ArticlePDF Available

A new formulation of oxalic acid for Varroa destructor control applied in Apis mellifera colonies in the presence of brood

Authors:
  • Instituto de Investigaciones en Producción Sanidad y Ambiente (IIPROSAM) UNMDP - CONICET
  • COOPERATIVA DE TRABAJO APICOLA PAMPERO LIMITADA

Abstract and Figures

An organic product based on oxalic acid was evaluated for use in Varroa control under spring/summer climatic conditions in Argentina. The formulation consists of four strips made of cellulose impregnated with a solution based on oxalid acid. Forty-eight beehives were used to assess the product efficacy. Residues of the product were also tested in honey, bees, and wax. Each trial had respective control groups without oxalic treatment. At the beginning of the experiment, four strips of the formulation were applied to the colonies belonging to the treated group. Falling mites were counted after 7, 14, 21, 28, 35, and 42 days. After the last count, the strips were removed and colonies received two flumethrin strips for 45 days. Falling mites were counted throughout this period. Average efficacy of the organic product was 93.1 % with low variability. This product is an organic treatment designed for Varroa control during brood presence and represents a good alternative to the synthetic treatments.
No caption available
… 
Content may be subject to copyright.
A new formulation of oxalic acid for Varroa destructor
control applied in Apis mellifera colonies in the presence
of brood
Matías MAGGI
1,2
,Elian TOURN
3,4,5
,Pedro NEGRI
1,2
,Nicolás SZAWARSKI
1
,
Alfredo MARCONI
3,4,5
,Liliana GALLEZ
6
,Sandra MEDICI
1,2
,Sergio RUFFINENGO
7
,
Constanza BRASESCO
1
,Leonardo De FEUDIS
1
,Silvina QUINTANA
8
,Diana SAMMATARO
9
,
Martin EGUARAS
1,2
1
CIAS, Centro de Investigación en Abejas Sociales (ex Laboratorio de Artrópodos), Facultad de Ciencias Exactas y
Naturales, Universidad Nacional de Mar del Plata, Funes 3350, 7600, Mar del Plata, Argentina
2
CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Rivadavia1917, C1033AJ Buenos Aires,
Argentina
3
Departamento de Agronomía, Universidad Nacional del Sur, Bahía Blanca, Buenos Aires, Argentina
4
Ministerio de Agricultura, Ganadería y Pesca de la Nación, EEA INTA Bordenave, Bahía Blanca, Buenos Aires,
Argentina
5
Cooperativa de Trabajo Apícola Pampero Ltda., Bahía Blanca, Buenos Aires, Argentina
6
LabEA, Depto. Agronomía, Universidad Nacional del Sur, 8000, Bahía Blanca, Argentina
7
Cátedra de Apicultura, Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, 7620, Balcarce, Argentina
8
Laboratorio de Biología Molecular, Fares Taie Instituto de Análisis, Mar del Plata, Argentina
9
USDA ARS Carl Hayden Honey Bee Research Center, Tucson, AZ, USA
Received 14 July 2014 Revised 4 August 2015 Accepted 26 October 2015
Abstract An organic product based on oxalic acid was evaluated for use in Varroa control under spring/summer
climatic conditions in Argentina. The formulation consists of four strips made of cellulose impregnated with a
solution based on oxalid acid. Forty-eight beehives were used toassess the product efficacy. Residues of the product
were also tested in honey, bees, and wax. Each trial had respective control groups without oxalic treatment. At the
beginning of the experiment, four strips of the formulation were applied to the colonies belonging to the treated
group. Falling mites were counted after 7, 14, 21, 28, 35, and 42 days. After the last count, the strips were removed
and colonies received two flumethrin strips for 45 days. Falling mites were counted throughout this period. Average
efficacy of the organic product was 93.1 % with low variability. This product is an organic treatment designed for
Varr oa control during brood presence and represents a good alternative to the synthetic treatments.
Varroa destructor / control / oxalic acid / bee brood / Argentina
1. INTRODUCTION
Varroa destructor (Acari: Varroidae), an obli-
gate ectoparasitic mite of the honey bee, Apis
mellifera (Hymenoptera: Apidae), feeds on the
hemolymph of adult bees, larvae, and pupae in
capped brood cells. In Argentina, severe
V. d e s t r u c t o r infestation of A. mellifera results
in honey bee colony death within 1 to 2 years of
initial infestation (Eguaras and Ruffinengo 2006).
In recent years, resistance to acaricides has be-
come a major problem in the control of mite
populations. Increased tolerance to the most wide-
ly used synthetic active ingredients has been
Corresponding author: M. Maggi,
biomaggi@gmail.com
Manuscript editor: Yves Le Conte
Apidologie Original article
*INRA, DIB and Springer-Verlag France, 2015
DOI: 10.1007/s13592-015-0405-7
observed (Maggi et al. 2010a,2011). Because of
the resistance to acaricides, there is a renewed
interest in Argentina for substances of natural
origin, such as essential oils and their components
or organic acids, especially formic acid and oxalic
acid (Eguaras et al. 2001,2003; Maggi et al.
2010b; Ruffinengo et al. 2014). This situation
related to Varr oa resistance has been observed
around the world (Sammataro et al. 2005).
Oxalic acid (OA) is widely used for controlling
V. destructor because of its high efficacy (>90 %)
and low risk of hive contamination (Gregorc and
Planinc 2001,2002; Nanetti et al. 2003; Marinelli
et al. 2006; Rademacher and Harz 2006;
Bacandritsos et al. 2007). OA is applied to colo-
nies by spraying or trickling a solution of OA and
sugar-water over the bees or by evaporating crys-
tals with heat (Rademacher and Harz 2006).
Hovewer, most tests have been carried out during
a broodless period, and have reported more than
95 % efficacy (Higes et al. 1999; Charriere and
Imdorf 2002). So, mite mortality after treatment
with oxalic acid seems to be directly influenced by
the presence of brood because oxalic acid does not
kill the mites in sealed brood cells (Imdorf et al.
2003). Several reports agree on the use of oxalic
acid when no brood is present in winter (Barbero
et al. 1997). Its efficacy when brood is present is
around 60 % (Charrière 1997; Rademacher and
Harz 2006). Thus, the usefulness of the acid
seems limited in warm climates with a long brood
rearing period.
Taking into account that oxalic acid is a suit-
able compound for the control of V. d e s t r u c t o r in
broodfree colonies during the autumn and winter
period within the concept of Integrated Va r ro a
Control, the major challenge to scientists is to
develop a newformulation that can be used during
permanent brood presence in colonies of
A. mellifera . The main goal of this article was to
evaluate the efficacy of a new formulation based
on oxalic acid for when brood was present.
2. MATERIAL AND METHODS
Location of study. Summer field trials were carried out
during March and April 2010 in the experimental apiary
located near Bahía Blanca city (Buenos Aires,
Argentina) and during January and February 2011 in
the experimental apiary of The Charrúas Government
(Downtown of Charrúas, Entre Ríos, Argentina). The
average temperature recorded during this period in
Bahia Blanca city was 22 °C (range 933 °C), and in
Charrúas, the average was 31 °C (range 1442 °C).
Autumn field trials were carried out during May and
June 2013, in the experimental apiary of Arthropods
Laboratory (National University of Mar del Plata), near
Mar del Plata city. The average temperature recorded
during this period was 14 °C (range 220 °C).
Field trials. Forty-eight beehives were used to assess
product efficacy. Three experiments were conducted to
test the efficacy of a new formulation with oxalic acid
(Aluen CAP) made by Cooperativa de Trabajo Apícola
Pampero Ltda. In the first two trials, the treatment
efficacy was assessed during the summer season: one
trial was performed in Bahía Blanca (15 colonies divid-
ed in three groups of five colonies each one: a control
group BA^without treatment, a second control group
BB^with celulose strips embebed with glycerin and a
treatment group BC^with Aluen CAP) and the other in
Charrúas (19 colonies divided in two groups: one of
nine (control group) and the other of ten colonies (treat-
ment group,Aluen CAP)). In a third trial, the honey and
wax was tested for any OA residues (apiary located at
Mar del Plata, 14 colonies divided in two groups of 7
colonies: control and treatment groups). All colonies
used during trials were previously equalized for bee
population, brood area, and honey and pollen stores.
Hive bottoms specially adapted for the collection of
dead mites were placed in each colony. In each trial,
control groups without oxalic treatment were
established. Apiaries were selected based on geographic
locations at least 5 km away to avoid reinfestation
phenomena.
At the beginning of the experiment, the new formulation
were applied to the treatment group. Aluen Cap treatment
consists of four strips U-shaped. The matrix of these
strips is composed of cellulose (45 cm×3 cm×1.5 mm);
each one contains 10 g of OA mixed with 20 mL of
glycerin. Each strip was placed astride on frames 2, 4, 6,
and 8 of the brood chamber (Figure 1). Falling mites
were counted after 7, 14, 21, 28, 35, and 42 days
using the hive bottoms specially adapted for the col-
lection of dead mites. After the last count, the strips
were removed and at the same day, colonies received
four flumethrin strips according to the instructions of
the manufacturer (registered trade name: Flumevar®,
M. Maggi et al.
supplied by APILAB SA, Argentina, http://
www.apilab.com/flumevarcostarica.pdf). No resistance
phenomena to flumethrin had been reported previously
in these apiaries or in the region where assays were
performed. This treatment was left in the colonies for
45 days. Falling mites also were counted throughout
this period.
The efficacy of oxalic acid treatment was calculated as a
percentage: ((number of dead mites during oxalic acid
treatment)/(number of dead mites collected during the
treatment with OA and flumethrin))×100. The cumula-
tive mite fall after oxalic acid and flumethrin treatment
was assumed to be 100 %. Data on percent efficacy
were analyzed by analysis of variance (ANOVA) after
arcsine transformation in the case of percentages, to
reduce the heterogeneity of the variance.
Colony population development. The progress of the
hives treated with the oxalic acid was monitored prior to
each treatment application and also 1 week after the
acaricide application. As an example, at T
0
, the colonies
were inspected and the first treatment application was
applied. Any change was compared with the untreated
control hives. All other conditions (weather, nourish-
ment, and supervision) were identical. The parameters
to quantify the general state of the colonies during the
evaluation were as follows: number of combs fully
covered with bees and open and sealed brood areas.
These procedures were satisfactory to assess colony
development in previous research (Maggi et al. 2013;
Negri et al. 2015). All colonies were checked by visual
observations for dead brood bees and queens after treat-
ment. Data were analyzed by ANOVA to evaluate if OA
treatment produces changes in the variables measured.
Oxalic acid extraction from bees, honey, and bees-
wax. During the autumn assay, samples of honey, bees,
and wax were collected from colonies to detect possible
residues generated by oxalic acid treatment. The bees
were analyzed as a whole. Samples of each colony were
taken prior the oxalic treatment application (control,
timepoint T
0
) and 42 days after it (timepoint T
2
).
Samples were collected according to the protocol of
the European Working Group (2001) and were stored
at 80 °C until analysis. Ten grams of sample was then
diluted with 80 % ethanol. Beeswax sampled was heat-
ed in a water bath 62±2 °C for 15 min); the samples had
been previously acidified with 100 μL of pure HCl
(Merck®). Tubes were shaken vigorously for 1 min.
An aliquot of 50 μL was placed in a 2-mL vial and
Figure 1. The application of the new formulation Aluen CAP, an organic product containing oxalic acid in strips of
cellulose and glicerine to a hive.
Varroa destructor control using oxalic acid
evaporated until dried, using a nitrogen stream. The
extract was resuspended in 1 mL of ethanol: acid solu-
tion. Vials were placed in incubator at 50±2 °C for 5 h.
GF-FID analysis. A gas chromatograph HP 6890
with a FID detector and an autosampler for 100 samples
was used. For GF-FID analysis, an Austosampler
Agilent 7683 was used. The injector conditions were:
temperature, 100 °C; pressure, 12.45 p.s.i.; split ratio,
10:1; and gas saver, 20 mL/min. An Agilent Column
(30 m×0.25 m×0.25 μm HP-5MS Ultra Inerte (p/n
19091S-433UI)) was employed using Helium 5.0
(Praxair) in constant pressure mode (flow, 1 mL/min;
oven temperature, 50 ° C; injection volume, 1 μL;
detector: FID: temperature, 250 °C) as gas carrier. The
average recovery of the oxalic acid ranged from 87 to
110 %, and detection limits were honey: detection limit,
0.5 mg/kgquantification limit, 1 mg/kg; wax: detection
limit, 1.5 mg/kgquantification limit, 12 mg/kg; bees:
detection limit, 0.8 mg/kgquantification limit, 2 mg/kg.
Data were analyzed by ANOVA to evaluate if OA
treatment produces changes in the variables measured.
3. RESULTS
Efficacy. The efficacy of the treatment in Var r o a
control was determined by comparing the number
of falling mites recorded during the oxalic acid
treatment period with the total number of falling
mites recorded during the whole trial (including
the flumethrin treatment). Results are presented in
Table I. The average final efficacy in colonies
treated with the new oxalic acid formulation was
94 % (in the experimental apiary located near to
Charrúas dowtown, summer trial), 92.7 % (in
experimental apiary placed near to Bahia Blanca
city, summer trial) and 92.8 % (in experimental
apiary placed near to Mar del Plata city, autumn
trial). Final efficacy of the OA treatment had
significant differences to the control (P<0.05).
All trials had a low variability in the final efficacy
(range between 85.9±98.8 %). The highest mor-
tality for the three assays was recorded during the
first 22 days, with an average partial efficacy of
74.4 %.
Effects on colony population Colony population
parameters before and after treatment are shown
in Table II. For summer trials, treated colonies
(oxalic acid treatment) finished with an average
of 4.5 brood combs and 8.2 frames of bees. In the
autumn trial, colonies finished with 3.2 combs
covered with brood (open+sealed brood) and 8
frames covered with adult bees. Adverse effects
on the colonies (dead bee brood or queens) were
not detected during and after treatment. Adverse
effects on the bee populations were not detected in
the treated colonies in all three trials (P>0.05).
Oxalic acid detection from bees, honey and
beeswax. Table III summarizes the measure-
ments of oxalic acid in all samples taken
before and after treatment. The natural oxalic
acid content varied between 2.5 and
33.8 mg/kg. There was no increase in oxalic
acid content of honey, wax, and bees after
treatments, in all three trials (P>0.05). All
samples of bees and beeswax were negative
before and after the OA treatment.
4. DISCUSSION
The new formulation with oxalic acid as the
active ingredient, presents some advantages over
the current methods of organic acid treatments.
Polymer-cellulose matrices not only have all the
benefits of the oxalic acid liquid treatments but
also delay the release of OA so that it can remain
longer in the colony (Eguaras et al. 2003). This
reduces the number of visits to apiaries to reapply
OA treatments. In this study, we report a new
formulation based on oxalic acid with high acar-
icide activity against V. destructor. However, tak-
ing into account that mite fall was registered with
hive bottom specially adapted, the estimated effi-
cacy results not exclusively from the application
of the test medication but also from a combinatory
effect (natural mite mortality). Nonetheless,
strong differences were detected with the control
group, demonstrating an excellent acaricide activ-
ity of the new treatment.
Other research has demonstrated that good ef-
ficacy has been obtained using at least three ap-
plications of liquid oxalic acid per colony. In other
cases, three or more applications were not enough
for effective Varroa control (Rademacher and
M. Maggi et al.
Table I. Number of falling mites with oxalic acid treatment and flumethrin treatment for each of the three field assays.
Trial Treatment Colony No. of falling mites with treatment at day Total No. of falling
mites with
shock treatment
Efficacy of
formulation
(%)
Mean efficacy of
formulation (%)
7 1421283542
Summer trial
(Bahia Blanca
2010)
Oxalic acid
formulation
1 32 0 56 8 11 18 125 15 89.3 92.7
2 395 852 872 212 77 52 2460 40 98.4
3 55 97 123 89 94 80 538 44 92.4
4 211 228 221 44 68 54 826 65 92.7
5 107 30 97 139 86 10 469 61 88.5
Control I (strips
with glicerine)
0 04530012 42 22.2 20.6
2 2681113444 49 47.3
1 1310005 164 2.9
12 1253201638 106 26.4
1 1210037 169 3.9
Control II (strips
without glicerine)
11 00477523 77 23 28.9
12 00204612 84 12.5
13 201001013 60 17.8
14 2586121851 142 26.4
15 14 8 11 9 17 74 133 72 64.9
Summer trial
(Charrúas, Bahia
Blanca 2011)
Oxalic acid
formulation
16 54 185 144 4 15 1 403 21 95 94
17 0 282 46 14 0 1 343 14 96.1
18 8 695 595 15 3 3 1,319 16 98.8
19 19 186 112 18 3 4 342 1 99.7
20 3670105337615 96.1
21 0 915 348 41 1 2 1,307 0 100
22 88 620 340 815 253 221 2,337 70 97
23 42 42 93 2 3 1 183 20 90.1
24 26 10 33 1 3 0 73 23 76
25 46 67 49 22 5 0 189 18 91.3
Untreated 26 8 14 8 1 10 0 41 2032 1.9 5.2
27 2069113251 1295 3.8
Varroa destructor control using oxalic acid
Tab le I (continued)
Trial Treatment Colony No. of falling mites with treatment at day Total No. of falling
mites with
shock treatment
Efficacy of
formulation
(%)
Mean efficacy of
formulation (%)
7 1421283542
28 163100222 592 3.6
29 625620176 1920 3.8
31 19211317 121 12.3
32 20 11 4 5 16 1 57 897 5.97
33 5492008192 1120 7.5
34 81692026 796 3.1
35 28 6 8 11 13 0 66 1234 5.1
Autumn trial
(Mar del Plata
2013)
Oxalic acid
formulation
36 3448271001109 92.4 92.8
37 120 106 24 1 0 0 251 21 92.2
38 56 214 56 0 2 0 328 13 96.1
39 12472220083 1 98.8
40 87 119 17 1 1 2 227 42 84.3
41 2042214271 3 95.9
42 4112900062 7 89.8
Untreated 43 1301207 246 2.7 13.7
44 0100416 326 1.8
45 00190010 128 7.2
40 00720211 147 6.9
446 283122027 56 32.5
47 3140008 16 33.3
48 13401312 91 11.6
M. Maggi et al.
Harz 2006). Also, during the summer season, the
efficacy obtained by liquid treatments is reduced
as oxalic acid does not kill the mites in sealed
brood cells. In addition, Hatjina and Haristos
(2005) have shown a detrimental effect on brood
development plus low effectiveness using the
trickling method of OAwhen open brood is pres-
ent. They suggest that this method is not as safe as
has been reported in the past.
Marinelli et al. (2006) evaluated the efficacy of
cellulose strips with oxalic acid in comparison
with other oxalic acid treatments (trickling and
vaporization methods). In spring trials, the effec-
tiveness ofthe cellulose strips was not statistically
different from the natural fall of Va r ro a . Similarly,
the autumn trials had the same results. However,
when spraying, trickling, and vaporizing oxalic
acid, good control of Varr o a was seen in central
Italy. They conclude that the unsatisfactory effi-
cacy of cellulose strips versus the good control
results of trickling and vaporization could be ex-
plained by the high acidity of the oxalic acid water
solutions. A pH around 1 may be responsible for
the best oxalic acid activity against the mites.
Here, we show that one application of the Aluen
Cap formulations is enough to have good mite
control even with the presence of bee brood. In
this study, the oxalic acid formulation had a high
efficacy and it was possible to keep low Va r ro a
prevalence indices in the colonies. The matrix of
the OA strip may help to keep an adequate acid
concentration inside the colonies for a long time
(42 days). In addition, the combination of glycerin
with AO could help to maintain the drug for a
longer time inside the beehive and consequently
with mites (including those that are emerging
from brood cells). As it was reported by Segur
and Oberstar (1951), glycerin possesses a high
viscosity. This chemical property would help to
disseminate the acid among bees during a longer
time in comparison with other strip formulations
without glycerin, increasing its efficacy (these
hypotheses should be examined in later studies).
During the season when this work was done, the
temperature range was 242 °C, and in the three
trials, there were no problems with the higher
temperatures in the colonies.
This new product offers a good alternative for
Varr o a control as it does not have the two most
Table II. Colony population parameters before and after treatment for the three trials.
Colony population
parameter
Treatment Apiary I (Bahía Blanca) Apiary II (Charrúas, Entre Ríos) Apiary III (Mar del Plata)
Before treatment After treatment Before treatment After treatment Before treatment After treatment
Number of combs covered
with adult bees
OA 9.8a±0.4 (5) 8.6a±0.4 (5) 8.4a±2.2 (10) 7.9a±2.1 (10) 8.7a±1.2 (7) 8a±0.5 (7)
Control 9.8a±0.4 (10) 8.8a±0.4 (10) 7.4b±1.6 (9) 7.4b±1.7 (9) 9a±0.4 (7) 8.6a±0.2 (7)
Number of combs covered
with brood
OA 6.4c±2 (5) 2.9d±.2 (5) 4.6d±1.4 (10) 4.7d±1.8 (10) 4.6d±0.8 (7) 3.2d±0.4 (7)
Control 5.8c±2.4 (10) 4.1d±1.7 (10) 4.8d±1.3 (9) 5d±1 (9) 4.7d±0.3 (7) 3.1d±0.3 (7)
Mean±standard deviations. The number of colony sampled are enclosed in parentheses. Uppercase (ad) letters indicate statistical differences among treatments (ttest, P<0.05)
Varroa destructor control using oxalic acid
frequent disadvantages of organic products used
for mite control. First, it is easy to use, safe for
beekeepers, and presents low variability between
colonies in its efficacy. Second, it does not present
a risk to colony development and so it can be used
to safely reduce the damage done by Va rr o a mites
even during the summer season.
In Argentina (as in many other parts of the
world), the use of synthetic acaricides is being
restricted due to the emergence of resistant mite
populations (Maggi et al. 2009,2010a,2011;
Sammataro et al. 2005), as well as honey and
wax contamination (Bogdanov et al. 2003;
Wallner 1999;Medicietal.2015). Oxalic acid is
a natural constituent of honey; values between 8
and 17,000 mg/kg have been found in different
honeys (Mutinelli et al. 1997;Bernardiniand
Gardi 2001;Bogdanovetal.2002).
Most vegetables contain much higher amounts
of oxalic acid than honey so the total daily intake
is negligible. Thus, from a nutritional point of
view, oxalic acid should, like formic acid, also
have a generally recognized as safe (GRAS) sta-
tus. Moreover, no significant residues are expect-
ed after oxalic acid treatments as demonstrated in
our research. Indeed, there is no risk of honey
residues after all types of oxalic acid treatments
(Radetzki 1994; Mutinelli et al. 1997; Del Nozal
et al. 2000; Bernardini and Gardi 2001;Radetzki
and Barmann 2001; Bogdanov et al. 2002).
Spraying and trickling of oxalic acid are accept-
ed for use against V. d e s t r u c t o r in most European
countries and are widely used by beekeepers
throughout Europe (Charriere and Imdorf 2002).
This new formulation is not dangerous for the user
or for the bee colony. Thus, Aluen CAP could be a
valid alternative for Varr oa mite control.
ACKNOWLEDGMENTS
The authors would like to thank the Universidad
Nacional de Mar del Plata (UNMDP) and Consejo
Nacional de Investigaciones Científicas y Técnicas
(CONICET). This research was supported by a grant
of ANPCyT, PICT 2011 to M.M.
Une nouvelle formulation de l'acide oxalique appliquée
dans les colonies d' Apis mellifera pour lutter contre
Varroa destructor,enprésenceducouvain
Acari / lutte antiparasitaire / couvain d'abeille /
Argentine
Eine neue Oxalsäure-Formulierung zur Bekämpfung
von Varroa destructor in Völkern von Apis mellifera
mit Brut
Varroa destructor / Bekämpfung / Oxalsäure /
Bienenbrut / Argentinien
REFERENCES
Bacandritsos, N., Papanastasiou, I., Saitanis, C., Nanetti,
A., Roinioti, E. (2007) Efficacy of repeated trickle
applications of oxalic acid in syrup for varroosis con-
trol in Apis mellifera : Influence of meteorological
conditions and presence of brood. Vet. Parasitol. 148 ,
174178
Table III. Oxalic acid residues in wax, bees and honey after treatment.
Treatment Matrix Before treatment After treatment
Control Wax 0 (7) 0 (7)
Bees 0 (7) 0 (7)
Honey 14.2
b
±11.6 (7) 25.6
c
±12.5 (7)
OA Wax 0 (7) 0 (7)
Bees 0 (7) 0 (7)
Honey 7.5
a
±5.2 (7) 17.3
b
±15 (7)
Mean±standard deviations (SD) and number of samples (n). Honey: detection limit, 0.5 mg/kgquantification limit, 1 mg/kg; wax
detectionlimit, 1.5 mg/kgquantification limit, 12 mg/kg; bees: detection limit, 0.8 mg/kgquantification limit, 2 mg/kg.Uppercase
letters (ac) indicate statistical differences among treatments (ttest, P<0.05)
M. Maggi et al.
Barbero, R., Panella, F., Bonizzoni, L. (1997) Ácido
oxálico y el tratamiento de limpieza radical de otoño-
invierno. Vida Apícola 85 ,813
Bernardini, M., Gardi, T. (2001) Influence of acaricide
treatments for Varroa control on the quality of honey
and beeswax. Apitalia 28(78), 2124
Bogdanov, S., Charriere, J., Imdorf, A., Kilcheman,
V., Fluri, P. (2002) Determination of residues in
honey after treatments under field conditions with
formic and oxalic acid. Apidologie 33 (4), 399
409
Bogdanov, S., Kilchenmann, V., Butikofer, U. (2003) De-
termination of acaricide residues in beeswax: Collabo-
rative study. Apiacta 38 (3), 235245
Charrière, J.D. (1997) Potentiel et limites de lemploi des
acides organiques. Sanitaire 161,219227
Charrière, J.D., Imdorf, A. (2002) Oxalic acid treat-
ment by trickling against Varroa de structor :rec-
ommendations for use in central Europe and un-
der temperate climate conditions. Bee World
83 (2), 5160
Del Nozal, M., Bernal, J., Diego, J., Gomez, L.,
Ruiz, J., Higes, M. (2000) Determination of ox-
alate, sulfate and nitrate in honey and honeydew
by ion-chromatography. J. Chromat. A 881 ,629
638
Eguaras, M., Ruffinengo, S. (2006) Estrategias para el
control de Var r o a . Ed. Martin, Mar del Plata.
Eguaras, M., del Hoyo, M., Palacio, A., Ruffinengo, S.,
Bedascarrasbure, E. (2001) A new product with formic
acid for Varroa jacobsoni control. I Efficacy. J. Vet.
Med., (Series b), 48 ,1114
Eguaras,M.,Palacio,A.,Faverin,C.,Basualdo,M.,
Del Hoyo, M., Velis, G., Bedascarrasbure, E.
(2003) Efficacy of formic acid in gel for Var ro a
control in Apis mellifera : importance of the dis-
penser position inside the hive. Vet. Parasitol.
111 ,241245
Gregorc, A., Planinc, I. (2001) Acaricidal effect of oxalic
acid in honeybee (Apis mellifera) colonies. Apidologie
32 ,333340
Gregorc, A., Planinc, I. (2002) The control of Varroa
destructor using oxalic acid. Vet. J 163 ,306310
Hatjina, F., Haristos, L. (2005) Indirect effects of oxalic
acid administered by trickling method on honey bee
brood. J. Apic. Res. 44 (4), 172174
Higes, M., Meana, A., Suárez, M., Llorente, J. (1999)
Negative long-term effects on bee colonies treated with
oxalic acid against Varroa jacobsoni Oud. Apidologie
30 ,289292
Imdorf, A., Charrière, J.D., Kilchenmann, V., Bogdanov,
S., Fluri, P. (2003) Alternative strategy in central Eu-
rope for the control of Varroa destructor in honey bee
colonies. Apiacta 38 ,258278
Maggi, M., Ruffinengo, S., Damiani, N., Sardella, N.,
Eguaras, M. (2009) A first detection of Va rr oa
destructor resistance to coumaphos in Argentina.
Exp. App. Acarol. 47 (4), 317320
Maggi, M., Ruffinengo, S., Negri, P., Eguaras, M. (2010a)
Resistance phenomena to amitraz from populations of
the ectoparasitic mite Varroa destructor of Argentina.
Parasitol. Res. 107 (5), 11891192
Maggi, M., Ruffinengo, S., Gende, L., Sarlo, G., Bailac, P.,
Ponzi, M., Eguaras, M. (2010b) Laboratory evalua-
tions of Syzygium aromaticum (L.) Merr. et Perry
essential oil against Varroa destructor . J. Ess. Oil
Res 22 ,119122
Maggi, M., Ruffinengo, S., Mendoza, Y., Ojeda, P.,
Ramallo, G., Floris, I., Eguaras, M. (2011) Suscepti-
bility of Varroa destructor (Acari: Varroidae) to syn-
thetic acaricides in Uruguay: Va rr o a mitespotential to
develop acaricide resistance. Parasitol. Res. 108 ,815
821
Maggi, M., Negri, P., Plischuk, S., Szawarski, N., De
Piano, F., De Feudis, L., Eguaras, M., Audisio,
C. (2013) Effects of the organic acids produced
by a lactic acid bacterium in Apis mellifera
colony development, Nosema ceranae control
and fumagillin efficiency. Vet. Microbiol. .
doi:10.1016/j.vetmic.2013.07.030
Marinelli, E., Formato, G., Vari, G., De Pace, F.M. (2006)
Va r ro a control using cellulose strips soaked in oxalic
acid water solution. Apiacta 41 ,5459
Medici, S., Maggi, M., Sarlo, E., Ruffinengo, S., Marioli, J.,
Eguaras, M. (2015) Presence of syntethic acaricides in
beeswax and its relationship with the development of
resistance in Varroa destructor. J. Apic. Res, in press
Mutinelli, F., Baggio, A., Capolongo, F., Piro, R., Prandin,
L., Biaison, L. (1997) A scientific note on oxalic acid
by topical application for the control of varroosis.
Apidologie 28 (6), 461462
Nanetti, A., Büchler, R., Charriere, J.-D., Fries, I., Helland,
S., Imdorf, A., Korpela, S., Kristiansen, P. (2003)
Oxalic acid treatments for Var ro a control (review).
Apiacta 38,8
187
Negri, P., Maggi, M., Ramirez, L., De Feudis, L., Szwarski,
N., Eguaras, M., Lamattina, L. (2015) Abscisic acid
enhances the immune response in Apis mellifera and
contributes to the colony fitness. Apidologie 46(4),
542557
Rademacher, E., Harz, M. (2006) Oxalic acid for the con-
trol of varroosis in honey bee colonies areview.
Apidologie 37 ,98120
Radetzki, T. (1994) Oxalsäure, eine weitere organische
Säure zur Varroabehandlung. Allgemeine Deutsche
Imkerzeitung 28 (12), 1115
Radetzki, T., Bärmann, M. (2001) Verdampfungsverfahren
mit Oxalsäure. Feldversuch mit 1509 Völkern im Jahr
2000. Allgemeine Deutsche Imkerzeitung 35 (9), 20
23
Ruffinengo, S., Maggi, M., Fuselli, S., De Piano, F., Negri,
P., Brasesco, C., Satta, A., Floris, I., Eguaras, E. (2014)
Bioactivity of microencapsulated essentials oils and
perspectives of their use in the control of Var roa
destructor. Bull. Insectol. 67(1), 8186
Varroa destructor control using oxalic acid
Sammataro,D.,Untalan,P.,Guerro,F.,Finley,J.
(2005) The resistance of Va rro a mites (Acari:
Varroidae) to acaricides and the presence of es-
terase.Int.J.Acarol.31 (1), 6774
Segur, J., Obrstar, H. (1951) Viscosity of glycerol and its
aqueous solutions. Ind. Eng. Chem. 43 (9), 21172120
Wallner, K. (1999) Varroacids and their residues in bee
products. Apidologie 30 ,235248
M. Maggi et al.
... Oxalic acid is not known to have a negative effect on honey bee health, hive development, or behaviour [11][12][13][14][15][16][17][18][19]. Oxalic acid is a natural compound in honey [20] and there is a low risk of accumulation in wax and honey [13,21,22]. There is no known resistance of Varroa destructor to oxalic acid to date [23]. ...
... "Bottom board sampling" means counting fallen mites before or after treatment on the bottom board of the hive. To guarantee the most comprehensive count and to avoid reinfestation, some studies used protective nets [60] or sticky bottom boards [1,[15][16][17][18][19]22,[32][33][34]38,[42][43][44][45]47,51,[55][56][57]. ...
... The effectiveness of a treatment can also be calculated in different ways. Some publications did not describe the calculation method exactly, but most of the studies divided the counted mites during the tested treatment by the total mite number, counted during the control treatment with another substance and the tested substance [14,22,36,38,40,43,44,47,63,66,70,75,77,81,[83][84][85][86][87] or calculated as a percentage of infested brood cells or mite number on bees after treatment compared to the initial number of infested brood cells or mite number on bees [46,59,64,76,82,88]. Overall, 89% of the efficacy values were determined by counting mites by bottom board sampling and dividing the number of counted mites during the tested treatment by the total mite number. ...
Article
Full-text available
As Varroa destructor is one of the most important pathogens of Apis mellifera, there are numerous treatment methods, including pharmaceutical and biotechnological approaches. However, the rapid development of resistance to synthetic acaricides by Varroa destructor has become a significant concern. To date, there have been no investigations into the development of resistance to organic acids. This review examines the potential risk of oxalic acid resistance development by evaluating literature sources from the past 30 years following the PRISMA 2020 guidelines. Median annual efficacies are calculated and reviewed over time for several application methods. An efficacy higher than 70% is determined as not resistant. Independent of the method of application, no resistance development can be observed, although there are some outliers of the annual median. These outliers can be explained by brood status or study setting. However, the result is limited by the low number of efficacy values, and further standardised studies are needed.
... Oxalic acid (OA), an organic acid, has been used for decades to control varroa mites, with a reported efficacy of approximately 90% (Nanetti et al., 2006;Rademacher and Harz, 2006;Maggi et al., 2016). The most used application methods are: (1) dissolving OA crystals in a sugar and water solution and trickling the solution between the frames (Rademacher and Harz, 2006;Al Toufailia et al., 2015); (2) fumigating the hives with vaporized OA (Rademacher and Harz, 2006;Al Toufailia et al., 2015;Jack et al., 2020;Jack et al., 2021;Berry et al., 2022); and (3) inserting slow-release OA-glycerin strips into the brood chamber (Maggi et al., 2016),which is currently under regulatory review for approval for use in Canadian beekeeping. ...
... Oxalic acid (OA), an organic acid, has been used for decades to control varroa mites, with a reported efficacy of approximately 90% (Nanetti et al., 2006;Rademacher and Harz, 2006;Maggi et al., 2016). The most used application methods are: (1) dissolving OA crystals in a sugar and water solution and trickling the solution between the frames (Rademacher and Harz, 2006;Al Toufailia et al., 2015); (2) fumigating the hives with vaporized OA (Rademacher and Harz, 2006;Al Toufailia et al., 2015;Jack et al., 2020;Jack et al., 2021;Berry et al., 2022); and (3) inserting slow-release OA-glycerin strips into the brood chamber (Maggi et al., 2016),which is currently under regulatory review for approval for use in Canadian beekeeping. In Canada, the most widespread application method is OA vaporization (Claing et al., 2023), in which crystals of oxalic acid dihydrate are heated above 100°C using a specialized application device. ...
Article
Full-text available
Introduction The honey bee ectoparasitic mite, Varroa destructor , is one of the main causes of honey bee colony loss worldwide. Synthetic acaricides are the most commonly used strategy for varroa control, however, resistance to these acaricides has emerged. Consequently, the use of organic acids for varroa control is gaining more interest among beekeepers. For example, oxalic acid (OA) is a natural compound that has been shown to be an effective acaricide against varroa mites, however, the potential toxicity of OA to adult bees and queens is poorly understood. The objective of the study was to evaluate the toxicity of incremental doses of vaporized OA on honey bee workers and queens. Methods We exposed 32 colonies to incremental doses (0, 5, 10 or 20 g per colony) of vaporized OA once per week over four consecutive weeks and we monitored the acute and long-term toxicity. We investigated the short-term effects of OA administration by evaluating adult bee mortality, brood production, and population size. Next, we evaluated the long-term effects of OA application on both worker bees and queens. Regarding workers, we investigated their ability to rear new queens. As for queens, we measured acceptance, performance, and sperm quality. Results We found that colonies treated with 20 g OA (20 times the label dose) had a statistically significant increase in worker bee mortality, with a non-significant, 23% decrease in brood relative to controls. No significant differences were observed in queen performance nor sperm quality. Discussion We found that repeated application of vaporized OA, at up to 20 times the label dose, had no significant short-term nor long-term, negative effects on colony or queen health, with the exception of a short-term increase in adult bee mortality in the 20 g OA-treated group. The results of this study support the safety of higher-than-label doses of OA for honey bee colonies. The observed increase in adult bee mortality in the 20 g OA dose group in this study suggests that OA doses should be maintained below 20 g per brood chamber.
... To defeat V. destructor and help honey bees, organic acids naturally present in honey like formic, oxalic and lactic acids are popular treatments used by beekeepers 8 . However, their efficacy is uneven worldwide [9][10][11] demonstrating that key elements are still not well understood such as their mechanism of action on V. destructor. Some studies showed that formic acid interferes with the cellular respiratory chain 12,13 while oxalic acid is supposed to create crystals penetrating the arolia of the mites 14 . ...
Article
Full-text available
Lactic acid is an alternative treatment to hard chemicals against Varroa destructor, the parasitic mite of the Western honey bee Apis mellifera. This soft acaricide is used only for small apiaries due to its laborious administration. However, the mode of action of this honey bee medication remains unknown. Previous studies showed that a direct contact between the arolia of V. destructor and lactic acid altered their morphology and led to an impairment of grip. Yet, there is no evidence for the way of action of lactic acid in a realistic in-hive scenario, i.e. after an indirect exposure of the mite through honey bees. We investigated the nature of lactic acid activity in the hive treatment context. The local and/or systemic way of action of this honey bee treatment against V. destructor was studied through a behavioural and toxicological approach at the individual level. On one hand, we confirmed the altered morphology for the arolia of mites and studied the evolution of the process over time. On the other hand, we found that haemolymph contaminated with lactic acid did not kill the feeding parasitic mite. These findings support a local mode of action. In order to unravel the sequence of events leading to the local contact between the acid and the mite on bees, we also documented the olfactory valence of lactic acid for A. mellifera and V. destructor. This work provides a new comprehension of lactic acid activity against the parasitic mite through honey bee exposure and gives new opportunities for control strategies against V. destructor.
... Natural products (NPs) and their derivatives present a more appealing alternative to synthetic drugs [27][28][29][30][31]. NPs have been shown to have important pharmacological properties that have been validated in experimental studies in human and veterinary medicine [30,[32][33][34][35]. Compounds belonging to the broad category of NPs are also attractive because they are often inexpensive and pose fewer health problems for both humans and honeybees [36,37]. As a result, beekeepers are increasingly interested in their use [38]. Because of this, the usage of organic acids and EOs is growing. ...
Article
Full-text available
Simple Summary Varroa destructor acariasis is currently the main threat to the health and survival of honeybee colonies. Chemicals are often used to control this parasitosis. However, overuse and misuse over the years has allowed the mite to acquire resistance to synthetic active ingredients. In this scenario, it is vital to search for alternative therapeutic solutions. Essential oils (EOs) are a promising therapeutic choice, as they have a complex chemical composition, making them unlikely to be prone to the development of resistance. In addition, they are easily degraded in the environment and have a low toxicity for humans, characteristics that make them particularly attractive. In this research study, four EOs from the Lamiaceae family, isolated from botanical species native to the Calabria region, Southern Italy, were tested in contact toxicity tests against V. destructor. Origanum vulgare subsp. viridulum, Thymus capitatus and Thymus longicaulis, used at 2 mg/mL, were found to have a high level of efficacy, neutralizing (dead + inactivated) 94%, 92% and 94% of parasites, respectively. These EOs could be chosen and tested in subsequent in vivo studies. Abstract The most significant ectoparasitic mite of honeybees, Varroa destructor, has a detrimental effect on bee health and honey output. The principal strategy used by the control programs is the application of synthetic acaricides. All of this has resulted in drug resistance, which is now a major worry for beekeeping. As a result, research on alternate products and techniques for mite management is now required. The aim of this study was to determine whether essential oils (EOs) extracted from botanical species of Lamiacae, typical of the Calabria region of Southern Italy, could reduce the population of the mite V. destructor. Among the best-known genera of the Lamiaceae family are oregano, rosemary and thyme, whose EOs were employed in this study. By steam distillation, the EOs were extracted from Origanum vulgare subsp. viridulum (Martrin-Donos) Nyman, Thymus capitatus Hoffmanns. and Link, Thymus longicaulis C.Presl and Salvia rosmarinus Schleid. plant species harvested directly on the Calabrian territory in their balsamic time. Each EO went to the test in vitro (contact toxicity) against V. destructor. Fifty adult female mites, five for each EO and the positive and negative control, were used in each experimental replicate. The positive controls comprised five individuals treated to Amitraz dilute in acetone, and the negative controls included five individuals exposed to acetone alone. To create the working solution to be tested (50 μL/tube), the EOs were diluted (0.5 mg/mL, 1 mg/mL, 2 mg/mL and 4 mg/mL) in HPLC-grade acetone. After 1 h of exposure, mite mortality was manually assessed. Origanum vulgare subsp. viridulum, Thymus capitatus and Thymus longicaulis were the EOs with the highest levels of efficiency at 2 mg/mL, neutralizing (dead + inactivated), 94%, 92% and 94% of parasites, respectively. Salvia rosmarinus EO gave a lower efficacy, resulting in a percentage of 38%. Interestingly, no adverse effects were highlighted in toxicity tests on honeybees. These results show that these OEs of the Lamiaceae family have antiparasitic action on V. destructor. Therefore, they could be used, individually or combined, to exploit the synergistic effect for a more sustainable control of this parasite mite in honeybee farms.
... Organic acids, such as crystallized oxalic acid (OA) dihydrate, have been used for decades in Europe and Canada (Johnson et al. 2010) since they have proven extremely effective at killing V. destructor with little evidence for mite resistance (Adjlane et al. 2016, Maggi et al. 2016. Recently, OA was approved for use even while honey for human consumption is on colonies (EPA Reg. ...
Article
Full-text available
The ectoparasitic mite, Varroa destructor (Anderson and Trueman), is the leading cause of western honey bee colony, Apis mellifera (L.), mortality in the United States. Due to mounting evidence of resistance to certain approved miticides, beekeepers are struggling to keep their colonies alive. To date, there are varied but limited approved options for V. destructor control. Vaporized oxalic acid (OA) has proven to be an effective treatment against the dispersal phase of V. destructor but has its limitations since the vapor cannot penetrate the protective wax cap of honey bee pupal cells where V. destructor reproduces. In the Southeastern United States, honey bee colonies often maintain brood throughout the year, limiting the usefulness of OA. Prior studies have shown that even repeated applications of OA while brood is present are ineffective at decreasing mite populations. In the summer of 2021, we studied whether incorporating a forced brood break while vaporizing with OA would be an effective treatment against V. destructor. Ninety experimental colonies were divided into 2 blocks, one with a brood break and the other with no brood break. Within the blocks, each colony was randomly assigned 1 of 3 treatments: no OA, 2 g OA, or 3 g OA. The combination of vaporizing with OA and a forced brood break increased mite mortality by 5× and reduced mite populations significantly. These results give beekeepers in mild climates an additional integrated pest management method for controlling V. destructor during the summer season.
... Chemical control against Varroa mites can be both effective and low risk in terms of selecting for resistance. However, there are severe restrictions in some countries to use certain chemicals (Milani 2001;Maggi et al. 2016). Accordingly, the success and viability of the global apicultural industry is based on the use of only a few compounds for the control of Varroosis, i.e., the organophosphate coumaphos, some pyrethroids and the formamidine amitraz (Ziegelmann et al. 2018). ...
Article
Full-text available
A 2-year field experiment was performed to test lithium chloride, LiCl, application in a normal beekeeping management system. The effect of LiCl on bee larval mortality, beehive weight (honey production) and Varroa mite mortality were tested. Spectrometric quantification of Li on honey and the larval body were made to test the effectiveness of the presence of LiCl. Li was detected in bee larval bodies and in honey over 2 years, from 2018 to 2019. According to the results, no effect of LiCl on mite mortality or bee larval mortality was detected in the first year of application. By assessing the weight variation of beehives, only one LiCl-treated hive showed a significantly higher weight, whereas no other differences were detected between treatments and control. The same trend seen in 2018 was repeated in 2019, while a total bee larval mortality was observed after the first LiCl application, and still no differences in Varroa mite mortality were observed. According to these results, it was concluded that LiCl has no effect on Varroa mite mortality during normal beekeeping practice; furthermore, the recommended amount of treatment (25 mM) had a lethal effect (i.e., total mortality) on larvae following repeated applications.
... Colonies also received oxalic acid for varroa control, but strips were used instead of liquid oxalic acid in this assay. Strips are safe for colony development, and effective against varroa, even in the presence of brood (Maggi et al., 2016). ...
Article
Honey bee colonies form a complex superorganism, with individual and social immune defences that control overall colony health. Sometimes these defences are not enough to overcome infections by parasites and pathogens. For that reason, several studies have been conducted to evaluate different strategies to improve honey bee health. A novel alternative that is being studied is the use of beneficial microbes. In a previous study, we isolated and characterised bacterial strains from the native gut microbiota of honey bees. Four Apilactobacillus kunkeei strains were mixed and administered in laboratory models to evaluate their potential beneficial effect on larvae and adult bees. This beneficial microbe mixture was safe; it did not affect the expression of immune-related genes, and it was able to decrease the mortality caused by Paenibacillus larvae infection in larvae and reduced the Nosema ceranae spore number in infected adult honey bees. In the present study, we aimed to delve into the impact of the administration of this beneficial microbe mixture on honey bee colonies, under field conditions. The mixture was administered in sugar syrup using lyophilised bacterial cells or fresh cultures, by aspersion or sprayed and feeder, once a week for three consecutive weeks, in autumn or spring 2015, 2017 and 2019. Colony strength parameters were estimated before the administration, and one and three months later. Simultaneously different samples were collected to evaluate the infection levels of parasites and pathogens. The results showed that administering the beneficial microbe mixture decreased or stabilised the infection by N. ceranae or Varroa destructor in some trials but not in others. However, it failed to improve the colony’s strength parameters or honey production. Therefore, field studies can be a game-changer when beneficial microbes for honey bees are tested, and meticulous studies should be performed to test their effectiveness.
Article
Full-text available
Despite the use of various integrated pest management strategies to control the honey bee mite, Varroa destructor, varroosis remains the most important threat to honey bee colony health in many countries. In Canada, ineffective varroa control is linked to high winter colony losses and new treatment options, such as a summer treatment, are greatly needed. In this study, a total of 135 colonies located in 6 apiaries were submitted to one of these 3 varroa treatment strategies: (i) an Apivar® fall treatment followed by an oxalic acid (OA) treatment by dripping method; (ii) same as in (i) with a summer treatment consisting of formic acid (Formic Pro™); and (iii) same as in (i) with a summer treatment consisting of slow-release OA/glycerin pads (total of 27 g of OA/colony). Treatment efficacy and their effects on colony performance, mortality, varroa population, and the abundance of 6 viruses (acute bee paralysis virus [ABPV], black queen cell virus [BQCV], deformed wing virus variant A [DWV-A], deformed wing virus variant B [DWV-B], Israeli acute paralysis virus [IAPV], and Kashmir bee virus [KBV]) were assessed. We show that a strategy with a Formic Pro summer treatment tended to reduce the varroa infestation rate to below the economic fall threshold of 15 daily varroa drop, which reduced colony mortality significantly but did not reduce the prevalence or viral load of the 6 tested viruses at the colony level. A strategy with glycerin/OA pads reduced hive weight gain and the varroa infestation rate, but not below the fall threshold. A high prevalence of DWV-B was measured in all groups, which could be related to colony mortality.
Article
Full-text available
Oxalic acid (OA) is a popular miticide used to control Varroa destructor (Mesostigmata: Varroidae) in western honey bee (Apis mellifera L.) (Hymenoptera: Apidae) colonies. Our aim was to investigate which method of OA application (dribbling, fogging, or vaporizing) was the most effective at reducing V. destructor infestations (Experiment 1) and to improve upon this method by determining the treatment interval that resulted in the greatest V. destructor control (Experiment 2). We used the product Api-Bioxal (97% OA) and maintained 40 honey bee colonies (10/treatment) in both experiments. In Experiment 1, the treatments included (i) dribbling 50 ml of 3% OA solution, (ii) vaporizing 4 g of solid OA, (iii) using an insect fogger supplied with 2.5% OA dissolved in ethyl alcohol, and (iv) an untreated control. After 3 weeks, only the vaporization method reduced V. destructor infestations (from 9.24 mites/100 bees pretreatment to 3.25 mites/100 bees posttreatment) and resulted in significantly increased brood amounts and numbers of adult bees over those of the controls. In Experiment 2, all colonies were treated with 4 applications of OA via vaporization at a constant concentration of 4 g OA/colony. In this experiment, the groups were separated by treatment intervals at either 3-, 5-, or 7-day intervals. We observed that 5- and 7-day treatment intervals significantly reduced V. destructor populations from pretreatment levels over that of the controls and 3-day intervals. Our data demonstrate the efficacy of OA in reducing V. destructor infestation, particularly vaporizing 4 g every 5–7 days as the most effective method of application.
Article
Full-text available
A significant amount of researcher and practitioner effort has focused on developing new chemical controls for the parasitic Varroa destructor mite in beekeeping. One outcome of that has been the development and testing of “glycerol–oxalic acid” mixtures to place in colonies for extended periods of time, an off-label use of the otherwise legal miticide oxalic acid. The majority of circulated work on this approach was led by practitioners and published in nonacademic journals, highlighting a lack of effective partnership between practitioners and scientists and a possible failure of the extension mandate in beekeeping in the United States. Here, we summarize the practitioner-led studies we could locate and partner with a commercial beekeeper in the Southeast of the United States to test the “shop towel–oxalic acid–glycerol” delivery system developed by those practitioners. Our study, using 129 commercial colonies between honey flows in 2017 split into 4 treatment groups, showed no effectiveness in reducing Varroa parasitism in colonies exposed to oxalic acid–glycerol shop towels. We highlight the discrepancy between our results and those circulated by practitioners, at least for the Southeast, and the failure of extension to support practitioners engaged in research.
Article
Full-text available
The effects of oxalic acid administered by the trickling method on brood development of honey bee colonies were evaluated (a) by observing the development of marked cells of young (< 3 days old) and old (> 3 days old) larvae, and (b) by measuring the area of open brood for several weeks post application. Oxalic acid, dissolved in a 50% sugar solution, with an end concentration of 3% w/v oxalic acid, was applied twice by the trickling method during summer to 10 colonies. A high percentage of young (12.6% and 9.5%) and old honey bee larvae (10.6% and 5.6%) were removed from their cells after the first and second oxalic acid applications, respectively. The surface of the open brood area was also reduced by 17.5% after the two oxalic acid applications and stayed low for about two months. For the same period of time the open brood area in 10 control colonies increased by 34.5%. The two oxalic acid applications removed 60 ± 12% of varroa mites adhering to adult honey bees, while the natural fall of mites measured in control colonies (for a period of 40 days) was 32 ± 4%. Combining the detrimental effect on brood development with the low relative effectiveness on varroa removal, oxalic acid application by the trickling method when open brood is present is not as safe as has been regarded in the past. Consideration needs to be given to the use of different sugar and oxalic acid concentrations in the treatment solution in order to minimize its adverse effects on open honey bee brood.
Article
Full-text available
Attractant/repellent and acaricidal effects of two microencapsulated essential oils, Acantholippia seriphioides (A. Gray) Mold. and Schinus molle L., were evaluated on the ectoparasitic mite Varroa destructor Anderson et Truemann using complete exposure and evaporation tests. Mites and honey bees (10 specimens of each per dish) were introduced in Petri dishes having different microencapsulated essential oil doses (0.25, 0.5 and 1 g). Mite and honey bee mortality were registered at 24, 48 and 72 hrs. An attractant/repellent test was performed using a device with two tubes of virgin wax closed on one side. Microencapsulated essential oils were placed at the end of one of the tubes. One mite was placed inside a tube with no oil and its position was observed after 90 min. Microencapsulated oils differed in the level of toxicity caused to V. destructor, A. seriphioides oil toxicity was higher than S. molle oil. Negative effects were registered on honey bees when they were completely exposed to microencapsulated oil of A. seriphioides. Microencapsulated oil of S. molle had attractant properties. None of the two microencapsulated oils tested had repellent effects on mites. This study might be a starting point for future researches of microencapsulated essential oils, as they offer a good alternative in the control of varroatosis.
Article
Full-text available
Treatment with oxalic acid against Varroa destructor in broodless colonies is very effective. The administration of this organic acid by trickling a solution onto the colony is up to now the easiest method of application. The formulation of this solution has however to be optimized to reach maximum efficacy without side effects on the bees. Results for central European conditions are presented in this article together with a small review of the subject.
Article
Full-text available
The primary food of adult honey bees (Apis mellifera) is honey prepared by bees from nectar, provided by plants in order to stimulate the bee’s pollination service. Nectar consists of carbohydrates, amino acids and water, as well as other minor compounds whose proportion varies among plant species and whose biological implications in the honey bee physiology require intense research. Several environmental stressors are causing the decline of bee colonies, and thereby, we tried to connect the nutritional quality of bee’s diet with the strength of the bee’s immune system. The phytohormone abscisic acid (ABA) is present in nectar, honey and adult honey bees. It has been demonstrated that ABA stimulates innate immune defences in animal cells. However, the influence of ABA on A. mellifera’s health and fitness is unknown. Here, we show that honey bees fed with an ABA supplement in field experiments resulted in (i) the appearance of ABA in larvae and adult bees, (ii) enhanced haemocyte response to non-self recognition, (iii) improved wound healing and granulocyte and plasmatocyte activation and (iv) maximum adult bee population after the winter and increased pesticide tolerance. The results indicate that the naturally occurring compound ABA has a positive influence in honey bee immunity. ABA emerges as a potent booster of immune defence in A. mellifera and may be useful in addressing the colony losses threatening apiculture and pollination service worldwide.
Article
Full-text available
Formic acid and oxalic acid field trials for control of Varroa destructor were carried out in autumn according to the Swiss prescriptions during three successive years in different apiaries in Switzerland. The following parameters were determined in honey that was harvested the year after treatment: formic acid, ox- alic acid and free acidity. The following range of values were found in honeys of untreated colonies: formic acid, from 17 to 284 mg/kg, n = 34; oxalic acid, from 11 to 119 mg/kg, n = 33. There was a small, but unproblematic increase in formic acid levels in comparison to the levels in the controls; average: 46 mg/kg, maximum: 139 mg/kg. No increase in formic acid was found with increasing number of treatment years. If emergency formic acid treatments were carried out in spring, the residue levels were much higher: average in- crease of 193 mg/kg, maximum 417 mg/kg. The oxalic acid content remained unchanged, even after two suc- cessive treatments during the same autumn. No rise of free acidity was encountered after a combined treatment with formic and oxalic acid during the three trial years. honey/residue/formic acid/oxalic acid/free acidity/Varroa destructor
Article
Full-text available
The oil obtained by hydrodistillation of the foral bottom of Syzygium aromaticum (L.) Merr. et Perry was analyzed by GC and GC/MS. Eugenol was the main constituent in the oil (86.7%). The biological activity of the oil applied to Varroa destructor and Apis mellifera was evaluated in two laboratory tests. Mite lethality was estimated using a complete exposure method test with the oil at different concentrations, and a systemic administration method of oil at different concentrations diluted in syrup was placed in feeders for bees. The LC50 for complete exposure method at 24 h was 0.59 μL/dish. The inferior and superior limits obtained were 0.47 x 10 μL/dish and 1.22 μL/dish, respectively. LC50 estimated at 48 h showed a slight decrease as compared to that recorded at 24 h. Ratio selection (LC50 of A. mellifera/LC50 of V. destructor) for complete exposure method was 26.46 and 13.35 for 24 h and 48 h, respectively. Regarding the systemic administration method, mites LC50 at 24 h was 12,300 ppm. The inferior and superior limits calculated were 9,214 ppm and 15,178 ppm, respectively. LC50 estimated at 48 h showed a slight decrease as compared to that recorded at 24 h. Ratio selection for systemic administration method was 3.05 and 2.22 for 24 h and 48 h, respectively. Syzygium aromaticum oil was found to be an attractant for V. destructor at 4.8% (w/w) concentration. The results showed that oil toxicity against V. destructor differed depending upon its administration. Nevertheless, the ratio selection calculated by this oil is expected to enable its application under field conditions with a good safety margin. This oil could also be used in combination with other oils in integrated pest management strategies in bee colonies.
Article
Full-text available
Oxalic acid treatments for varroa control (review) Antonio Nanetti, Ralph Buechler, Jean-Daniel Charriere, Ingemar Fries, Stine Helland, Anton Imdorf, Seppo Korpela, Preben Kristiansen A two-year set of experiments focusing on efficacy against varroa mites and tolerability for the colonies of the tricking method for oxalic acid (OA) administration against varroa mites was made in six European countries (Finland, Germany, Italy, Norway, Sweden, Switzerland). During the cold season, about 1100 naturally varroa infested colonies were treated with solutions having different OA and sugar concentrations. Either OA or sugar concentration played an influence on the mite mortality. The efficacy was usually higher than 90% when the most concentrated solution (4,2% OA; 60% sugar) was used. Lower OA concentrations yielded worse and more variable efficacy but, in many cases, 3.2% seemed an acceptable balance between efficacy and tolerability. Unsatisfactory mite mortality was attained with non-sugar OA solutions. Generally, the 30% sugar solutions were comparatively slightly less effective than the 60% ones, when the OA concentration was fixed at a certain level. No evidence for unfair treatment tolerability was attained. In some instances colonies receiving solutions at the highest concentration (4.2%) sized smaller at the end of the winter, but no higher colony losses were seen in treated groups in comparison to the controls.
Article
After honey production, beeswax ranks second as regards hive product used in industry and cosmetics. In Argentina, the use of commercial wax adulterated with paraffin and other olefins for comb foundation is a common practice. As regards beehives, the progressive accumulation of synthetic acaricides in wax has caused adverse effects on bees, mainly on individuals at different stages of development. Another issue associated with the use of synthetic acaricides is the phenomenon of resistance. This study aimed to determine the presence of adulterants and acaricide residues in commercial wax used in Argentina. Furthermore, the relationship between coumaphos content in wax and the development of mite resistance reported in recent years in Argentina was investigated. The results demonstrate that paraffin is the most common contaminant substance present in recycled beeswax and commercial wax used for comb foundation in the country. Coumaphos was also found to be the most common acaricide present in wax; 87% in commercial and 80% in recycled wax. Fluvalinate was detected in 33% of commercial wax samples and in 27% of recycled wax. A relationship between coumaphos residues and resistance was also established. Future studies should be conducted to establish the mechanisms by which the buildup of acaricides in the beeswax affects the development of resistance in populations of varroa.
Article
The European honey bee Apis mellifera is known to be affected by many parasites and pathogens that have great impact over the insect development. Among parasites affecting bee health, Nosema ceranae is one of the main biotic factors affecting colony populations. As honey bee populations decline, interest in pathogenic and mutualistic relationships between bees and microorganisms has increased. The main goal of the current study was to assess the effect of the oral administration of the metabolites produced by Lactobacillus johnsonii CRL1647 (mainly organic acids) supplemented in syrup, on: (I) N. ceranae sporulation dynamics before and after fumagillin application, and (II) performance of A. mellifera colonies. Different experiments were conducted to evaluate the effects of these bacterial metabolites on bees: in vitro administration revealed no toxic effects against bees. Colonies fed with the lactic acids incremented their beehive population and also the amount of fat bodies per bee. Finally, the organic acids reduced the intensity of the pathogen after the second application of treatment as well as enhanced the fumagillin efficiency. This study provides important information for the development of new control substances against nosemosis.