Maria Alice de Medeiros

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.

Interferência das plantas daninhas na cultura do tomate para processamento

ABSTRACT Weed interference in processing tomato crops Weed control efficiency depends on the information about itsinterference on the crops. The interference of weed on tomato plantsof a processing variety, transplanted directly into the field wasevaluated. The field experiment was carried out, in a randomizedblock design with three replications, at Embrapa Hortalicas inBrasilia, Brazil. Plots were laid out with increasing periods of timein the presence or absence of weeds. In the first case, plots remainedunder weed interference from seedling stage until the followingperiods (days) of the tomato life cycle: 1-28, 1-35, 1-49, 1-63, 1-77and 1-91(whole cycle, harvest). After these periods the weeds grewfreely until harvesting time. In the second case, plots were weededfrom seedling stage until the previously described periods. After theseperiods weeds were removed by hand through the rest of the tomatocycle. Among 24 of the most frequent weed species, Bidens pilosa , Brachiaria plantaginea

Alternative food sources and overwintering feeding behavior of the boll weevil, Anthonomus grandis boheman (coleoptera: curculionidae) underthe tropical conditions of central Brazil

The boll weevil causes serious damage to the cotton crop in South America. Several studies have been published on this pest, but its phenology and behavior under the tropical conditions prevailing in Brazil are not well-known. In this study the feeding behavior and main food sources of adult boll weevils throughout the year in Central Brazil was investigated. The digestive tract contents of insects captured in pheromone traps in two cotton fields and two areas of native vegetation (gallery forest and cerrado sensu stricto) were analyzed. The insect was captured all through the year only in the cerrado. It fed on pollen of 19 different plant families, on Pteridophyta and fungi spores and algae cysts. Simpson Index test showed that the cerrado provided greater diversity of pollen sources. In the beginning of the cotton cycle, the plant families used for pollen feeding were varied: in cotton area 1, the weevil fed on Poaceae(50%), Malvaceae and Smilacaceae (25% each); in cotton area 2 the pollen sources were Malvaceae (50%), Asteraceae (25%) and Fabaceae and Clusiaceae (25% each); in the cerrado they were Chenopodiaceae (67%) and Scheuchzeriaceae (33%). No weevils were collected in the gallery forest in this period. After cotton was harvested, the family Smilacaceae was predominant among the food plants exploited in all the study areas. These results help to explain the survivorship of adult boll weevil during cotton fallow season in Central Brazil and they are discussed in the context of behavioral adaptations to the prevailing tropical environmental conditions.

Parasitismo e predação em ovos de Euschistus heros (Fab.) (Heteroptera: Pentatomidae) no Distrito Federal, Brasil

The mortality of Euschistus heros (F.) at the egg stage was studied at the field. The experiments were carried out in Planaltina - D.F., Brazil, in 1993 and 1994, on sunflower (Helianthus annuus) cultivated following the soybean (Glycine max) crop season. Egg masses found in the field were marked and checked daily for four days, and taken to the laboratory to check the total number of eggs, eggs that failed to hatch and those parasitized or destroyed by predators. The incidence of parasitism in eggs of E. heros was high in 1993 (65%) and in 1994 (80%). Five species of parasitoids were recovered: Telenomus podisi Ashmead, Trissolcus basalis (Wollaston), Trissolcus teretis Johnson, Trissolcus urichi Crawford (Scelionidae) and Eupelmus sp. (Eupelmidae). T. podisi was the most frequent species. Egg mortality due to predators was 17% in 1993 and 13% in 1994.

Effect of plant diversification on abundance of South American tomato pinworm and predators in two cropping systems

Several studies have demonstrated that the diversification of the agroecosystem may reduce insect pest infestation using the strategy of companion planting. We studied the effect of the presence of coriander and Gallant soldier as companion plants in the tomato crop under organic and conventional management on abundance of the tomato pests and predators. The experiment was carried out under field conditions, at Distrito Federal, Brazil, from July to October, 2004. The experimental design was of randomized blocks with three replicates in a 3 x 2 factorial arrangement [Three crop diversification levels: tomato in monoculture, tomato intercropped with coriander, and tomato intercropped with coriander and Gallant soldier; and two cropping systems: organic and conventional]. Each plot had 80 plants of the tomato and the pest-insects and predaceous arthropods were collected every week in five tomato plants/plot. Tuta absoluta (Meyr.) was the commonest pest species in both cropping systems. The tomato intercropped with coriander and Gallant soldier in organic cropping system had lower abundance and higher diversity of pests, and higher abundance and diversity of predaceous arthropods, mainly at 80 days after the tomato transplanting, coinciding with the population peak of T. absoluta (eggs and adults). The more abundant predators were spiders, lady beetles and ants. The spiders were abundant and uniformly distributed in both systems. The lady beetles appeared lately in the organic system, at the flowering season of the coriander. The ants were more abundant in the conventional systems.

Impacto de inseticidas sobre parasitóides da traça-das-crucíferas em repolho, no Distrito Federal

The objective of this work was to identify parasitoids of Diamondback Moth in the Federal District. Larvae of the insect were collected in areas treated with insecticides or in untreated areas. Four species of parasitoids were identified: Apantelessp. (Braconidae), Oomyzus sokolowiskii (Kurdjumov) (Eulophidae), Diadegmasp. (Ichneumonidae) and Actiasp. (Tachnidae). The total rate of parasitism ranged from 5% to 94% in fields untreated with insecticides, while they ranged between 11% to 87% in treated ones. Most Diamondback Moth larvae were found on cabbage head and on the underside of outer cabbage leaves. The larvae distribution could allow them to escape insecticide residues and so also allow parasitoid survival.

Efficiency on cabbage production and impact of insecticide mixtures on parasitoids of diamondback moth

A producao comercial de repolho foi obtida de parcelas que re ceberam combinacoes de doses de deltametrina 25 CE e abamectin 18 CE as quais proporcionaram controle dos danos causados pela traca-das-cruciferas, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae). Os resultados foram comparaveis aqueles obtidos pela pulverizacao de formulacao concentrada emulsionada de Bacillus thuringiensis. A utilizacao isolada de deltametrina 25 CE e abamectin 18 CE (0,5 1/ha) resultou em baixos niveis de producao comercial, respectivamente 7 e 8%. As misturas deltametrina e abamectin produziram mais de 42%. A elevada densidade populacional da praga fez com que nao fosse obtida producao co mercial na area nao tratada. Os inseticidas ou suas combinacoes tes tadas nao provocaram qualquer impacto, estatisticamente mensuravel, sobre populacoes das especies dos parasitoides Diadegma spp. (Hymenoptera: Ichneumonidae) e Apanteles spp. (Hymenoptera: Braconidae).

Fatores de mortalidade na fase de ovo de Tuta absoluta em sistemas de produção orgânica e convencional de tomate

A traca-do-tomateiro Tuta absoluta (Meyrick) (Lep.: Gelechiidae) esta sujeita a fatores de mortalidade bioticos como predadores e parasitoides e fatores abioticos como agua da irrigacao e da chuva que influenciam sua dinâmica populacional. O objetivo deste trabalho foi quantificar a importância desses fatores na sobrevivencia de ovos da traca-do-tomateiro. Os experimentos foram desenvolvidos na Embrapa Hortalicas, de 1/8/2004 a 7/11/2005, em plantio de tomate e tomate consorciado em sistema orgânico e tomate em sistema convencional. As avaliacoes consistiram em: 1) coleta de ovos no campo em diferentes epocas do ciclo da cultura e sua incubacao em laboratorio ate a emergencia do parasitoide ou eclosao da lagarta; 2) exposicao de ovos sentinelas no campo por 72 horas; 3) ovos marcados e acompanhados a cada 24 horas ate eclosao das lagartas em campo. Ovos coletados no campo e incubados em laboratorio mostraram que a mortalidade por Trichogramma sp. foi de 32%. A mortalidade dos ovos que permaneceram no campo (metodologia 2 e 3), evidenciaram que o parasitismo por Trichogramma sp. foi de 12% e que os predadores e o efeito mecânico da agua produziram 36% de mortalidade dos ovos. Essa diferenca revela que a permanencia dos ovos no campo os expoe a competicao com predadores e a mortalidade causada pelo efeito mecânico da agua reduzindo o recrutamento de Trichogramma sp. Parasitoides de ovos, predadores generalistas associados a acao da agua acarretaram maior mortalidade de T. absoluta em sistemas de producao orgânica de tomate.

Eficiência técnica e econômica do controle biológico da traça-do-tomateiro em ambiente protegido

Technical and economic efficiency of biological control of the South American tomato pinworm in protected environment The economic and technical efficiency of controlling the South American tomato pinworm (Tuta absoluta) by the parasitoid Trichogramma pretiosum was evaluated in protected environment, in Luziania, Goias State, Brazil, during the summer of 1999-2000. The research was conducted in two greenhouses, each one submitted to the following pest control regimes: (1) habitual farmer practices: pesticides sprayed based on presence/absence of the pest and rotation of products (deltamethrin; abamectin; Bacillus thuringiensis (at the recommended dose); and soap at 0,5% concentration). (2) inundative release of T. pretiosum associated with weekly sprays of Bacillus thuringiensis as an emulsifiable concentrate formulation (at the recommended dose). Insecticide sprays and parasitoid mass release were initiated just after the first adults were observed. Mass release consisted of weekly display of two cards (20x30 cm) of parasitized eggs by T. pretiosum that were gradually increased until the reached six cards each week, by the time of tomato harvest. Once a week, 50 leaflets were collected in each greenhouse. The number of eggs was determined in the laboratory and kept inside chambers to determine the number of larvae or the percentage of parasitism. Tomato production and damage to the fruits were determined weekly from 50 tomato plants randomly chosen in each treatment. The productivity of the treatment using biological control was 6,160 polystyrene trays/600g and 6,833 trays/600g when chemical control was used. The variable costs of production were R

Estudo preliminar do controle biológico da traça-do-tomateiro com o parasitóide Trichogramma pretiosum em ambientes protegidos

3,9 thousands and R