Ervino Bleicher

Aphid antixenosis in cotton is activated by the natural plant defence elicitor cis-jasmone

Upon insect herbivory, plants can release blends of volatile organic compounds (VOCs) that modify herbivore and natural enemy behaviour. We have shown recently that cotton, Gossypium hirsutum, emits a blend of defence VOCs that repels the cotton aphid, Aphis gossypii, upon herbivory by this notorious crop pest, including (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). In this study, we investigated changes in the defence VOC profile of G. hirsutum induced by the naturally-occurring plant elicitor cis-jasmone (CJ) and whether these changes modify the behaviour of A. gossypii. In four-arm olfactometer assays, VOCs from untreated plants were significantly attractive (P<0.05), whilst VOCs from CJ-treated plants were significantly repellent (P<0.05). The VOCs induced by CJ appeared to comprise (Z)-3-hexenyl acetate, DMNT, methyl salicylate and TMTT. In quantitative VOC collection studies, sustained release of DMNT and TMTT was observed in CJ-treated plants over a period of five days, with levels becoming statistically significantly higher than for control treated plants on the fifth day in most cases. Despite earlier indications, no statistically significant differences were observed in levels of (Z)-3-hexenyl acetate or methyl salicylate between CJ and control treatments on any day. Furthermore, DMNT and TMTT emissions from CJ-treated plants were further enhanced by subsequent addition of A. gossypii. CJ treatment induced statistically significantly higher DMNT and TMTT expression levels as early as day three, when A. gossypii was present. The results in this study show that CJ can induce the production of A. gossypii-induced VOCs from G. hirsutum, with potential for deployment in novel crop protection strategies.

Identification of Semiochemicals Released by Cotton, Gossypium hirsutum, Upon Infestation by the Cotton Aphid, Aphis gossypii

The cotton aphid, Aphis gossypii (Homoptera: Aphididae), is increasing in importance as a pest worldwide since the introduction of Bt-cotton, which controls lepidopteran but not homopteran pests. The chemical ecology of interactions between cotton, Gossypium hirsutum (Malvaceae), A. gossypii, and the predatory lacewing Chrysoperla lucasina (Neuroptera: Chrysopidae), was investigated with a view to providing new pest management strategies. Behavioral tests using a four-arm (Pettersson) olfactometer showed that alate A. gossypii spent significantly more time in the presence of odor from uninfested cotton seedlings compared to clean air, but significantly less time in the presence of odor from A. gossypii infested plants. A. gossypii also spent significantly more time in the presence of headspace samples of volatile organic compounds (VOCs) obtained from uninfested cotton seedlings, but significantly less time with those from A. gossypii infested plants. VOCs from uninfested and A. gossypii infested cotton seedlings were analyzed by gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS), leading to the identification of (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), which were produced in larger amounts from A. gossypii infested plants compared to uninfested plants. In behavioral tests, A. gossypii spent significantly more time in the control (solvent) arms when presented with a synthetic blend of these four compounds, with and without the presence of VOCs from uninfested cotton. Coupled GC-electroantennogram (EAG) recordings with the lacewing C. lucasina showed significant antennal responses to VOCs from A. gossypii infested cotton, suggesting they have a role in indirect defense and indicating a likely behavioral role for these compounds for the predator as well as the aphid.

Monitoring the susceptibility to insecticides in Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) populations from Brazil

Monitoring the susceptibility of a pest population to pesticides is essential for resistance management programs. The objective of this research was to evaluate the genetic variability in pesticide susceptibility in populations of Bemisia tabaci (Gennadius) collected from different Brazilian agricultural regions through the use of two different tests. Four whitefly populations, two from Goiás state (GO-1 and GO-2) e two from Bahia state (BA-1 and BA-2), were tested against a susceptible reference one (SusIAC). A residual contact bioassay was used to evaluate the pesticide susceptibility of each population by using diagnostic concentration bioassays and by estimating the baseline susceptibility data to each one of the tested insecticides, acetamiprid, imidacloprid, thiamethoxam, chlorpyrifos and endosulfan. Adult insects of unknown age and sex were tested. Evaluations were performed after 24h for endosulfan and 48 h for the other chemicals. Both procedures showed significant differences in the susceptibility to the pesticides among B. tabaci populations. However, the discrimination among B. tabaci populations was more evident with the use of diagnosis tests. The population GO-2 was significantly less susceptible to the tested pesticides than SusIAC, mainly to neonicotinoids. The most critical resistance situation of B. tabaci was detected to thiamethoxam, followed by imidacloprid.

Eficiência de Azadiractina no controle de mosca-branca em meloeiro sob condições de casa de vegetação e de campo

Melons are of great importance for exportation by the Brazilian northeast region, actually being threatened by the whitefly pest, which is only controlled by the use of the conventional chemical insecticides actually used in the crop. In this study a potential botanical insecticide containing 1% Azadirachtin was evaluated against Bemisia argentifolii on melon, under greenhouse and field conditions. A randomized complete block design was used in both cases, with four replicates. Evaluating nymphs in greenhouse and nymphs and adults in field, we observed an increase in mortality by increasing dosages. In field, efficiency was 67.83 and 70.13% for adults and 80.36 and 88.10% for nymphs using 4.0 and 8.0 ml/L of the commercial Azadirachtin formulation, respectively.

Efeito de derivados de nim aplicados por pulverização sobre a mosca-branca em meloeiro

A mosca-branca e uma das principais pragas do meloeiro na regiao Nordeste do Brasil. Estudou-se neste trabalho o efeito de extratos aquosos de folhas e de sementes de nim (Azadirachta indica A. Juss.) e uma formulacao a base de azadiractina comparados com o inseticida buprofezin, aplicados por pulverizacao, sobre ninfas da mosca-branca, Bemisia tabaci biotipo B, em melao cv. Torreon, sob condicoes de casa de vegetacao. Tres experimentos independentes foram realizados no delineamento inteiramente casualizado, com sete tratamentos e numero variavel de cinco a sete repeticoes. Cada planta constituiu uma unidade experimental. No primeiro experimento, os tratamentos foram: testemunha absoluta (agua), Neemazal® (1,2% de azadiractina) nas doses 12; 24; 48; 96 e 192 ppm de azadiractina. No segundo: testemunha absoluta (agua), extrato de semente a 1; 2; 4; 8 e 16 g/100ml. No terceiro, o extrato de folhas foi aplicado nas mesmas proporcoes que o de sementes. Para cada experimento aplicou-se como testemunha positiva, o produto comercial Applaud® (buprofezin) na dose de 1,5g. p.c./L, que corresponde a 0,375 g de ingrediente ativo(i.a)/L de calda. A azadiractina foi eficiente em todas as doses causando reducao de ate 98% na media de ninfas vivas. Quando aplicado acima de 24 ppm, este composto apresentou desempenho semelhante ao inseticida padrao buprofezin. Os extratos de sementes a 1; 2; 4; 8 e 16g/100 ml reduziram significativamente a media de ninfas vivas, nao diferindo da acao do inseticida padrao. Os extratos de folha nao foram eficientes no controle de ninfas.

Preferência do pulgão-preto, Aphis craccivora Koch, a diferentes genótipos de feijão-de-corda, Vigna unguiculata (L.) Walp

This research was conducted with the intention of evaluating the response of different cowpea, Vigna unguiculata (L.) Walp, cultivars to the black aphid (Aphis craccivora Koch). The bioassays were conducted from August through October of 2004 in a greenhouse at the Ceara Federal University (UFC) campus. The cowpea cultivars used were: Epace-10, Epace-11, Patativa, Pingo de Ouro, Pitiuba, BR-10 Piaui, BR-12 Caninde, BR-14 Mulato and BR-17 Gurgueia. Each assay had five treatments and six replications in a completely randomized block design. The genotypes were raised in a 300ml plastic cup and maintained in cages protected by an insect proof net. Plants were infested twelve days after planting with five adult females per plant. Evaluations were performed three and five days after infestation by visual counting of the adults and nymph forms present on the plants. A variance and Tukey analysis were done with the obtained data at a 5% level of probability. The Epace 10 and Patativa cultivars were less preferred by A. craccivora.

Mutantes morfológicos de algodoeiro herbáceo como fonte de resistência ao bicudo

This work aimed to evaluate the effects of three morphological mutants of upland cotton lines (Gossypium hirsutm L. r. latifolium Hutch.), isolated or in combination in the same cotton genotype, as a source of resistance to boll weevil, Anthonomus grandis Boheman, 1843 (Coleoptera, Curculionidae). The experiment was carried out in the field, under natural infestation, with a completely randomized block design arranged in a factorial 2× 3 plus an additional treatment, with four replications. In a multiple choice test, the character mutant frego bract presented the higher reduction on boll weevil oviposition damage (34.71%), in relation to the normal equivalent. The okra leaf reduced the boll weevil damage only when associated with frego bract (40%). The combination of the three mutant characters in the same plant presented the least square percent with oviposition damage (23.13%).

Distribuição vertical e setorial das ninfas de mosca-branca nas folhas do meloeiro

The spatial nymphs distribution of Bemisia argentifolii Bellows & Perring (Hemiptera: Aleyrodidae) among and within melon leaves was observed. The vertical distribution among leaves was done, selecting randomly leaves from node 5th through 20th. The counting of nymphs was performed on a weekly basis, at 49; 56 and 63 days after planting, using a circular leaf disc with an area of 2.8 cm2. Higher nymph concentration was observed from the 8th to the 10th leaf counted from the top to the bottom of the melon plant. These leaves were considered the best ones to be sampled. The distribution of nymphs over the leaf sectors was performed, selecting randomly leaves and dividing them into four sectors (distal left, proximal left, distal right, and proximal right). The number of nymphs was similar in both proximal sectors, however in the proximal sectors the number of nymphs was greater than those found in distal sectors. From the total nymphs found, 13.70% were found on distal left sector, 35.70% on proximal left sector, 36.70 on proximal right sector and 14.25% on distal right sector. Sampling nymphs close to the central leaf rib is more effective.

The use of different clustering methods in the evaluation of genetic diversity in upland cotton

A geracao e avaliacao continua de novos genotipos, por meio do melhoramento genetico, e fundamental para a obtencao de novas cultivares. Foi o objetivo deste trabalho avaliar a divergencia genetica entre cultivares de algodoeiro herbaceo (Gossypium hirsutum L.), por meio de caracteristicas agronomicas e tecnologicas da fibra, visando a selecao de parentais superiores. O experimento foi implantado na Universidade Federal do Ceara, Fortaleza/CE, em 2010. Foram usadas 11 cultivares de algodao herbaceo, utilizando o delineamento experimental em blocos casualizados, com tres repeticoes. Para avaliacao da divergencia genetica entre as cultivares foi obtida a matriz de distâncias generalizada de Mahalanobis, e em seguida, realizado agrupamento por diferentes metodos, sendo eles o metodo da ligacao simples, de Ward, da ligacao completa, da mediana, da ligacao media dentro de grupo e da ligacao media entre grupo. Ha variabilidade genetica entre os genotipos avaliados. O metodo de agrupamento que apresentou maior consistencia foi a ligacao media entre grupo. O peso medio do capulho apresentou a maior contribuicao para a diversidade genetica, seguida do alongamento a ruptura dentre os caracteres avaliados. As cultivares de maior divergencia genetica, usando o metodo de ligacao media entre grupo, foram a BRS Acacia e LD Frego; as de maior similaridade foram a BRS Itauba e BRS Araripe.

Correlations and path analysis in components of fiber yield in cultivars of upland cotton

This study evaluated the relative contribution of agronomic and technological components on the fiber yield in upland cotton cultivars. The experiment was carried out with 11 upland cotton cultivars in a completely randomized blocks design with three replications. Initially, we performed analysis of variance, with the F test at 5% probability for the effect of cultivar as fixed ef - fects as well as block and environment effects as random. Then the values were ordered according to cluster test Scott-Knott, at 5% probability level. The significance of the null hypothesis that all possible canonical correlations are null was evaluated using the chi-square test. The correlations were estimated through the path analysis. By examining the canonical correla- tions there was dependence between the two groups of variables and therefore it is possible to promote changes in certain characteristics through the selection of others correlated. Plants of upland cotton with higher fiber yield were influenced by the decrease in average weight of the cotton boll. When there is a reduced fiber yield, there is also an increase in uniformity and strength thereof. The fiber resistance had negative indirect effects on the fiber uniformity and length.