Short communication

The influence of ‘time since last blood meal’ on the toxicity of

essential oils to the poultry red mite (Dermanyssus gallinae)

D.R. George *, T.J. Smith, O.A.E. Sparagano, J.H. Guy

School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne NE1 7RU, UK

Received 15 February 2008; received in revised form 15 April 2008; accepted 6 May 2008

www.elsevier.com/locate/vetpar

Available online at www.sciencedirect.com

Veterinary Parasitology 155 (2008) 333–335

Abstract

The poultry red mite, Dermanyssus gallinae (De Geer) is a serious ectoparasitic pest of layer hens that can survive for long

periods in the poultry house sub-structure without taking a blood meal from its host. The research undertaken in this study found that

‘time since last blood meal’ had a notable effect on how toxic a selection of plant essential oils were to D. gallinae under laboratory

conditions.

In general, the essential oils had a greater toxic effect on D. gallinae if mites had been starved of a blood meal for around 3

weeks, than if they had been more recently fed 3–13 days prior to tests. This result was consistent across the four essential oils used

(thyme, palmarosa, caraway and juniper leaf). This suggests that plant essential oils may be of use in management schemes for D.

gallinae, particularly if used to sanitise houses between flocks, when mites will have been starved.

# 2008 Elsevier B.V. All rights reserved.

Keywords: Dermanyssus gallinae; Essential oil; Toxicity; Diet

1. Introduction

Pest management by conventional means (the use of

synthetic pesticides) has become increasingly hampered

by issues including stricter legislation, pest resistance

and an increase in consumer demand for foodstuffs

produced in an environmentally responsible manner. As

a result, increased interest is being shown in developing

alternative methods of pest control to reduce or

eliminate reliance on synthetic pesticides. One such

method involves the use of plant-derived-products, such

as plant essential oils, as pesticides (Isman, 2000).

* Corresponding author at: School of Agriculture, Food and Rural

Development, Agriculture Building, Newcastle University, Newcastle

upon Tyne, NE1 7RU, UK. Tel.: +44 1912228893;

fax: +44 1912226720.

E-mail address: D.R.George@ncl.ac.uk (D.R. George).

0304-4017/$ – see front matter # 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.vetpar.2008.05.005

Studies (e.g. Kim et al., 2004) have investigated the

potential of plant-derived products to manage the

poultry red mite, Dermanyssus gallinae (De Geer), a

serious ectoparasite of laying hens in the UK and

Europe. In taking a blood meal from its host, D. gallinae

can cause stress and even anaemia in the birds it feeds

from, and may serve as a vector for numerous poultry

pathogens (Kim et al., 2004). Several plant essential oils

have already been identified as being toxic to these

mites (Kim et al., 2004). Such work, however, has only

tested the toxicity of essential oils on D. gallinae that

have been recently fed. Other research has shown that

the toxicity of products to invertebrates may depend on

engorgement levels at the time of exposure. Fed grass

shrimp larvae (Palaemonetes vulgaris Say.), for

example, tended to be more resistant to mercury

exposure than unfed counterparts (Shealy and Sandifer,

1975) and EC50 values for copper in five cladoceran

species where consistently lower when comparing

D.R. George et al. / Veterinary Parasitology 155 (2008) 333–335334

Fig. 1. Mean percentage mortality rate of Dermanyssus gallinae

deprived of the opportunity to feed for varying periods, when exposed

to filter papers impregnated with different plant essential oils. Means

are displayed with standard errors. n = 8 for all means. Different

letters and numbers displayed with means are used to depict sig-

nificant differences between pairs of means identified by Tukey’s test

(P < 0.05). Means (between ‘time since last blood-meal’ treatments

for any one essential oil) not sharing a common letter are significantly

different. Means (between essential oils under any given ‘time since

last blood-meal’ treatment) not sharing a common number are also

significantly different.

unfed to fed neonates (Kovisto et al., 1992). Also, honey

bees (Apis mellifera L.) fed on a low as opposed to a

high quality diet were more sensitive to insecticides

(Wahl and Ulm, 1983).

D. gallinae may survive for long periods without

feeding (Axtell, 1999) allowing populations to persist

between flocks. It is therefore important to understand

how ‘time since last blood meal’ will affect the toxicity

of essential oils to D. gallinae if these are to be

considered as a potential control agent in poultry pest

management. The aim of this study was to test the

toxicity of several essential oils to D. gallinae which

had been deprived of the opportunity to take a blood

meal for varying periods.

2. Methods

Experiments were conducted at Newcastle Univer-

sity, UK. Essential oils (New Directions, Southampton,

UK) of thyme (Thymus vulgaris L.), palmarosa

(Cymbopogon martini Roxb.), caraway (Carum carvi

L.) and juniper leaf (Juniperus communis L.) were

applied to filter papers (Whatman No. 2, 4.25 cm

diameter) at a known concentration (0.21 mg/cm2) in

50 ml of ethanol as a solvent. Treated (or untreated

control filter papers which had received 50 ml of ethanol

only) were placed into glass Petri-dishes (4.8 cm

diameter � 1.2 cm height) with approximately 23 adult

female D. gallinae deprived of the opportunity to take a

blood meal for varying periods of time depending on

treatment.

Six ‘time since last blood meal’ treatments were used

with mites that had been collected from a commercial

free-range poultry unit and stored at 22 8C, 16:8

light:dark cycle, until required for use. These treatments

used mites that had been collected 3, 6, 10, 13, 17 and 20

days prior to experimentation. D. gallinae is known to

take a blood meal every few days (Maurer et al., 1988),

such that distinctions in mite engorgement statuses

between ‘time since last blood meal’ treatments could

be generally assumed.

Mite mortality was assessed after 24 h (at 22 8C,

16:8 light:dark cycle). Percentage mortality between

essential oils and treatments was then assessed by a two-

way ANOVA (with corresponding Tukey tests). Data

did not require transformation to satisfy the assump-

tions of the test.

3. Results

There was a significant difference in mite mortality

between essential oils (P < 0.001) and between ‘time

since last blood meal’ treatments (P < 0.001). There

was also a significant interaction between these two

variables (P < 0.05). Higher mite mortality was

observed following prolonged starvation for all essen-

tial oil treatments, but not for mites in the control

treatment (Fig. 1). Significant differences in mite

mortality between different essential oils under a given

‘time since last blood meal’ treatment are displayed in

Fig. 1.

4. Discussion

These results suggest that D. gallinae that have been

deprived of the opportunity to feed are more susceptible

to the toxic effects of plant essential oils than those that

have been allowed to feed more recently. The reason for

this may be a weakening in mite physiological condition

that occurs as a result of food deprivation, although this

remains to be confirmed. This result is in agreement

with work elsewhere that has found invertebrate

sensitivity to toxins to increase when starved, or when

provided with a sub-optimal diet (Shealy and Sandifer,

1975; Wahl and Ulm, 1983; Kovisto et al., 1992).

Typically, D. gallinae infesting one flock of hens

may survive in the hen house sub-structure for long

enough to infest any new flock once introduced as,

under suitable conditions, D. gallinae may live without

a blood meal for up to 9 months (Axtell, 1999). Across

the EU, the empty period between layer flocks averages

D.R. George et al. / Veterinary Parasitology 155 (2008) 333–335 335

just over 3 weeks, with exact figures between 22

(traditional cage) and 26 (organic) days depending on

the production system (Agra CEAS, 2004). If, prior to

the introduction of a new flock, the housing system was

treated with an appropriate plant essential oil-based

pesticide, the results presented suggest that mortality of

D. gallinae could be expected to be high, as mites would

have been starved sufficiently since the removal of the

old flock. It is possible that D. gallinae deprived of a

blood meal for a sufficient period would also be more

susceptible to the toxic effects of standard synthetic

acaricides, although this cannot be confirmed by the

present work.

Following exposure to thyme and caraway essential

oil, D. gallinae mortality was generally higher under

most treatments than if mites were exposed to the

essential oil of either juniper leaf or palmarosa.

Mortality after exposure to the former two oils was

consistently significantly increased after 17 days of mite

starvation, whereas for the later two oils it was not (in

comparison to baseline mortality after 3 days of

starvation). It follows that either caraway or thyme

essential oil might make for a more effective acaricide

(or component of an acaricide) for use against D.

gallinae than either juniper leaf or palmarosa essential

oil. It may be possible to increase the toxicity of juniper

leaf and palmarosa essential oils to D. gallinae by

deploying them at a higher dose. In practise, however,

this would mean that these essential oils would need to

be used in greater amounts than either caraway or thyme

essential oil to achieve a similar toxic effect.

The current study, although only preliminary in

nature, suggests that essential oils may be useful in the

management of pests such as D. gallinae. If incorpo-

rated as acaricides, they may be especially effective in

limiting any carry-over of mite infestations from one

flock to the next if applied prior to repopulation of the

poultry house. Such data highlights the benefit of

considering the biology and ecology of target organisms

when attempting to construct effective pest manage-

ment protocols against them.

Acknowledgements

This study was funded by Newcastle University’s

(UK) Vacation Scholarship scheme and formed part of a

larger Defra (UK) funded study called MITEeHEN

being undertaken at Newcastle University investigating

the use of plant-derived products for management of D.

gallinae. The authors gratefully acknowledge statistical

assistance provided by Dr. Robert Shiel (Newcastle

University, UK).

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