Simone Alves Oliveira

Seleção de genótipos de capim-elefante quanto à resistência à cigarrinha-das-pastagens

The objective of this work was to evaluate genotypes of elephant grass (Pennisetum purpureum Schum.) regarding resistance to the spittlebug Mahanarva spectabilis. For antibiosis evaluation, each plant was infested with six eggs near hatching, thirty days after planting, in a completely randomized design with 30 genotypes and ten repetitions. Forty-five days after the nymphs hatched, the insect survival rate was evaluated on the different genotypes. For nonpreference mechanism evaluation, the size and number of the nymphs per pot were assessed every 15 days, in plants kept at greenhouse, where adults of M. spectabilis were periodically released, in a completely randomized design, with three repetitions per genotype in two sampling periods. Cameroon de Piracicaba, Pioneiro, Cuba 169, Santa Rita, Mineiro Ipeaco, Mercker Comum de Pinda and CNPGL 96-27-3 genotypes were selected for resistance, by antibiosis mechanism. In the study of the nonpreference mechanism, the number and average size of the nymphs varied significantly as a function of the elephant grass genotype. Roxo de Botucatu and Pioneiro genotypes are, respectively, susceptible and resistant check candidates by the antibiosis mechanism, and Cameroon and Cameroon Piracicaba genotypes are promising by the nonpreference mechanism.

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.

Can larval lacewings Chrysoperla externa (Hagen) (Neuroptera, Chrysopidae) be reared on pollen?

O objetivo do presente estudo foi verificar a viabilidade do uso exclusivo de polen de capim-elefante Pennisetum purpureum (Schum) como dieta para larvas de Chrysoperla externa (Hagen, 1861). Os insetos foram mantidos a 24oC, avaliando-se a duracao e a sobrevivencia em cada instar e em todo o estagio larval e pupal. Verificou-se que a dieta proporcionou o desenvolvimento completo das larvas do crisopideo, que apresentaram a mesma duracao media para o primeiro e segundo instares (6,9 dias) e permaneceram 10,0 e 13,2 dias no terceiro instar e no estagio pupal, respectivamente. A sobrevivencia media das larvas de C. externa foi superior a 80% para o primeiro, segundo e terceiro instares, e de 70,0% e 33,3% para o estagio larval e pupal, respectivamente. Verificou-se que o uso exclusivo de polen de capim-elefante como alimento para larvas de C. externa proporcionou o completo desenvolvimento dos estagios imaturos do predador.

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.