Temporal dynamics of Apis mellifera (Hymenoptera: Apidae) during flowering in indeterminate soybean (Glycine max).

Soybean varieties with indeterminate growth habit are widely used in the state of Mato Grosso do Sul and are characterized by not having well-defined phenological stages. Due to the importance of bee conservation, studies on the frequency and time of visitation in indeterminate soybean are needed. Samples were collected in a 4-ha plot of soybeans not treated with insecticides. Sampling was carried out at random spots, throughout the flowering period, starting at 08h:00min, during 15 min/hour, successively until 16h:00min. Generalized Linear Models were generated and the Poisson regression model provided the best fit, reflecting the significant differences revealed by the deviance analysis. The association between bees and climatic variables was tested with the Spearman's correlation. The temporal pattern of bee visitation was independently influenced by flowering period and time of day. However climatic variables did not influence significantly bee visitation rate. In the first days of flowering, bees were more abundant, especially between 10h and 15h. These results have practical implications in the maintenance of this species during soybean management practices, contributing to a balanced coexistence between beekeepers and soybean growers, by avoiding applications of phytosanitary products during the periods of high bee visitation.

Intercropped Bt and non-Bt corn with ruzigrass (Urochloa ruziziensis) as a tool to resistance management of Spodoptera frugiperda (JE Smith, 1797) (Lepidoptera: Noctuidae).

BACKGROUND: Corn intercropped with ruzigrass is common in Brazil, and it can improve the physicochemical features of soils, increase water retention, and suppress the emergence of resistant weeds and soil nematodes. As both corn and ruzigrass are hosts to Spodoptera frugiperda (the main corn pest in South America), the cultivation of both these plants in the same place at one time motivates investigation into the pest population dynamics. We hypothesize that the intercropping system influences S. frugiperda pressure and leaf injury in corn. Considering that if corn hybrids with high dose toxin expression are used, ruzigrass may be a potential host to susceptible S. frugiperda larvae, consequently an alternative refuge and be included as a tool for the resistant management of Bt corn. To test these hypotheses about the use of ruzigrass as an alternative host of S. frugiperda in an intercropping system with corn, we conducted field trials in three seasons to verify S. frugiperda population dynamics and leaf injury to crop systems. In addition to phenotypic evaluation, we also characterized molecularly S. frugiperda strains collected in corn and ruzigrass to identify strain differences. RESULTS: The insects collected in both corn and ruzigrass were identified as corn strains. Ruzigrass was used as a S. frugiperda host during all crop cycles. The intercropped system did not increase the S. frugiperda population or leaf injury on Bt corn. CONCLUSION: The results suggest that the intercropped system is not prejudicial to Bt corn cultivation since high dose concept applies to all larvae instars. The results also suggest that ruzigrass may be used as a promising alternative refuge in Bt corn agroecosystems, if compliance with management strategies is followed. © 2021 Society of Chemical Industry.

Spatial Distribution of Euschistus heros (Hemiptera: Pentatomidae) in Cotton (Gossypium hirsutum Linnaeus).

Recently, the Neotropical brown stink bug, Euschistus heros (Pentatomidae: Hemiptera), has been detected in cotton in the Brazilian Cerrado. Several reliable surveys have been conducted on the spatial distribution of stink bugs in soybean; however, few studies have examined the behavior of this insect in cotton in Brazil. Thus, this study examined the spatial distribution of E. heros in cotton using aggregation indices based on the variance-to-mean ratio, Morisita index, exponent k, Poisson and negative binomial distributions. Inverse Distance Weighting interpolation maps were also used to represent insect density. The study was conducted in a 1.1 hectare experimental cotton field in which 64 equally-sized plots were sampled on a weekly basis. Our findings revealed that stink bugs presented an aggregate distribution in 2 sampling weeks based on aggregation indices, and this pattern was best described by a negative binomial distribution. Maps showing the density of pests can be an important tool for sampling pests in crops and control measures in early stages of infestation, when there is an edge effect on the distribution of E. heros, can be an efficient strategy in cotton.

Spatial Distribution of Eggs of Alabama argillacea Hübner and Heliothis virescens Fabricius (Lepidoptera: Noctuidae) on Bt and non-Bt Cotton.

Among the options to control Alabama argillacea (Hübner, 1818) and Heliothis virescens (Fabricius, 1781) on cotton, insecticide spraying and biological control have been extensively used. The GM'Bt' cotton has been introduced as an extremely viable alternative, but it is yet not known how transgenic plants affect populations of organisms that are interrelated in an agroecosystem. For this reason, it is important to know how the spatial arrangement of pests and beneficial insect are affected, which may call for changes in the methods used for sampling these species. This study was conducted with the goal to investigate the pattern of spatial distribution of eggs of A. argillacea and H. virescens in DeltaOpal™ (non-Bt) and DP90B™ Bt cotton cultivars. Data were collected during the agricultural year 2006/2007 in two areas of 5,000 m2, located in in the district of Nova América, Caarapó municipality. In each sampling area, comprising 100 plots of 50 m2, 15 evaluations were performed on two plants per plot. The sampling consisted in counting the eggs. The aggregation index (variance/mean ratio, Morisita index and exponent k of the negative binomial distribution) and chi-square fit of the observed and expected values to the theoretical frequency distribution (Poisson, Binomial and Negative Binomial Positive), showed that in both cultivars, the eggs of these species are distributed according to the aggregate distribution model, fitting the pattern of negative binomial distribution.

[Effects of nitrogen fertilization in cotton crop on Aphis gossypii Glover (Hemiptera: Aphididae) biology]. / Efeitos da adubação nitrogenada em algodoeiro sobre a biologia de Aphis gossypii Glover (Hemiptera: Aphididae).

The cotton aphid, Aphis gossypii Glove, is one of the pests of cotton crop and its relation with the host seem to depend on the amount of nitrogen available to the plant. The biology of A. gossypii using different cotton nitrogen fertility regimes was studied under greenhouse conditions, in Dourados, MS. A completely randomized design with nine replications in a factorial scheme (2x4x2)+1 was used. Two nitrogen sources (sulphate of ammonium and urea), four doses of nitrogen (50, 100, 150 and 200 kg ha-1), two different times of nitrogen application and one additional treatment without nitrogen were taken as factors. The nymphal phases, the pre-reproductive, reproductive and pos-reproductive periods, longevity, the life cycle and fecundity of the cotton aphid were evaluated. The doses of nitrogen influenced the cotton aphid biology in both sources and times of application, favoring its development and fecundity.

Efeitos da adubação nitrogenada em algodoeiro sobre a biologia de Aphis gossypii Glover (Hemiptera: Aphididae) / Effects of nitrogen fertilization in cotton crop on Aphis gossypii Glover (Hemiptera: Aphididae) biology

O pulgão Aphis gossypii Glover é uma das pragas do algodoeiro e suas relações com o hospedeiro são dependentes da quantidade de nitrogênio disponível para a planta. A biologia do A. gossypii, em função do regime de adubação nitrogenada no algodoeiro, foi estudada em condições de casa-de-vegetação, em Dourados, MS. Para isto foi utilizado o delineamento experimental inteiramente casualizado com nove repetições, com os tratamentos arranjados em fatorial (2 x 4 x 2) + 1, com duas fontes de adubo nitrogenado, quatro doses de nitrogênio (50, 100, 150 e 200 kg ha-1), duas épocas de aplicação do nitrogênio em cobertura e um tratamento adicional sem a adição do nitrogênio. Foram avaliadas as durações dos estádios ninfais e da fase ninfal, os períodos pré-reprodutivo, reprodutivo e pós-reprodutivo, a longevidade, o ciclo biológico e a fecundidade dos pulgões. Concluiu-se que apenas as doses de nitrogênio influenciaram a biologia do pulgão-do-algodoeiro, independente da fonte e época de aplicação, favorecendo seu desenvolvimento e fecundidade.

The cotton aphid, Aphis gossypii Glove, is one of the pests of cotton crop and its relation with the host seem to depend on the amount of nitrogen available to the plant. The biology of A. gossypii using different cotton nitrogen fertility regimes was studied under greenhouse conditions, in Dourados, MS. A completely randomized design with nine replications in a factorial scheme (2x4x2)+1 was used. Two nitrogen sources (sulphate of ammonium and urea), four doses of nitrogen (50, 100, 150 and 200 kg ha-1), two different times of nitrogen application and one additional treatment without nitrogen were taken as factors. The nymphal phases, the pre-reproductive, reproductive and pos-reproductive periods, longevity, the life cycle and fecundity of the cotton aphid were evaluated. The doses of nitrogen influenced the cotton aphid biology in both sources and times of application, favoring its development and fecundity.

[Spatial distribution of plants infested with Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) on corn crop]. / Distribuição espacial de plantas infestadas por Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) na cultura do Milho.

The importance of the fall armyworm, Spodoptera frugiperda (J.E. Smith), is not only due to the damage it can cause, but also to its difficult control. It is essential to know the pest population parameters, such as its standard scattering in the crop, because depending on the space arrangement of the insects in the area, different sampling methods are required. For the present work, three experimental fields were installed in different areas: the first one had 66 plots with seven plants each; the second one had 55 plots with four plants each; and the third field had 55 plots with six plants each. The presence or absence of the pest in the plant was evaluated in the samples. According to the data observed, either to the scattering index or to the theoretical scattering models, S. frugiperda dispersion is scattered at random and strongly depends on the infestation level.

Distribuição espacial de plantas infestadas por Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) na cultura do milho / Spatial distribution of plants infested with Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) on corn crop

A importância da lagarta-do-cartucho, Spodoptera frugiperda (J.E. Smith), deve-se não somente aos danos causados, mas especialmente à dificuldade de seu controle. É imprescindível o conhecimento dos parâmetros populacionais da praga, como seu padrão de dispersão na cultura, pois, dependendo do arranjo espacial do inseto na área são necessários diferentes métodos de amostragem, variando o número e o tamanho da amostra. Para o presente trabalho foram instalados três campos experimentais em três diferentes áreas. No Campo I foram alocadas 66 parcelas, compostas por sete plantas cada; no Campo II foram demarcadas 55 parcelas, compostas por quatro plantas, e por fim, o Campo III também foi formado por 55 parcelas compostas por seis plantas cada uma. Nas amostragens realizadas avaliou-se a presença ou ausência da praga na planta. De acordo com os dados observados tanto para os índices de dispersão como para os modelos teóricas de distribuições de freqüência, S. frugiperda possui padrão de dispersão espacial definido mais adequadamente pela aleatoriedade, sendo esse modelo de distribuição muito influenciado pelo nível da infestação.

The importance of the fall armyworm, Spodoptera frugiperda (J.E. Smith), is not only due to the damage it can cause, but also to its difficult control. It is essential to know the pest population parameters, such as its standard scattering in the crop, because depending on the space arrangement of the insects in the area, different sampling methods are required. For the present work, three experimental fields were installed in different areas: the first one had 66 plots with seven plants each; the second one had 55 plots with four plants each; and the third field had 55 plots with six plants each. The presence or absence of the pest in the plant was evaluated in the samples. According to the data observed, either to the scattering index or to the theoretical scattering models, S. frugiperda dispersion is scattered at random and strongly depends on the infestation level.