Maria R.V. de Oliveira

Natural enemies of Bemisia tabaci (Gennadius) B biotype and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) in Brasília, Brazil.

Uma investigacao foi conduzida em Brasilia, DF, de janeiro de 1999 ate marco de 2001, sobre fumo, algodao, tomate, couve, soja, feijao, melao, jilo e a planta daninha Emilia sonchifolia DC, a fim de se obter inimigos naturais das moscas-brancas Bemisia tabaci (Gennadius) e Trialeurodes vaporariorum (Westwood). Ao todo, 14 predadores, 12 parasitoides e dois hiperparasitoides foram coletados. Entre os parasitoides, Encarsia inaron (Walker) ainda nao havia sido registrada na America do Sul, e E. basicincta Gahan e um novo registro para o Brasil. E. aleurothrixi Evans & Polaszek e tambem registrada pela primeira vez parasitando B. tabaci. Os besouros Nephaspis hydra Gordon e Delphastus davidsoni Gordon sao registrados pela primeira vez predando B. tabaci.

Screening of Beauveria bassiana (Deuteromycotina: Hyphomycetes) isolates against nymphs of Bemisia tabaci (Genn.) biotype B (Hemiptera: Aleyrodidae) with description of a new bioassay method

A bioassay method that uses melon leaves as substrate for eggs and nymphs of the biotype B of Bemisia tabaci (Genn.) was established. Root formation of petioles immersed in tap water guaranteed the turgidity and normal coloration of leaves for a period of 20 to 25 days, enabling the execution of tests with entomopathogenic fungi. The virulence of 50 isolates of Beauveria bassiana (Balsamo) Vuillemin was assessed, as an initial action of a research project that aims the development of a bioinsecticide for controlling Bemisia tabaci nymphs in melon crops. Melon leaves were infested with 18 couples of biotype B adults for 26 hours. First-instar nymphs were selected through microscopic observation approximately 4-5 days after adults removal. Application of fungal isolates was performed with a spray tower. Average number (± SEM) of infective propagules deposited on leaf surface was 1.2x104 ± 9.12x102 conidia per cm2. For the control it was applied a Tween 80 solution at 0.1%. Three or four replicates were performed per treatment. Incubation was in chamber regulated to 27±1oC, 70±5% RH and 12 hours photophase. Assessments of dead nymphs were performed at seven and 14 days following spraying. Average mortality in the control treatment was 1.2% at day 14, and 94.4% of the nymphs became adults. Average nymphal mortality at day seven post-spray reached a maximum value of 25.7%. Average mortality at day 14 post-spray varied from 6.1% to 92.3%.

Does the presence of weeds affect Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) infestation on tomato plants in a semi-arid agro-ecosystem?

Integrated Bemisia tabaci (Gennadius) management requires quantitative knowledge on the mechanisms of persistence of pest populations in non-commercial host plants. We investigated B. tabaci oviposition preference among tomato and four weed species, and the insect population fluctuation under field conditions in the semi-arid region. At weekly intervals, we determined the level (number of eggs and nymphs per leaf) and the density of infestation (number of eggs and nymphs per leaf area) in all species. We observed an oviposition preference gradient among the species, with different degrees of attractiveness; Acanthospermum hispidum was the most infested species whereas Amaranthus deflexus was the least infested one. We also detected a significantly higher infestation on tomato when planted solely, which indicates a dilution effect on tomato infestation in the presence of weeds. Weeds can act as important reservoirs for whiteflies and/or their natural enemies or even as viral sources for cultivated plants. Their incorporation in integrated B. tabaci management programs depends on how those variables can be manoeuvred for the reduction of insect damage.

Diversity analysis of Bemisia tabaci biotypes: RAPD, PCR-RFLP and sequencing of the ITS1 rDNA region

The Bemisia tabaci complex is formed by approximately 41 biotypes, two of which (B and BR) occur in Brazil. In this work we aimed at obtaining genetic markers to assess the genetic diversity of the different biotypes. In order to do that we analyzed Bemisia tabaci biotypes B, BR, Q and Cassava using molecular techniques including RAPD, PCR-RFLP and sequencing of the ITS1 rDNA region. The analyses revealed a high similarity between the individuals of the B and Q biotypes, which could be distinguished from the BR individuals. A phylogenetic tree based on ITS1 rDNA sequence was constructed. This is the first report of the ITS1 rDNA sequence of Bemisia tuberculata and of the BR biotype of B. tabaci.