Candelario Santillán-Ortega

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.

Fluctuation in Abundance of Adult Fruit Flies1 at Rosamorada and San Blas, Nayarit, México

Abstract. The economy of Nayarit depends on fruit, especially mango, Mangifera indica L., and citrus. However commercialization of fruit is affected by abundant fruit flies (Diptera: Tephritidae). To know the diversity of Anastrepha Schiner and determine its population dynamics on species in marginal areas of the municipalities of Rosamorada and San Blas, between January and December 2011, 128 McPhail traps baited with hydrolyzed protein were prepared each week. Fruit flies captured were preserved in 70% ethanol and sorted by sex and species according to an FTD index of numbers of flies trapped per day. Of 563 specimens collected, 442 (78.51%) were from Rosamorada and 121 (21.49%) at San Blas, with a male: female sex ratio of 1:1.9 and 1:1.6, respectively, at each municipality. At Rosamorada (FTD 0.143), species identified were Anastrepha ludens (Loew) (210: 47.51%), A. striata Schiner (114: 25.79%), and A. obliqua (Macquart) (113: 25.57%), captured 70.2, 81.0 and 51.3% of the time, respectively, while A. sp. (3: 0.68%) and A. serpentina (2: 0.45%) occurred only rarely (2.7 and 8.1%, respectively). At San Blas (FTD 0.0111), A. obliqua (57: 47.11%) and A. striata (57: 47.11%) were captured 70.3 and 62.9% of the time, respectively; A. ludens (6: 4.96%) was found less commonly (14.8%), and A. sp. (1: 0.82%) was found rarely (3.7%). Most fruit flies were trapped between February and August, coinciding with the fruiting period, with no apparent effect of abiotic factors such as temperature or precipitation on abundance.