal CONCLUSION: The results provided the first evidence of a tolerance limit for RWW larval damage that, even though similar between cultivars of contrasting resistance, corresponds to twice the current conventional level for larval control in Brazil. We also discuss here the potential of applying tolerance limits to manage the RWW adult population in rice fields. © 2022 Society of Chemical Industry.

Resistance of rice genotypes to Tibraca limbativentris (Hemiptera: Pentatomidae).

The Tibraca limbativentris is a pest that causes rice crop damage and may lead to grain yield reductions of up to 90%. The most commonly used tactic for T. limbativentris control is chemical, which causes adverse effects on the environment. This study was conducted to identify sources of antixenosis and antibiosis resistance to T. limbativentris mediated by the hardness and diameter of the stem of the rice plant. Antibiosis and antixenosis tests were carried out with 22 rice genotypes of Brazilian and Asian origin. The Canela de Ferro, BRS Esmeralda, and Desconhecido Branco genotypes had the lowest proportions of stems showing symptoms of the damage caused by T. limbativentris. Canela de Ferro, Primavera, and IR 22 genotypes had the lowest nymphs survivorship and the genotypes Marabá Branco, Marabá, Skirivimankoti, Pepita, BR IRGA 409, Curinga, IR 40, Bonança, Desconhecido Branco, Bico Ganga, Primavera, and BRS Esmeralda were the least attractive to the insects. The genotypes BRS Esmeralda, Primavera, Desconhecido Branco, and Canela de Ferro were resistant to the rice stalk stink bug by antibiosis and/or antixenosis. These genotypes can be used directly by rice farmers for T. limbativentris management. Molecular biology studies should be conducted to identify and characterize resistance genes in these genotypes so that they can be used in breeding programs.

Economic Injury Levels and Economic Thresholds for Tibraca limbativentris (Hemiptera: Pentatomidae) on Paddy Rice Based on Insect-Days.

The rice stalk stink bug Tibraca limbativentris Stal, 1860 (Hemiptera: Pentatomidae) is an important pest of paddy rice (Oryza sativa L.) in South America. Current records of economic injury levels (EILs) and economic thresholds (ETs) for this insect are scarce. In this study, we determined EILs and ETs through cumulative insect-days of T. limbativentris adults in two phenological stages of paddy rice. Five field trials were established for the 2015/16 and 2016/17 crop season. To evaluate the relationship between insect-day and yield, rice plants were infested at V4 and R2 with adult male-female pairs of T. limbativentris. Mixed linear models were fitted utilizing the year and block as random factors to estimate the damage to plant, irrespective of the interference of environmental factors. The yield loss per insect-day was then used to calculate EILs using current market values and control costs. Rice grain yields were reduced by 5.91 kg/ha for each insect-day/m2 when infested during V4 stage, with EILs ranging from 3.88 to 11.61 insect-days/m2, while infestation during R2 stage resulted in a yield reduction of 3.16 kg/ha, with EILs ranging from 8.05 to 21.72 insect-days/m2. The results indicate that yield losses of paddy rice due to T. limbativentris infestation vary according to plant phenological stages and management should consider control cost and market value of rice. These EILs and ETs based on insect-days may be an efficient strategy for decision-making in the management of T. limbativentris on paddy rice.

Spatial Distribution and Coexisting Patterns of Adults and Nymphs of Tibraca limbativentris (Hemiptera: Pentatomidae) in Paddy Rice Fields.

The rice stem stink bug, Tibraca limbativentris Stål (Hemiptera: Pentatomidae), is a primary insect pest of paddy rice in South America. Knowledge of its spatial distribution can support sampling plans needed for timely decisions about pest control. This study aimed to investigate the spatial distribution of adults and nymphs of T. limbativentris and determine the spatial coexistence of these stages of development. Fifteen paddy rice fields were scouted once each season to estimate insect densities. Scouting was performed on regular grids with sampling points separated by ∼50 m. Moran's I and semivariograms were used to determine spatial distribution patterns. Spatial coexistence of nymphs and adults was explored via spatial point process. Here, adults and nymphs had typically contrasting spatial distribution patterns within the same field; however, the frequency of aggregation was not different between these developmental stages. Adults and nymphs were aggregated in seven fields and randomly distributed in the other eight fields. Uniform distribution of adults or nymphs was not observed. The study-wide semivariogram ranges were ∼40 m for adults and ∼55 m for nymphs. Nymphs and adults spatially coexisted on 67% of the fields. Coexisting patterns were classified using one of the following processes: stage-independent, bidirectional attractive, unidirectional attractive, bidirectional inhibiting, or unidirectional inhibiting. The information presented herein can be important for developing sampling plans for decision-making, implementing tactics for site-specific management, and monitoring areas free of T. limbativentris.

O percevejo-do-colmo Tibraca limbativentris Stål (Hemiptera: Pentatomidae) é uma praga primária na cultura do arroz irrigado na América do Sul. O conhecimento de sua distribuição espacial é essencial para desenvolver planos de amostragem e para o controle desta praga. Nosso objetivo foi investigar a distribuição espacial de adultos e ninfas de T. limbativentris e determinar a coexistência espacial entre os estágios de desenvolvimento. As densidades de adultos e ninfas foram estimadas em quinze campos de arroz irrigado. A amostragem foi realizada em grades regulares com pontos de amostragem separados por ∼50 m. Moran's I e semivariogramas foram usados para determinar os padrões de distribuição espacial. A coexistência espacial foi explorada pela análise de processos pontuais. Foi observado que adultos e ninfas tiveram padrões contrastantes de distribuição espacial dentro do mesmo campo; no entanto, a frequência de agregação não foi diferente entre esses estágios de desenvolvimento. Adultos e ninfas estavam agregados em sete campos e distribuídos aleatoriamente nos outros oito campos. Não foi observada a distribuição uniforme de adultos ou ninfas. O alcance médio dos semivariogramas foi de ∼40 m para os adultos e ∼55 m para as ninfas. Ninfas e adultos coexistiram espacialmente em 67% dos campos. Os padrões de coexistência foram classificados usando um dos seguintes processos: independente do estágio de desenvolvimento, atração bilateral, atração unilateral, inibição bilateral, ou inibição unilateral. Nosso estudo poderá contribuir para o desenvolvimento de planos de amostragem para tomada de decisão e implementação de táticas para o manejo de sítios específicos.

[Natural egg parasitism of Tibraca limbativentris Stal (Hemiptera: Pentatomidae) in rice crop in the State of Maranhão, Brazil]. / Parasitismo de ovos de Tibraca limbativentris Stal (Hemiptera: Pentatomidae) na cultura do arroz no Maranhão.

The rice stem bug, Tibraca limbativentris Stal, is an important pest of rice in Brazil. This work evaluated the occurrence of parasitoids in eggs of T.limbativentris egg parasitism in rice crops in the Maranhão State. The eggs collected exhibited an average parasitism of 32%. The parasitoids collected were Telenomus podisi (Ashmead), Trissolcus urichi (Crawford) (Hymenoptera: Scelionidae) and Oencyrtus submetallicus (Howard) (Hymenoptera: Encyrtidae).

Parasitismo de ovos de Tibraca limbativentris Stal (Hemiptera: Pentatomidae) na cultura do arroz no Maranhão / Natural egg parasitism of Tibraca limbativentris Stal (Hemiptera: Pentatomidae) in rice crop in the State of Maranhão, Brazil

O percevejo-do-colmo, Tibraca limbativentris Stal, é um dos insetos mais prejudiciais à cultura do arroz no Brasil. Este trabalho avaliou a ocorrência de parasitóides em ovos de T. limbativentris no Maranhão. Os ovos coletados apresentaram em média um parasitismo de 32 por cento. Os parasitóides identificados foram Telenomus podisi (Ashmead), Trissolcus urichi (Crawford) (Hymenoptera: Scelionidae) e Oencyrtus submetallicus (Howard) (Hymenoptera: Encyrtidae).

The rice stem bug, Tibraca limbativentris Stal, is an important pest of rice in Brazil. This work evaluated the occurrence of parasitoids in eggs of T.limbativentris egg parasitism in rice crops in the Maranhão State. The eggs collected exhibited an average parasitism of 32 percent. The parasitoids collected were Telenomus podisi (Ashmead), Trissolcus urichi (Crawford) (Hymenoptera: Scelionidae) and Oencyrtus submetallicus (Howard) (Hymenoptera: Encyrtidae).

Economic injury levels and sequential sampling plans for Mexican bean beetle (Coleoptera: Coccinellidae) on dry beans.

Field studies were conducted during the growing seasons of 1995 and 1996, in Scotts-bluff, Nebraska, to determine yield-loss relationships for Mexican bean beetle (Epilachna varivestis Mulsant) on dry bean (Phaseolus vulgaris L.). Results of those experiments were combined with data from other studies previously conducted to develop economic injury levels (EILs), economic thresholds (ETs), and a sequential sampling program for Mexican bean beetle. Yield loss was regressed against larvae/row-m, and the slope of the linear regression (113 kg/ha per larvae/row-m) was used as the DI (yield loss/insect density) variable in EIL calculations. The EILs calculated in larvae/row-m were converted to egg masses/row-m and adjusted to reflect average survivorship to the adult stage. An example EIL for esfenvalerate at 0.509 (formulation) liter/ha (0.0453 gal/a) and crop value of 0.44 dollars/kg (20 dollars/100 lbs) was 17.78 larvae/row-m. The corresponding ET is 1.04 egg masses/row-m, which reflects an average of 54.6 eggs/egg mass and 33% survival rate from egg to injurious stages. Sequential sampling plans were calculated based on a negative binomial distribution using parameter k estimated from previous research. Because sampling is based on egg masses, growers can make management decisions and take management actions before significant injury occurs. Also, ETs can be adjusted to include the occurrence of natural mortality in the egg and early instars. Analyses demonstrated that relatively minor variation in ETs has substantial impact on sequential sampling plans, including parameters such as average sample number. An interactive spreadsheet was developed that allows users to input economic and other data specific to their situation to calculate Mexican bean beetle EILs, ETs, and sequential sampling plans.

A Field technique for infesting rice with Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) and evaluating insecticide treatments / Técnica para infestar arroz com a lagarta Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) no campo e avaliar tratamentos com inseticidas

A technique for rearing Elasmopalpus lignosellus (Zeller),larvae in laboratory, infesting plants in the field and evaluating treatments was described and tested in rice. In addition, the performance of insecticides as seed treatments to control larvae, under artificial and natural infestations, was evaluated on three planting dates. The experimental design was a Latin 6x6 square and the experimental unit consisted of seven 4 m long rows and 0.4 m spacing between rows. Treatments consisted of the following insecticides and doses: thiamethoxam (52.5, 70, and 105 g a.i./100 kg seeds), furathiocarb (320 g a.i./100kg seeds), carbofuran (525 g a.i./100kg seeds), and an untreated control. Artificial infestations were made, in two groups of three selected tillers at the border rows in each plot and confined in PVC cylinders on three dates of each planting. Tillers were infested with three 7-day old E. lignosellus larvae. Immediately after infestation, cylinders containing three rice tillers were protected to avoid the effect of rain on the larvae. Damage was evaluated 20 days after the infestations. Artificial infestations increased the damage 32 fold, in relation to natural infestations in the untreated control. Insecticides reduced larval survival significantly for 60 days after planting compared to the untreated control.

Uma técnica para produzir lagartas Elasmopalpus lignosellus (Zeller), no laboratório, infestar plantas em campo e avaliar tratamentos foi descrita e testada em arroz. A ação de inseticidas para tratamento de sementes no controle da lagarta elasmo, utilizando infestação artificial e natural, também foi avaliada em experimentos de três datas de plantios. O delineamento experimental foi quadrado latino 6x6. A unidade experimental era formada de sete fileiras de arroz de 4 m de comprimento, espaçadas de 0,4 m. Os tratamentos consistiram dos seguintes inseticidas e doses: tiametoxam (52,5; 70 e 105 g i.a./100 kg sementes), furatiocarbe (320 g i.a./100kg sementes), carbofuram (525 g i.a./100 kg sementes) e testemunha não tratada. Infestações artificiais foram realizadas em dois grupos de três colmos, selecionados nas fileiras bordadura das parcelas e confinados em cilindros de PVC, em três datas de cada plantio. Colmos de cada cilindro foram infestados com três lagartas de E. lignosellus com sete dias de idade. Imediatamente após as infestações, os cilindros contendo três colmos de arroz foram protegidos do efeito das chuvas sobre as lagartas. Os danos foram avaliados 20 dias após as infestações. Infestações artificiais usadas neste estudo aumentaram o dano em 32 vezes, em relação à infestação natural das testemunhas. Inseticidas reduziram significativamente a sobrevivência de larvas até 60 dias após o plantio, comparados com a testemunha.

Consumption Rates and Performance of Erinnyis ello L. on Four Cassava Varieties / Taxas de Consumo e Desempenho de Erinnyis ello L. em Quatro Variedades de Mandioca

O consumo foliar de mandioca (Manihot esculenta Crantz) e a caracterização da injúria potencial por Erinnyis ello L. foram determinados em quatro variedades de mandioca. Lagartas deprimeiro ínstar foram criadas individualmente em folhas de quatro variedades de mandioca. Foi usado o delineamento experimental de blocos ao acaso com nove repetições. Folhas frescas com áreas previamente determinadas foram fornecidas às larvas diariamente. O consumo foliar em cada ínstar e o peso das lagartas e pupas foram registrados. Não houve diferença significativa no consumo foliar nas quatro variedades (P=0,82). O total de área foliar consumida (cm2) para as variedades testadas foi: 1030,5 (Fio de Ouro), 971,5 (Aipim Bravo), 968,6 (Urubu), 956,1 (Jaburu), sendo de 981,7 o consumo médio das quatro variedades. Aproximadamente 94% do consumo ocorreu durante os dois últimosínstares. Variedades não afetaram o desenvolvimento larval (P=0,96). Os pesos médios de lagartas (g) em cada variedade foram: 4,9 (Jaburu), 4,8 (Fio de Ouro), 4,7 (Urubu), 4,6 (Aipim Bravo) e 4,8 (média das quatro variedades). Dois modelos, um relacionando a área foliar consumida e desenvolvimento larval ( y = abxcx2) e outro do crescimento larval (y=5/1+ea+bx), foram estabelecidos. Os dados obtidos indicam que as variedades testadas neste estudo foram nutricionalmente semelhantes para odesenvolvimento de E. ello. Como o consumo foliar de E. ello foi semelhante para todas as variedades, a mesma taxa de consumo pode ser usada para o cálculo dos níveis de dano econômico para manejar E. ello nessas variedades.

A laboratory experiment to determine the consumption rates of cassava (Manihot esculenta Crantz) and characterize the injury potential by Erinnyis ello L. was conducted. First instar larvae were individually reared on excised cassava leaves of four varieties. A randomized block designwith nine replications was used. Fresh leaves were provided to the larvae daily. Leaf area was determined for each leaf before the leaves were provided to the larvae. Foliage consumption per instar, developmentaltime and weight of larvae and pupae were recorded. There were no significant differences in the larvalconsumption on the four varieties (P=0.82). Total leaf area consumption (square cm) for the varieties were: 1030.5 (Fio de Ouro), 971.5 (Aipim Bravo), 968.6 (Urubu), 956.1 (Jaburu) and across varieties was 981.6. About 94% of the feeding occurred during the last two larval instars. Varieties also had no effect on larval development (P=0.96). Mean larval weight (g) were: 4.9 (Jaburu), 4.8 (Fio de Ouro), 4.7 (Urubu), 4.6 (Aipim Bravo), and across varieties was 4.8. Two models, one relating larval leaffeeding and larval development ( y = abxcx2) and another for larval growing (y=5/1+ea+bx), were established. These data indicate that the varieties tested in this study were equally suitable for E. ello development. In addition, because the consumption rates of E. ello are the same across varieties, a single value can be used in determining economic injury levels to manage E. ello on these varieties.