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The sweet potato whitefly, Bemisia tabaci MED (Gennadius) (Hemiptera: Aleyrodidae), is highly harmful to solanaceous crops. The use of essential oils (EOs) is promising for the management of several insect pests, promoting both lethal and sublethal effects. This study aimed to evaluate the effects of sublethal concentrations of Pelargonium graveolens L'Her (Geraniaceae) EO on the feeding behavior of B. tabaci MED on tomato plants (Solanum lycopersicum L., Solanaceae). For this research, the electrical penetration graph (EPG) technique was used to monitor whitefly stylet activities on their host plants. Two sets of plants were previously sprayed with two concentrations of EO (the LC25 and LC50, which were determined in a mortality test), a third set was treated with the insecticide cyantraniliprole, and a fourth set received a control treatment. Our results indicate that the insecticide cyantraniliprole and the EO could both reduce the stylet feeding activity of B. tabaci MED, as well as reduce the number and duration of phloem sap ingestion events (waveform E2), which could avoid or reduce the transmission of viruses. Thus, the application of sublethal concentrations of P. graveolens EO, as well as exposure to cyantraniliprole, negatively affected the feeding behavior of B. tabaci MED. This information may contribute to the management of this pest and the reduction of the incidence of viruses in tomato production. [ABSTRACT FROM AUTHOR]

Ants build underground nests to protect their colonies and to improve conditions for their offspring. The excavation of nests, by ants, modifies the soil structure, facilitating gas exchange and circulation, which needs further studies. Do initial nests modify the initial chamber soil matrix and gas exchange? The objective was to study the soil micromorphology of the wall of the chamber of initial nests of the leaf-cutting ant A. sexdens and how the CO2 diffuses into the soil matrix. The CO2 concentration in initial four-month-old A. sexdens nests was measured for 24 h using a respirometric system with a gas meter and closed nest holes (obliterated). After this period, they were opened and the CO2 concentration measured again. In addition, 15 cm deep holes were drilled into the ground 15 and 60 cm away from the ant nest hole. The CO2 was measured in these orifices and then they were sealed for 24 h and new ones made after this period. The contents of the nest chambers were removed, after the CO2 measures and the soil micromorphology of the walls of the initial chamber analyzed. The CO2 concentration in the nest chamber was greater than that in the soil at 15 and 60 cm distant from it. The CO2 accumulation did not increase with the obliteration of the nest entrance for 24 h. Coarse material, mainly quartz and charcoal fragments, besides fine material of clay, organic matter and iron oxides composed the soil of the wall of initial nests. The soil porosity in the chamber walls of the initial nests was lower than that of the matrix of the adjacent soil and differed between those of the nests. Initial nests of A. sexdens modifies the soil matrix of their walls, allowing to CO2 exchange between its chamber and adjacent soil. [ABSTRACT FROM AUTHOR]

Pest populations in a given agroecosystem may be influenced by several abiotic and biotic variables, including the host plant cultivar. We compared the population fluctuation of pest mites in twenty citrus scion cultivars grafted on Rangpur lime (Citrus limonia). Adults of citrus rust mite Phyllocoptruta oleivora (Acari: Eriophyidae), Texas citrus mite Eutetranychus banksi and Tetranychus mexicanus (Acari: Tetranychidae) were monthly counted in each scion cultivar from April 2011 to February 2013 in Sergipe state, northeastern Brazil. Larger E. banksi population peak was recorded on sweet orange 'Valência Montemorellos' in February 2012 compared to the other cultivars and larger populations of T. mexicanus were found on sweet orange 'Lima' in January 2013 in comparison to acid limes 'Tahiti IAC 5' and 'IAC 5-1'. The population of P. oleivora, however was not different among scion cultivars and varied only with time. Abiotic and biotic variables were important mechanisms underlying such responses. We conclude the mites abundances E. banksi and T. mexicanus were influenced by scion cultivars only in some periods, suggesting putative resistance mechanisms in some genotypes to these pests. Las poblaciones de ácaros plaga en un agroecosistema, pueden desarrollarse bajo la influencia de varias variables abióticas y bióticas, incluyendo el cultivar de la planta huésped. Se compararon la fluctuación poblacional de ácaros plaga en veinte cultivares de cítricos injertados en limón (Citrus limonia). Ácaros adultos de herrumbre Phyllocoptruta oleivora (Acari: Eriophyidae), Tejano Eutetranychus banksi y Tetranychus mexicanus (Acari: Tetranychidae) se contaron mensualmente en cada cultivar copa a partir de abril de 2011 a febrero de 2013 en el estado de Sergipe, noreste de Brasil. Los ácaros E. banksi y T. mexicanus fueron influenciados, registrando un pico poblacional superior de E. banksi en naranja dulce 'Valencia Montemorellos' en febrero de 2012 comparada con los otros cultivares y poblaciones más grandes de T. mexicanus que fueron encontrados en naranja dulce 'Lima' en enero de 2013 comparado con los limones 'Tahití IAC 5' y 'IAC 5-1'. Sin embargo; la población de P. oleivora, no fue diferente entre cultivares cítricos y solo se observó una variación con respecto al tiempo. Variables bióticas y abióticas fueran importantes mecanismos que subyacen a este tipo de respuestas. Se concluye que las abundancias de los ácaros E. banksi y T. mexicanus fueron influenciadas por cultivares copa sólo en algunos períodos; lo que sugiere mecanismos de resistencia putativos en algunos genotipos a estas plagas. [ABSTRACT FROM AUTHOR]