Aislamiento de hongos entomopatógenos en suelo y sobre gallinas ciegas (Coleoptera: Melolonthidae) en agroecosistemas de maíz

The knowledge on the presence and abundance of natural enemies of white grubs in Mexico is limited. Therefore the aim of the present work is to isolate, identify and preserve entomopathogens from corn cultivated soils and from collections made directly on white grubs in Morelos. Altitudes of these georeferenced (GPS) sites ranged between 1000 to 2300 masl. Forty four soil sample collectionswere made in these sites. Fungal detection was made by the trap insect technique using Galleria mellonella (Lepidoptera: Pyralidae) as a bait. Besides, white grub species present in each site belonging to different larval instars. These larvae were identified to morphospecies on the basis of the raster palidia and were observed until death or adult emergence. Field collected dead larvae with fungal infections were also identified in the same way. Both the larvae of G. mellonela and white grubs were used to isolate and identify the fugal species present. Fungal identification was made on the basis of morphology and fungal development on the insect which correlates with conidial size and shape and the conidial formation in colonies of purified isolates. Fourty eight fungal isolates (seven from white grubs and 41 G. mellonella) have been preserved in the Biological Control Laboratory of the CEIB-UAEM (a replicate has been placed in Fungal Entomopathogens Colllection of CNRCB). In this collection 15 strains of Metarhizium anisopliae, 30 strains of Beauveria bassiana and three strains of Paecilomyces sp. are present. This fungal diversity is valuable in the zone for conservation purposes and for its potencial as biocontrol agents against white grubs and other corn pests.En México se conoce poco sobre la presencia y abundancia de enemigos naturales de plagas suelo como las Phyllophaga spp. Por lo anterior se realizó el presente trabajo con los objetivos de aislar, identificar y conservar entomopatógenos en suelos cultivados con maíz y sobre inmaduros de gallina ciega en el estado de Morelos. En altitudes de 1000 a 2300 msnm, se realizaron cuarenta y cuatro colectas de suelo en sitios georeferenciados (GPS). La detección de hongos se realizó mediante la técnica de insecto trampa, Galleria mellonella (Lepidoptera: Pyralidae). Además, se colectaron inmaduros de gallina ciega de diversos estadios larvales en diferentes localidades, se separaron por morfoespecie de acuerdo a la forma del ráster y se tomaron fotografías de cada morfoespecie. Tanto de las larvas de G. mellonela como de las gallinas ciegas se realizaron aislamientos e identificación de hongos entomopatógenos. Se identificaron siete morfoespecies y tres especies de Phyllophaga, alimentándose sobre raíces de plantas de maíz, además de tres especies de Paranomala. Se conservan en la Colección del Laboratorio de Control Biológico del Centro de Investigación en Biotecnología de la Universidad Autónoma del Estado de Morelos (con respaldo en la Colección de Hongos Entomopatógenos del CNRCB) cuarenta y ocho aislamientos de hongos entomopatógenos (siete aislados de gallina ciega y 41 de larvas de G. mellonella). De éstos, 15 corresponden a Metarhizium anisopliae, 30 a Beauveria bassiana y tres a Paecilomyces sp. Estos aislamientos poseen un gran valor para la zona, desde el punto de vista de conservación de la biodiversidad de enemigos naturales de plagas agrícolas y por su potencial como agentes de control biológico de GC y otras plagas del maíz.

Evaluation of Bacillus thuringiensis Pathogenicity for a Strain of the Tick, Rhipicephalus microplus, Resistant to Chemical Pesticides

The pathogenicity of four native strains of Bacillus thuringiensis against Rhipicephalus (Boophilus) microplus (Canestrine) (Acari: Ixodidae) was evaluated. A R. microplus strain that is resistant to organophosphates, pyrethroids, and amidines, was used in this study. Adult R. microplus females were bioassayed using the immersion test of Drummond against 60 B. thuringiensis strains. Four strains, GP123, GP138, GP130, and GP140, were found to be toxic. For the immersion test, the total protein concentration for each bacterial strain was 1.25 mg/ml. Mortality, oviposition, and egg hatch were recorded. All of the bacterial strains had significant effects compared to the controls, but no significant differences were seen between the 4 strains. It is evident that these B. thuringiensis strains have a considerable detrimental effect on the R. microplus strain that is resistant to pesticides

Effects of passages through a suitable host of the fungus, Metarhizium anisopliae, on the virulence of acaricide-susceptible and resistant strains of the tick, Rhipicephalus microplus.

The aim of this work was to assess the virulence of strain M379 of the fungus, Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) after different passages through a suitable host and at different concentrations for the control of both acaricide-susceptible and resistant strains of the tick, Rhipicephalus (formerly Boophilus) microplus Canestrini (Ixodida:Ixodidae) in vitro. The highest value of LC50 for the susceptible strain corresponded to zero passage with 7.68 × 107 conidia/ml followed by the fourth passage with 2.68 × 107, which reduced 2.87-fold the lethal concentration. When comparing LC50 values of the fourth vs. the seventh passage (2.59 × 105 conidia/ml), the lethal concentration was reduced 103.47-fold by the seventh passage. In addition, in the resistant strain the LC50 highest value corresponded to zero passage with 4.95 × 107 conidia/ml followed by the fourth passage with 7.86 × 106, which reduced 6.30-fold the lethal concentration. When comparing LC50 values of the fourth vs. the seventh passage (1.04 × 105 conidia/ml) in the resistant strain, the lethal concentration was reduced 75.58-fold by the seventh passage. These results suggest that the number of passages on M. anisopliae through a suitable host increased its virulence on both R. microplus strains. When comparing LC50 of the zero passage through a suitable host of both acaricide-susceptible and resistant strains, the highest LC50 values corresponded to the susceptible strain with 7.68 × 107 conidia/ml followed by the resistant one with 4.95 × 107, showing that on the resistant strain the lethal concentration is reduced by 1.55-fold. When comparing the fourth passage, the highest values of LC50 corresponded to the susceptible strain with 2.68 x 107 conidia/ml followed by the resistant one with 7.86 × 106 conidia/ml, showing for the resistant strain a 3.41-fold reduced lethal concentration. Moreover, when comparing the seventh passages, the highest values of LC50 corresponded to the susceptible strain with 2.59 × 105 followed by the resistant with 1.04 × 105 conidia/ml, revealing for the resistant strain a 2.49-fold reduced lethal concentration. These results suggest that the resistant strain needs a lower concentration of conidia than the susceptible strain. In this case, the acaricide-resistant strain is more susceptible to M. anisopliae of zero- and seven-passage strains

In vitro susceptibility of Varroa destructor and Apis mellifera to native strains of Bacillus thuringiensis

International audienceFifty-four Bacillus-like strains were isolated from dead Varroa destructor collected in 24 colonies of bees from seven apiaries. The total proteins of 22 isolates were evaluated against adult female V. destructor (100 μg/mL), but only nine caused over 80 % mortality. The LC50 of EA26.1, EA3 and EA11.3 isolates were calculated. The most virulent isolate was EA26.1, as 96.7 % of the mites were killed 36 h after treatment, and the LC50 was 1.50 μg/mL. EA3 produced 93.3 % mite mortality after 48 h treatment, with an LC50 of 7.1 μg/mL. Finally, EA11.3 produced 93.3 % mite mortality after 60 h treatment, with an LC50 of 22.8 μg/mL. Additionally, the EA3 and EA26.1 isolates were used to determine mortality on adults and larvae of worker bees of A. mellifera. When the 16S rRNA gene was amplified and sequenced, the three strains were found to belong to the species B. thuringiensis. The results showed that honey bee adults and larvae are not negatively affected by identified B. thuringiensis isolates, indicating that they could be successfully used for the biological control of V. destructor without adverse effects on adults and larvae of A. mellifera, and reduce the negative impact of this mite on colonies

Pathogens Associated with Sugarcane Borers, Diatraea spp. (Lepidoptera: Crambidae): A Review

The objective of this paper was to analyze information related to entomopathogenic-associated Diatraea spp. Gaining a better understanding of the effects of these microorganisms will help in the development of successful microbial control strategies against stem borers that attack sugarcane plants