Marina Castelo Branco

Forecasting insecticide susceptibility in Diamondback Moth populations from different areas of Brazil

The Diamondback Moth (DBM) is an important brassica pest and is controlled by several types of insecticides. On some occasions, the fields are sprayed two-four times per week without success. Sometimes this occurs because ineffective insecticides are used. Works showed that laboratory tests using the recommended field rate of insecticides can detect the ineffective ones. Here, we collected DBM larvae and pupae from the States of Ceara (Tiangua), Minas Gerais (Barroso), Bahia (Mucuge), Mato Grosso (Sinop) and the Federal District (Brazlândia and Embrapa Hortalicas). We reared the populations in the laboratory and larvae of the first laboratory generation were treated with the recommended field rate of abamectin, acephate, B. thuringiensis, cartap, chlorfluazuron, deltamethrin, and spinosad. We previously determined that an effective insecticide should cause more than 90% larval mortality. Insecticide effectiveness was different from field to field. Spinosad killed 100% of larvae; acephate, B. thuringiensis and cartap killed less than 90% of the larvae in Tiangua; abamectin and chlorfluazuron did not control the insect in Brazlândia and Mucuge respectively. Deltamethrin was inneffective in all areas tested. Diamondback Moth populations were resistant to one or more active ingredients and programmes to manage insecticide resistance must be implemented in Brazil.

Insecticide resistance in Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) in the Federal District, Brazil

(L.) prove-nientes do Distrito Federal em laboratorio. Os niveis de resistencia a deltametrinavariaram de 4 a 47 vezes quando comparados a uma populacao susceptivel delaboratorio. Ja os niveis de resistencia a metamidofos se situaram entre 2 e 9vezes. Nao foi encontrada resistencia a cartap.PALAVRAS-CHAVE: Insecta, traca das cruciferas, resistencia a inseticidas.ABSTRACT - The levels of resistance to the insecticides cartap, deltamethrinand metamidophos were evaluated for three populations of the DiamondbackMoth

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.

A survey of insecticide susceptibility in Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) in the Federal District, Brazil

The level of insecticide susceptibility of strains of Plutella xylostella (L.) from the Federal District was evaluated in 1995 and 1996. A homogeneity in acephate and phentoate susceptibility was observed in the surveyed strains. One strain, highly susceptible to Bacillus thuringiensis lost its susceptibility after 10 insecticide sprays in two generations in the field with a 36-fold increase in its LC50. Movements of the pest could have accounted for the observed results.

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.

Efeito de Bacillus thuringiensis Berliner e inseticidas químicos sobre a traça-das-crucíferas, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) e seus parasitóides

Three biopesticides based on Bacillus thuringiensis (Dipel, Florbac and Biobit), and two chemical insecticides (deltamethrin and abamectin) were evaluated in field trials against Plutella xylostella (L.) and its parasitoids in Brazil. Plots treated with Florbac, Biobit and abamectin produced 100% marketable cabbages. Dipel and deltamethrin also resulted in acceptable control (85% yield). In the control plot, 97.2% of the yield was lost. The rate of parasitism on the plots treated with biopesticides was between 35.7 and 60.5%, in the control was 42.9% and in those treated with chemical insecticides was 9.0 and 25.8 %. These results indicate that the biopesticides had no adverse effect on the parasitoids, in contrast to the classic chemical products.

Resistência a abamectin e cartap em populações de traça-das-crucíferas

ABSTRACT Susceptibility to cartap and abamectin in DiamondbackMoth strains Susceptibility of Diamondback Moth to cartap and abamectin,from five areas with different histories of insecticide spray, wascompared using a leaf-dip bioassay. Six concentrations of eachinsecticide plus water control were evaluated with three to sevenreplications per concentration. Cabbage leaf disks (2 cm diameter)from 35-day old plants were immersed in test solutions for 10 s. Thedisks were allowed to air dry for 2 h and then placed in Petri dishes.Ten second-instar larvae were then transferred to each disk. Afterthe treatments insects were maintained in a chamber at temperaturesof 20 ± 1oC and a photoperiod of 13L:11D. Larval mortality wasassessed after 48 h of cartap treatment and after 72 h of abamectintreatment. Bioassay results for each insecticide were analysed usingthe probit method. Resistance ratios were calculated dividing theLC 50 of each strain by the LC 50 of the most susceptible one, whichwas collected in a field with no insecticide spray. The resistanceratio to cartap ranged from 2.8 to 7.1, with the most resistant straincoming from a field sprayed several times with the insecticide. Toabamectin, the resistance ratios ranged from 1.1 to 12.1. The mostresistant strain was from a field without abamectin spray. One causeof this result could be the migration of resistant insects into the field.

Insecticides for the control of the South American tomato pinworm and the corn earworm and impact of those products on Trichogramma pretiosum

Experimentos de campo foram conduzidos entre maio e outubro de 2000 para determinar a eficiencia de diversos inseticidas para o controle de Tuta absoluta e Helicoverpa zea e o impacto desses produtos sobre a emergencia do parasitoide Trichogramma pretiosum. Os inseticidas testados, bem como as doses em g i.a./ha foram: metoxifenozide (120; 144), clorpirifos (540; 675), tiacloprid (72; 96) e triflumuron (144). O delineamento experimental foi de blocos ao acaso com oito tratamentos (inseticidas e testemunha) e cinco repeticoes, com 40 plantas/parcela. Frutos de tomate foram coletados aos 58, 80 e 87 dias apos o transplante das mudas para a determinacao da percentagem de frutos danificados pelos insetos. O impacto dos inseticidas sobre T. pretiosum foi avaliado mediante a coleta de 20 ovos de H. zea por parcela aos 61 dias apos o transplante, onde foi realizada a avaliacao da emergencia do parasitoide. Todos os inseticidas reduziram significativamente os danos causados por H. zea. Contudo, nenhum deles foi eficiente para o controle de T. absoluta. Metoxifenozide e clorpirifos (540) nao reduziram significativamente o numero de ovos parasitados por T. pretiosum quando comparados a testemunha.

Avaliação da eficiência de formulações de Bacillus thuringiensis para o controle de traça-das-crucíferas em repolho no Distrito Federal

The Diamondback Moth (Plutella xylostella) is the most important cabbage pest in the Federal District. New insecticides are frequently tested for its control and in this study two new Bacillus thuringiensis formulations [B. thuringiensis var. aizawai (350 and 500 g/ha) and B. thuringiensis var. kurstaki x B. thuringiensis var. aizawai (350 and 500 ml/ha)] were tested between May and October 1995. The insecticides B. thuringiensis var. kurstaki (500 ml/ha), deltamethrin (240 ml/ha) and an untreated check were also included in the experiment. A randomized block, with seven treatments and four replications was used. The results showed that B. thuringiensis var. aizawai at the two dosages and B. thuringiensis var. kurstaki x B. thuringiensis var. aizawai at a dosage of 500 ml/ha were the most efficient products. After the end of the field experiment, Diamondback Moth larvae and pupae were collected from the experimental area. The insects were reared in the laboratory and second instar larvae from the first generation were fed with leaf discs treated with the B. thuringiensis dosages used in the field experiment. All products caused more than 97% larval mortality. The laboratory test suggests that the reduced efficiency of B. thuringiensis var. kurstaki (500 ml/ha) and B. thuringiensis var. kurstaki x B. thuringiensis var. aizawai (350 ml/ha) in the field test may be due to the poor persistence of the products in the environment.

Eficiência de tiacloprid para o controle de mosca-branca

O impacto de tiacloprid sobre a mortalidade de adultos, fertilidade de femeas, viabilidade de ovos e desenvolvimento de ninfas de Bemisia argentifolii foi determinado em quatro experimentos. No primeiro experimento, para avaliar a eficacia de tiacloprid em causar a mortalidade de adultos, foram utilizadas folhas de repolho tratadas com tiacloprid (96 g i.a./ha), imidacloprid (14 g i.a./ha), acefato (750 g i.a./ha), deltametrina (6 g i.a./ha) e agua e adultos liberados nas gaiolas contendo as folhas tratadas. A mortalidade de adultos foi avaliada apos 72 h. No segundo experimento, para avaliar o impacto de tiacloprid sobre a fertilidade das femeas, utilizaram-se folhas de repolho tratadas com o inseticida ou agua colocadas nas gaiolas, seguida da liberacao de 50 adultos por 24 h. Transcorrido este tempo, os adultos foram transferidos para uma outra gaiola contendo folhas de repolho sem tratamento com inseticida por mais 24 h, quando foram entao removidos. O numero de ovos sobre cada folha foi determinado e as folhas foram colocadas em uma câmara por dez dias, quando o numero de ninfas foi determinado. No terceiro experimento, para avaliar o impacto de tiacloprid na eclosao de ninfas, utilizou-se ovos de mosca-branca com idades de um e cinco dias tratados com tiacloprid ou agua e, apos 10 dias, foi avaliado o numero de ninfas de primeiro estadio em cada tratamento. No quarto experimento avaliou-se o impacto de tiacloprid no desenvolvimento de ninfas. Estas foram tratadas com o inseticida ou agua e apos cinco dias foi feita a contagem do numero de ninfas de terceiro estadio. Tiacloprid e imidacloprid causaram a mortalidade de 99% dos adultos enquanto acefato e deltametrina causaram menos de 32% de mortalidade. O resultado indicou uma boa eficiencia de tiacloprid para o controle de adultos. A viabilidade dos ovos nao foi afetada pela exposicao das femeas ao inseticida, ja que mais de 97% destes se desenvolveram. Mais de 97% dos ovos tratados com tiacloprid com idades de um e cinco dias nao se desenvolveram indicando que o inseticida causa a inibicao do desenvolvimento dos ovos independentemente da idade destes. Apenas 1,2% das ninfas de segundo estadio tratadas com tiacloprid alcancaram o terceiro estadio, indicando que o inseticida afeta o desenvolvimento das ninfas.