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Cereals constitute a relevant part of human and domestic animal diet. Under storage conditions, one of the most significant problems of these crops is insect pests as the maize weevil (Sitophilus zeamais Motschulsky). This insect species is usually controlled by means of synthetic insecticides but problems as toxic residues and resistance has led to the search for more friendly control alternatives such as botanical insecticides. The aim of this research was to evaluate, under laboratory conditions, the insecticidal properties of the powder and the essential oil of peumo (Cryptocarya alba [Molina] Looser; Lauraceae) leaves against S. zeamais. The variables assessed were toxicity by contact and fumigant activity, adult emergence (F1), repellent effect, and impact on wheat (Triticum aestivum L.) seed germination. A completely randomized design was used with five treatments and 10 replicates. The higher mortality levels were obtained at 80 g powder kg -1 grain and 40 mL essential oil kg -1 grain of C. alba; in both cases, the mortality of adult S. zeamais surpassed 80%. The emergence of adults S. zeamais (F1) was reduced by 100% at 80 g powder kg -1 grain and 40 mL essential oil kg -1 grain. Germination of wheat seeds treated with C. alba powder and essential oil was not affected. Both, the powder and the oil treatments showed repellent effect, but not fumigant activity.

Sitophilus granarius (L.) (Coleoptera: Dryophthoridae) is one of the most important pests of stored cereals worldwide. Sustainable control means of this pest are urgently needed mainly owing to legislative limits to the commonly used fumigants and broad-spectrum contact insecticides. The effectiveness of one alcohol and seven aliphatic aldehydes, previously identified as repellents, to disrupt adult granary weevils orientation towards wheat grains were assessed in two-choice olfactometer bioassays. In the dose range tested, all compounds effectively reduced wheat grains attractiveness and inhibited the preferential orientation of adult weevils towards the host substrate. Moreover, at the highest doses the three aldehydes butanal, (E)-2-hexenal, and (E,E)-2,4-nonadienal, their binary (1:1) and the ternary (1:1:1) blends induced a significant preferential orientation of insects to the control, indicating actual repellence. Among all repellent stimuli, the ternary blend and the binary blends of butanal plus (E)-2-hexenal and (E)-2-hexenal plus (E,E)-2,4-nonadienal were the most effective. At certain doses, the observed insect response to these blends was more intense than that expected from individual compounds, demonstrating synergistic interactions between the blend components. Repellent aldehydes and their mixtures were effective in disrupting the olfactory orientation of adult granary weevil to a highly attractive oviposition and food substrate. Future development of proper formulations of these bioactive compounds is promising to set up semiochemical-based control means for this pest.

Sitophilus zeamais (Mots.) (Coleoptera: Curculionidae) is considered a major pest of maize, responsible for reducing grain quality and making the corn inappropriate for industrial use and human consumption. S. zeamais has been controlled exclusively with chemical products. The objective of this research was to select isolates of Beauveria bassiana (Bals.) Vuill. to control S. zeamais. Beetles were immersed in conidia suspensions of each isolate for five seconds and placed in a gerbox container with maize grains. In pathogenicity tests, the isolates that caused the highest mortality to the maize weevil were ESALQ-447 (68.0%), CCA-UFES/ Bb-36 (57.3%) and CCA-UFES/Bb-31 (51.3%). ESALQ-447 was the most virulent, with an LC50 of 1.7 x 10(7) conidia/ml and shows promise for controlling maize weevils. These isolates of B. bassiana can be used as effective substitutes for conventional chemical control, normally carried out with phosphine. Further tests should be performed under field and semi-field conditions to develop an appropriate strategy for the use of this entomopathogen to manage S. zeamais.

The maize weevil (Sitophilus zeamais Motschulsky) is one of most important pest of stored seeds worldwide, but its current control method is based on the use of synthetic insecticides, usually leading to undesirable problems such as insecticide residues on treated food, human intoxications, and insect resistance development. Therefore the search of friendly alternative methods is required. The aim of this study was to assess, under laboratory conditions, the insecticidal properties of Peumus boldus Molina, Laurelia sempervirens (Ruiz & Pav.) Tul., and Laureliopsis philippiana (Looser) Schodde essential oils against S. zeamais. The phytochemical analysis of the three essential oils showed 1,8-cineole, safrole and methyleugenol as the common components; all of them documented with insecticidal activity from essential oils from other plant species. The highest toxicity (100% mortality) of these three oils acting as a contact insecticide was observed at 24 h exposure at 4% concentration. The estimated LC50 values for P. boldus, L. sempervirens, and L. philippiana were 0.37, 1.02, and 0.28 μL g-1, respectively. Peumus boldus exhibited the highest fumigant activity with 100% adult mortality at 30 μL oil L-1 air. At ≥ 0.5% (v/w) concentration, all essential oils showed repellent activity. These three essential oils showed a promissory insecticidal activity against the maize weevil.

The maize weevil Sitophilus zeamais Motschulsky is a worldwide key pest of stored products. Usually contact insecticides or fumigants are used against it, but problems as toxic residues, human intoxications, and resistance have triggered the search for alternative control methods as the use of essential oils. The objective of this research was to assess under laboratory conditions, the insecticidal properties of Laurelia sempervirens (Ruiz & Pav.) Tul. essential oil against S. zeamais. In contact toxicity bioassay assessed treatments were 0 (control), 1.25, 2.5, 5.0, 10, 20, and 40 mL essential oil kg-1 grain and 0 (control), 25, 50, 75, 100, 125, 150, and 175 μL essential oil L-1 air in fumigant toxicity tests. The highest toxicity by contact activity was reached by concentrations higher than 10 mL essential oil kg-1 grain (100% mortality). The same treatments totally inhibit F1. The dose of 175 μL essential oil L-1 air showed a significant toxicity by fumigant activity causing 72.5% of dead insects. The other treatments did not surpass 5% mortality. In offspring effect (F1) bioassay, all treatments had an insect emergence significantly lower than the control but concentrations equal or higher than 10 mL essential oil kg-1 grain prevented the emergence of F1 during the 7 wk of bioassay. The residual effect of contact toxicity remained by 15 d. The treatments based on essential oil lead to a weight grain loss lower than control and germination was not affected. All assessed treatments showed repellent effect. The essential oil of L. sempervirens has promissory perspectives to maize weevil control.

The maize weevil (Sitophilus zeamais Motschulsky) and the red flour beetle (Tribolium castaneum Herbst) are two key pests of stored-grain products worldwide. The insecticidal activity of boldo (Peumus boldus Molina) powder, liquid ethanolic and hexanic extracts against S. zeamais and T. castaneum were evaluated under laboratory conditions. The evaluated variables were mortality, emergence of adult insects (F1), and grain weight loss. The experimental design was completely randomized. The mortality in S. zeamais was 100% even at the lowest powder concentration (0.5% w/w), whereas emergence of F1 adult insects was 0% and grain weight loss was ≤ 0.08%. For T. castaneum, only 8 and 16% w/w powder concentrations reached 100% mortality. The liquid ethanolic and hexanic extracts caused 100% mortality of S. zeamais, whereas only the ethanolic extract reached this value for T. castaneum. Therefore, the powder and the evaluated extracts of P. boldus were toxic for S. zeamais and T. castaneum and are promising against these and other stored-grain pests.

El gorgojo del maiz (Sitophilus zeamais Motschulsky) es una de las plagas que provoca perdidas a los granos almacenados mas importantes a nivel mundial. El control de esta especie se realiza fundamentalmente con aplicaciones continuas de insecticidas organofosforados y piretroides y fumigantes como fosfuro de aluminio, pero problemas con estos han hecho necesaria la busqueda y desarrollo de nuevos metodos de control. Se evaluo el efecto insecticida del polvo de hojas de tepa, Laureliopsis philippiana (Looser) Shodde, sobre el gorgojo del maiz en condiciones de laboratorio. Los parametros evaluados fueron mortalidad y emergencia de insectos adultos, perdida de peso y germinacion de los granos, ademas de residualidad, repelencia y efecto fumigante. La mayor mortalidad de insectos se registro con los tratamientos 1, 2 y 4%, con valores entre 94,7 y 100%. Con estas mismas concentraciones se obtuvo una emergencia de insectos adultos de 0%. La perdida de peso de los granos no supero los 5,7 g en todos los tratamientos y la germinacion de semillas no fue afectada. El polvo de L.philippiana mostro efecto repelente en todas las concentraciones y ninguna de ellas presento accion fumigante. El efecto insecticida del polvo se mantuvo durante 14 d. Finalmente, se concluye que el polvo de L. philippiana tiene gran potencial para el control de S. zeamais.

Phenotypic plasticity contributes to the adaptative evolution of populations exposed to new or altered environments. Feeding plasticity is a component of phenotypic plasticity not usually considered in insect strains adapted to insecticide-altered environments, but which may either accentuate or mitigate insecticide resistance. This is a concern in the pyrethroid-resistant strains of the maize weevil Sitophilus zeamais Motsch. (Col., Curculionidae), and the reason for this study. A pyrethroid-susceptible and two pyrethroid-resistant strains of maize weevil were subjected to free-choice and no-choice tests with maize grains sprayed with increasing doses of the pyrethroid, deltamethrin. The insects from the pyrethroid-resistant strains exhibited higher feeding avoidance with increased deltamethrin doses than insects from the susceptible strain when subjected to free-choice tests. The strains of maize weevil physiologically resistant to pyrethroids were also behaviourally resistant to deltamethrin – an additional management concern. The resistant strains avoid deltamethrin-sprayed grains and are less nutritionally affected by this compound, with divergent responses from the susceptible strain with increased doses of deltamethrin. Furthermore, the higher relative growth rate and consequently higher efficiency of food conversion observed in the insecticide-resistant strains were significant even without insecticide exposure, indicating that these traits are stimulus-independent and may persist even without further insecticide selection, potentially limiting the options available for their management.

Insects have evolved a variety of physiological and behavioral responses to various toxins in natural and managed ecosystems. However, insect behavior is seldom considered in insecticide studies although insects are capable of changing their behavior in response to their sensory perception of insecticides, which may compromise insecticide efficacy. This is particularly serious for insect pests that are physiologically resistant to insecticides since insecticide avoidance may further compromise their management. Locomotion plays a major role determining insecticide exposure and was, therefore, considered in investigating the behavioral responses of male and female adult insects from an insecticide-susceptible and two insecticide-resistant strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), a major pest of stored cereals. Different dose-dependent behavioral responses were expected among strains with behavioral resistance less likely to occur in physiologically resistant insects since they are able to withstand higher doses of insecticide. The behavioral responses to deltamethrin-sprayed surfaces differed among the maize weevil strains. Such responses were concentration-independent for all of the strains. Stimulus-independent behavioral resistance was unrelated to physiological resistance with one resistant strain exhibiting higher rates of flight take-off and the other resistant strain exhibiting lower flight take-off. Female mobility was similar for all strains, unlike male mobility. Males of each strain exhibited a pattern of mobility following the same trend of flight take-off. Behavioral patterns of response to insecticide are, therefore, variable among strains, particularly among insecticide-resistant strains, and worth considering in resistance surveys and management programs.

Se evaluaron polvos vegetales de Chenopodium ambrosioides L., Chenopodium album L. y Chenopodium quinoa Willd. para el control de Sitophilus zeamais Motschulsky, bajo condiciones de laboratorio. Los parámetros evaluados fueron mortalidad y emergencia de insectos adultos, pérdida de peso y germinación de los granos, efecto ovicida y larvicida, fumigación, repelencia y residualidad de los polvos. El diseño experimental fue completamente al azar, con un arreglo factorial y tres repeticiones. La mayor mortalidad de insectos se obtuvo con los polvos de la inflorescencia y la mezcla de hojas y tallos de Chenopodium ambrosioides L., al 2% (p/p) con valores de 69,4% y 67,9% respectivamente. La menor emergencia de adultos se obtuvo con los mismos tratamientos. La pérdida de peso de granos, en todos los tratamientos de C. ambrosioides, no superó el 3%. Para el tratamiento inflorescencia de C. ambrosioides al 2% (p/p), la residualidad de los polvos se mantuvo hasta los 15 días, con una mortalidad de 98,3%. Esta misma especie presentó una mortalidad de huevos y larvas de 100%, además de presentar un efecto fumigante con una mortalidad de adultos de 100%, en todos los tratamientos evaluados. El polvo de C. ambrosioides es repelente para S. zeamais. Powders of Chenopodium ambrosioides L., Chenopodium album L. and Chenopodium quinoa Willd. were evaluated under laboratory conditions for Sitophilus zeamais Motschulsky control. Evaluated parameters were insect mortality and adult emergence, grain weight loss, grain germination and the following effects of powders: ovicide and larvicide, fumigant, repellent and residual. A completely randomized experimental design with factorial arrangement and three replicates was used. The highest levels of insect mortality were obtained with the powders of Chenopodium ambrosioides L. inflorescence and the mixture of leaves and stems at 2% (w/w), with values of 69.4% and 67.9% respectively. Best emergence reductions were obtained with the same treatments. In all treatments with powders of C. ambrosioides seeds weight were reduced in less than 3%. The residual effect lasted for 15 days, obtaining a mortality of 98.3% of adult insects, when powders of C. ambrosioides inflorescence were used at 2% (w/w) concentration. Powders of C. ambrosioides showed a mortality of 100% of eggs and larvae, and a fumigation effect against adult insects with a mortality of 100% in all treatments was evaluated. Powders of C. ambrosioides have a repellent effect for S. zeamais.