Understanding the factors influencing fall armyworm (Spodoptera frugiperda J.E. Smith) damage in African smallholder maize fields and quantifying its impact on yield. A case study in Eastern Zimbabwe

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.

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[Spatial distribution of plants infested with Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) on corn crop].

O estudo da distribuicao espacial de pragas e fundamental para elaboracao de planos de amostragem para o uso do manejo integrado de pragas. Para o afideo Toxoptera citricida (Kirkaldy), estudou-se a distribuicao espacial em talhoes de pomares de citros comerciais de laranja-doce [Citrus sinensis (L.) Osbeck] da variedade Pera, com 5; 9 e 15 anos de idade, durante o periodo de setembro de 2004 a abril de 2005. Foram realizadas 14 amostragens de numero de T. citricida em intervalos aproximados de 15 dias entre as mesmas, utilizando-se de armadilhas adesivas de cor amarela (0,11 x 0,11 m) fixadas a planta, a 1,5 m de altura aproximadamente. As armadilhas foram distribuidas na area, a cada cinco plantas na linha, em linhas alternadas, totalizando 137 armadilhas no talhao com 5 anos, 140 no talhao com 9 anos e 80 no talhao com 15 anos. Os indices de dispersao utilizados foram: razao variância media (I), indice de Morisita (Id), coeficiente de Green (Cx) e expoente k da distribuicao Binomial Negativa. O indice que melhor representou a agregacao do pulgao foi o expoente k da distribuicao Binomial Negativa, e a distribuicao binomial negativa foi o modelo que melhor se ajustou aos dados. Atraves destas analises, verificou-se que a maioria das amostragens apresentou uma distribuicao agregada da populacao de T. citricida.

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Distribuição espacial de Toxoptera citricida (Kirkaldy) (Hemiptera: Aphididae) na cultura de citros

The cotton boll weevil Anthonomus grandis Boheman (Coleoptera: Curculionidae) is the main pest in cotton crop around the world, directly affecting cotton production. In order to establish a sequential sampling plan, it is crucial to understand the spatial distribution of the pest population and the damage it causes to the crop through the different developmental stages of cotton plants. Therefore, this study aimed to investigate the spatial distribution of adults in the cultivation area and their oviposition and feeding behavior throughout the development of the cotton plants. The experiment was conducted in Maracaju, Mato Grosso do Sul, Brazil, in the 2012/2013 and 2013/2014 growing seasons, in an area of 10,000 m2, planted with the cotton cultivar FM 993. The experimental area was divided into 100 plots of 100 m2 (10 × 10 m) each, and five plants per plot were sampled weekly throughout the crop cycle. The number of flower buds with feeding and oviposition punctures and of adult A. grandis was recorded throughout the crop cycle in five plants per plot. After determining the aggregation indices (variance/mean ratio, Morisita's index, exponent k of the negative binomial distribution, and Green's coefficient) and adjusting the frequencies observed in the field to the distribution of frequencies (Poisson, negative binomial, and positive binomial) using the chi-squared test, it was observed that flower buds with punctures derived from feeding, oviposition, and feeding + oviposition showed an aggregated distribution in the cultivation area until 85 days after emergence and a random distribution after this stage. The adults of A. grandis presented a random distribution in the cultivation area.

Spatial Distribution of Adult Anthonomus grandis Boheman (Coleoptera: Curculionidae) and Damage to Cotton Flower Buds Due to Feeding and Oviposition

The fall armyworm ( Spodoptera frugiperda) causes damage and reduction in maize production and is considered a pest difficult to control, thus determining its spatial distribution pattern contributes to the development of suitable sampling and control strategies. The aim of this study was to evaluate the spatial distribution of Spodoptera frugiperda in maize culture under the conditions of the wasteland of southern Pernambuco state. The experiment was conducted at the Experimental Station of Brejao - ‘Instituto Agronomico do Pernambuco’ (IPA) from April to May 2012. The study area consisted of 100 plots of 60 m2, where 10 plants per plot were weekly sampled at random. In each plant, the number of small and large larvae of S. frugiperda was counted on the leaves and the husk of ears. According to the data observed, the aggregation indices (variance/mean ratio, Morisita’s index, Green’s Index, and Exponential k of a negative binomial distribution) indicated aggregate distribution for both small and large caterpillars, and the negative binomial distribution was the most appropriate model to represent the distribution pattern of small larvae of this pest in the field. In maize crop in the wasteland of southern Pernambuco state, S. frugiperda presents aggregate pattern of distribution and tends to spread from the points of aggregation and colonize form the border into the center of cultures.

https://cepnor.ufra.edu.br/index.php?journal=ajaes&page=article&op=download&path%5B%5D=1461&path%5B%5D=507

J.C Barbosa

Papers

Modelos probabilisticos para distribuicoes de lagartas de spodoptera frugiperda (j. E. Smith, 1797) na cultura do milho