-The knowledge of the dispersion pattern of the pests on a crop is fundamental for establishing an appropriated sequential sampling method. Also it permits the correct utilization of control strategies and optimization of sampling techniques. The objective of this research was to determine the spatial distribution of larvae of Alabama argillacea (Hübner) on cotton crop, CNPA ITA-90 cultivar. During the 1998/99 growing season a sampling system was applied in three experimental areas located at Itamarati Sul S.A. farm in the region of Ponta Porã, estate of Mato Grosso do Sul, Brazil. The areas measured 1 ha and contained 100 plots with 100 m 2 . In a weekly basis the number of small, medium and large larvae were counted on five plants per plot. The aggregation indexes (variance/ mean ratio and Morisita index), the chi-square test and the adjust of observed and expected values to theoretical distributions of frequencies (Poisson, positive binomial and negative binomial) showed that all stages of cotton leafworm larvae were distributed according to the contagious model, fitting the Negative Binomial Distribution during the whole period of infestation.

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ABSTRACT. Spatial distribution of Aphis gossypii (Glover) (Hemiptera, Aphididae) and Bemisia tabaci (Gennadius) biotype B (Hemiptera, Aleyrodidae) on Bt and non-Bt cotton. The study of spatial distribution of the adults of Bemisia tabaci and the colonies of Aphis gossypii on Bt and non-Bt cotton crop is fundamental for improving the sampling techniques and revealing differences in the behavior of non-target species between both cultivars. So, this experiment aimed to investigate the spatial distribution pattern of those species on the conventional non-Bt cotton crop, compared to the Bt cultivar. The samplings took place in two areas of 5.000 m 2 each, where it was done 14 evaluations counting adults of white-flies and colonies of aphids. The aggregation indexes (variance/ mean rate, index of Morisita and Exponent k of the Negative Binomial Distribution) were calculated and accomplished the fitness tests of the individuals' numeric classes found and expected to the theoretical distributions of frequency (Poisson, Negative Binomial and Positive Binomial). Those analyses showed that in both cultivars, the spatial distribution of B. tabaci fitted to negative binomial distribution throughout the study period, indicating that the transgenic cultivar did not influence the pattern of aggregate distribution of this insect. With respect to the analysis for A. gossypii, the aggregation indexes showed aggregated distribution in both cultivars, but the distributions of frequency pointed to the occurrence of aggregate distribution only on conventional cotton, since there was no adjustment to the data on Bt crop. This indicates that Bt cotton has altered the aphids normal pattern of dispersion in the crop.

Knowledge of insect diversity is essential for ecological studies and pest management. The aim of this study was to study the occurrence, abundance of target and non-target pests in genetically modified insect resistant (Bt) and glyphosate-tolerant soybeans (RR1 and RR2), with and without the application of insecticides. Experiments were carried out in the agricultural year of 2011/2012 in four municipalities in the State of Mato Grosso do Sul. The treatments were: 1 -Roundup Ready ® RR1 soybeans without insecticide application; 2 -Roundup Ready ® RR1 soybeans with application whenever the control level was reached; 3 -Intacta RR2 PRO ® soybeans without insecticide application; and 4 -Intacta RR2 PRO ® soybeans with application whenever the control level was reached. The evaluations were initiated soon after emergence of the plants at weekly intervals. In order to obtain representative gradients of species composition, we used the method of ordering by non-metric multidimensional scaling (NMDS) and the Bray-Curtis dissimilarity index. Insects of the order Lepidoptera presented 7547 specimens, composing more than 70% of the insect community. The orders Coleoptera and Hemiptera also stood out, consisting of 2066 and 331 insects, respectively. Most of the samples were recorded in stages V8 to R2 for defoliating caterpillars and between R5.2 and R6 for the phytophagous stink bug complex. The Bt technology significantly reduced the target insect pests and favored populations of natural enemies. The treatments with insecticide application resulted in reduction of arthropods collected and changes in population outbreaks when compared to areas without spraying.

A recent shift in managing insect resistance to genetically engineered (GE) maize consists of mixing non-GE seed with GE seed known as “refuge in a bag”, which increases the likelihood of predators encountering both prey fed Bt and prey fed non-Bt maize. We therefore conducted laboratory choice-test feeding studies to determine if a predator, Harmonia axyridis, shows any preference between prey fed Bt and non-Bt maize leaves. The prey species was Spodoptera frugiperda, which were fed Bt maize (MON-810), expressing the single Cry1Ab protein, or non-Bt maize. The predators were third instar larvae and female adults of H. axyridis. Individual predators were offered Bt and non-Bt fed prey larvae that had fed for 24, 48 or 72 h. Ten and 15 larvae of each prey type were offered to third instar and adult predators, respectively. Observations of arenas were conducted at 1, 2, 3, 6, 15 and 24 h after the start of the experiment to determine the number and type of prey eaten by each individual predator. Prey larvae that fed on non-Bt leaves were significantly larger than larvae fed Bt leaves. Both predator stages had eaten nearly all the prey by the end of the experiment. However, in all combinations of predator stage and prey age, the number of each prey type consumed did not differ significantly. ELISA measurements confirmed the presence of Cry1Ab in leaf tissue (23–33 µg/g dry weight) and S. frugiperda (2.1–2.2 µg/g), while mean concentrations in H. axyridis were very low (0.01–0.2 µg/g). These results confirm the predatory status of H. axyridis on S. frugiperda and that both H. axyridis adults and larvae show no preference between prey types. The lack of preference between Bt-fed and non-Bt-fed prey should act in favor of insect resistance management strategies using mixtures of GE and non-GE maize seed.

The knowledge of the arrangements of dispersion of insect pests in soybean cultivars is needed to improve the monitoring and control. The objective of this study was to evaluate the spatial distribution of adults and nymphs of Euschistus heros in Bt and non-Bt soybean into two regions, under field conditions. The experimental area located in Dourados and Douradina, Mato Grosso do Sul. For the evaluations we used the method of cloth-to-beat, where we collected one sample per plot randomly from each experimental area. Evaluations were performed at 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98 days after emergence (DAE). For data analysis, the rates of dispersion (variance/average Morisita index and exponent k  Negative Binomial Distribution) and theoretical frequency distributions (Poisson, Binomial and Negative Binomial Positive) were estimated at 1-5 % probability. Adults of E. heros are arranged differently for Bt and non-Bt soybean and between regions, since in both cultivars and locations, individuals of the populations evaluated in probabilistic set arrangements negative binomial distribution (aggregate), Poisson (random) and positive binomial distribution (uniform), as the days after soybean emergence. The nymphs of E. heros showed aggregated spatial arrangement, being distributed similarly for Bt and non-Bt soybean and regions, setting a negative binomial distribution model.

We have implemented the solid-on-solid (SOS) kinetic model in the framework of electrochemistry to study the evolution of surface morphology during driven metal dissolution. Our results show that the surface roughens with increasing applied electrical potential, as demonstrated by the increase of the interface width and of the surface high-frequency-power spectrum. An abrupt change on the roughness is observed at a certain value of the applied potential, which indicates the possibility of an electrochemically driven kinetic-roughening transition. A change in the dissolution mechanism is proposed from a regime of kink propagation at steps to a situation where low-coordination sites participate just as actively in the dissolution process.

This study aimed to know the patterns of spatial distribution of Anastrepha spp. and establish a criterion for determining the appropriate time for pest control. For this, 90 McPhail traps were used as Sampling Units (SU) divided into three commercial orchards of Novo Milênio guava with a total area of 14 ha. Traps were interspersed between the rows of plants, systematically in the orchards, hung and baited with 5% hydrolyzed corn protein with weekly collections. We caught 8,170 Anastrepha spp. in 840 SU. The mean infestation index was compared to the three types of distribution: random, uniform, aggregate, and fit by the theoretical frequency distributions of Poisson, negative binomial and positive binomial. The populations of Anastrepha presented aggregate distribution according to the mean variance method (I), tested by distance from randomness. The economic damage risk potential of Anastrepha spp. was associated with the aggregate distribution behavior. The most appropriate moment for the use of control techniques is when reaching 20 flies by the negative binomial. On the other hand, number of fruit fly adults per trap per day (FTD), underestimates population index, which will allow population growth, leading to risk of crop production loss.