Lack of prolonged activity of lavender essential oils as acaricides [621717]

Lack of prolonged activity of lavender essential oils as acaricides
against the poultry red mite ( Dermanyssus gallinae )
under laboratory conditions
D.R. Georgea,*, K. Callaghana,b, J.H. Guya, O.A.E. Sparaganoa
aSchool of Agriculture, Food and Rural Development, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK
bSchool of Medical Sciences, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK
Accepted 4 February 2008
Abstract
Managing the poultry red mite, Dermanyssus gallinae (De Geer) by conventional means (i.e., synthetic acaricides) has become increas-
ingly problematic. As a possible alternative, research has identified several plant essential oils that are toxic to D. gallinae . However,
essential oils are highly volatile and any acaricidal effect they exert could be short-lived in practice.
This study investigated the short-lived toxicity of six lavender essential oils to D. gallinae . In sealed Petri-dishes, mites were exposed to
filter papers impregnated with essential oil at a concentration of 0.14 mg/cm3. When filter papers were used immediately after impreg-
nation, 66–90% D. gallinae mortality was observed after 24 h, depending upon the essential oil used. If impregnated filter papers were left
in a fume cupboard for 24 h prior to use, mortality rates of D. gallinae fell to 11% or less.
/C2112008 Elsevier Ltd. All rights reserved.
Keywords: Dermayssus gallinae ; Novel control; Essential oil
The poultry red mite, Dermanyssus gallinae (De Geer), is
currently the most economically deleterious ectoparasite oflaying hens in Europe ( Chauve, 1998 ). Infestations of D.
gallinae can result in significant stress to hens with subse-
quent declines in bird condition, growth rate, egg quality
and egg production ( Chauve, 1998 ). In extreme cases, mite
population levels may be so high as to cause anaemia, andeven death of hens ( Wojcik et al., 2000; Cosoroaba, 2001 ).
Furthermore, D. gallinae may serve as a vector for numer-
ous poultry pathogens ( Chirico et al., 2003; Kim et al.,
2007).
Control of D. gallinae has typically been achieved
through synthetic acaricides. However, the continued use
of these products may be hampered by issues of mite resis-tance ( Kim et al., 2004; Fiddes et al., 2005 ) and decreasingproduct availability as a result of more stringent legislation
(Chirico and Tauson, 2002; Fiddes et al., 2005 ). The use
of conventional cage systems may alleviate the problemofD. gallinae infestation ( Axtell, 1999 ), but these are
scheduled to be prohibited within the EU in 2012. It is
therefore becoming increasingly important to identifynew approaches for management of D. gallinae in poultry
systems.
One alternative approach focuses on studying the toxic
effects of plant-derived products for managing D. gallinae .
Work by Kim et al. (2004) tested 56 plant essential oils for
their acaricidal effect on D. gallinae , a dozen of which gave
100% mite mortality in contact toxicity tests at a concentra-
tion of 0.07 mg oil per cm
2. Whilst this acaricidal effect
against D. gallinae may be encouraging, essential oils are
highly volatile in nature. Consequently, any pesticidal effectexerted by an acaricide based on these essential oils mightbe short-lived.
0034-5288/$ – see front matter /C2112008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rvsc.2008.02.001*Corresponding author. Tel.: +44 01912223591; fax: +44 01912226720.
E-mail address: [anonimizat] (D.R. George).www.elsevier.com/locate/rvscAvailable online at www.sciencedirect.com
Research in Veterinary Science 85 (2008) 540–542

To investigate any lack of prolonged toxicity of plant
essential oils to D. gallinae , contact toxicity tests were car-
ried out using six different types of lavender essential oilpurchased from ‘New Directions’ (Unit 12A Central Trad-ing Estate, Marine Parade, Northam, Southampton, SO145JP, UK) (see Fig. 1 ). These essential oils were used to
impregnate filter papers (Whatman No. 2, 4.25 cm diame-
ter) at a concentration of 0.21 mg/cm
2(in 50 ll of ethanol,
where control filter papers received 50 ll of ethanol only).
According to treatment, these filter papers were then addedto Petri-dishes (4.8 cm diameter /C21.2 cm height), such that
each dish contained 0.14 mg/cm
3of essential oil. After
either 3 min or 24 h storage time in a fume cupboard,where conditions of continuous air-flow were maintained
in an attempt to reconstruct conditions in a ventilated
poultry house, approximately 25 adult female D. gallinae
(collected from a free range poultry unit no more thansix days prior to study) were added to each dish and sealedtherein for 24 h (at 22 /C176C, 16:8 light:dark cycle). Mortality
was then assessed under magnification, where a mite wasconsidered dead if no movement was observed followingrepeated agitation with an entomological pin. Percentage
mortality of D. gallinae (with Abbots Correction to
account for control mortality) was calculated for eachessential oil in each of the two treatments. A total of eightreplicates were undertaken for each essential oil in eachtreatment.
Following arcsin square-root transformation, an Analy-
sis of Variance (ANOVA) was used to test for differences inpercentage D. gallinae mortality between different essential
oils under the same storage time treatment. The same test
was also used to look for differences in mortality betweenessential oils under different storage time treatments. The
results are displayed graphically in Fig. 1 .
There was no significant difference between any of the
six lavender essential oils with respect to their acaricidaleffect on D. gallinae (P> 0.05).
When filter papers impregnated with essential oil were
used almost immediately after impregnation in toxicity
tests, a strong acaricidal effect was observed. For fourout of the six lavender essential oils tested, greater than80% average mite mortality was achieved (see Fig. 1 ). This
suggests that these oils might make for effective activeingredients against D. gallinae if further testing was able
to confirm that this toxicity is maintained under field con-ditions. If the lavender essential oils used in the current
study were to be developed to this end, it may be necessary
to increase the concentration of oil applied to achieve ade-quate control of D. gallinae . At an increased concentration
of 0.35 mg/cm
2, exposure to the essential oil of L. officinalis
resulted in 100% mortality of D. gallinae over 24 h ( Kim
et al., 2004 ).
When filter papers impregnated with lavender essential
oils were left in a fume cupboard for 24 h prior to use in
toxicity tests, there was a marked decline in the acaricidal
effect of the oils against D. gallinae , where average mortal-
ity rates fell to between 2% and 11% (see Fig. 1 ). The
difference in the acaricidal effect of any one lavender essen-tial oil between treatments was consistently highly signifi-cant ( P< 0.001). This suggests that the toxicity of
essential oils will be short-lived if they are employed as aca-ricides. Where plant essential oils have been found to be
toxic to D. gallinae , this toxicity has been expressed in
the vapour phase ( Kim et al., 2004, 2007 ). As essential oils
rapidly break down in the environment, this vapour phasetoxicity would be expected to be short-lived.
It may therefore be necessary to reapply lavender, or
any essential oil (or rather any product containing theessential oil) to achieve adequate control of D. gallinae
in practise. Some essential oils such as thyme may dis-
play rapid knock-down of D. gallinae which may allevi-
ate the problem of short-lived toxicity (unpublisheddata). Alternatively, it may be possible to promote theslow-release of essential oils through the use of appropri-ate carriers to prolong their toxic effect ( Ahn et al.,
1998). As the toxicity of these oils is expressed in the
vapour phase, it may even be possible to incorporatethem into poultry house ventilation systems so that any
issue of short-lived toxicity is overcome through continu-
ous exposure. Either way, it seems that plant essentialoils warrant further attention as acaricides in poultrypest management, but that consideration must be givento the lack of prolonged toxicity afforded as well as tox-icity on initial exposure.
Acknowledgement
Financial support from Defra (UK) for this project is
gratefully acknowledged.********* *********
-100102030405060708090100110
465213
Lavender essential oil number% mortality after 24 hr of exposure Filter paper left for 3 min prior to use Filter paper left for 24 hr prior to use
Fig. 1. Mean percentage mortality rate (with Abbots Correction) of
Dermanyssus gallinae, when exposed to filter papers 3 min and 24 h after
being impregnated with six different lavender essential oils./C3/C3/C3Represents
a significant difference in mite mortality between different storage time
treatments using the same oil, where/C3/C3/C3P< 0.001. Means and 95%
confidence limits have been back-transformed from data used in ANOVA.
Lavender 1 = Lavandula angustifolia (Mill.), origin Australia. Lavenders 2
and 3 = Lavandula angustifolia , origin France (different regions). Laven-
der 4 = Lavandula angustifolia , origin Croatia. Lavender 5 = Lavandula
officinalis (Chaix), origin France. Lavender 6 = Lavandula dentata (L.),
origin France.D.R. George et al. / Research in Veterinary Science 85 (2008) 540–542 541

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