The behavior of Aphis gossypii and Aphis craccivora (Hemiptera: Aphididae) and of their predator Cycloneda sanguinea (Coleoptera: Coccinellidae) in cotton-cowpea intercropping systems

ABSTRACT The intercropping is an important cultural practice commonly used in pest management. It is based on the principle that increased plant diversity in the agro-ecosystem can lead to reductions of pest populations in the crop. The current study aimed to assess the impact the colored fiber cotton-cowpea intercropped systems on Aphis gossypii and Aphis craccivora and on their predator Cycloneda sanguinea and the losses and the dispersion behavior of these aphids and their predator in these cropping systems. The experiment had a randomized block experimental design with two bioassays and four treatments. The number of apterous and alate aphids (A. gossypii) per cotton plant was 1.46 and 1.73 or 1.97 and 2.19 times highest in the solid cotton system than that found in the cotton-cowpea intercropped systems (S1) and (S2), respectively. On the other hand, the cotton-cowpea intercropped systems (S1 and S2) reduced, respectively, in 43% and 31% the number of apterousA. gossypiiper cotton plant compared to the control. Implementing cotton-cowpea intercropped system in the S1 scheme reduced A. gossypii infestation, favored the multiplication of C. sanguinea, and allowed obtaining heavier open bolls.

Population dynamics of Aphis gossypii Glover and in sole and intercropping systems of cotton and cowpea

ABSTRACT Population dynamics of aphids have been studied in sole and intercropping systems. These studies have required the use of more precise analytical tools in order to better understand patterns in quantitative data. Mathematical models are among the most important tools to explain the dynamics of insect populations. This study investigated the population dynamics of aphids Aphis gossypii and Aphis craccivora over time, using mathematical models composed of a set of differential equations as a helpful analytical tool to understand the population dynamics of aphids in arrangements of cotton and cowpea. The treatments were sole cotton, sole cowpea, and three arrangements of cotton intercropped with cowpea (t1, t2 and t3). The plants were infested with two aphid species and were evaluated at 7, 14, 28, 35, 42, and 49 days after the infestations. Mathematical models were used to fit the population dynamics of two aphid species. There were good fits for aphid dynamics by mathematical model over time. The highest population peak of both species A. gossypii and A. craccivora was found in the sole crops, and the lowest population peak was found in crop system t2. These results are important for integrated management programs of aphids in cotton and cowpea.

Ecological modeling and pest population management: a possible and necessary connection in a changing world / Modelagem ecológica e manejo de populações de pragas: uma conexão possível e necessária para um mundo em transformação

Ecological modeling is an important tool for investigating dynamic behavior patterns in populations, trophic interactions, and behavioral ecology. However, the ecological patterns that reflect population oscillation trends are often not clearly visible without analytical instruments such as ecological models. Thus, ecological modeling plays a fundamental role in describing demographic processes that are important for population dynamics. Ecological models, besides making possible the visualization of ecological patterns, may also reveal patterns of population persistence in many trophic systems, including prey-predator or host-parasitoid relationships, interactions that are commonly present in integrated pest management programs. In this forum, we present the main ecological aspects important for model building and implementation of integrated pest management programs for insects. Particularly, in this study, we analyze the combination between host-parasitoid models and the concept of economic threshold level on a spatio-temporal scale. As a conclusion about the model combination, spatial structure is essential for models of this nature, since its introduction into the system significantly alters the economic threshold-level values.

A modelagem ecológica é uma ferramenta importante para a investigação de padrões de comportamento dinâmico em populações, interações tróficas e também em ecologia comportamental. Contudo, os padrões ecológicos que refletem tendências de oscilação populacional muitas vezes não são claramente visíveis sem instrumentos analíticos, como os modelos ecológicos. Dessa forma, a modelagem ecológica exerce papel fundamental na descrição de processos demográficos importantes para a dinâmica populacional. Os modelos ecológicos, além de tornarem possível a visualização de padrões ecológicos, podem também revelar padrões de persistência populacional nos diversos sistemas tróficos, incluindo as relações presa-predador ou hospedeiro-parasitóide, interações comumente presentes em programas de manejo integrado de pragas. Neste fórum apresentamos os principais aspectos ecológicos importantes para a construção de modelos e implementação de programa de manejo de pragas em insetos. Em particular, analisamos a combinação entre modelos hospedeiro-parasitóide e o conceito de nível de dano em escala espaço-temporal. Como conclusão sobre a combinação de modelos, evidencia-se que a estrutura espacial é essencial para modelos desta natureza, já que sua introdução no sistema altera significativamente os valores de nível de dano econômico.

Seasonal population dynamics in Lucilia eximia (Wiedemann) (Diptera: Calliphoridae)

In this study the seasonal variation of fecundity, wing and tibia sizes were investigated in natural populations of Lucilia eximia (Wiedemann) as an attempt to determine the variations in life history of the species associated to seasonality. Specimens of L. eximia were monthly collected in Botucatu, São Paulo, Brazil, during two years and the adult females dissected to estimate fecundity. Body size was estimated by measuring wing and tibia. Fecundity and body size were seasonally analysed. A relatively constant temporal trajectory was found for fecundity, wing and tibia size over twenty-four months. Strong positive correlations between wing and tibia size, fecundity and wing and fecundity and tibia were observed. The maintenance of stable values in L. eximia indicates that it has suffered little seasonal influence over the period analysed. This result confirms the demographics and life history stable profile of the species in spite of seasonal climatic changes observed in the study area.

Neste estudo variações sazonais da fecundidade, tamanhos de asa e tíbia foram investigadas em populações naturais de Lucilia eximia (Wiedemann), na tentativa de determinar as alterações bionômicas da espécie, associadas à sazonalidade. Exemplares de L. eximia foram coletados mensalmente em Botucatu, SP, durante dois anos e as fêmeas adultas dissecadas para estimar a fecundidade. O tamanho do corpo foi estimado por medições de asa e tíbia. A fecundidade e o tamanho do corpo foram analisados sazonalmente. Uma trajetória temporal relativamente constante foi encontrada para fecundidade e tamanhos de asa e tíbia durante os 24 meses de estudo. Fortes correlações positivas entre tamanhos de asa e tíbia, fecundidade e tamanho de asa e fecundidade e tamanho de tíbia foram observadas. A manutenção dos valores estáveis em L. eximia indica que a espécie sofreu pouca influência sazonal durante o período analisado. Esse resultado confirma o perfil demográfico e bionômico estável da espécie a despeito das variações climáticas sazonais observadas na área de estudo.

The dynamics of intraguild predation in Chrysomya albiceps Wied. (Diptera: Calliphoridae): interactions between instars and species under different abundances of food

The pattern of larval interaction in blowflies confined with Chrysomya albiceps Wied. and C. rufifacies Maquart can be changed in response to the predatory behaviour of the two species to a contest-type process instead of the scramble competition that usually occurs in blowflies. Facultative predation is a frequent behaviour in C. albiceps and C. rufifacies that occurs as an alternative food source during the larval stage. In this study, we investigated the dynamics of intraguild predation by C. albiceps on other fly species in order to analyse interspecific and intraspecific survival in C. albiceps, C. megacephala and C. macellaria Fabricius. The experimental design of the study allowed us to evaluate how factors such as species, density and abundance of food influenced the survival of the calliphorid species. When C. albiceps was confined with C. megacephala or C. macellaria, only adults of C. albiceps survived at different larval densities and abundance of food. In addition, the survival of C. albiceps was higher in two-species experiments when compared to single species experiments. The implications of these results for the dynamics of C. albiceps were discussed.

O padrão de interação larval em moscas-varejeiras na presença de Chrysomya albiceps Wied. e C. rufifacies Maquart pode ser alterado em função do comportamento predatório das duas espécies, mudando a estratégia de competição do tipo explorativa para competição por interferência. A predação facultativa é um comportamento freqüente em C. albiceps e C. rufifacies durante o estágio larval. Neste estudo, investigamos a dinâmica de predação intraguilda por C. albiceps sobre outras espécies de moscas, em experimentos delineados para analisar a sobrevivência interespecífica e intraespecífica em C. albiceps, C. megacephala Fabricius e C. macellaria Fabricius. O delineamento experimental do estudo permitiu avaliar de que modo fatores como, espécies, densidade e abundância de alimento, influenciaram a sobrevivência das espécies em culturas puras e mistas. Quando C. albiceps foi confinada com C. megacephala ou C. macellaria, somente adultos de C. albiceps sobreviveram em diferentes densidades e abundância de alimento. Além disso, a sobrevivência de C. albiceps foi superior em culturas mistas se comparada aos experimentos com culturas puras. As implicações desses resultados para a dinâmica de C. albiceps foram discutidas.

Fuzzy subset approach in coupled population dynamics of blowflies

This paper is a study on the population dynamics of blowflies employing a density-dependent, non-linear mathematical model and a coupled population formalism. In this study, we investigated the coupled population dynamics applying fuzzy subsets to model the population trajectory, analyzing demographic parameters such as fecundity, survival, and migration. The main results suggest different possibilities in terms of dynamic behavior produced by migration in coupled populations between distinct environments and the rescue effect generated by the connection between populations. It was possible to conclude that environmental heterogeneity can play an important role in blowfly metapopulation systems. The implications of these results for population dynamics of blowflies are discussed.

Seasonal fecundity and body size in Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae)

In this study the seasonal variation of fecundity, wing and tibia size was investigated in natural populations of Chrysomya megacephala (Fabricius) aiming at determining the variations in life history of the species as a function of seasonality. A relative constant temporal trajectory was found for fecundity, wing and tibia size over twelve months. Strong positive correlations between wing size and temperature, tibia size and temperature and between wing and tibia sizes were observed. The implications of the results for population dynamics of C. megacephala were discussed.

Neste estudo a variação sazonal da fecundidade, tamanhos de asa e tíbia, foi investigada em populações naturais de Chrysomya megacephala (Fabricius) a fim de determinar variações nas características bionômicas da espécie em função da sazonalidade. Uma trajetória temporal relativamente constante foi encontrada para fecundidade, tamanhos de asa e tíbia durante doze meses. Correlações positivas e significativas entre tamanho da asa e temperatura, tamanho da tíbia e temperatura e tamanhos da asa e tíbia foram observadas. As implicações desses resultados para a dinâmica populacional de C. megacephala foram discutidas.

Delayed density dependence at the immature stage in insects and the dynamic behavior of nonlinear difference equations

A growing body of evidence indicates that the conditions experienced by immatures in insects, in particular crowding, have a lasting consequence for the population dynamics o adults. In this case, as first demonstrated by Prout (1), the dynamic characteristics of populations sampled at the adult stage may not be derived. We examine the dynamic properties of the model proposed by Prout to take into account the delayed effect of two life-history traits, survival and fecundity, occurring at the immature stage. Two parameters are present in the model> Beta, which describes the rate of change in survival and fecundity with respect to increasing density of immatures, and alpha which combines maximum survival and fecundity. The latter parameter is found to determine the dynamic behavior of Prount'a model, and this model is shown to tbe a reparametrization of the classical discrete logistic equation. In the interval 1 < alpha < e2 there is one fixed point, at alpha = e2 there is period doubling bifuraction, and due to the appearance of period three Prout's model shows chaotic behavior. The theoretical results are briefly discussed in the light of data on the equilibrium dynamics of Drosophila and blowflies.