Elenice Mouro Varanda

Resistance and susceptibility of alfalfa (Medicago sativa L.) cultivars to the aphid Therioaphis maculata (Homoptera: Aphididae): insect biology and cultivar evaluation

Abstract Biology of the aphid Therioaphis maculata was studied on alfalfa (Medicago sativa L.), including four resistant (Mesa‐Sirsa, CUF101, Baker and Lahontan) and two susceptible (ARC and Caliverde) alfalfa cultivars, and one of the most cropped Brazilian cultivars, Crioula. Under controlled conditions, antibiosis (i.e., reduced longevity, fecundity and increased mortality of the aphid) was observed mainly on the resistant alfalfa cultivars, except on Lahontan. Crioula seemed to be tolerant to aphids. Present data support geographic limitation usage of cultivars, and we suggest Baker and Mesa‐Sirsa as sources of antibiosis, and provide biological information of a tropical T. maculata biotype on alfalfa.

Effect of the inherent variation in the mineral concentration of alfalfa cultivars on aphid populations

Plants have inherent variability of mineral content which affects their physiology and consequently the herbivorous insects feeding on them. Besides, insects need considerable amounts of potassium, phosphorus and magnesium in their diets, whereas little calcium, sodium and chloride are required. In this study, the inherent variation on mineral (Ca, S, Mg, N, P, K and also C:N ratio) concentrations and aphid (Acyrthosiphon spp., Therioaphis maculata, Aphis craccivora) populations on three alfalfa (Medicago sativa) cultivars (P3; Crioula, the most widely cultivated in Brazil, and CUF 101, an aphid-resistant) were studied between September/1997 and August/1998. A significant variation on mineral concentrations and aphid populations was observed among different sampling times and cultivars. The correlations between C:N ratio, Mg, N, P and S concentrations and aphid density variation suggest that the mineral status affects aphid population dynamics under field conditions.

Variation in plant defenses of Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae) across a vegetation gradient in a Brazilian cerrado

Cerrado vegetation is composed of a mosaic of vegetation types, from campo sujo, dominated by herbs; campo cerrado and cerrado sensu stricto, with shrubby vegetation; to cerradao, with trees forming a denser forest. This physiognomic mosaic is related to differences in the water availability in the soil. Cerrado plants are considered physically and chemically well defended against herbivores, but there are no studies showing how plants allocate investment to various types of defensive mechanisms in different habitat physiognomies. The defensive mechanisms and the nutritional traits of a cerrado plant, Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae), were compared along a vegetation gradient. Toughness, as well as water, nitrogen, cellulose, lignin, and tannin contents were measured in young and mature leaves of D. vinosum collected in campo cerrado, cerrado sensu stricto (s.s.) and cerradao. Plants from cerrado s.s. and cerradao were of better nutritional quality but also had higher tannin contents than campo cerrado plants. Some type of compensation mechanism could have been selected to provide an optimum investment in defense, according to limitations imposed by water deficits in the habitat.

Weather, cultivar and density-dependent processes influence on aphid in alfalfa

E importante entender os efeitos do clima, da densidade dos insetos e da cultivar sobre a abundância de insetos para se predizer e prevenir perdas na producao das culturas. O objetivo do presente trabalho foi analisar a influencia desses fatores sobre afideos em alfafa no periodo de um ano. Os dados foram coletados de setembro/1997 a agosto/1998 na Fazenda Canchin (CPPSE-EMBRAPA), Sao Carlos, Sao Paulo, Brasil. As condicoes climaticas, em geral, tiveram pequeno efeito sobre a variacao populacional dos afideos, mas a abundância de Therioaphis maculata esteve negativamente correlacionada a umidade. Alem disso, as altas temperaturas maximas e os baixos niveis de precipitacao pluvial possivelmente favoreceram a alta abundância dessa especie nas cultivares Crioula e P3. Portanto, torna-se importante o manejo desse afideo durante periodos quentes e secos. As variacoes populacionais de Acyrthosiphon spp., T. maculata e Aphis craccivora parecem ser reguladas principalmente por processos dependentes da densidade. Na cultivar resistente CUF 101 observou-se menor abundância de T. maculata e A. craccivora e uma variacao populacional menos pronunciada do que nas demais cultivares, podendo ser utilizada para reducao da populacao dessas especies em campo. Estudos de longa duracao, incluindo os efeitos do clima e da densidade sobre a qualidade da planta, vao contribuir para o manejo de afideos nos alfafais.

Flower-visiting insects of five tree species in a restored area of semideciduous seasonal forest.

The reinstatement of biodiversity and ecological processes must be the major goal in restoration projects, which requires the establishment of biological interactions in addition to native plant population recovery. Therefore, we assessed the flower visitors of five tree species in a restored area of Semideciduous Seasonal Forest, in Ribeirão Preto, SP, Brazil. The specimens were collected using entomological net on flowers of Acacia polyphylla, Aegiphila sellowianna, Croton floribundus, Croton urucurana and Schinus terebinthifolius from October 2007 to September 2008. A total of 139 insect species belonging to five orders were collected. Hymenoptera was the most diverse order collected. From a total of 37 families, Vespidae (15 species), Cabronidae (12), Apidae (10), Halictidae (10), Syrphidae (12), Tachinidae (6) and Hesperidae (7) were the richest ones. Schinus terebinthifolius flowers presented the most abundant and diverse insect visitors (60), suggesting it is an important attractive species to the fauna in restoration programs. Our data suggest that mutualistic interactions between some of these plants and their flower-visiting insects may be in a reinstatement process, and will support the design and monitoring of future restoration efforts.

Ceras foliares epicuticulares de espécies congêneres da mata e do cerrado

Four woody species of cerrado and five woody species of seasonal semideciduous forest were analysed concerning the contents of epicuticular waxes and their parafinic profiles. The cerrado species showed a tendency to higher contents of epicuticular waxes and lower proportion of hydrocarbons than the forest species. The C29 and C31 alkanes were dominant in all species and the average lenght of the hydrocarbon chains were around 30,5 in the forest species and from 28,5 to 31,3 in the cerrado species. The ecological and taxonomic aspects of this characteristics are discussed.