Lêda R. A. Faroni

Locomotory and physiological responses induced by clove and cinnamon essential oils in the maize weevil Sitophilus zeamais

Plant essential oils have been suggested as a suitable alternative for controlling stored pests worldwide. However, very little is known about the physiological or behavioral responses induced by these compounds in insect populations that are resistant to traditional insecticides. Thus, this investigation evaluated the toxicity (including the impacts on population growth) as well as the locomotory and respiratory responses induced by clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L., essential oils in Brazilian populations of the maize weevil Sitophilus zeamais. We used populations that are resistant to phosphine and pyrethroids (PyPhR), only resistant to pyrethroids (PyR1 and PyR2) or susceptible to both insecticide types (SUS). The PyPhR population was more tolerant to cinnamon essential oil, and its population growth rate was less affected by both oil types. Insects from this population reduced their respiratory rates (i.e., CO2 production) after being exposed to both oil types and avoided (in free choice-experiments) or reduced their mobility on essential oil-treated surfaces. The PyR1 and PyR2 populations reduced their respiratory rates, avoided (without changing their locomotory behavior in no-choice experiments) essential oil-treated surfaces and their population growth rates were severely affected by both oil types. Individuals from SUS population increased their mobility on surfaces that were treated with both oil types and showed the highest levels of susceptibility to these oils. Our findings indicate that S. zeamais populations that are resistant to traditional insecticides might have distinct but possibly overlapping mechanisms to mitigate the actions of essential oils and traditional insecticides.

Phosphine‐induced walking response of the lesser grain borer (Rhyzopertha dominica)

BACKGROUND In spite of the intensive worldwide use of phosphine against stored-product insects, its potential sublethal effects on targeted insect species is seldom recognised and may compromise the efficacy of this fumigant, particularly against phosphine-resistant insects. Therefore, the behavioural response of three populations of the lesser grain borer Rhyzopertha dominica (Coleoptera: Bostrichidae) to sublethal phosphine exposure was assessed. RESULTS Concentration-mortality bioassays with phosphine confirmed the resistance status of the insect populations studied, with levels of phosphine resistance of 40.8-fold and 85.7-fold compared with the susceptible population. Regarding walking behaviour, determined using a digital video-tracking system, the phosphine-resistant populations were less active than the susceptible population. In addition, sublethal phosphine exposure decreased the walking activity of all three populations. CONCLUSION Phosphine exposure decreased walking activity. Such reduced walking activity is likely to lower the respiration rate, thereby minimising phosphine uptake. As higher phosphine resistance was also associated with reduced walking activity, phosphine-resistant populations may resist phosphine fumigation even more efficiently on account of this behavioural trait, further aiding their physiological resistance, and should be a matter of concern.

Sublethal Exposure to Clove and Cinnamon Essential Oils Induces Hormetic-Like Responses and Disturbs Behavioral and Respiratory Responses in Sitophilus zeamais (Coleoptera: Curculionidae)

ABSTRACT Essential oils have been suggested as suitable alternatives for controlling insect pests. However, the potential adaptive responses elicited in insects for mitigating the actions of these compounds have not received adequate attention. Furthermore, as is widely reported with traditional insecticides, sublethal exposure to essential oils might induce stimulatory responses or contribute to the development of resistance strategies that can compromise the management of insect pests. The current study evaluated the locomotory and respiratory responses as well as the number of larvae per grain produced by the maize weevil, Sitophilus zeamais Motschulsky, after being sublethally exposed to the essential oils of clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L. The essential oils showed similar insecticidal toxicity (exposure route: contact with dried residues; Clove LC95 = 3.96 [2.78-6.75] µl/cm2; Cinnamon LC95 = 3.47 [2.75-4.73] ml/cm2). A stimulatory effect on the median survival time (TL50) was observed when insects were exposed to low concentrations of each oil. Moreover, a higher number of larvae per grain was produced under sublethal exposure to clove essential oil. S. zeamais avoided the treated areas (in free-choice experiments) and altered their mobility when sublethally exposed to both essential oils. The respiratory rates of S. zeamais (i.e., CO2 production) were significantly reduced under low concentrations of the essential oils.We recommend the consideration of the potential sublethal effects elicited by botanical pesticides during the development of integrated pest management programs aiming to control S. zeamais.

Aplicação de ozônio contra Sitophilus zeamais e Tribolium castaneum em milho armazenado

The main goal of this work was to assess the susceptibility of adults of Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the physiological quality of maize grains subjected to ozone treatment in different grain layers. PVC cages 3.0 cm high and 15.0 cm diameter were built with their bottom and cover closed with organza-like cloth; the cages were placed in cylindrical containers of PVC with 20 cm diameters and 100 cm heights and connections for injection and exhaustion of the ozone gas. Insects and maize grains were subjected to a modified atmosphere with 50 mg kg-1 ozone injected at a flow of 8.0 L min-1 through a connection at the bottom of the container (plenum) for different exposure times. Sitophilus zeamais was the most susceptible species regardless of its distribution in the grain mass. The exposure periods required to achieve 95% control of adults of S. zeamais and T. castaneum were 23.76 and 64.19 h respectively, when distributed near the ozone injection; overall the treatments with atmosphere modified by ozone injection at 50 mg kg-1 did not affect the physiological quality of maize grain.

Effects of ozone fumigation treatment on the removal of residual difenoconazole from strawberries and on their quality

The effect of ozone fumigation on the reduction of difenoconazole residue on strawberries was studied. Strawberries were immersed in 1.0 L of aqueous solution containing 400 μL of the commercial product (250 g L−1 of difenoconazole) for 1 min. Then, they were dried and exposed to ozone gas (O3) at concentrations of 0.3, 0.6 and 0.8 mg L−1 for 1 h. The ozone fumigation treatments reduced the difenoconazole residue on strawberries to concentrations below 0.5 mg kg−1, which corresponds to a 95% reduction. The strawberries treated with ozone and the control group, which was not treated with ozone, were stored at 4°C for 10 days. Some characteristics of the fruit were monitored throughout this period. Among these, pH, weight loss and total color difference did not change significantly (P > 0.05). The fumigation with ozone significantly affected the soluble solids, titratable acidity and ascorbic acid content (vitamin C) of the strawberries preventing a sharp reduction of these parameters during storage.

Ozone Toxicity and Walking Response of Populations of Sitophilus zeamais (Coleoptera: Curculionidae)

ABSTRACT Ozone is a recognized alternative to the fumigants methyl bromide and phosphine for the control of stored product insects. However, as with fumigants in general, the potential sublethal effects of ozone on targeted insect species may compromise its efficacy and has yet to be investigated. Here, we determined ozone toxicity of 30 field-collected populations of the maize weevil, Sitophilus zeamais (Coleoptera: Curculionidae), and assessed the walking response of adult insects from these populations to sublethal ozone exposure. Time-mortality toxicity to ozone at 50 ppm concentration in a continuous 2 liter/min flow indicated uniform susceptibility among the populations studied without any indication of ozone resistance (toxicity ratios [at LT50] > two-fold). In contrast, there was significant variation in walking activity among the maize weevil populations, which was not correlated with ozone susceptibility. This was not surprising because of the relatively uniform susceptibility to ozone among the maize weevil populations. Respiration rate affected ozone toxicity but not walking activity, whereas body mass was negatively correlated with walking activity but was not correlated with ozone toxicity. Based on our data, lower respiration rates may potentially lead to reduced ozone uptake whereas larger body mass limits walking activity. Ozone seems a promising alternative fumigant with low short-term risk of resistance development because of the high susceptibility and low variability of response to this compound. Furthermore, ozone reduces walking activity of S. zeamais that implies it likely reduces the chances of insects escaping exposure at the early stages of fumigation.

Diffusion and sorption of allyl isothiocyanate in the process of fumigation of maize

The purpose of this work was to evaluate the transport of allyl isothiocyanate (AITC) by means of the sorption mechanism and the diffusion of AITC through maize grains. The experimental procedure to study the sorption mechanism was conducted by injection of AITC in glass flasks containing the grains. Kinetic models of zero, first and second order were fitted to AITC concentration data, with the purpose of determining the sorption rate (k). For the study of diffusion, a prototype was utilized in which the components are a gas chamber and a cylindrical column in which the grains were stored. At the interval of 110 min, samples in the chamber and in the column were collected, which were immediately injected into the gas chromatograph. In order to determine the effective diffusion coefficient (Def) of AITC through maize grains, the term referring to the sorption rate was added to the diffusion equation. The kinetic model of the first order was the one that best fitted the experimental data for the sorption mechanism, and k was 6.26 x 10-4 s-1. The Def of AITC through grains was 7.2 x 10-3 cm2 s-1. It was concluded that the transport of AITC through maize grains is slow, due to the low value of Def and high sorption rate of this component by the grains.

Soybean storage in bag type silos

Avaliaram-se as principais alteracoes qualitativas de soja armazenada em silos tipo bolsa e do oleo bruto extraido de soja com teores de agua de 17,4% e 13,3%, armazenada em dois silos tipo bolsa, por 180 dias. Realizaram-se amostragens no dia do enchimento das bolsas, aos 30; 90 e 180 dias de armazenamento. Analisaram-se o teor de agua, a condutividade eletrica, o percentual de germinacao, a massa especifica aparente da soja, alem do teor de acidos graxos livres e o indice de peroxido do oleo bruto extraido dela. Os teores de agua da soja armazenada umida e seca mantiveram-se proximos dos valores obtidos no inicio do periodo de armazenamento. Observou-se tendencia de elevacao da condutividade eletrica e decrescimo do percentual de germinacao somente na soja umida, principalmente apos 90 dias de armazenamento. Nao foi verificado decrescimo da massa especifica aparente do material armazenado umido e seco. Com relacao aos parâmetros qualitativos do oleo bruto, observou-se que os valores obtidos se mantiveram abaixo do limite maximo exigido pela legislacao para a comercializacao de oleo bruto de soja. Pode-se concluir que os silos tipo bolsa representam alternativa viavel do ponto de vista qualitativo para armazenagem de soja, e esse tipo de estrutura nao ocasiona alteracoes qualitativas significativas no oleo bruto obtido desse material, em condicoes similares aquelas deste estudo.

Aqueous ozone solutions for pesticide removal from potatoes

The presence of pesticide residues in potatoes is of concern because of the potential impact to human health due to the high consumption of this vegetable. In this study, aqueous solutions with and without ozone saturation as postharvest wash treatment at pH 4.0, 7.0, and 9.0 were tested to remove chlorothalonil from potatoes. The method used for pesticide analysis has been validated, presenting recovery values of 94–103%, with variations in the repeatability coefficients of ≤10.6%, and a quantification limit of 0.05 mg kg−1. Regardless of pH, treatment with aqueous ozone solutions removed 70–76% of the pesticide present in the potato. In the no-ozone treatments, the percentage average removal of chlorothalonil residues in potatoes was only 36%. Over 24 days of storage, the quality of potatoes washed with aqueous ozone solutions was not significantly different from those washed with pure water.

Suscetibilidade de Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) ao enxofre

The laboratory rearing of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) is frequently infested by the parasite mite Acarophenax lacunatus (Cross and Krantz) (Prostigmata: Acarophenacidae). This study was aimed at evaluating the sulfur doses, an effective acaricide against A. lacunatus, not harmful to the development of with R. dominica. The experimental units were Petri dishes containing 30g of whole wheat grains powdered with the different doses of the sulfur (0.0, 0.6, 0.9, 1.2, 1.5, 3.0, 6.0, 12.0, 24.0 and 48.0mg a i g-1) infested with 30 adults of R. dominica, in ten replicates. All treatments were maintained under controlled conditions (30±1°C, 60±5% r h and 24h scotophase) for 60 days after the insect infestation. Sulfur doses higher than 3.0mg a i g-1 negatively affected R. dominica development.