Spatial distribution of parasitism on Phyllocnistis citrella Stainton, 1856 (Lepidoptera: Gracillariidae) in citrus orchards / Distribuição espacial do parasitismo Phyllocnistis citrella Stainton, 1856 (Lepidoptera: Gracillaridae) em pomares de citros

Many species of microhymenopterous parasitoids have been registered on Phyllocnistis citrella, the citrus leafminer. The present study aimed to identify the spatial distribution pattern of the native and introduced parasitoids of P. citrella in two citrus orchards in Montenegro, RS. The new shoots from 24 randomly selected trees in each orchard were inspected at the bottom (0-1.5 m) and top (1.5-2.5 m) stratum and had their position relative to the quadrants (North, South, East and West) registered at every 15 days from July/2002 to June/2003. The leaves with pupae were collected and kept isolated until the emergence of parasitoids or of the leaf miner; so, the sampling was biased towards parasitoids that emerge in the host pupal phase. The horizontal spatial distribution was evaluated testing the fitness of data to the Poisson and negative binomial distributions. In Montenegrina, there was no significant difference in the number of parasitoids and in the mean number of pupae found in the top and bottom strata (χ2 = 0.66; df = 1; P > 0.05) (χ2 = 0.27; df =1; P > 0.05), respectively. In relation to the quadrants, the highest average numbers of the leafminer pupae and of parasitoids were registered at the East quadrant (χ2 = 11.81; df = 3; P < 0.05), (χ2 = 10.36; df = 3; P < 0.05). In the Murcott orchard, a higher number of parasitoids was found at the top stratum (63.5 percent) (χ2 = 7.24; df =1 P < 0.05), the same occurring with the average number of P. citrella pupae (62.9 percent) (χ2 = 6.66; df = 1; P < 0.05). The highest number of parasitoids and of miners was registered at the North quadrant (χ2 = 19. 29; df = 3; P < 0.05), (χ2 = 4.39; df = 3; P < 0.05). In both orchards, there was no difference between the numbers of shoots either relative to the strata as well as to the quadrants. As the number of shoots did not varied much relative to the quadrants, it is possible that the higher number...

Vários microimenópteros parasitóides têm sido registrados em populações de Phyllocnistis citrella (minador-dos-citros). Este estudo objetivou identificar o padrão de distribuição espacial de parasitóides nativos de P. citrella e do introduzido Ageniaspis citricola em dois pomares de citros em Montenegro, RS. Em amostragens quinzenais de julho de 2002 a junho de 2003, todos os brotos de 24 plantas sorteadas aleatoriamente em cada pomar foram inspecionados no estrato inferior (0-1,5 m) e superior (1,5-2,5 m) e registrada a localização destes em relação aos quadrantes (Norte, Sul, Leste e Oeste). As folhas com pupas foram coletadas e individualizadas até a emergência dos parasitóides ou do minador, assim, a amostragem foi focada em parasitóides que emergem na fase pupal do hospedeiro. A distribuição espacial horizontal foi avaliada testando-se os ajustes dos dados à distribuição Poisson e binomial negativa. Em Montenegrina não houve diferença significativa no número de parasitóides e no número médio de pupas encontrados no estrato superior e inferior, (χ2 = 0,66; gl = 1; P > 0,05) e (χ2 = 0,27; gl = 1; P > 0,05), respectivamente. Em relação aos quadrantes, o maior número médio de pupas do minador e de parasitóides encontra-se no quadrante Leste (χ2 = 11,81; gl = 3; P < 0,05), (χ2 =10,36; gl = 3; P < 0,05). No pomar de Murcott, um maior número de parasitóides foi constatado no estrato superior (63,5 por cento) (χ2 = 7,24; gl = 1 P < 0,05), o mesmo ocorrendo com o número médio de pupas de P. citrella (62,9 por cento) (χ2 = 6,66; gl =1; P < 0,05). O maior número de parasitóides e de minadores foi registrado no quadrante Norte (χ2 = 19,29; gl = 3; P < 0,05), (χ2 = 4,39; gl = 3; P < 0,05). Em ambos os pomares, não houve diferença entre o número de brotos nos dois estratos ou entre os quadrantes. Como o número de brotos não variou muito em relação aos diferentes quadrantes, é possível que a presença maior...

Seasonal abundance and mortality of Oebalus poecilus (Dallas) (Hemiptera: Pentatomidae) in a hibernation refuge

Oebalus poecilus (Dallas) é praga importante do arroz irrigado no Rio Grande do Sul, Brasil. Este inseto hiberna durante os meses mais frios em refúgios como o folhedo de bambu. Este estudo objetivou elucidar a hibernação de O. poecilus e determinar as causas de mortalidade durante este período. O estudo foi realizado em um bambuzal com cerca de 140 m2, situado em área orizícola, em Eldorado do Sul (30° 02’ S e 51° 23’ W), RS. De junho/2000 à abril/2002, foram realizadas 63 amostragens de folhedo, em intervalos semanais ou quinzenais e o número de percevejos registrado em laboratório. A entrada no refúgio de hibernação (folhedo de bambu) iniciou na primeira semana de março, completando-se no início de maio. O. poecilus abandonou o refúgio da metade de outubro até o final de dezembro. O parasitismo por mosca (taquinídeos) e o fungo Beauveria bassiana (Bals.) Vuill. foram os principais fatores de mortalidade.

Internal reproductive organs of Cosmoclopius nigroannulatus (Hemiptera: Reduviidae)

Os órgãos internos de reprodução de machos e fêmeas de Cosmoclopius nigroannulatus são descritos, ilustrados e mensurados. Não se registrou diferença significativa entre machos imaturos e reprodutivos quanto ao tamanho das estruturas, sendo o aspecto destas similar em ambos. Já nas fêmeas, constataram-se diferenças notáveis tanto no aspecto quanto no tamanho.

Larval and pupal stage of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in sweet and field corn genotypes

Spodoptera frugiperda, the fall armyworm, is a very significant polyphagous pest due to the damages it causes, and control difficulties. Lack of information about its impact on sweet corn motivated a comparison of its biology, with respect to the larval and pupal stages, among the genotypes ELISA, BR 400 (sweet corns), and BR PAMPA (field corn). In laboratory conditions (25 ± 1ºC; 70 ± 10 percent RH; photophase 12 hours), 35 caterpillars were individualized and fed daily with 3.14 cm² sections of corn leaves from the referred-to genotypes, cultivated in plots in the experimental area of the Departament of Fitossanidade, UFRGS, Porto Alegre, RS from October to November 2000. The caterpillars were weighed daily; after each molt, the cephalic capsules were collected and measured (in width), to establish growth rate; pupae were weighed and sexed when 24 hours old. The duration of the larval instars, the pupal sex ratio, and the mortality of larvae and pupae were evaluated. In the first three instars there were no differences registered in capsule width. In the fourth and fifth instars, capsules of caterpillars kept in BR 400 were smaller. The weight of caterpillars and pupae, instar duration and sex ratio did not differ among the genotypes. Pupal phase duration was less in females kept in BR 400. Mortality was greater in the larval phase in ELISA and in the pupal phase in BR PAMPA.

Characterization of the imaginal reproductive diapause of Oebalus poecilus (Dallas) (Hemiptera: Pentatomidae)

The state of development of the internal reproductive organs of male and female Oebalus poecilus (Dallas) as well as the body fat amount in the abdominal cavity during hibernation, of individuals sampled in bamboo litter in Eldorado do Sul (30º02'S and 51º23'W), RS, Brazil was investigated. Females and males showed the abdominal cavity filled with body fat in the beginning of the hibernation phase. The decrease in fat reserve level occurred from August on for males and from October on for females. Ovaries and testis doubled in length and tripled in width from immature to the reproductive phase. Male sexual maturation occurred in the hibernation sites while for females it occurred later on outside of the sites. Reproductive organ immaturity and abdominal body fat hypertrophy characterized the diapause of O. poecilus.

Population dynamics of Cosmoclopius nigroannulatus Stal (Hemiptera, Reduviidae) in tobacco culture

The role of predators influencing populations of insects considered as pests is extremely important for agroecosystems. The population ecology of Cosmoclopius nigroannulatus, a predatory reduvid associated with the tobacco culture was investigated aiming to study the population dynamics of adults, along the culture cycle. In an experimental plot of approximately 300 m², in Porto Alegre (30°0'S; 51°13'W), RS, Brazil, 270 tobacco plants were grown; each plant identified by alphanumeric coordinates. Using the mark-release-recapture method, daily samplings were done from August to December 1999, and three times a week from this date until April 2000. The adults were captured by hand, marked, sexed and released on the same plant they were captured. The individual number and plant coordinate were registered. Population estimates were analyzed by the Fisher-Ford method. In 107 sampling occasions, 604 individuals were marked, 273 males and 331 females. Three generations of C. nigroannulatus were registered during the culture cycle. The colonizing generation was represented by 14 males and 15 females (a sex ratio of 0.48), the first by 109 males and 137 females (0.44) and the second by 150 males and 179 females (0.46). The estimated daily survival rate varied between generations decreasing from 98 percent in the colonizing generation to 87 percent in the second. The observed longevity or permanence time in the experimental area varied significantly among generations, being at about 40 days in the colonizing generation, 13 days in the first and 5 days in the second. It was observed that as the population increases, the survival and/or permanence time in the area decreases, suggesting a relation between this and a decline in the available resources probably with an associated increase in intra-specific competition