Efficacy of entomopathogenic fungi (Ascomycetes: Hypocreales) against adult Haematobia irritans (Diptera: Muscidae) under stable conditions in the Mexican dry tropics

The purpose of this paper is to evaluate the effect of five strains of Metarhizium anisopliae (Ma) and three strains of Isaria fumosorosea (Ifr) at a concentration of 1×10(8)colony-forming units/ml applied by spraying onto bovines with controlled infestation of Haematobia irritans under stable conditions in the Mexican dry tropics. Four experiments were performed, in each of which three treatments (two fungal strains and one control) were evaluated with eight repetitions for each one, by carrying out a single application of the aqueous suspension of each strain. The animals were isolated in individual cages and direct counts of the infestation were carried out for 13 days. It was observed that strains Ma2, Ma6, Ma10, Ma14, and Ma34 caused 94-100% reduction in infestation between days 12 and 13 post-treatment, while strains Ifr19, Ifr11, and Ifr12 reduced infestation from 90% to 98% up to day 13 post-application. There was an effect in the generation of horn flies from the excrement of bovines that were treated with different strains, reducing the reproduction of subsequent generations. It was concluded that the strains of M. anisopliae and I. fumosorosea evaluated in this study can be used as biocontrol agents in infestations of H. irritans in stabled bovines.

Virulence of Mexican isolates of entomopathogenic fungi (Hypocreales: Clavicipitaceae) upon Rhipicephalus=Boophilus microplus (Acari: Ixodidae) larvae and the efficacy of conidia formulations to reduce larval tick density under field conditions

The first objective was laboratory evaluation of the virulence of 53 Mexican isolates of fungi against larvae of Rhipicephalus (Boophilus) microplus. Thirty-three isolates of Metarhizium anisopliae var. anisopliae (Metschnickoff) Sorokin (Hypocreales: Clavicipitaceae) and 20 isolates of Isaria (Paecilomyces) fumosorosea (fumosoroseus) (Wize) (Eurotiales: Trichomaceae) were tested on 7-day-old larvae under laboratory conditions. Larvae were immersed in a suspension containing 10(8)conidia/mL and the CL(50) values were estimated. Then, field tests were conducted to determine the efficacy of formulations of the isolate with the highest virulence. M. anisopliae (Ma 14 isolate) was formulated with four carriers: Tween, Celite, wheat bran, and Citroline (mineral oil) and applied on pasture beds of Cynodon plectostachyus (L.), at a dose of 2 x 10(9)CFU/m(2). In the first trial, M. anisopliae was applied on plots naturally infested with larvae; in the second trial, tick populations in the experimental plots were eliminated and then re-infested with 20,000 7-day-old larvae. In the laboratory, all M. anisopliae isolates infected larvae with a mortality range between 2 and 100%; also, 13 of 20 I. fumosorosea isolates caused mortality rates between 7 and 94%. In the first field trial, 14 days post-application, conidial formulations in Celite and wheat bran caused 67.8 and 94.2% population reduction, respectively. In the second trial, the Tween formulation caused the highest larval reduction, reaching up to 61% (28 days post-application). Wheat bran formulation caused 58.3% larval reduction (21 days post-application) and was one of the most effective. The carriers and emulsifiers have a large impact on the effectiveness of conidial formulations.

Laboratory and field evaluation of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) for the control of Rhipicephalus microplus (Acari: Ixodidae) in the Mexican tropics

The aim of the present study was to evaluate the effect of Metarhizium anisopliae to control Rhipicephalus microplus under laboratory and field conditions (larvae on vegetation) in the Mexican tropics. In the laboratory study, Ma34, Ma14 and a mixture of Ma34+Ma14 strains of M. anisopliae were evaluated for their control of the adult and larval stages of R. microplus, using the adult and larval immersion test respectively. The reproductive efficiency index of engorged females was determined in the treated and control groups. In the adults, the Ma34 and MA14 strains both produced an efficacy of 100% on engorged females at 1 x 10(8), 1 x 10(7) and 1 x 10(6)conidia/ml; however, only Ma34 killed 100% at 1 x 10(6)conidia/ml dose. The mixture of both strains (Ma34+Ma14) produced an efficacy of 100% on engorged females at 1 x 10(8)conidia/ml. R. microplus engorged females treated with Ma34 and a mixture of strains Ma34 and Ma14 reduced egg oviposition by 55.5% and 39.1% respectively compared to treated controls (P<0.001). In the larval evaluation, Ma14 produced an efficacy of 45-62%; however, Ma34+Ma14 increased the efficacy reaching 90% (1 x 10(8)conidia/ml concentrations, P<0.05). In the field study, twelve 9 m(2) plots with vegetation were artificially infested with R. microplus larvae. Six plots were used as control and six as test areas. The treated plots received the Ma34+Ma14 (1 x 10(8)conidia/ml) by manual scattering at 0, 14 and 28 days post-treatment (PT). The number of larvae in the treated and control group was determined at 0, 7, 14, 21, 28 and 35 days PT by the tick drag method. This field study was carried out in two different seasons (January-March, wet, April-May, dry). In the wet season trial the efficacy of M. anisopliae to control R. microplus was 67.7% and 100% in the dry season trial .In conclusion, the mixture of Ma34 and Ma14 strains of M. anisopliae showed a high efficacy to control both larval and adult stages of R. microplus under laboratory conditions, and in field conditions these strains were efficient to control larval stages on vegetation.

Evaluation of Metarhizium anisopliae (Hyphomycetes) for the control of Boophilus microplus (Acari: Ixodidae) on naturally infested cattle in the Mexican tropics

The efficacy of Metarhizium anisopliae on the control of Boophilus microplus in cattle infested naturally in the Mexican tropics was evaluated. The study was carried out on a ranch in Veracruz, Mexico. Twenty steers were randomly allocated into two groups of 10 cattle. Animals were naturally infested with B. microplus. Animals in the treated group were sprayed with M. anisopliae (strain Ma34) at a concentration of 1x10(8)conidia/ml every 15 days (four treatments). The other group remained as untreated control. Standard engorged female ticks were recorded on days 0, 1, 3, 5, 7 and 14 post-treatment. From the second application treatment (day 7) to the end of the experiment, animals in the treated group had lower tick infestation (P<0.05) with an efficacy of 40.0-91.2%. The results demonstrate the efficacy of repeated treatment with M. anisopiae (Ma34 strain) to control natural infestation of engorged female B. microplus on cattle in the Mexican tropics.

Susceptibility of biological stages of the horn fly, Haematobia irritans, to entomopathogenic fungi (Hyphomycetes)

The susceptibility of the egg, pupa, and adult of Haematobia irritans (L.) (Diptera: Muscidae) to isolates of the fungi Metarhizium anisopliae (Metsch.) Sor., Beauveria bassiana (Bals.) Vuill., and Paecilomyces fumosoroseus (Wize) Brown and Smith, was evaluated under laboratory conditions. Groups of 20 eggs than 4 h old, pupae less than 48h old and adults were sprayed with a conidial suspension of each isolate. Eggs, pupae and adults of horn fly were susceptible to these entomopathogenic fungi. For treated eggs, the isolates Ma3, Ma 15, Ma25, Pfr1, and Pfr8 reduced adult emergence to 3.8% to 6.3% in comparison with the control (72%). The mortality of pupae infected by the isolates Ma2, Ma25, and Pfr10 ranged between 50% and 71.3%. Mortality of adults after treatment with the isolates Ma6, Ma 10, Ma 14, Ma 15, Pfr 1, Pfr 9, Pfr 10, Pfr 11, and Pfr12 were higher than 90%. The isolate Ma6 produced the lowest LC(50) against adult horn flies (8.08 × 10(2)conidia/ml). These findings supported the hypotheses that isolates of M. anisopliae, and P. fumosoroseus are pathogenic against the different biological stages of horn flies by reducing adult emergence when applied on groups of eggs and pupae, and producing mortality when applied to adults.