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EUROPEAN JOURNAL OF ENTOMOLOG
Y
EUROPEAN JOURNAL OF ENTOMOLOGY
ISSN (online): 1802-8829
http://www.eje.cz
cluding the major pest beetle Anobium punctatum (de Geer
1774) (Coleoptera: Ptinidae, formerly Anobiidae) (Becker,
1942; Vité, 1952; Hickin, 1963a, b; Belmain, 1998; Bel-
main et al., 1999a; Unger et al., 2001; Petzoldt, 2011).
Adults of K. caeruleus are believed to feed on all stages
(egg to imago) of A. punctatum (Becker, 1954). The larvae
of K. caeruleus can consume all but the adults of A. punc-
tatum when these are alive, but may be able to consume
dead ones (Ott, 2007). Predators in general can feed on a
variety of different prey and are present in different habi-
tats, but K. caeruleus seems to be strongly associated with
pests of structures made of wood. This species is mainly a
synanthrope (Becker, 1954; Gerstmeier, 1998; Belmain et
al., 1999b; Belmain & Ridout, 2000; Franke, 2001; Haus-
tein & von Laar, 2007; Haustein et al., 2007; Noldt, 2007;
Mosneagu, 2012; Niehuis, 2013) because it is rarely re-
corded and if ever in out-door faunistic surveys in Central
and Northern Europe only in limited numbers (Alexander,
2004; Nikitsky & Schigel, 2004; Esser & Kielhorn, 2005;
Müller et al., 2007; Ostrauskas & Ferenca, 2010; Johans-
son, 2011; Niehuis, 2013; Finch 2015; Háva & Kovařík,
2015).
Laboratory breeding of Korynetes caeruleus (Coleoptera: Cleridae)
for the biological control of Anobium punctatum (Coleoptera: Ptinidae)
TILO HAUSTEIN 1, SABINE BUSWEILER 2, VERA HAUSTEIN 1, CLAUDIA VON LAAR 3 and RUDY PLARRE 2, *
1 Sachverständigenbüro Haustein, Königsteinstraße 8, 01277 Dresden, Germany; e-mail: info@dr-haustein.com
2 Bundesanstalt für Materialforschung und -prüfung (BAM), Biologische Materialschädigung und Referenzorganismen,
Unter den Eichen 87, 12205 Berlin, Germany; e-mails: sabine.busweiler@bam.de, ruediger.plarre@bam.de
3 Hochschule Wismar, University of Applied Sciences, Technology, Business and Design, Faculty of Engineering,
Civil Engineering, Philipp-Müller-Straße 14, 23952 Wismar, Germany; e-mail: claudia.von_laar@hs-wismar.de
Key words. Coleoptera, Cleridae, Korynetes caeruleus, Ptinidae, Anobium punctatum, biological pest control, life history data,
laboratory breeding, wood protection, cultural heritage
Abstract. Larvae and adults of Korynetes caeruleus (de Geer 1775) (Coleoptera: Cleridae) were collected from old churches and
reared in the laboratory on Anobium punctatum (de Geer 1774) (Coleoptera: Ptinidae). Breeding success of K. caeruleus was
low, but basic parameters of this species’ developmental cycle were identifi ed. At 21°C and 75% relative humidity and a four-
month cold period at 4°C, the development of K. caeruleus from egg to adult appearance lasted 2 years. The pupal stage may be
reached and completed after one and a half years. Feeding on larvae of A. punctatum by larvae of K. caeruleus was observed and
consisted of a combination of sucking haemolymph and consuming body parts. The sickle-like mandibles of larvae of K. caeruleus
penetrate the cuticle of prey larvae; this is followed by pumping and sucking body movements. Adult beetles of A. punctatum were
not attacked by K. caeruleus larvae. Feeding behaviour of adult K. caeruleus was not investigated.
* Corresponding author; e-mail: ruediger.plarre@bam.de
INTRODUCTION
Biological control of pests is one cornerstone of Integrat-
ed Pest Management (IPM). To evaluate the potential of a
predator as biological control agent of a pest species in the
fi eld, autecological studies and reliable life history data of
the benefi cial species are needed.
Although several parasitoids and predators of wood
boring pest insects are well known (Becker, 1954; Paul
et al., 2008), their utilization in biological control to pro-
tect structural timbers, wooden furniture or art is still lim-
ited and unexploited (Steidle et al., 2007; Schöller, 2010;
Schöller & Prozell, 2011; Auer & Kassel, 2014; Biebl &
Auer, 2017; Querner, 2017). Major reason for this is the
lack of detailed knowledge of their biology, absence of
standard procedures for their mass rearing and reliable
data on their pest control effi ciency (Haustein et al., 2014).
Establishing a sustainable laboratory culture of benefi cial
insects in order to determine their life histories is therefore
an important prerequisite before promoting the use of clas-
sical biological control for the protection of wooden struc-
tures (Faulds, 1987; Reeve et al., 2003; Kassel et al., 2018).
Korynetes caeruleus (de Geer 1775) (Coleoptera: Cleri-
dae) is known to be a predator of wood boring anobiids, in-
Eur. J. Entomol. 116: 362–371, 2019
doi: 10.14411/eje.2019.038
ORIGINAL ARTICLE
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of the wood throughout the year (Franzen et al., 2009; Haustein,
2010). At the time when the beetles were collected in spring (see
below) ambient temperatures ranged from 9.5 to 20.3°C (mean
14.0°C), with relative humidity’s of 47.5 to 67.5% (mean 54.8%).
There are records of the occurrence of A. punctatum, K. cae-
ruleus and other wood associated beetle species at the collection
sites since 2005 (Haustein & von Laar, 2007; Haustein, 2010).
However, it is assumed that they were present earlier. According
to Haustein & von Laar (2007) high numbers of live adult beetles
of K. caeruleus (Fig. 1) occur in churches from the beginning of
May for about four weeks and then decline. They are regularly
observed on the surfaces of wooden structures, where they mate.
So far, they have not been detected in the woodlands surround-
ing these buildings. I dentifi cation of K. caeruleus was based on
the description provided by Gerstmeier (1998), who also verifi ed
their identity (Haustein, 2010).
Late instar larvae of K. caeruleus occur about two to three
weeks earlier in the year than the adults. They were also found
on the surface of wood structures, where they presumably search
for suitable prey by frequently entering and exiting from the fl ight
holes made by their prey (Fig. 2). Wood worm (A. punctatum)
frass which fi lls the fl ight holes and the connecting tunnels is
ejected during this process and yellowish wood powder piles up
near fl ight holes (Ott, 2007). Often other larvae of K. caeruleus,
while searching the surface of wood, move through these piles of
powder leaving typical tracks (Fig. 3). This kind of larval activ-
ity may last until late summer, however with declining frequency
over time.
Because the occurrence of larvae and adults of K. caeruleus
partially overlap each year, it is assumed this species takes several
years to complete its development. Thus, at least two distinct gen-
erations at different developmental stages may co-occur. Adult
beetles of the prey species, A. punctatum, were not detected be-
fore the end of June and the beginning of July and must therefore
We collected adult beetles and large larvae of K. caerule-
us in old, small village churches in north-eastern Germany
and fed them on a laboratory culture of A. punctatum. Al-
though mass rearing of this predator was not achieved, this
is to our knowledge the fi rst communication on the suc-
cessful reproduction of K. caeruleus under controlled labo-
ratory conditions and record of reliable life history data.
MATERIAL AND METHODS
Collection of K. caeruleus
Korynetes caeruleus was collected from small churches in
Mecklenburg-Vorpommern (north-east Germany). Many of these
churches are currently not regularly used with only four to fi ve
services per year. Most of them were erected or largely restored
during the late 18th and middle 19th century. Building materials
were local boulder and cobble stones combined with bricks and
wood. The interior, mainly the seating and the choir stalls, were
made from wood. Today, the buildings are unheated with high
relative humidity in the inside resulting in a high moisture content
Fig. 1. Adult beetle of Korynetes caeruleus walking on soft wood
infested with Anobium punctatum.
Fig. 2. Larva of Korynetes caeruleus about to enter a fl ight hole of
Anobium punctatum.
Table 1. Number of larvae and adults of Korynetes caeruleus col-
lected over the period 2013 to 2017.
Larvae Adult beetles
Time of collection Total (n) Time of collection Total (n)
2013, May 6 12 2013, May 6 14
2014, May 5 17 2014, May 5 54
2015, May 4 19 2015, May 11 60
2016, May 3 16 2016, May 13 54
2017, May 7 13 2017, May 24 50
Fig. 3. Tracks of Korynetes caeruleus larvae that moved through
wood worm frass thrown out by other K. caeruleus larvae search-
ing for prey in fl ight holes of Anobium punctatum.
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be excluded as a source of food for at least the mating and egg
laying adult beetles of K. caeruleus.
Collection of K. caeruleus and breeding in a laboratory
Manual collection of late instar larvae and adult beetles of K.
caeruleus was carried out in fi ve consecutive years from 2013
to 2017, twice during mid and late spring for two to three days,
respectively (Table 1). In between the mid and late spring collec-
tion dates in 2014 and 2015, a variety of traps of different designs
were tested. Trap lures were made from an artifi cial wood-like
diet containing large larvae of A. punctatum (see below) and oak
saw dust. Unfortunately, none of these traps caught signifi cant
numbers of K. caeruleus. Thus, the manual collection of larvae
and beetles was the only effi cient method of collection.
After collection, insects were caged individually for transport
to avoid cannibalism, especially among larvae. Beetles were only
confi ned as pairs when captured in copulation. Insects were im-
mediately transported to BAM (Federal Institute for Materials
Research and Testing) in Berlin and placed in 3 to 4 months old
cultures of A. punctatum larvae for further breeding (Table 2 and
Table 4). First, due to the diffi culties associated with determin-
ing the sex of live K. caeruleus, all individually transported adult
beetles were collectively released into a large petri-dish of ap-
proximately 9 cm in diameter for mating. Pairs or groups of four
to six beetles were then added to the cultures of A. punctatum lar-
vae. Individuals which did not mate after collection were pooled
as one group. Five to six of these adults were added to cultures
of A. punctatum.
Combined cultures of A. punctatum / K. caeruleus were kept at
21 ± 1°C and 75 ± 5% r. h. on an artifi cial wood diet as described
in the standard protocols for rearing A. punctatum (Cymorek,
1965, 1975; Baker & Bletchly, 1966). Part of that standard rear-
ing protocol is the temporary storage of cultures for two to four
months at 4°C, when A. punctatum larvae reach the age of ten
months. Bringing the cultures back to normal rearing conditions
of 21 ± 1°C and 75 ± 5% r. h. after cold storage triggers pupation
and the development of adults in A. punctatum. It was assumed
that the predator, K. caeruleus, needs the same abiotic conditions
to complete its development, therefore, the A. punctatum / K.
caeruleus cultures were treated similarly. Some of the A. punc-
tatum / K. caeruleus cultures were examined after particular in-
tervals of time to determine the stage of development reached by
K. caeruleus (see white boxes in Table 2 and Table 4). The larvae
of K. caeruleus retrieved from these cultures were reintroduced
into other A. punctatum cultures of similar age.
Feeding behaviour of larvae
In addition to the rearing program, four larvae of K. caeru-
leus from the May 2016 collection continuously fed larvae of A.
punctatum were observed for long periods of time. For this, one
larva of each species (prey and predator) were confi ned in small
Petri dishes of approximately 4 cm in diameter, which functioned
as an arena for behavioural observation. The arena contained no
Table 2. Results of rearing fi eld collected adult beetles of Korynetes caeruleus in fi ve consecutive years. Life history data were recorded in
terms of the developmental stages present at particular times. Only those individuals that were alive are listed. Further details in the text.
Year of collection of adult beetles of parental generation
2013 2014 2015a 2015b 2016 2017
Number of adult beetles in parental generation
May 14 54 10 50 49 24
Number and developmental stage (L – larva, P – pupa, A – adult) of next generation after particular time intervals
Jun.
Jul.
Aug.
Sep. 16L active 2L active
1L cocoon
Oct. 1L active
Nov. 3L active
Dec.
Jan.
Feb. 3L active
Mar.
Apr. 9L active
May
1L active
11L cocoon
5P
1L cocoon
Jun. 1P 10P
Jul. 1A cocoon 1A active
3A cocoon
Aug.
Sep. 1 L active
Oct.
X
2A active
3A cocoon 3A cocoon
Nov.
scheduled cold
period
Dec.
Jan.
Feb.
Mar. 1A active 1A active To be continued
Apr. x 1A active 3A active x
Light grey boxes indicate rearing conditions of 21 ± 1°C and 75 ± 5% r. H. Dark grey boxes indicate rearing at 4°C. White boxes indicate
stages present at that time. X indicates end of experiment.
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wood or any other kind of matrix other than a small shelter made
of corrugated paper.
Life larvae of A. punctatum were placed in the open but were
unable to move around. When they were consumed or killed by
the predator they were replaced. Arenas were kept in a rearing
room at 21 ± 1°C and 75 ± 5% r. h.
Changes in body mass of each larva of K. caeruleus were re-
corded once every month by weighing them on a Sartorius LE
225D-OCE laboratory scale to the nearest 0.01 mg (Table 5).
For observing feeding behaviour, mainly after adding A. punc-
tatum larvae, the arenas were carefully placed on a laboratory
bench at ambient room temperature and under normal light condi-
tions. When contact between predator and prey was established
the arena was placed under a binocular for observation and the
feeding behaviour recorded.
Scanning electron microscope (SEM) pictures
of mouthparts of K. caeruleus
SEM was carried out at the University of Wismar, depart-
ment of civil engineering, section building material technology,
Germany. The head of a late instar larva of K. caeruleus with all
its mouthparts was carefully straightened out and mounted on a
specimen holder stub using a conductive adhesive pad. Specimens
and holder were bridged with conductive silver and fi nally coated
with gold using a BALZERS SCD 050 Sputter Coater (BAL-TEC
AG), resulting in a coat thickness of 16 nm. SEM pictures were
taken using a FEI Quanta FEG 250 s.e.m. in high vacuum mode
at a magnifi cation of 2040 times. An Everhart Thornlay Detector
was used as a secondary electron detector.
RESULTS
Collection and breeding
From previous studies it is known that larvae of K.
caeruleus can best be collected on the surface of wooden
objects inside churches from late April to early May and
the adults about one to two months later (Haustein & von
Laar, 2007; Haustein, 2010). Total numbers of hand col-
lected larvae and adult beetles are listed in Table 1. The
rearing of K. caeruleus varied slightly over the years due to
minor changes in physical handling of diets (as described
above), which were adjusted as new insights were gained
(see below).
Rearing from beetles
Although carried out very carefully the examinations
of the K. caeruleus / A. punctatum cultures to record life
history data, always severely damaged the cultures and
stressed the individuals. Many of them did not recover and
were unable to complete their development. Table 2 lists
individuals that completed their development.
In 2013, fourteen beetles of K. caeruleus were placed in
cultures of larvae of A. punctatum. Six months later three
active K. caeruleus larvae of the next generation were re-
trieved, of which, unfortunately, just one survived to be
transferred the following month to cold conditions (Table
2/2013). This larva remained dormant for two months after
which it was active for another eight months, but died of
unknown causes without developing further.
The breeding experiment in 2014 started with twenty-
seven pairs of adult beetles of K. caeruleus. Four months
later the sixteen active larvae collected were induced to be-
come dormant (Table 2/2014) of which nine became active
when returned to standard rearing conditions. Six months
later fi ve adult beetles were found. Three of them were in
cocoons (Fig. 4). Adult beetles in cocoons were transferred
one month later and subjected to a second cold period for
three months, after which they were kept under standard
rearing conditions during which one adult beetle emerged,
but the other two died.
From the 2015 collection of adult beetles thirty pairs of
K. caeruleus were transferred to cultures of larvae of A.
punctatum. Five cultures were examined four months later
to check the numbers, size, and condition of the larvae of
Table 3. Number, size and weight of the larvae of Korynetes caeruleus collected from 2015 to 2017. Same letters indicate no signifi cant
difference; not deter. – not determined.
Year Total (n) Body size (mm) Body weight (mg)
min. – max. Average ± standard deviation min. – max. Average ± standard deviation
2015, May 4 19 5–9 6.9 ± 1.2anot deter. not deter.
2016, May 3 16 5–9 7.0 ± 1.2a0.82–6.90 3.3 ± 1.6b
2017, May 7 13 5–9 7.5 ± 1.4a0.92–5.56 3.3 ± 1.6b
Table 4. Results of rearing fi eld collected larvae of Korynetes caer-
uleus in fi ve consecutive years. Life history data were recorded
in terms of the developmental stages present at particular times.
Only individuals recorded alive are listed. Further details in the text.
Year of collection of large larvae
2013 2014 2015 2016 2017
Number of large larvae collected
May 9 15 19
12 14
Development stage recorded at particular time intervals
Jun.
Jul. 6L active
Aug.
Sep.
Oct. 3A cocoon
Nov. 2A active
Dec. 1A active
Jan.
Feb.
Mar. 2L active 3A active
To be
continued
Apr.
x
3A active
May
x
Jun.
Jul.
Aug.
Sep. 3A active
Oct.
x
1A cocoon
Nov.
Dec.
Jan.
Feb.
Mar. 1A active
Light grey boxes indicate rearing at 21°C and 75% r. h. Dark grey
boxes indicate rearing at 4°C. White boxes indicate stages present
at particular intervals of time. X indicates end of experiment.
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K. caeruleus of the next generation (Table 2/2015a). Five
larvae were detected, two of them were actively moving,
one was motionless in a self-spun cocoon and two were
dead, and several empty cocoons were found (Fig. 5 on
the right). The two active larvae were both 7 mm long and
weighed 6.4 and 8.5 mg, respectively. The dormant larva
was carefully taken out of its cocoon. It weighed 10.3 mg
and was 9.0 mm long. Each larva was reintroduced into a
new A. punctatum culture of equal age. Later this culture
was transferred to cold conditions to induce dormancy and
fi ve months after returning it to standard rearing conditions
it was examined. One of the three K. caeruleus had pupated
inside a cocoon and the other two were dead. Finally, after
one month the only live K. caeruleus was a fully sclero-
tized adult beetle of blue colour, which remained inside
its cocoon for another four more months, when the next
cold treatment was initiated. When returned to the standard
rearing conditions the adult became active the next day.
Table 5. Biometric data, development and number of larvae and adults A. punctatum consumed by the larvae of Korynetes caeruleus
collected in the fi eld in 2016.
Date Recorded Larvae of Korynetes caeruleus
Larva 1 Larva 2 Larva 3 Larva 4
17.05.16 Initial weight (mg) 1.9 3.6 4.0 6.9
1st month Consumption of A. punctatum 3 large larvae
0 adult beetle
3 large larvae
0 adult beetle
2 large larvae
0 adult beetle
4 large larvae
0 adult beetle
17.06.16
Weight (mg) 8.2 8.7 8.0 17.7
Δ weight (mg) 6.3 5.1 4.0 10.8
No. of moults 0 0 0 0
2st month Consumption of A. punctatum 0 large larvae 1.5 large larvae 2 × 0.5 large larvae 0 large larva
21.07.16
Weight (mg) 10 9.1 14.6 20.6
Δ weight (mg) 1.8 0.4 6.6 2.9
No. of moults 0 1 1 1
3rd month Consumption of A. punctatum 1 large larva 1 large larva 2 large larvae 2 large larvae
11.08.16
Weight (mg) 9.1 11.1 14.2 26.2
Δ weight (mg) –0.9 2 0.4 5.6
No. of moults 0 0 0 0
4rd month Consumption of A. punctatum
Died during
4th month
0 large larva 0 large larva 0 large larva
28.09.16
Weight (mg) 12.1 11.8 23.4
Δ weight (mg) 1 –2.4 –2.8
No. of molts 000
5th–9th month Placed in saw dust and transferred to cold conditions of 4°C
06.04.17
Weight (mg) 11.2
Death during
cold period
17.6
Δ weight (mg) –0.9 –5.8
No. of moults 10
10th month Consumption of A. punctatum 1 large larva 3 large larvae
11th–12th month Consumption of A. punctatum 0 large larva
Died during 11th month
13th month No. of moults 1 pupated followed by
emergence of 1 adult
14th–15th month Cold treatment of 4°C
16th month Adult emerged
Fig. 4. Adult beetle of Korynetes caeruleus that has emerged from
a pupa but is still in its cocoon.
Fig. 5. Cocoons made by larvae of Korynetes caeruleus for pupa-
tion. The left cocoon is intact and encloses a pupa, the right one is
partly destroyed and empty.
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The rest of the 2015 cultures of K. caeruleus / A. punc-
tatum were left undisturbed for one year before examining
them (Table 2/2015b). These cultures were fi rst subject-
ed to cold treatment from the sixth to the eighth month.
Twelve live larvae, and fi ve pupae of K. caeruleus were
detected. Eleven of the live larvae were in cocoons. Only
one live larva (2.9 mg and 7 mm) was active. The larvae
in two of the cocoons that broke open during the examina-
tion of the cultures were 7 mm long and weighed 9.4 and
9.6 mg, respectively. All of the pupae were in the same
kind of cocoon and one that was accessible weighed 9.0
mg (Fig. 5). All cocoons were placed in saw dust and kept
at standard rearing conditions and one month later ten of
the larvae had pupated. Only one developed into an adult
beetle, which however remained inside its cocoon for the
next three months, when the second cold treatment was ini-
tiated. When returned to standard rearing conditions this
beetle emerged from its cocoon the next day. Of the fi ve
pupae, two produced adults, which remained inside their
cocoons until the end of the second cold treatment, after
which they emerged from their cocoons one and four days
later, respectively. In addition, one adult beetle emerged
before the second cold treatment. Thus, the 2015 cultures
produced a total of fi ve beetles, four of them emerged after
the second cold treatment early in 2017 and one during the
second season in 2016.
For the 2016 and 2017 cultures, the K. caeruleus beetles
were placed on pieces of wood previously infested with
larvae of A. punctatum. For the 2016 culture, the duration
of the cold treatment was shortened to two months. How-
ever, this did not shorten the period to the emergence of ac-
tive adults, because the beetles did not emerge immediately
after the end of the cold treatment (Table 2/2016) as in the
previous treatments (Table 2/2014 and Table 2/2015).
It appears that cold treatment is not the only stimulus
inducing adult emergence. Under moderate conditions
a period of about four months between the onset of dor-
mancy and emergence of adult beetles from their cocoons
seems equally important (see below). The second dorman-
cy of the 2017 cultures was, therefore, scheduled for four
months (Table 2/2017).
Rearing larvae
Larvae of K. caeruleus collected in churches in 2013,
2014, 2015 and 2017 (Table 1) were transferred to cultures
of A. punctatum larvae as described above. Food for K.
caeruleus larvae collected in 2016 was provided in such
a form that both larvae in diets and wood infested with A.
punctatum larvae, were offered.
Four K. caeruleus larvae from the 2016 collection were
kept separately in order to observe their feeding behaviour
(see below). The size and weight of the K. caeruleus larvae
collected in 2015, 2016 and 2017 did not differ statistically
(Table 3).
Of the nine K. caeruleus larvae collected in 2013, six
completed their development and emerged as adults (Table
4/2013) without being subjected to cold treatment.
Six larvae of K. caeruleus collected in 2014 survived the
fi rst two months and two of them survived a period of cold
treatment (Table 4/2014). In the next season one of them
completed development to the adult stage, remained in its
cocoon during the following cold period and emerged im-
mediately after the end of the cold treatment.
From the 2015 collection three adults emerged after the
cold treatment, which they entered as dormant adults in
their cocoons (Table 4/2015).
The 2016 collection of K. caeruleus larvae were left un-
disturbed and subjected to a cold period after six months
and then on returning to standard rearing conditions three
beetles emerged (Table 4/2016).
Korynetes caeruleus larvae collected in 2017 were ex-
amined three months later when eleven of them were dead.
However, each of them had spun a cocoon in preparation
for pupation.
In summary, the collected larvae of K. caeruleus were on
average 7.1 mm long and weighed 3.3 mg. With presum-
ably unlimited access to food in form of larvae of A. punc-
tatum, larvae of K. caeruleus completed their development
to the adult stage between six and twenty-two months after
collection. Subjection to a period of cold triggered the
emergence of the adult beetles that remained inside their
cocoon after emerging from pupae. However, emergence
of adults may also occur without their experiencing a pe-
riod of cold (Table 4/2013).
Feeding behaviour
Four of the larvae of K. caeruleus collected in 2016 were
kept individually in small arenas. They were continuously
Fig. 6. Pupa of Korynetes caeruleus in an accidentally opened co-
coon.
Fig. 7. Larva of Korynetes caeruleus attacking a larva of Anobium
punctatum by inserting its mandibles into its soft abdominal tis-
sues.
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fed with A. punctatum (Table 5). Food was successively re-
placed when previous larvae were completely or partially
consumed.
When larvae of K. caeruleus were confi ned with one ma-
ture larva of A. punctatum in an arena, they initially sought
refuge in the shelter provided for several minutes and then
slowly moved around the arena. First contact with prey
did not automatically result in an attack, even though all
the K. caeruleus larvae had not been fed since they were
collected. Eventually a larva of K. caeruleus initiated an
attack by driving its sickle-like-mandibles into the abdo-
men of a larva of A. punctatum (Fig. 7). Due to their being
in the open the larvae of A. punctatum were unable to es-
cape. Observation under a binocular microscope at 10-fold
magnifi cation revealed pumping motions in the body of the
predator once its mandibles penetrated the prey’s cuticle.
These repeated motions are interpreted as results of the
muscular contractions involved in injecting digestive en-
zymes into the body cavity of the prey followed by the in-
gestion of predigested food. There is a depressed grove in
the proximal part of each mandible (Fig. 8), which presum-
ably function as a canal for injecting digestive enzymes
into the prey’s body and ingesting predigested food. The
woodworm larvae markedly shrank during this process and
fi nally the larva was consumed almost entirely. The entire
process was not observed. However, it can readily be de-
duced from the subsequent absence of the body of the prey
other than the indigestible parts, such as the head capsule
and parts of the outer cuticle. Adult beetles of A. punctatum
were also offered once, but after a week none had been at-
tacked (Table 5, 1st month).
At monthly intervals all the larvae of K. caeruleus were
weighed to determine their gain in body mass and the num-
ber of moults were recorded (Table 5). When K. cearuleus
larvae did not attack freshly offered food, they were pro-
vided with saw dust as refuge prior to transferring them to
cold conditions of 4°C, during which the surviving larvae
burrowed into the saw dust, however, it is unclear when
this occurred.
After the cold treatment the larvae of K. caeruleus were
acclimatized to ambient temperatures, weighed and fed lar-
vae of A. punctatum (Table 5, 10th month). Finally, larva
No. 2 spun a cocoon and pupated, which later developed
into a soft skinned whitish imago and then a fully scler-
otized blue coloured beetle. The adult beetle remained
motionless inside the cocoon and was then subjected to a
second cold period. When returned to standard rearing con-
ditions, the imago emerged six days later.
In summary, K. caeruleus larvae readily and continually
consumed larvae of A. punctatum. Some larvae moulted
and larva No. 2 consumed six and a half A. punctatum lar-
vae, moulted twice and increased in weight by 7.6 mg be-
fore pupating and completing its development to the adult
stage after being subjected to a cold period. Larva No. 4,
which was also subjected to a cold period failed to pupate
successfully but consumed eight larvae of A. punctatum,
moulted twice and increased in weight by 10.7 mg before
starting to make a cocoon. Live adult beetles of A. punc-
tatum were not attacked by larvae of K. caeruleus and dead
adult beetles of A. punctatum were not offered (Ott, 2007).
DISCUSSION
Development of K. caeruleus does not follow a par-
ticular pattern. Like its most important prey A. punctatum
and other wood boring beetles, K. caeruleus is also able
to adapt its growth and moulting intervals to existing bi-
otic and abiotic conditions (Amman, 1970; Ott, 2007; Pet-
zoldt, 2011; Niehuis, 2013; Youssef et al., 2013). Within
this range of conditions for development, it is likely we
have identifi ed the minimum requirements for the fastest
possible life cycle under controlled laboratory conditions.
Our data indicates that in K. caeruleus the development
from the mating of adults to the appearance of active adult
Fig. 8. SEM photograph of the head of a larva of Korynetes caer-
uleus. Dorsal/frontal view of the open right mandible (RM) showing
its prominent proximal groove (L – labrum; RMP – right maxillar
palpus).
Fig. 9. Postulated two-year developmental cycle of Korynetes
caeruleus with active life stages (white part of the pie-chart) and in-
active dormant life stages (grey part of the pie-chart), starting with
1 “adult emerging” at the end of April and ending with 13 “adults
emerging”, which during the second cold treatment were dormant
in their cocoons.
369
Haustein et al., Eur. J. Entomol. 11 6: 362–371, 2019 doi: 10.14411/eje.2019.038
beetles of the next generation takes two years (Fig. 9:
1–13), given it is reared at 21°C and a relative humidity of
approximately 75%, and provided with suffi cient food in
the form of live prey larvae, shelter and subjected to two
cold periods. Currently, we have not observed egg laying
and only thirteen adult beetles have completed develop-
ment under these laboratory conditions (Table 2). Some
basic life history data revealed it takes approximately six
months for the eggs to become larvae of about 7 to 9 mm
in length and a weight of around 8 mg (Fig. 9: 3–6). At this
stage a larva is large enough to enter dormancy when sub-
jected to a period of low temperature (Fig. 9: 6).
When returned to laboratory rearing conditions after ap-
proximately two to four months at a low temperature, lar-
vae feed and complete their development in about six to
eight months (Fig. 9: 7–8) then spin a cocoon (Fig. 9: 9),
pupate (Fig. 9: 10) and, fi nally, emerge as an adult (Fig. 9:
11). However, if subjected to low temperature again, the
adult beetles remain in their cocoons (Fig. 9: 12) and on
returning to standard rearing conditions emerge from their
cocoons after a few days (Fig. 9: 13).
Development lasted only one and a half to two seasons
(10 months) with one cold period in between. The need for
a second cold period seems to be facultative with young
adults remaining inside their cocoons when temperatures
start to decrease. A minimum duration of approximately
three to four months appears optimal for the second cold
period. Sho rtening the cold period did not result in an
early emergence of adult beetles. If, however, the onset of
declining temperature, which triggers the entering of dor-
mancy, is delayed, e.g. by being transferred to favourable
conditions in the laboratory, adult beetles may emerge at
the end of the second season. This was recorded for three
adults, two in the 2014 culture (Table 2/2014) and one in
the 2015 culture (Table 2/2015b). Whether these “fast de-
velopers” could survive another cold period is unknown
and needs further study.
The timing of development recorded accords with natu-
rally occurring seasonal conditions if the mating of paren-
tal beetles occurs around mid to late spring as temperatures
are increasing (Fig. 9: 2). Feeding and growth of larvae
occurs from late spring to late summer. Before tempera-
tures decrease in autumn, larvae have suffi cient reserves to
survive in a dormant state to the following year (Fig. 9: 6).
The following spring these larvae start feeding again and
prepare to complete their metamorphoses (Fig. 9: 7–11)
at which time temperatures are slowly decreasing, which
results in adult emergence being delayed to next spring
(Fig. 9: 13). The second dormant phase in effect synchro-
nizes adult emergence in the next season. Early emergence
of adults in the fi eld is therefore very unlikely. The ob-
servations of Haustein & von Laar (2007) and Haustein
(2010) on the occurrence of active larvae and beetles in old
churches and those of Noldt (2007) in historic houses seem
to fi t this model.
Number and duration of the larval instars in K. caeru-
leus, however, are unknown. In the feeding experiments
using large larvae (presumably in their second season) col-
lected from churches, up to two additional larval moults
were recorded before pupation. In other clerid beetles there
are three larval instars before pupation (Amman, 1970,
1972; White & Franklin, 1982). This might not apply to K.
caeruleus, because it is unlikely that the young and small
larvae moult only once in their fi rst season.
However, it cannot be ruled out that the two moults of
the old larvae in our experiments were an artefact due to an
abundance of food. Three larval instars may be the mini-
mum with more if conditions are unfavourable. As was the
case reported by Haustein (2010) in which large second
season larvae of K. caeruleus moulted up to six times with-
out pupating and fi nally died. In this study, food was con-
tinuously available but there was nowhere where the larvae
could construct pupal chambers. Without suitable material
(wood, saw dust or similar material) larvae of K. caeruleus
are probably incapable of forming and fi xing cocoons for
metamorphoses. Forming “free pupae” might not be pos-
sible and larvae continue to feed and grow and eventually
die. When saw dust was provided in our feeding experi-
ments, larvae of K. caeruleus stopped foraging for food
and started to prepare cocoons.
The cocoon is made of a thin layer of a sticky whitish se-
cretion. Inside wood, the secretion is attached to the inner
wall of the pupal chamber, loosely surrounding the pupa
inside. Becker (1942) postulates that K. caeruleus does not
build a pupal chamber but readily lines old pupal chambers
of A. punctatum or other anobiids with its secretion. In our
experiments, when constructed in saw dust, small wooden
particles adhered to the sticky outer surface and thus pro-
vided anchoring supports for the cocoon before it hardened
(Fig. 5 left). The inner layer of a cocoon appears glossy
(Fig. 5 right).
The feeding behaviour of larvae of K. caeruleus is best
described as a combination of sucking haemolymph and
consuming small body parts. This method of feeding is
called extra-oral digestion (EOD) and is typical of many
predaceous arthropods (Lövei & Sunderland, 1996; Cohen,
1998). We recorded all the classical processes of EOD
(Frazier et al., 1981; Cohen, 1995) when larvae of A. punc-
tatum were provided as food. The sickle shaped mandibles
of larvae of K. caeruleus with their depressed groove for
injecting digestive enzymes are well suited for EOD and
are similar morphologically to the mandibles of other
predatory clerid larvae, e.g. Thanasimus dubius (White &
Franklin, 1982) and Dermestoides sanguinicollis (Kolibáč,
2002).
We present a method for rearing K. caeruleus success-
fully in the laboratory. Field collected adults and larvae
should be placed on soft wood infested with all stages of
A. punctatum. Rearing should be done at approximately
21°C and 75% relative humidity. A period at 4°C lasting
for four months should be provided after six months. This
should be followed by another six months of rearing under
standard condition and then a second period at 4°C for four
months. After which beetles can be expected to emerge,
when cultures are returned to standard rearing conditions.
Using this method the total time to reproduction in K. cae-
370
Haustein et al., Eur. J. Entomol. 11 6: 362–371, 2019 doi: 10.14411/eje.2019.038
ruleus is less than two years and could be even less than
one and a half years, if the second cold period is short-
ened. When using artifi cial diets instead of wood, growth
of mould and mites are a serious problem.
We are confi dent that it will be possible to mass produce
K. caeruleus in the future and determine whether this bee-
tle can be used as a biological control agent of A. puncta-
tum. It is possible that the mass release of predators and
parasitoids will reduce Anobium infestations in historical
buildings, such as small churches in northern Germany,
and provide the time necessary for obtaining the funding
for sustainable restoration. Furthermore, it is likely that
conventional pest control using biocides will become less
popular in the future and IPM and biological pest control
will increase in importance in the preservation of our cul-
tural heritage.
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Received June 20, 2019; revised and accepted September 23, 2019
Published online November 4, 2019
