Sotero Aguilar-Medel

Toxicity of Boldo Peumus boldus Molina for Sitophilus zeamais Motschulsky and Tribolium castaneum Herbst

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.

Susceptibility of Females and Males of Bemisia tabaci (Gennadius) B-Biotype and Trialeurodes vaporariorum (Westwood) to Thiamethoxam

Abstract. Differences in susceptibility to insecticides based on adult insect sex indicate that males are more susceptible than females. Hence, it may be necessary to sex the insects before a bioassay is conducted, but this activity is tedious, takes time, and this manipulation might cause harm to the insects. Monitoring the evolution of resistance to the neonicotinoid insecticides in field whitefly populations is important and usually based on adult exposure to these toxicants. The aim of this study was to correlate the susceptibility to thiamethoxam with sex in susceptible populations of Bemisia tabaci (Genn.) B-Biotype and Trialeurodes vaporariorum (West.). Five-day-old males, females, and a mixture of female and male (80:20) adults were evaluated to determine log doses-Probit lines for this insecticide. In B. tabaci, the CL50 ranged of 1.4 mg [lA] L-1 to 2.8 mg and the relative proportion RR50 ranged from 1.0 to 2x. The CL95 ranged from 12.3 to 16.7 mg and the RR95 values varied from 0.8 to 1.0x. In T. vaporariorum, the CL50 fluctuated from 14.2 to 30.3 mg and the value of RR50 between 1.0 and 2.1x. The CL95 ranged of 180.4 to 314.0 mg and the RR95 from 1.0 to 1.7x. In both species, no differences were found between insect sex and susceptibility to thiemathoxam. Hence, to conduct bioassays with thiamethoxam on these species, the use of one sex or the other is irrelevant.

Susceptibilities of Geographic Populations of Helicoverpa zea (Lepidoptera: Noctuidae) in Mexico to Bt ∂-Endotoxins Cry1Ac and Cry2Ab: An 18-Yr Study

Abstract An insect resistance monitoring program was developed for Mexico to accommodate the commercial introduction and stewardship of Bt cotton. Between 1998 and 2015, field-collected geographic populations of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) were evaluated against Cry1Ac and Cry2Ab proteins of Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) to establish baseline susceptibility data before the commercial use of Bollgard (Cry1Ac) and Bollgard II (Cry1Ac and Cry2Ab) cotton. An annual monitoring program was subsequently established in which a single diagnostic concentration of each Bt protein was used in a diet overlay bioassay. The diagnostic concentration represented the concentration where larvae, evaluated in baseline studies, were reduced in weight by ≥97% relative to untreated controls or failed to molt to third instar after 5 d. In the monitoring study, populations were tested against Cry1Ac from 1998 through 2015, and against Cry2Ab from 2002 through 2004 and again from 2007 through 2015. None of the Cry1Ac-exposed larvae tested during the 18-yr period reached the third larval instar after an exposure of 5 d, and weight reduction relative to untreated control larvae was uniform at about 98–99%. For the 12 yr of Cry2Ab monitoring, no larvae reached third instar, and weight reduction was uniform at >97% relative to controls.These results indicate that H. zea susceptibility to Cry1Ac and Cry2Ab has not changed during the period Bollgard and Bollgard II have been cultivated in Mexico.

Resistencia de Tetranychus urticae Koch a Acaricidas Usados en la Producción de Rosal de Invernadero en México

Abstract. In the State of Mexico, Mexico, Rosa sp. production is one of the most important economic activities. However, the two-spotted mite, Tetranychus urticae Koch, is a pest that limits this crops productivity, and its control is carried out mainly with acaricides. Therefore, we estimated the levels of resistance to six acaricides in three field-collected populations of T. urticae from greenhouses of this growing region, and compared their response with a susceptible population of the same species. The products tested were abamectin, fenbutatin oxide, chlorfenapyr, amitraz, bifenthrin, and propargite. Significant differences were found in the response to the applied concentrations of acaricides. The levels of resistance were high to all tested acaricides, except fenbutatin oxide, in the Villa Guerrero and Tenancingo populations. The Coatepec population was susceptible to fenbutatin oxide and abamectin and had higher levels of tolerance to bifenthrin, amitraz, and chlorfenapyr. The RR50 values in resistant populations, ranged from 10 (propargite in Tenancingo population) to 6.400-fold (amitraz in Villa Guerrero population), in comparison to the susceptible reference. Amendments to both pest management strategies and the use of acaricides against T. urticae in Rosa sp. are proposed.

New Records of Cherimola Fruit Borer Talponia batesi Heinrich (Lepidoptera: Tortricidae) in Mexico

En la región Neotropical, el principal problema que enfrenta las anonáceas (Magnoliales: Annonaceae) como la guanábana (Annona muricata L.), chirimoya (A. cherimola Mill.), saramuyo (A. squamosa L.), ilama (A. diversifolia Saff.), y anona colorada (A. reticulata L.), es la alta incidencia de insectos barrenadores de frutos que limitan el crecimiento de la superficie de cultivo (Peña et al. 2002). Se tienen identificadas cinco especies de insectos que perforan frutos de anonáceas. La avispa de las anonáceas Bephratelloides cubensis Ashmead (Hymenoptera: Eurytomidae), palomilla de las anonáceas Cerconota anonella (Lepidoptera: Elachistidae), el gusano de la cáscara Oenomaus ortygnus Cramer (Lepidoptera: Lycaenidae), picudo de las anonáceas Optatus palmaris Pascoe (Coleoptera: Curculionidae), y el barrenador de frutos del chirimoyo Talponia batesi Heinrich (Lepidoptera: Tortricidae) (Peña et al. 2002). Las larvas de estos insectos, causan daño directo al alimentarse del endocarpio y semillas, destruyéndolos en su totalidad, además las perforaciones que realizan las larvas y adultos sirven de entrada a hongos como Colletotrichum spp, causante de la antracnosis de frutos de anonáceas (Peña et al. 2002; Boscán y Godoy 2004). En México, el chirimoyo es un árbol frutal cultivado a nivel traspatio y en pequeños huertos comerciales; produce frutos que son muy apreciados por su agradable sabor y alto valor comercial en los mercados locales (Agustín 1999). Esta especie presenta baja producción de frutos, atribuido a una deficiente polinización y la presencia de T. batesi; constituyen la principal limitante para su cultivo (Castañeda-Vildózola et al. 1996). Heinrich (1932), describió al adulto de T. batesi de larvas criadas de frutos de chirimoya provenientes de Antigua, Guatemala. Registros de esta especie han sido documentados en Costa Rica, México y Venezuela (Nava-Díaz et al. 2000, Boscán y Godoy 2004, Castrejón-Gómez y Valdez-Carrasco 2008, Razowski 2011).