André Luiz Lourenção

Atratividade e preferência para oviposição de Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biótipo B em genótipos de tomateiro

Tomato genotypes of different species were evaluated regarding to attractiveness and oviposition preference of Bemisia tabaci (Gennadius) biotype B under greenhouse conditions. The experiment was conducted in a randomized block design, with a split-pot scheme and three replicates. Plant infestation was done at 40-45 days after seedling transplanting by introducing highly whitefly-infested soybean plants. The variables evaluated were adult number and egg number on the adaxial and abaxial surfaces of the leaflets, during five weeks. Each observation was composed by the mean numbers obtained for three leaflets. Leaf area of each genotype was determined to estimate whitefly population per cm2. There were no significant differences among genotypes and evaluations regarding to the presence of live adult whiteflies on the adaxial surfaces of the leaflets. For the number of live adult whiteflies on the abaxial surface, the least attractive genotypes were LA716 (Lycopersicon pennellii) and PI134417 (L. hirsutum f. glabratum); LA1609 (L. peruvianum) was one of the most attractive ones. Great number of dead adult whiteflies was registered on LA716, due to the sticky secretion produced by the glandular trichomes that cover leaves and stalks, trapping whiteflies when they contact the leaflet. Similar behavior was verified for LA1739, LA1740, PI127826 (L. hirsutum), PI134417 and PI134418 (L. hirsutum f. glabratum). LA716 and PI134418 were the least preferred genotypes for oviposition. The preferred genotypes for oviposition on the abaxial surface of the leaflets were CNPH1039, Japao (L. pimpinellifolium) and LA1609.

Adult attractiveness and oviposition preference of Bemisia tabaci biotype B in soybean genotypes with different trichome density

Bemisia tabaci consists of a complex of morphologically indistinct biotypes, varying with respect to their host ranges and ability to transmit plant viruses. Biotype “B” has increased in importance at every growing season in soybean crops in Brazil. The objective was to evaluate B. tabaci biotype B infestations in 24 soybean genotypes, including cultivars of expression for planting and the main sources of insect resistance. The study was performed in a greenhouse with evaluations for adult attractiveness and oviposition preference (free-choice test); these parameters were correlated with trichome density. Three evaluations were carried out, and counts were obtained for number of adults, eggs, and trichomes on the abaxial surface of the leaves. The experimental design consisted of randomized blocks (192 plots). In all three evaluations, “Coodetec 215” was the most attractive to adults; the least attractive cultivars were “IAC 18” (first); PI 274453, “IAC 18,” and D 75-10169 (second); and “IAC 24” (third). As to oviposition preference, “Coodetec 215” showed the highest mean in all evaluations; the lowest means corresponded to “IAC 18” (1st); PI 274453 (2nd); and PI 274453 and L1-1-01 (3rd). No significant correlation was observed between trichome density and oviposition preference and adult attractiveness. Considering all parameters and focusing on commercial germplasm, “IAC 24,” as well as “BRS Barreiras,” “IAC 18,” “IAC 17,” and “IAC 19” can be indicated for planting in regions and/or seasons where B. tabaci biotype B is a problem for soybean production or even in properties where other crops affected by this whitefly are grown simultaneously with soybean or after this legume is grown.

Molecular characterization and genetic divergence of Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae) on different crops and growing areas

Knowledge on the genetic variation of populations of Bemisia tabaci (Genn.) can improve the understanding of genetic diversity found in their biotypes and, consequently, offer guidelines for its management. In this study, the molecular characterization was performed and genetic diversity data were obtained for this insect from three regions of Brazil on different crops [cotton and soybean (Mato Grosso - MT); cabbage (Distrito Federal - DF); soybean and potato (São Paulo - SP)], using RAPD markers. RAPD analysis indicated 80.6% polymorphic loci and the average genetic similarity obtained by the Jaccard coefficient was 0.67. The whitefly populations collected on potato (SP) and soybean (MT) had higher genetic diversity values (0.75 and 0.72, respectively). Shannons index (Ho) showed higher values for potato and soybean (SP e MT), and a smaller value for cabbage (DF). A high genetic divergence within and among the collected populations occurred, structured according to the regions of collection. Moreover, the great genetic similarity observed between potato (SP) and soybean (SP) populations suggested that both belong to the same biotype B and reinforces the polyphagous behavior of the species.

Epizootia de Aschersonia cf. goldiana em Bemisia tabaci (Homoptera: Aleyrodidae) biótipo B no estado de São Paulo

The first observations on the presence of Bemisia tabaci biotype B (=B. argentifolii) in Brazil were made in the beginning of the 1990s in the State of Sao Paulo. from then on, that whitefly has spread out to other States. In the summer of 1997/98, B. tabaci biotype B reached Guaira-Miguelopolis, an area of the State of Sao Paulo not yet infested, with high populations of the insect, mainly in soybean, cotton and vegetable crops. In the the first week of February 1998, during a survey in an abandoned field of soybean, an epizootic of Aschersonia cf. goldiana was verified on that whitefly in the whole area, with total infection of nymphs in the lower surface of the leaves. At the same date, in two other soybean fields of the region, the incidence of this entomopathogen was low, but it increased in the following two weeks, reaching high control levels of the insect, which was similar to the previously observed field. This occurrence indicates A. cf. goldiana as a potential agent for biological control of B. tabaci biotype B.

Variation in the host preferences and responses of Ascia monuste orseis Godart (Lepidoptera: Pieridae) to cultivars of collard greens Brassica oleracea (L.) var. acephala

This work evaluated the preference of Ascia monuste orseis among 29 cultivars of collard greens through free- and no-choice assays using female adults (attractiveness and oviposition) and third-instar larvae (feeding preference), in both laboratory and greenhouse conditions. In free-choice tests with female adults, the L, V, Y, H, A, and Z cultivars produced oviposition non-preference in butterflies. Cultivars R, P, C, and D produced feeding non-preference in third-instar larvae of A. monuste orseis in free- and no-choice tests. Our findings may be useful for genetic improvement focusing on the development of B. oleracea var. acephala cultivars resistant to A. monuste orseis.

Spatial distribution of Pseudaletia sequax Franclemlont in triticale under no-till management

The knowledge of the spatial distribution of insect populations in crops allows the estimation of the population density in space, the classification of damage impact on yield as well as decisions to be made about control measures. To evaluate the spatial distribution of the wheat armyworm Pseudaletia sequax Franclemont, in relation to the development and yield of triticale (Triticum secale Wittmack) under no-till management, samplings were taken at 302 points in a square grid measuring 10 x 10 m, in Campinas, SP, Brazil. The caterpillar population was evaluated by counting their number per meter at the base of triticale plants. Grain yield (kg ha-1), cover of the above-ground part (kg ha-1), mean plant height (m), and ground cover percentage were evaluated after the triticale crop was mechanically harvested, with the measurement of the mass of straw left on soil surface. Geostatistics was used to analyze spatial variability, by means of semivariogram analysis, and interpolation of data by both ordinary and indicator kriging, considering the injury threshold level of ten caterpillars per square meter to construct isoline maps. Spatial dependence occurred for all variables, demonstrating an aggregate spatial distribution pattern of the caterpillar in triticale. Random sampling in this area would fail to reveal that grain yield was affected at the location with the greatest occurrence of the caterpillar. At that location, the economic injury level was exceeded, which would justify the adoption of control measures against the pest.

Ocorrência epizoótica de Verticillium lecanii em Bemisia tabaci biótipo B (Hemiptera: Aleyrodidae) no Estado do Maranhão

High infestations of Bemisia tabaci B biotype were observed in 1999, in a 50 ha soybean field in Balsas region, State of Maranhao, Brazil. The field was sown in May and irrigated with a pivot system, ininterruptedly, during the whole crop season. Whitefly infestation initiated when plants were at the beginning of the vegetative stage, and persisted in variable levels up to plant maturation. Alternate applications of imidacloprid and piridaben were made at ten-day intervals to control insect population. The applications were descontinued between September 10 and 20, during a period of continuous rainfall. After this period, an epizootic occurrence of Verticillium lecanii, infecting whiteflies, was verified in the whole area, reducing the insect population to very low densities. A progressive increase in these populations was observed later on. This reinfestation probably occurred due to the absence of new periods of rainfall, indicating that the humidity supplied by irrigation under pivot was insufficient to promote V. lecanii epizootics in that region since the wind activity is continuous during the crop season.

PERFORMANCE OF GINGER GRASS (Lippia alba) FOR TRAITS RELATED TO THE PRODUCTION OF ESSENTIAL OIL

Lippia alba (Verbenaceae) is a shrub whose essential oil has important biological, pharmacological, and aromatizing properties. To reach the sustained cultivation of new species with economic potential, the present study aimed to evaluate L. alba performance for fresh leaf matter (FM), leaf dry matter (DM), virus symptoms (VS - Cucumber mosaic virus, CMV), oil yield (OY), and oil chemical composition (OC), and to evaluate DM stability and adaptability. Ten genotypes of four chemical groups (chemotypes) were evaluated in six experiments designed as randomized blocks with two plants per plot, over the whole State of Sao Paulo, Brazil. A 2.0 x 0.4 x 1.6 m spacing was used in Monte Alegre do Sul and Pindorama, while a 1.0 x 0.4 x 0.6 m spacing was used in Campinas, where four experiments were established under different irrigation and fertilization conditions. The genotype effect was significant (p < 0.05) for all traits evaluated, with high leaf productivity of IAC-16 (citral chemotype), best OY means in the linalool and limonene/carvone chemotypes, and susceptibility of the latter chemotype to CMV. The genotype performance oscillations in the six environments were significant for FM and DM, and despite their significance for phytochemical traits (OY and OC), they were of low magnitude. No qualitative variation was detected for OC. The IAC-2 (linalool) and IAC-13 (limonene/carvone) genotypes showed high stability and wide adaptability, and are recommended to establish initial cultivations of this species. This research also indicated genetic sources to start Lippia alba genetic breeding programs.

Exsudato glandular de genótipos de tomateiro e desenvolvimento de Bemisia tabaci (Genn.) (Sternorryncha: Aleyrodidae) biótipo B

Bemisia tabaci (Genn.) is one of the most important tomato pests in Brazil and causes severe losses due to the sap suction, the induction of the irregular ripening of the fruit and virus transmission. The objective of this study was to determine the effect of exudates released by the glandular trichomes on the development of B. tabaci biotype B on eight tomato genotypes, under greenhouse conditions. The experiment was arranged as a factorial scheme (genotype x exudate) in a randomized block design, with three replications, being the genotypes evaluated in two conditions (with and without exudate). Whitefly adults were transferred to a voile cage for 24h. The variables evaluated were number of eggs and viability, incubation period, number of nymphs, duration and viability of the nymphal stage. Trichome counts and determination of pH and acylglucose content were made for all the genotypes. Intact leaflets of LA716 were less accepted for oviposition than leaflets without exudate, which suggests an antixenotic effect. Antixenotic resistance in LA1739 and PI134417 was not associated to the glandular exudate. The effect of exudates on the insect oviposition was explained by the acylglucose content. The pH showed secondary role on the whitefly oviposition. Trichomes density improved the insect development. LA1584 reduced the insect survival and increased its cycle, besides promoting an intermediate oviposition. For this reason, it can be useful in breeding programs. However, further studies are needed to determine the potential of this genotype and hybrids for future utilization in integrated pest management.

Fontes de resistência a Scrobipalpula absoluta (Meyrick, 1917) em tomateiro

Eighty-five wild and cultivated tomato accessions, being 71 Lycopersicon esculentum, 10 L. pimpinellifolium and 4 L. peruvianum, were evaluated in greenhouse, under artificial infestation, for resistance to Scrobipalpula absoluta (Meyr.) (Lepidoptera: Gelechiidae). NAV 29 and NAV 115 (L. peruvianum) showed the least foliar damage while NAV 98 (L. pimpinellifolium) was less attacked in the buds than cultivated tomatoes (L. esculentum). Then, a comparative trial was carried out among the Rio Grande and Pacesetter tomato cultivars, NAV 98 and NAV 29/115 (mixed offsprings of NAV 29 and NAV 115, because of self-incompatibility). The highest level of resistance to the pest was presented by NAV 29/115.