Resumo -O objetivo deste trabalho foi avaliar genótipos de capim-elefante (Pennisetum purpureum Schum.) quanto à resistência à cigarrinha-das-pastagens (Mahanarva spectabilis). Para avaliação da antibiose, aos trinta dias após o plantio, cada planta foi infestada com seis ovos próximos à eclosão, em delineamento inteiramente casualizado, com 30 genótipos e dez repetições. Quarenta e cinco dias após a eclosão das ninfas, avaliou-se a porcentagem de sobrevivência do inseto-praga nos diferentes genótipos. Para avaliação da não-preferência, foram quantificados, quinzenalmente, o número e tamanho de ninfas por vaso, em plantas mantidas em casa de vegetação, onde adultos de M. spectabilis eram periodicamente liberados, em delineamento inteiramente casualizado, com três repetições por genótipo, em dois períodos de amostragem. Os genótipos Cameroon de Piracicaba, Pioneiro, Cuba 169, Santa Rita, Mineiro Ipeaco, Mercker Comum de Pinda e CNPGL 96-27-3 foram selecionados quanto à resistência, pelo mecanismo de antibiose. O número e o tamanho médio das ninfas variaram significativamente em razão do genótipo de capim-elefante, no estudo da não-preferência. Os genótipos Roxo de Botucatu e Pioneiro são candidatos à testemunha suscetível e resistente, respectivamente, pelo mecanismo de antibiose, e os genótipos Cameroon e Cameroon Piracicaba são promissores pelo mecanismo de não-preferência.Termos para indexação: Pennisetum purpureum, Mahanarva spectabilis, resistência a pragas, forrageiras, antibiose, não-preferência. Selection of elephant grass genotypes for resistance to spittlebugAbstract -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.

This work examines the occurrence, duration and viability of diapause eggs of Mahanarva spectabilis (Distant, 1909) at different periods of the year. Adult insects were gathered twice a month in a greenhouse from September 2005 to May 2006 as well as in the same period in 2006-2007. The spittlebugs collected were taken to the laboratory, sexed and kept in cages containing one elephant grass plant potted in a 500 mL plastic cup with the upper part wrapped in gauze to serve as a substrate for egg laying. Around one hundred eggs obtained on each sample date were kept in climate-controlled chambers. The duration and viability of the eggs were analyzed daily. The viability was greater than 50% and 72%, respectively, in the evaluations for September 2005 to May 2006 and the same period of 2006-2007. The average embryonic period from September 2005 the first half of March 2006 varied from 15.79 to 28.24 days, except in the first half of January. In the other samples it varied from 94.80 to 139.04 days, with these being considered diapause. In the second study period (2006-2007), an embryonic period under 27 days was registered from September to the first half of November 2006 and again in January and February 2007. In the other evaluations the insects remained in the egg phase from 55.30 to 196.42 days. The largest number of diapause eggs occurred in the autumn, with 100% and 90% for the first and second evaluation periods, respectively.

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The effects of varying photophase conditions on biological parameters of Mahanarva fimbriolata (Stal) (Hemiptera: Cercopidae), nymphs and adults were evaluated. Eggs of a late developmental stage were placed near sugarcane roots (cultivar RB739735) maintained in a greenhouse (21 ± 7° C, 90 ± 10% RH). Nymphs and adults were exposed to the following photophase conditions: a) 13:11 L:D as nymphs and adults, b) 13:11 as nymphs and 12:12 as adults, c) 12:12 as nymphs and adults, and d) 12:12 as nymphs and 13:11 as adults. Exposure of nymphs to 13 hr of light significantly reduced the duration of the nymphal stage and the number of nymphs that matured to adults. The duration of the nymphal stage was longer in individuals developing into females than in those developing into males. There was an increase in the longevity of adults kept at 13 hr of light since the nymphal stage. The average longevity of adult males and females was approximately the same. The sex ratio was similar under all photophase conditions. The life cycle of insects kept at 12 and 13 hr of light during nymphal and adult stages respectively was extended. The total life cycle was significantly longer in M. fimbriolata females than males. The different photophase conditions did not affect the reproductive potential of M. fimbriolata. Females produced more diapausing than non-diapausing eggs, except when under 13- and 12-hr light conditions. There was no significant difference in the number of diapausing and non-diapausing eggs produced by females under the other photophase conditions.