Phylogenetic Relationships and Acaricidal Effects of Beauveria bassiana Obtained from Cattle Farm Soils Against Rhipicephalus microplus.

The objectives of the present study were to isolate Beauveria bassiana strains from cattle farm soils, analyze the phylogenetic relationships among the fungal strains isolated from these soils, and determine the acaricidal effect of B. bassiana isolates on engorged Rhipicephalus microplus tick strains resistant or susceptible to chemical acaricides. Six strains of B. bassiana were obtained and isolated from cattle farm soils in the Mexican tropics using the Galleria bait method, and their acaricidal effect was assessed against 2 populations of R. microplus ("Media Joya" chemical acaricide-resistant strain or "CLAR" chemical acaricide-susceptible strain) using the adult immersion test. The BbV03 strain produced 86.7% and 60% mortality in resistant and susceptible ticks on day 20, respectively, whereas the BbV04 strain produced 66.7% and 53.5% mortality in resistant and susceptible ticks on day 20, respectively. The BbV03 and BbV04 strains reduced egg laying on both R. microplus populations. There was no statistical difference in the acaricidal effect of B. bassiana strains among chemical acaricide-susceptible or -resistant R. microplus populations ( P > 0.05). The BbV03 strain was the most virulent against R. microplus with an LC50 of 2 × 107 and LC99 of 7 × 108 conidia/ml. We found that the 6 B. bassiana isolated clustered in the same clade with other previously reported B. bassiana strains (from GenBank) but were separated into 3 different sub-clades. This study shows that some B. bassiana strains are a promising coadjuvant alternative for biological tick control, including tick populations that are resistant to chemical acaricides. Beauveria bassiana is present in the pastures of tropic cattle farms, and there are genetic variations between B. bassiana strains living in this ecosystem that might play an important role in the natural control of R. microplus in cattle farm paddocks.

Effect of Metarhizium anisopliae (Ascomycete), Cypermethrin, and D-Limonene, Alone and Combined, on Larval Mortality of Rhipicephalus sanguineus (Acari: Ixodidae).

The effect of the fungus Metarhizium anisopliae Ma14 strain, D-limonene, and cypermethrin, alone and combined, on the mortality of Rhipicephalus sanguineus Latreille larvae was evaluated. Eight separate groups with 25 tick larvae were inoculated with the fungus, cypermethrin, and D-limonene, and four groups were used as untreated controls. The groups were inoculated with serial dilutions of each treatment material: for example, conidial concentrations were 1 × 101, 1 × 102, 1 × 103, 1 × 104, 1 × 105, 1 × 106, 1 × 107, and 1 × 108. A complete randomized experimental design was used. Significant differences were obtained between fungal concentrations, with larval mortalities ranging from 29 to 100%; the D-limonene concentrations showed significant differences, with mortalities that ranged from 47.9 to 82.6%, and cypermethrin mortalities ranged from 69.9 to 89.9% when each was applied alone. In the combined application, the serial dilution of the Ma14 fungus plus cypermethrin at 0.1% concentration caused mortalities ranging from 92.9 to 100%; the mix of serially diluted Ma14 plus D-limonene at 0.1% caused mortalities from 10.3 to 100%; and the mix consisting of serially diluted D-limonene plus cypermethrin at 0.1% caused mortalities from 7.4 to 35.9%. Further laboratory and field research could show that these materials, alone and in combinations, are useful in future tick management and control programs.

Fluctuación poblacional de Haematobia irritans (Diptera: Muscidae) en un hato bovino en Tecomán, Colima, México / Population fluctuation of Haematobia irritans (Diptera: Muscidae) in a cattle herd in Tecoman, Colima, Mexico

The objective of the work was to study H. irritans population fluctuation in a cattle herd in Tecoman, Colima, Mexico. The cattle herd was visited weekly from March 2003 to May 2004; on each occasion, ten animals were randomly selected to estimate infestation by direct visualization method. Temperature and relative humidity (RH) were recorded daily. Population fluctuation was described and periods and population peaks were identified. Pearson's correlation analysis was calculated (P < 0.05) between temperature and RH, with fly average number per animal for each population period. H. irritans infestation had fluctuations, but with presence of flies all the year; the highest infestation was observed in summer, where two population peaks were present, with 236 and 120 flies per animal, respectively; the activity in autumn and winter also showed fluctuations and the population had an increment in spring, where a population peak could be observed, as well as at the beginning of the study (156 flies/animal) and at the end (323 flies/animal). In the first population period, a significant correlation coefficient (0.93) was found with temperature, similar situation was observed in the fourth period (-0.57); no significant coefficients were found in other population periods for the climatic factors in study.

El objetivo del trabajo fue estudiar la fluctuación poblacional de H. irritans en un hato de ganado bovino en el municipio de Tecomán, Colima, México. El hato fue visitado semanalmente de marzo de 2003 a mayo de 2004; en cada ocasión se seleccionaron al azar diez animales para estimar la infestación mediante el método de visualización directa. Se registró la temperatura y la humedad relativa (HR) diariamente. Se describió la fluctuación poblacional presentada y se identificaron los periodos y picos poblacionales. Se realizó un análisis de correlación de Pearson (P < 0.05) entre la temperatura y la HR, con los valores promedio del número de moscas por animal para cada uno de los periodos poblacionales. La infestación por H. irritans fue fluctuante, pero con presencia de moscas durante todo el año; los momentos de mayor infestación se observaron en verano, al presentarse dos picos poblacionales, con 236 y 120 moscas/animal; la actividad en otoño e invierno también fluctuó; se incrementó en primavera, durante la cual se observó un pico poblacional, tanto al inicio del estudio (156 moscas/animal) como al final (323 moscas/animal). Para el primer periodo poblacional se encontró un coeficiente de correlación significativo (0.93) con la temperatura, algo similar ocurrió para el cuarto periodo (-0.57); no fue posible detectar coeficientes significativos en otros periodos poblacionales para los factores climáticos en estudio.