Does Bacillus thuringiensis have adverse effects on the host egg location by parasitoid wasps?

ABSTRACT This study investigated the interaction between two pest biological control agents, the parasitoid wasp Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) and the entomopathogen Bacillus thuringiensis (Bacillales: Bacillacea) (Bt). The aim of this study was to evaluate if the presence of Bt (formulated products Agree®, Dipel® and HD1 and HD11 strains) interferes in the oviposition preference of T. pretiosum to eggs of Helicoverpa zea (Lepidoptera: Noctuidae). Using an olfactometry test, the eggs of H. zea were bathed with the commercial formulations, with the Bt suspensions or distilled water, and offered to the parasitoid wasps in order to evaluate parasitism. The results showed that H. zea eggs sprayed with commercial formulations and Bt strains did not interfere in the choice made by the parasitoid. The parasitoid wasp is not able to distinguish between eggs with or without B. thuringiensis treatment, independently of strains suspension or commercial formulations. Therefore, these two control agents may be used together without negative interaction.

Silicon influence on resistance induction against Bemisia tabaci biotype B (Genn.) (Hemiptera: Aleyrodidae) and on vegetative development in two soybean cultivars

The potential of populations of Bemisia tabaci (Genn.) to become resistant to insecticides has stimulated research into alternative tactics of integrated pest management such as the induction of host-plant resistance. Recent data have shown that silicon can increase the degree of resistance of host plants to insect pests. Therefore the aim of our work was to study the effects of silicon application on the vegetative development of soybean plants and on the induction of resistance to the silverleaf whitefly, B. tabaci biotype B. We performed choice and no-choice tests of oviposition preference on two soybean cultivars, IAC-19 (moderately resistant to B. tabaci biotype B) and MONSOY-8001 (susceptible), with and without application of silicon. Silicon did not affect silverleaf whitefly oviposition preferences, but caused significant mortality in nymphs. Thus, silicon increased the degree of resistance to silverleaf whitefly. Silicon decreased the production of phenolic compounds, but did not affect lignin production. However, when applied to cultivar IAC-19, it increased the production of non-protein organic nitrogen. Silicon had no effect on the vegetative development of soybean plants, but it increased the degree of resistance to the silverleaf whitefly. We conclude that silicon applications combined with cultivar IAC-19 can significantly decrease silverleaf whitefly populations, having a positive impact both on the soybean plant and on the environment.

Fatores que afetam a oviposição de Bemisia tabaci (Genn. ) Biótipo B (Hemiptera: aleyrodidae) em feijoeiro / Factors acting on Bemisia tabaci (Genn. ) biotype B (Hemiptera: aleyrodidae) oviposition in common bean

Este trabalho teve por objetivo avaliar o comportamento de oviposição de Bemisia tabaci (Genn.) biótipo B, em relação à idade da planta, densidade de adultos e regiões da planta de feijoeiro, sendo utilizado o genótipo Pérola. No teste com chance de escolha foram utilizadas plantas com 20, 30 e 40 dias de idade para avaliar a preferência de oviposição do inseto. Para o teste sem chance de escolha, referentes às diferentes densidades de adultos, foram utilizadas plantas com 30 dias de idade, liberando-se 50, 100 e 150 adultos por planta. Quanto ao teste sem chance de escolha para a posição da planta (ápice, mediana e basal), adotou-se a idade de 40 dias para a liberação dos adultos. As plantas com 30 dias de idade foram preferidas para oviposição. A densidade de 100 adultos por planta propiciou oviposição adequada para discriminar genótipos quanto aos graus de resistência enquanto a região apical da planta foi a preferida para postura, portanto a mais adequada para as amostragens de ovos de B. tabaci biótipo B em plantas de feijoeiro, visando um manejo adequado da praga.

The objective of this work was to evaluate the oviposition behavior of the whitefly Bemisia tabaci (Genn.) biotype B in relation to plant age, adult density and plant region on common beans plants. The genotype Perola was used to do the test. In free-choice tests 20, 30 and 40 day-old plants were used where evaluated the oviposition Fatores que afetam... JESUS, F. G. et al. Biosci. J., Uberlândia, v. 27, n. 2, p. 190-195, Mar./Apr. 2011 194 preference of the insect. In no-choice test, 30 day-old plants were used to evaluate densities of 50, 100 and 150 adults per plants. No-choice test for plant position (apex, median, base) 40 day-old plants were adopted for liberation of adults. The 30 and 40 day-old plants were preferred for oviposition, the densities of 100 adults per plants ensured the number of eggs enough to discriminate common beans genotypes with different whitefly resistance degrees, and apical region of plant were preferred for whitefly egg laying and therefore more suitable for egg sampling in common bean plants.

Comportamento de oviposição da mosca-branca Bemisia tabaci (Genn. ) (Hemiptera: Aleyrodidae) biótipo B em tomateiro / Oviposition behavior of the silverleaf whitefly Bemisia tabaci biotype B on tomato

Avaliou-se a influência da face foliar, do comportamento geotrópico do inseto e do tipo de tricoma foliar sobre a oviposição de Bemisia tabaci (Genn.) biótipo B em folhas de tomateiro. Para avaliação desses efeitos foram realizados vários ensaios nos quais as fêmeas foram confinadas em caixas de acrílico. Folíolos de tomateiro foram fixados no topo e na base das caixas, de tal forma a permitir o acesso dos insetos às faces adaxial e abaxial de maneira isolada e concomitante (com e sem chance de escolha). Os insetos sempre depositaram maior número de ovos quando a superfície foliar se encontrava no topo da caixa e, de maneira geral, preferiram depositar seus ovos na face abaxial dos folíolos. Para avaliar o efeito do tipo de tricoma (glandular e não-glandular) sobre a oviposição de B. tabaci, a face abaxial dos folíolos de tomateiro foi oferecida a cerca de 30 fêmeas para oviposição em cada caixa de acrílico. Foram oferecidos folíolos previamente lavados com etanol a 70 por cento (de forma a eliminar os exsudatos glandulares) e sem lavagem prévia. A maior parte da oviposição ocorreu ao lado dos tricomas não-glandulares, demonstrando que o inseto discrimina o tipo de tricoma.

The objective of this work was to evaluate the influence of the leaf surface, the insect geotropic behavior and the type of foliar trichome on Bemisia tabaci (Genn.) biotype B oviposition on tomato leaves. Bemisia tabaci females were confined in acrylic boxes in which tomato leaflets were fixed at the bottom and top part of the boxes to allow insects to access the leaf surface to be tested (adaxial and/or abaxial) in both no-choice and free choice tests. Oviposition was always higher when the leaf was offered at the top of the box and preferably at the abaxial leaf surface. The effects of leaf trichomes (glandular and non glandular) on B. tabaci oviposition was evaluated by offering the abaxial surface of tomato leaflets to females after a 70 percent ethanol wash to remove glandular exsudates against a control treatment (without a ethanol wash). Oviposition was concentrated mostly near to non glandular trichomes, showing whitefly females can discriminate among the trichomes.

Fatores que Afetam a Oviposição de Bemisia tabaci (Genn. ) Biótipo B (Hemiptera: Aleyrodidae) em Tomateiro / Factors Acting on Bemisia tabaci (Genn. ) B Biotype (Hemiptera: Aleyrodidae) Oviposition in Tomato

The aim of the present work was to determine the oviposition preference of the silverleaf whitefly on tomato (Lycopersicon esculentum). Preferred plant age and leaflet position on the plant were studied and the number of adults per plant necessary for selecting hosts was determined. Bruna VFN hybrid plants at different ages (30-, 45- and 60-days old) were offered to adult whiteflies in free choice test and 30-day old plants in no-choice test. Leaves were collected from upper and lower part of the plant; the leaflets were divided into three categories: basis (those near the steam of plant), middle and apex (terminal leaflet). The 30-day old plants were more preferred for oviposition in free choice test. In the upper part of the plant, whitefly adults preferred to oviposit on the leaflets at the apex and the middle of the leaves. However, in the lower part of the plant, the basal leaflets were preferred in relation to middle and apex. The densities of 100 or 150 adults per tomato plant were considered adequate for genotypes screening, using no-choice test.

Com o objetivo de avaliar os fatores que interferem na preferência para oviposição da mosca-branca (B. tabaci biótipo B) em tomateiro, estudou-se a idade da planta e a posição dos folíolos de maior preferência. Determinou-se, também, a densidade de adultos necessária para se selecionar hospedeiros. Utilizaram-se plantas do híbrido Bruna VFN (Lycopersicon esculentum) com 30, 45 e 60 dias de idade em teste com chance de escolha e plantas com 30 dias em teste sem chance de escolha. As folhas foram coletadas nos terços superior e inferior das plantas e os folíolos foram divididos em três categorias: base (aqueles próximos ao caule da planta), meio e ápice (folíolo terminal da folha). Plantas com 30 dias foram preferidas para oviposição em teste com chance de escolha. Os folíolos do meio e do ápice foram os preferidos para oviposição na parte superior da planta. Os folíolos da base da folha foram os mais ovipositados na parte inferior da planta. As densidades de 100 ou 150 adultos de mosca-branca por planta de tomateiro foram suficientes para assegurar a oviposição adequada do inseto, podendo ser utilizadas em futuros estudos relacionados com a discriminação de genótipos em teste sem chance de escolha.

Resistência de genótipos de soja a Bemisia tabaci (Genn. ) biótipo B (Hemiptera: Aleyrodidae) / Resistance of soybean genotypes to Bemisia tabaci (Genn. ) biotype B (Hemiptera: Aleyrodidae)

Twenty soybean genotypes were evaluated in relation to silverleaf whitefly [Bemisia tabaci (Genn.) biotype B] resistance, in a free-choice test, under greenhouse conditions. The experiment was carried out with artificially infested soybean plants and evaluated during vegetative and reproductive stages. Line D 75-10169 and cultivars IAC 17 and IAC 19 presented nonpreference for oviposition, weak colonization and low adult attractiveness. Trichome density at abaxial trifoliolate surface was also measured in twenty soybean genotypes, at three plant positions (upper, middle and lower canopies), at the same development stages of the free-choice test. The line D 75-10169 presented the lowest trichome density while the cultivar 'IAC Holambra Stwart' showed the highest one. Significant correlations were detected between adult attractiveness and oviposition preference and between adult attractiveness and colonization level. To confirm the oviposition preference results, a no-choice test was carried out, also in greenhouse conditions, and the performance of five soybean genotypes (one highly susceptible and four with the smallest levels of oviposition) was checked. The line PI 227687, though showing multiple resistance to insects, was highly oviposited by silverleaf whitefly, while 'IAC 19', 'IAC 17', 'Coodetec 201' and line D 75-10169 showed oviposition nonpreference as the mecanism of resistance. The results strongly suggest that the resistance observed in those genotypes is stable.

O comportamento de 20 genótipos de soja foi avaliado em relação à preferência para oviposição, atratividade para adultos e colonização das plantas pela mosca branca Bemisia tabaci (Genn.) biótipo B, em teste de livre escolha, em casa de vegetação. O experimento foi conduzido com plantas de soja nas fases vegetativa e reprodutiva, infestadas artificialmente com esse inseto. As cultivares IAC 17, IAC 19 e a linhagem D 75-10169 apresentaram resistência do tipo não preferência para oviposição, baixos níveis de colonização e atratividade para adultos em relação a B. tabaci biótipo B. Também em casa de vegetação, foi avaliada a densidade de tricomas na superfície abaxial de folíolos dos 20 genótipos de soja, nos estratos superior, médio e inferior das plantas, nas fases de desenvolvimento em que as plantas foram avaliadas no teste de livre escolha. A linhagem D 75-10169 apresentou baixa densidade de tricomas, enquanto a cultivar IAC Holambra Stwart mostrou-se altamente pubescente. Foram verificadas correlações entre atratividade para adultos e preferência para oviposição e entre atratividade para adultos e colonização das plantas. Para confirmação dos resultados de preferência para oviposição, foi realizado teste sem chance de escolha, em casa de vegetação, no qual foi avaliado o comportamento de cinco genótipos (um altamente suscetível e os quatro menos preferidos para oviposição no teste com chance de escolha). A linhagem PI 227687, embora apresente resistência múltipla a insetos, foi altamente ovipositada por B. tabaci biótipo B, enquanto que 'IAC 19', 'IAC 17', 'Coodetec 201' e a linhagem D 75-10169 mantiveram a resistência do tipo não-preferência para oviposição.

Within- and among-population variation in oviposition preference of urea-supplemented food in Drosophila melanogaster.

Oviposition preference for urea-supplemented food was assayed by simultaneous choice trials on five pairs of closely related laboratory populations of Drosophila melanogaster. Each pair of populations had been derived from a separate ancestral population about 85 generations prior to this study. One population in each pair had been subjected to selection for larval tolerance to the toxic effects of urea; the other population served as a control. Considerable variation in oviposition preference was seen both within and among populations, with four of the ten populations showing a significant mean preference for urea-supplemented food. The degree of specificity shown by individual females was surprisingly high, leading to a bi-modal distribution of oviposition preference in some populations. Overall, selection for larval tolerance to urea did not significantly affect oviposition preference. However, the data indicated that pair-wise comparisons between randomly selected populations from the two larval selection regimes would lead to a range of possible outcomes, suggesting, in several cases, that selection for larval urea tolerance had led to significant differentiation of adult oviposition preference for urea in one or the other direction. The results, therefore, highlight the importance of population level replication and caution against the practice, common in ecological studies, of assaying oviposition preference in two populations that utilize different hosts in nature, and then drawing broad evolutionary inferences from the results.