Daniela Maria da Silva

Desenvolvimento e reprodução de Sipha flava (Forbes) (Hemiptera: Aphididae) em diferentes temperaturas

The aphid Sipha flava (Forbes) is a pest on elephant grass, but little is known about its biology. The objective of this work was to evaluate the temperature effects on the development, survival and reproduction of S. flava fed on Pennisetum purpureum. Twelve-hour-old nymphs were individualized on sections of elephant grass blades and maintained at 12, 16, 20, 24, 28 and 32 degrees C+/-1 degrees C, UR 70+/-10% and 12 h photophase. A total of 150 nymphs were used per treatment divided in 30 replicates, using a totally random design. The lower threshold temperatures (LTT) for first, second, third and fourth instars were 0.83, 1.05, 3.01 and 4.98 degrees C, respectively, indicating a change in thermal requirements as the development progress. The LTT for the whole nymphal stage was 2.08 degrees C, pointing to the tolerance of this species to low temperatures. A significant reduction in survival was observed at high temperatures (28 and 32 degrees C). Although the reproductive periods were longer and insects lived longer at 12 degrees C as compared with those at higher temperatures, the total fecundity was substantially reduced. The overall life cycle duration was almost twice as long at 12 degrees C than at 24 degrees C. The greatest daily production of nymphs and greatest number of nymphs produced overall occurred at 24 degrees C. The temperatures of 20 degrees C and 24 degrees C were more suitable to S. flava development and reproduction.

Tabela de esperança de vida e de fertilidade de Sipha flava (Forbes) (Hemiptera, Aphididae) alimentado com capim-elefante em diferentes temperaturas

Objetivou-se estimar as tabelas de esperanca de vida e de fertilidade para Sipha flava (Forbes, 1884) alimentados com capim-elefante, em diferentes temperaturas. Foram utilizadas câmaras climatizadas a 12, 16, 20, 24, 28 e 32oC, UR 70 ± 10% e fotofase de 12 horas, contendo 150 insetos em cada condicao termica. Foi constatada mortalidade gradual em todas as temperaturas. A maior longevidade e maior esperanca de vida dos afideos foi a 12oC. As taxas liquidas de reproducao (Ro) e o tempo necessario para a populacao duplicar em numero (TD) tambem foram maiores a 12oC. A sobrevivencia (lx) comecou a diminuir a partir de 3,5 dias a 24oC e a partir do primeiro dia nas demais temperaturas, seguindo uma reducao gradativa com o desenvolvimento do inseto. O intervalo de tempo entre cada geracao (T) diminuiu com o aumento da temperatura, ate 28oC. A maior fertilidade especifica (mx) e a maior fecundidade total media ocorreram a 24oC. A capacidade inata de aumentar em numero (rm) foi menor a 12oC. A razao finita de aumento (λ) foi maior a 20 e 24oC. A temperatura de 24oC mostrou-se mais adequada para o desenvolvimento de S. flava em capim-elefante por proporcionar maiores valores para os parâmetros reprodutivos.

Flutuação populacional de cigarrinhas-das-pastagens em braquiária e capim-elefante

O objetivo deste trabalho foi avaliar a flutuacao populacional de cigarrinhas-das-pastagens em Brachiaria brizantha, Brachiaria decumbens e Pennisetum purpureum. As avaliacoes foram realizadas em campo, entre setembro de 2005 e marco de 2007. Ninfas e adultos de cigarrinhas-das-pastagens foram contabilizados em: B. brizantha cultivares Marandu, Xaraes e Arapoti, submetidas a rodizios de carga animal; em B. decumbens, em sistema silvipastoril; e em 78 genotipos de P. purpureum. A densidade populacional de Deois schach, na cultivar Arapoti, foi superior a de Xaraes e de Marandu. Em B. decumbens, o numero de cigarrinhas-das-pastagens foi quatro vezes maior que em B. brizantha. Nao foram observadas diferencas significativas no numero de cigarrinhas-das-pastagens nos diferentes genotipos de P. purpureum.

Hymenoptera (Insecta: Hymenoptera) associated with silvopastoral systems

The objective of this work was to estimate the abundance, diversity and constancy of families from the order Hymenoptera, such as the seasonality of those through a survey on the insect population in a silvopastoral system. We installed a Malaise-type trap in a Brachiaria decumbens area managed by a silvopastoral system in Coronel Pacheco, MG, from August 2006 to July 2008. The trapped insects were screened, and those of the order Hymenoptera were classified into their respective family categories and quantified. We adopted the methodology of Bodenheimer to calculate the indices of constancy, while other indices were estimated PAST program. We sampled 5841 specimens in total, which included 549 morphospecies and were distributed among 11 families. Of the total specimens sampled, 80% were Formicidae, which besides being the most abundant, was also the most diverse and constant family. When entomophagous insects were analyzed, the highest values for these indices were recorded for the families Ichneumonidae, Braconidae, and Vespidae. Pollinators were less prevalent compared to the total number of sampled individuals. The population density in the Hymenoptera was not correlated between the two sampling years and climate factors.

Respostas biológicas de Sipha flava (Forbes, 1884) (Hemiptera: Aphididae) alimentados em diferentes genótipos de capim-elefante

This work aimed to evaluate the effect of genotypes of elephant grass, Pennisetum purpureum Schum, on some biological aspects of Sipha flava (Forbes). Foliar disks of 15 elephant grass genotypes were used, on which individual nymphs up to 12 hours old were placed in dishes and kept at 25 oC, RH of 70 ± 10% and 12-hour photophase. We evaluated the number of instars, duration and survival of each instar and the entire nymphal period, duration of the pre-reproductive, reproductive and post-reproductive period, daily and total nymph production capacity and longevity of the adults and biological cycle (nymph-adult). The nymphs passed through four instars on all the elephant grass genotypes studied. There were no significant differences in the duration of the first and last nymph stages on the different genotypes, unlike observed for the intermediate instars and nymphal period . The biological parameters of the adult phase of the aphid, such as pre-reproductive, reproductive and post-reproductive period and longevity, were also affected by the genotype. Cameroon de Piracicaba and Guacu IZ2 were the most suitable genotypes for development of the aphids, providing higher values for overall production of nymphs/female, daily production of nymphs/female, reproductive period and adult longevity. On the other hand, the Sem Pelo genotype was the least suitable for the aphids’ development and reproduction according to the biological parameters studied.