Dermanyssus gallinae (De Geer) (Mesostigmata: Dermanyssidae) is one of the most important hematophagous ectoparasites of laying hens. Chemical acaricides are the basis of a control program of this mite. In addition to their relative efficiency, there are many side effects associated with these chemical products. In an effort to generate more options for the mite control, entomopathogenic fungi were evaluated for use in the control of D. gallinae in laboratory and field conditions. Conidia suspensions of Beauveria bassiana strains were applied to mites (1×108 viable conidia/ml). Out of 39 strains, four isolates were selected according to their acaricidal activity (confirmed mortality ≥70%). Growth and reproduction parameters on culture media and fungal development at different temperatures were also evaluated. Finally, the efficacy of the selected strain was determined in a commercial laying hen house. A suspension of conidia (1 × 109 viable conidia/ml) was sprayed around the cages. Seven days later, another suspension was applied. A control group was sprayed with water. Paper towel traps were used to estimate the mite population before and after treatments. Mite traps were placed one week before the first fungal application and changed weekly for up to three weeks after application (-7; 0; 7; 14 and 21 days). In lab studies, B. bassiana strain Unioeste 88 was the most effective, causing 73.8% mortality and showing high conidia production (7.1 × 108 conidia/colony and 7.7 × 108 conidia/g, respectively, on PDA and rice). There was no fungal development at temperatures ranging from 35 to 45 °C. In the field test, the fungus reduced the mite population efficiently (64.8%), while the mite population increased by 281% in untreated plots. B. bassiana strain Unioeste 88 has the potential to be commercially used to control the poultry red mite.
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Vol. 25 • No. 5