Acaricidal effects of Beauveria bassiana in combination with Eucalyptus globulus essential oil against Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae, is the most economically damaging ectoparasite of laying hens worldwide. The disadvantages of using chemicals against this mite (i.e., environmental and food contamination and drug resistance) have spurred the interest of the scientific community in developing alternative methods for its control. Eucalyptus globulus essential oil (EgEO) and Beauveria bassiana (Bb) have the potential to be used as alternative approaches for D. gallinae control. These compounds have some limitations in their use: the acaricidal effect of EgEO is rapid, but short-lived, whilst that of Bb is delayed, but longlived. This study reports the effect of a native strain of Bb in combination with EgEO, against D. gallinae nymphs and adults. Batches of nymphs and adult mites (i.e., 360 individuals for each stage) for the treatment groups (TGs) were placed on paper soaked with a 0.1% tween 80 suspension of 109 conidia/ml of Bb (CIS) in combination with two different EgEO concentrations (i.e., 0.2% and 0.1%), whilst 720 control mites for each stage (CGs) were exposed to 0.1% tween 80 (CG1), to Bb 109 CIS (CG2), to 0.2% EgEO (CG3) and to 0.1% EgEO (CG4). A 100% mortality was recorded in adults at 9 days post infection (DPI) and at 10 DPI in nymphs, when using CIS in combination with 0.2% EgEO, but in CG2 at 12 DPI for adults and 14 DPI for nymphs. Used in combination with 0.2% EgEO, Bb displayed an earlier acaricidal effect towards both D. gallinae stages. The combination of B.bassiana 109 CIS and E. globulus essential oil at 0.2% might be a promising natural control method for use in a pest management strategy against mite infestations in poultry houses.