RESUMO

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is an important pest capable of colonizing several species of cultivated plants, including soybean [Glycine max (L.) Merrill]. The primary management strategy for this insect is chemical control and adoption of Bt plants. However, alternative environmentally friendly strategies should be investigated and adopted as available for sustainable management of this insect pest. One potential underutilized method for insect control is plant resistance. The objective of this study was to categorize resistance (antixenosis and antibiosis) of 22 soybean genotypes on H. armigera in a laboratory setting. A preliminary experiment was conducted using soybean leaves and pods to determine the most promising genotypes for resistance. For each selected genotype, we collected biological parameters, leaf intake, and performed confinement tests. The genotypes PI 227687, PI 274453, PI 274454, PI 229358, PI 171451, ‘IAC 17’, and ‘IAC 19’ expressed resistance against H. armigera. Each genotype lowered larval survivorship. The genotypes PI 229358, PI 227687, PI 274453, and PI 274454 expressed resistance by prolonging larval development and reducing fifth-instar larvae weight. ‘IAC 19’ reduced leaf consumption and lowered the weight of fifth-instar larvae. Antixenosis was found in genotypes PI 227687, PI 274454, and ‘IAC 19’. These genotypes might be used in breeding programs focusing on soybean resistance to lepidopterans.

Soybean is considered one of the most valuable crops in the United States of America. Helicoverpa zea (Boddie) is among several insect pests which are associated with soybean, damaging leaves when infestations occur during the vegetative stages, and flowers and pods during the reproductive stages, which can directly impact yield. Artificial fruit removal is a method used to understand insect damage and to adjust action levels for control. The objective of this work was to evaluate the impact of five levels of fruit removal (0%, 25%, 50%, 75% and 100%) at four stages (R2, R3, R4 and R5) on maturity and yield of soybean. These methods were used to simulate H. zea damage under controlled conditions in non-irrigated environments, during 2016 and 2017. There was a significant interaction between fruit removal timing and fruit removal level for the percentage of non-senesced main stems and abscised leaves. For soybean yield, there was no significant interaction between fruit removal timing and fruit removal level. Plots that received fruit removal treatments at R5 had significantly lower soybean yields compared to plots that received damage at other growth stages and the nontreated control. Plots with 100% fruit removal had significantly lower yields compared to plots that received any of the other fruit removal treatments. These data demonstrate that indeterminate midmaturity group IV soybeans that are commonly grown in the midsouthern region of the United States may be able to compensate for even severe levels of fruit loss early during the reproductive portion of the growing season if favorable growing conditions occur.

In this study, the effects of a silicon (Si) application on the biomass, chlorophyll level and silicon level of sugarcane moderate pest resistance (RB72454) and susceptible (SP801842) cultivars were tested. Investigations were also carried out to assess the effect of silicon on Diatraea saccharalis infestation. The experiments were conducted in a greenhouse using the treatments consisting moderate pest resistant and susceptible culivar, with or without silicon application. The silicon was applied to the soil around the plants. The experiment was laid in complete randomized design with 4 treatments and 10 replicates. The data were subjected to an analysis of variance, and the averages were compared using the Tukey test (p ≤ 0.05). Significant changes were observed in the fresh and dry masses of the aerial portions and the root system, as well as in the plant chlorophyll and silicon levels. The silicon content increased in the susceptible variety which was significantly equal for moderate resistance variety. Chlorophyll content increased in silicon treated cultivars. Sixty days after the last application, 10 adult D. saccharalis moths were released onto each pot. However, due to the low infestation, the effects of silicon on the insect incidence could not be determined. One can conclude that silicon is beneficial for the growth of the aerial portions of sugarcane and causes a significant increase in chlorophyll levels.

<p><strong>Background.</strong><em> Zabrotes subfasciatus</em> (Boh., 1833) (Coleoptera: Chrysomelidae: Bruchinae), is considered one of the most important pest of stored beans. <strong>Objective. </strong>This study reports the possible toxicity and repellence of powders prepared from eight plant species against the Mexican bean weevil in two formulations (dry powder and sachets). <strong>Methodology.</strong> A 10 _˟ 2 factorial design (10 species _˟ 2 formulations) with 8 repetitions in a completely randomized design was employed. Pots with no powder were used as a negative control, and a pyrethroid insecticide [K-Obiol^® 2 DP (deltamethrin, 0.5 g a.i. ton^-1)] was applied as a positive control. <strong>Results.</strong> A mixture of powdered <em>Chenopodium ambrosioides </em>L., <em>Ruta graveolens </em>L. and <em>Mentha pulegium</em> L. added to bean grains was confirmed to be toxic to <em>Z. subfasciatus</em> adults with promising grain protector properties. <em>C. ambrosioides </em>powder had the same effect when in a sachet. A mixture of powdered <em>R. graveolens</em>, <em>M. pulegium </em>and <em>C. ambrosioides </em>with the beans inhibited weevil oviposition. The same effect was achieved for <em>M. pulegium </em>and <em>C. ambrosioides </em>in sachets. A mixture of powdered <em>C. ambrosioides</em>, <em>M. pulegium</em>, <em>R. officinalis</em> and <em>R. graveolens </em>repelled <em>Z. subfasciatus</em> adults from bean grains. <strong>Implications.</strong> This is the first report of using botanical derivatives by means of sachets or dry formulations, a pre-commercial purpose for aromatic plants with insecticidal/repellent activities. <strong>Conclusions.</strong> Sachets containing powdered <em>C. ambrosioides </em>and <em>M. pulegium </em>efficiently controlled the Mexican bean weevil in stored beans and constitute an useful tools for domestic grain stock or post-harvest management of organic grains.</p>