M. Ortega-Nieblas

Toxic and Persistent Effect of Oregano's Essential Oil against Zabrotes subfasciatus (Coleoptera: Bruchidae) in Stored Dry Beans

Abstract. Zabrotes subfasciatus (Coleoptera: Bruchidae), is one of the most destructive species with greater abundance and distribution in stored beans Phaseolus vulgaris L., causing great economic losses in Sonora, Mexico. Control of this pest has been based mainly on the use of broad-spectrum synthetic insecticides. Their intensive application has caused insect resistance, environmental pollution and impact on human health, therefore increasing research to control it has the aim of developing safe alternatives with potential to replace synthetic insecticides, while not being harmful. We studied the toxic effect and persistence of the essential oil (EO) of Lippia palmeri (Watson) (Verbenaceae) on Zabrotes subfasciatus (Boheman) in stored beans. The EO was compared between plant leaves collected from two locations: Puerto of Oregano (POEO) and Alamos Sonora (AEO). Beans were treated with 0, 0.135, 1.35, 4.0, and 8.0 µl/g of EO and infested with Z. subfasciatus. Mortality, oviposition, insect emergence, and percentage of damaged grain were assessed for 4 months. The POEO caused greater mortality, and both EOs showed ovicidal effects that persisted for 2 months with the 1.35 µl/g dose. Moreover, lethal effects after 3 months of storage at 4 and 8 µl/g were observed, either in insect emergence or damaged grain. This seems to be caused by the persistence of the essential oils carvacrol, thymol, and p-cymene in the Lippia palmeri samples.

Características de la germinación de Lippiapalmeri (Wats) proveniente de regiones silvestres del desierto de Altar, Sonora, México

espanolExisten varias especies del genero de Lippia nativas e introducidas, que son de gran potencial en zonas aridas del noroeste de Mexico; estas especies presentan bajo porcentaje de germinacion debido a la dureza y/o dormancia de la semilla. El objetivo del presente estudio consistio en dilucidar el efecto del acido giberelico sobre la germinacion de la semillas silvestre de Lippia palmeri. Para ello se recolecto la semilla en dos regiones nativas (Puerto del Oregano y Santa Ana, Sonora). Se probaron tres concentraciones con acido giberelico (GA3) (100, 200 y 300 ppm, sometidas a tres tiempos de remojo de la semilla (30, 60 y 120 min.) y como control agua destilada. Para cada tratamiento se utilizaron 100 semillas por caja Petri por triplicado siendo un total de 72 cajas Petri colocadas a una temperatura ambiente de 27 °C y 80% de humedad relativa. Para la concentracion de 100 ppm en los tres tratamientos de remojo la semilla de Puerto del Oregano, mostro un alto porcentaje de germinacion (90, 100 y 100%), para los tratamientos de 200 y 300 ppm el porcentaje de semilla germinada fue menor (80%). La semilla de Santa Ana mostro el porcentaje mas alto de germinacion con (80%) obtenido a 300 ppm y 120 minutos en remojo, el resto de los tratamientos no supero el 70% de germinacion. Se concluye que Lippia palmeri requieren ser estimuladas por la giberelina a fin de promover la accion enzimatica que induce la ruptura de las sustancias de reserva de la semilla. EnglishThere are several species of native and introduced Lippia, which are of great potential in arid areas of Northwest Mexico; these species have low germination percentage due to the hardness and / or seed dormancy. The aim of this study was to elucidate the effect of gibberellic acid on germination of seeds of wild Lippia palmeri. To do this, the seed was collected in two native sites (Puerto del Oregano and Santa Ana, Sonora). Three concentrations with gibberellic acid (GA3) (100, 200 and 300ppm), subjected to three times of soaking the seed (30, 60 and 120 min.) were tested and as a control distilled water. For each treatment 100 seeds were used by Petri dish in triplicate with a total of 72 Petri plates placed in an ambient of 27 °C and 80% relative humidity. For the concentration of 100 ppm in the three treatments soaking seed port oregano, showed a high percentage of germination (90, 100 and 100%); for treatments of 200 and 300 ppm the percentage of germinated seed was lower (80%). The seed of Santa Ana showed the highest percentage of germination (80%) obtained 300 ppm and 120 minute soak; the other treatments did not exceed 70% germination. It is concluded that Lippia palmeri require stimulated by giberalina to promote the enzymatic action inducing breakdown of reserve substances seed.

Insecticidal Efficacy and Repellency of Oregano (Lippia palmeri) Essential Oil for Control of Sitophilus zeamais and Prostephanus truncatus in Stored Maize

Abstract. Maize, Zea mays L., is the most important crop in Mexico. The maize weevil, Sitophilus zeamais Motschulsky, and larger grain borer, Prostephanus truncatus (Horn), cause significant loss to stored maize. The insects are controlled by insecticides that are toxic to humans and pollute the environment. An alternative to control insect damage is essential oil from plants. The aim of this research was to evaluate the effect of oregano (Lippia palmeri S. Watson) oil at different concentrations on repellence, emergence, and mortality of maize weevil and larger grain borer. All maize weevils died at 48 hours, while most (92%) larger grain borer died at 72 hours with 1,000 µl/liter of oregano oil. Emergence of treated insects was significantly (p < 0.05) less than the check. The repellency index at 24 hours for larger grain borer was 0.15 at a concentration of 20 µl/liter of oregano oil. The repellency index for maize weevil was zero, indicating total repellence at 24 hours. Components of the oil were determined by gas chromatography-mass spectrometry to be thymol (58.9%) and p-cymene (21.8%). Oregano oil concentration and time were important in controlling both insect species.