File: Size of this preview: × pixels. Other resolutions: × pixels | × pixels | 1, × Determinacao de danos da cigarrinha-das-pastagens (Deois incompleta) a Brachiaria humidicola E.B. decumbens . Silva, A.B.. Access the full text. Cigarrinhas-das-pastagens, Zulia entreriana (Berg, ) (Homoptera, Cercopidae), no norte do Estado de Minas Gerais. II. Controle de ninfas com inseticidas.
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Cohorts of quiescent eggs, when exposed to increasing periods of high moisture free waterproduced higher proportions of eggs resuming embryonic development in laboratory experiments. Periods of paastagens and high temperatures after the beginning of postdiapause development increased embryonic and nymphal mortality. Mortality was modeled with a linear function, and in combination with the development model allowed the simulation of varying mortality rates in the newly emerged nymphal population.
Comparisons with field data demonstrated a close fit to the observed and expected proportion of nymphs hatching daily. By accurately simulating natural mortality, hatching distribution and population dynamics, the model promises to be useful for managing the spittlebug in the field.
The insect’s life history strategy includes survival over pastagenss dry season May-August as diapausing eggs, and risk distribution bet-hedging in which females vary both the proportion of diapausing eggs and the duration of the dormancy in its progeny Fontes et al. Other characteristics such as oviposition in protected places e. In central Brazil, D.
After the dry season, postdiapause eggs remain quiescent waiting for favorable conditions to hatch Pires et al. The occurrence of high densities of D. Although many studies show how patterns of climatic variation can influence insect population abundance in the tropics e.
The occurrence of sparse and irregular rainfalls, alternating with periods of elevated evapotranspiration, produce a prominent water deficit that appears to control the annual abundance of D. It is possible that sudden weather variation after the beginning of the rainy season may play an important role in the survivorship of first-generation nymphs and thus the size of subsequent population peaks.
In this work we evaluated mortality rates during three distinct stages of spittlebug development: Our goal was to understand how mortality rates vary during D. During the months of April and May in and end of the third population peakD. Approximately pairs were placed in each of 12 cages randomly distributed over the same pasture from which they were captured. Cages consisted of cylindrical iron frames 0.
The cages did not have bottoms and were placed directly over the pasture to allow access to grass for feeding and to soil for oviposition. At the beginning of each month, from June to September, the soil under three cages was collected to a depth of 2 cm.
Eggs were recovered using soil filtration, flotation in a saturated solution of NaCl WV and a supernatant wash with distilled water Sujii All recovered eggs, even those with alterations in color or form, suggesting that they were dead, were included in the sample. Empty chorions were excluded.
Cigarrinha das Pastagens – Biofaces – Bring Nature Closer
Cohorts of 50 eggs were placed in a cm-diameter petri dish containing a layer of cotton covered with moist filter paper. D cigzrrinha until the emergence of nymphs. Egg hatching was monitored every other day until the emergence or death of all eggs in each replicate. Eggs that did not hatch and became flat and black were considered dead for the mortality evaluation. Monthly mortality rates within a given year were compared using analysis of variance ANOVA and Tukey digarrinha, after arcsine transformation.
The proportion of postdiapause eggs that starts final embryonic development was tested in the laboratory by varying the periods of an initial high moisture condition direct exposure to free water. D] h ;astagens the laboratory from May to August Sujii et al.
At the beginning of September, when the eggs naturally enter the postdiapause or quiescence without any token stimuli Pires et al. D h condition 1 in an environmental chamber.
Moisture was provided by adding water ad libitum to the cotton paetagens the filter paper. For the treatments longer than 2 d, this layer was moistened every other day to ensure continuous contact between water and eggs.
Following this dry period, eggs were again transferred to moist conditions condition 3paatagens described above for condition 1, until hatching of quiescent eggs or death of all individuals. Nymphs that emerged under condition 1 were considered representative of the group that started final embryonic development and then died under condition 2, and did not emerge under condition 3.
Nymphs trapped inside eggs after 60 d were considered dead. With this procedure, it was possible to distinguish the proportion of eggs that resumed final embryonic development in response to different periods of exposure to moisture condition 1 from those that were naturally infertile. To estimate the average proportion of natural infertility in the population and the time of exposure to moist conditions required for postdiapause eggs to resume embryonic development, a group of four Petri dishes with 15 eggs each was kept under moist conditions until hatching or death of all eggs.
The last egg hatching in this group allowed the estimation of the time necessary under moist conditions to induce all eggs of a population to start final embryonic development.
Egg hatching was monitored every other day throughout the experiment. For each period of moisture exposure, hatching time and egg mortality rates were calculated. Because cigarribha mortality was due to either low moisture lack of contact with free water or infertility, the average rate of infertility in the cas The parameter k was given a value of 2, which has been used to describe the cumulative emergence of several insect species Stinner et al.
The value of h was estimated from comparisons of model predictions equation 1 with the frequency distribution observed in the experiment. Modeled and observed curves of hatching proportion were compared using the Kolmogorov-Smirnov test Wilkinson Comparing the means among the treatments, using the Kruskal-Wallis ANOVA, we tested if initial exposure to moisture condition 1 could be initiating embryonic development in some eggs that then wait for condition 3 to resume embryonic development.
If so, these eggs would hatch early reducing the average time in some treatments.
Cigarrinha-das-pastagens (Pasture planthopper) | Project Noah
D h until the eggs reached the final stage of embryonic development, following the description of Koller et al. Groups of 20 eggs with fully developed embryos were chosen randomly and placed at the base of potted plants of B. These pots had been watered to saturation 24 h before the experiment. After initial watering, pots were kept without water for periods of 4, 8, 12, and 16 d treatments.
Pots were then watered daily using overhead sprinklers. Each treatment had eight replications. A control set of eight pots was kept under daily irrigation throughout the experiment.
The plants were observed three times weekly, and examined for the presence of first instars.
Newly emerged first instars of spittlebug move directly to the nearest suitable plant and establish themselves at the base of stems and exposed roots, where they immediately start feeding and producing spittle Pires et al. First instars usually feed gregariously in the same spittle, and all nymphs that died were removed with a small paintbrush. Observations stopped when all surviving nymphs reached the second instar. The relationship between period of water deficit and mortality of eggs and newly emerged nymphs was described by linear regressions.
Cohorts with variable numbers of D. Each cohort was protected from predators by cages consisting of a wooden frame 0. The base of the cage was buried 10 cm deep to impede the entrance of soil insects from beneath.
Teste de insecticidas para controle da cigarrinha-das-pastagens Deois incompleta Walk
To determine the movement and survivorship of each individual during the nymphal stage, the position of each nymph within cages was marked with a small numbered wooden stake. Records about the position and development stage of nymphs were made every d following Sujii Proportional mortalities for each instar were compared among the different generations to evaluate the effects of seasonal weather variation.
Nymphal density in each cage was recorded and correlated with mortality estimates. Monthly mortality of diapausing eggs collected during the dry season June-September over 2 yr varied from 4. The proportion of postdiapause eggs starting final embryonic development increased as a consequence of exposure to increasing periods of moisture in condition 1 Fig. The proportion of these that died from the hydric stress of condition 2 was detected under condition 3. This rate of natural infertility was subtracted from all moisture-exposed treatments to better estimate the proportion of eggs starting final embryonic development Fig.
The last hatching, in this group of eggs continuously exposed to moisture, occurred after 38 d. Thus, postdiapause eggs need 26 d of moisture to ensure initiation of embryonic development in all individuals of a population. Postdiapause eggs of the spittlebug resuming embryonic development after exposure to moist conditions for different periods.
Natural infertility of eggs 0. The first postdiapause eggs resuming embryonic development, parameter A equation 1were observed after 4 d of exposure to moist conditions, and the last diapausing egg resuming embryonic development, parameter B equation 1was observed after 26 d.
The average time for egg hatch in all treatments Fig. Time taken for eggs of D. Bars represent only the time spent in condition 3. Increasing exposure to low moisture progressively raised mortality rates of newly emerged nymphs and embryos Fig. Plants under field conditions may provide better or worse conditions for nymphs survivorship because at microclimate or root size, and additional tests in the field are warranted.
At the other extreme, 16 d of drought after initial intense and frequent rain keeping the soil moist for 14 d maximize mortality in local populations of D. Predicted mortality of eggs in final stage of em-bryonic development and of newly emerged nymphs of D. Proportional mortality of the spittlebug, D. Relationship between nymphal density and the mortality observed in the same cage during the immature phase of the spittlebug D.
Nymphal mortality in cohorts of D. The low mortality rates of eggs observed during the middle of the dry season July and August indicate that lack of moisture and warm soil do not preclude outbreaks of D. Although mortality rates varied from 4. Such eggs die when faced with drought conditions, but they were still found in the June-July soil samples. By July, these eggs had decomposed and the chorions were excluded from the samples. The termination of diapause at the beginning of the rainy season, when the frequency of rain is unpredictable, probably caused the increase of egg mortality in September.
The mortality rate of around 9.
pastagehs Although Hewitt observed that only 8. A number of studies have confirmed the low response of diapausing eggs to environmental factors during the dry season in June and July Sujii et dws. The interplay among diapause and rainfall distribution at the beginning of the rainy season results in a variable pattern of population dynamics from ras to year.
In the current study, we propose a model that explains how different combinations of precipitation and drought periods at the beginning of the rainy season can influence the mortality of eggs in the final embryonic stage and of newly emerged nymphs.
In contrast, sparse rainfall keeps postdiapause eggs quiescent, and hatching occurs asynchronously over a long period of weeks in accordance with the distribution of precipitation. Other species of spittlebugs, Aeneolamia occidentalis Walker and Prosapia simulans Walkershow the same pattern of occurrence in Mexico Oomensuggesting that this mechanism of risk distribution related to rain frequency may be common for this subgroup of the family Cercopidae.
Newly emerged nymphs desiccate quickly and die if they do not find a host plant, or if a drought period with high temperature cigwrrinha at this nymphal stage Pires et al.