Study on weevil pests of oilseed rape at Keszthely, Hungary

Abstract

One of the most important pests of rape in early spring are weevils (Ceutorhynchus spp.). The aim of our studies was to identify the occurring weevil species and to study their emergence, swarming, mating and damage. Our observations were performed on an experimental plot at Keszthely (Hungary, Zala County) in early spring of four consecutive years. Following species were collected and identified: Ceutorhynchus pallidactylus MARSHAM, Ceutorhynchus obstrictus MARSHAM, Ceutorhynchus napi GYLLENHAL, Ceutorhynchus pleurostigma MARSHAM. The obvious dominance of C. pallidactylus and C. obstrictus was detected. Their frequency of occurrence was 88-90% among the identified adults. We found that C. obstrictus was the last species to settle. Complete developmental period was 68 +/- 7 days in case of C. pallidactylus and 70 +/- 7 days in case of C. obstrictus. Average number of eggs laid by one female was 176 +/- 23 in case of C. obstrictus and 21 +/- 6 in case of C. pallidactylus.

Full text

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Comm. Appl. Biol. Sci, Ghent University, 75/3, 2010
STUDY ON WEEVIL PESTS OF OILSEED RAPE AT
KESZTHELY, HUNGARY
ZS. MARCZALI1, S. KESZTHELYI2, M. NÁDASY1, P. BUDAI1 and É. LEHOCZKY
1
1University of Pannonia Georgikon Faculty, Institute of Plant Protection, Dept. of Applied Zoology
Deák Ferenc st. 57. HU-8360 Keszthely, Hungary
2
Corresponding author E-mail: marczali@georgikon.hu
University of Kaposvár Faculty of Animal Sciences, Dept. of Botany and Plant Production, Guba
Sándor st. 40. HU-7400 Kaposvár, Hungary
SUMMARY
One of the most important pests of rape in early spring are weevils (Ceutorhynchus spp.). The aim
of our studies was to identify the occurring weevil species and to study their emergence,
swarming, mating and damage. Our observations were performed on an experimental plot at
Keszthely (Hungary, Zala County) in early spring of four consecutive years. Following species were
collected and identified: Ceutorhynchus pallidactylus MARSHAM, Ceutorhynchus obstrictus MARSHAM,
Ceutorhynchus napi GYLLENHAL, Ceutorhynchus pleurostigma MARSHAM. The obvious dominance of C.
pallidactylus and C. obstrictus was detected. Their frequency of occurrence was 88-90% among
the identified adults. We found that C. obstrictus was the last species to settle. Complete
developmental period was 68±7days in case of C. pallidactylus and 70±7 days in case of C.
obstrictus. Avarage number of eggs laid by one female was 176±23 in case of C. obstrictus and
21±6 in case of C. pallidactylus.
Key words: Ceutorhynchus spp., weevil species, oilseed rape
INTRODUCTION
One of the preconditions of attaining outstanding yield averages of oilseed rape is a
successful pest control. We are only able to protect against them effectively if we have
more profound knowledge about their biology and ecology. There are numerous species
of cruciferous plants (Brassicaceae) cultivated in Hungary on about 250-300 thousand
hectares every year. Among cruciferous plants, winter canola is cultivated on the
largest field. Although pests under Hungarian ecological circumstances would not
damage summer canola to a degree, its growing is not economical because of its much
lower crop yield.
In our studies emergence of Ceutorhynchus adults from their overwintering places,
their further swarming and damage on rape field was observed.
In case of oilseed rape, one of the preconditions of attaining
outstanding yield averages is to satisfy its agrotechnical demands (e.g. soil cultivation,
sowing time, nutrient replenishment, etc.) the other is a successful pest control. The
most important pests of rape in early spring are pollen beetles (Meligethes spp.) and
weevils (Ceutorhynchus spp.), which can endanger the yield greatly (MARCZALI et al.
2006). They cause considerable damage only in years when their settling is followed by
changeable weather, colder and warmer periods alternating each other (KUROLI and
NÉMETH 2003, GRAHAM and GOULD 1980, FERGUSON et al. 2003). Among Ceutorhynchus
species C. pallidactylus causes reasonable damage but C. obstrictus can cause severe
problems (HERTELENDY et al. 1975, BUNTIN 1999) (Figure 5-6.). Ceutorhynchus napi has
greater importance in Western Europe than in Central Europe. The importance of C.
pleurostigma as a rape pest can be considered moderate or occasional (JAKABFI and
RUSZIN 1977) (Figure 7-8.).
MATERIALS AND METHODS
Our studies were aimed at studying Ceutorhynchus species damaging oilseed rape.

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Observations were performed on swarming phenology of weevils on an experimental
plot (40x30 m) in early spring of four consecutive years (1999-2002). Our investigations
were conducted at Keszthely (Hungary, Zala county). In order to be able to follow the
emergence of adults from the wintering places, leaf litter samples were collected in
late autumns of each year. Dead fallen leaf samples were collected from 0.25 m2
Developmental stages of Ceutorhynchus pallidactylus and Ceutorhynchus obstrictus
were examined in each year, therewith the feeding and mating behaviour of these
species was observed as well. At the beginning of the swarming, rape plants were
planted out into five plastic bins and covered with mesh tissue. These newly
established isolators were placed in open-air circumstances beside the trial plot.
Thereafter the isolators were checked regularly making notes of the egg laying and the
point of time when different larval stages, pupae and new adults emerged. With the
help of field isolators we were able to make comparisons among species in the four
consecutive years.
areas
as sampling units. The samples were then placed in three-ply paper bags. Glass
receptacles were attached to the openings of the bags establishing separator bags,
which then were put on the insectary of the Department of Applied Zoology. The
separator bags were checked up every day. After the emergence of the first beetles in
the receptacles yellow plates were placed in the trial plot. Some salt was added to the
water in order to decrease its freezing point avoiding the night frost. In addition to it,
five drops (approx. 1g/l) of washing-up liquid was dribbled into the water to reduce the
surface tension avoiding the get-out of beetles. The plates were used for signalization
and prediction of the beginning of the mass swarming into the plant stock. Every three
days after settling beetles were collected only by netting, using sweep-net. In order to
obtain a sufficient number of adults for the later identification of species, on each
occasion three times ten net-strokes were made both on the edge and in the middle of
the experimental plot. Adults caught per ten net-strokes were handled separately.
Stereo microscopes were used for identifying the weevils.
RESULTS AND DISCUSSION
Meteorological conditions of the four examined years were different but there were
similarities between the features of the temperatures and the swarming periods as
well. The early spring of 1999 and 2002 was quite similar. The coming out of
Ceutorhynchus species from their hibernation places started early in February in both
years. The curve of the swarming had two peculiar peaks in 1999 and in 2002. The peak
in early March was followed by cold snap so the swarming culminated only from the end
of April. The weather conditions in spring of 2000 were comparable to those in 2001.
The coming of spring was not so early than in the two other examined years. Settling
into the field became multitudinous from the end of March. There were not two
specific peaks on the curve of swarming instead there was a progressive rise and a
decline in the number of adults netted in the field. The obvious dominance of two
species was detected within the Ceutorhynchus genus. C. pallidactylus and C.
obstrictus were dominant among the four discovered species in each examined year. C.
napi occurred in each year but in a substantially lower number than the dominating
species. The appearance of C. pleurostigma in early spring can be ascribed to the
adults of the spring-race of this species, which never lays eggs in winter canola.
Individuals netted in early summer were however the adults of the autumnal race of C.
pleurostigma which had taken nourishment before their summer aestivation (Figure 1-
4.).

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27.03.1999
03.04.1999
10.04.1999
17.04.1999
24.04.1999
01.05.1999
08.05.1999
15.05.1999
22.05.1999
29.05.1999
05.06.1999
12.06.1999
19.06.1999
26.06.1999
03.07.1999
10.07.1999
C. pleurosti gma
C.napi
C. obstric tus
C. pallidact ylus
0
10
20
30
40
50
60
70
80
90
100
110
120
130
number of adults /10 netsrokes
Figure 1. Swarming of Ceutorhynchus species in 1999
31.03.2000
07.04.2000
14.04.2000
21.04.2000
28.04.2000
05.05.2000
12.05.2000
19.05.2000
26.05.2000
02.06.2000
09.06.2000
16.06.2000
23.06.2000
30.06.2000
07.07.2000
14.07.2000
C. pleurosti gma
C.napi
C. pallidact ylus
C. obstric tus
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
number of adults/10 netstrokes
Figure 2. Swarming of Ceutorhynchus species in 2000
17.03.2001
24.03.2001
31.03.2001
07.04.2001
14.04.2001
21.04.2001
28.04.2001
05.05.2001
12.05.2001
19.05.2001
26.05.2001
02.06.2001
09.06.2001
16.06.2001
23.06.2001
30.06.2001
07.07.2001
C. pleurosti gma
C.napi
C. pallidact ylus
C. obstric tus
0
10
20
30
40
50
60
70
80
90
number of adults/10 netstrokes
Figure 3. Swarming of Ceutorhynchus species in 2001

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Comm. Appl. Biol. Sci, Ghent University, 75/3, 2010
06.03.2002
13.03.2002
20.03.2002
27.03.2002
03.04.2002
10.04.2002
17.04.2002
24.04.2002
01.05.2002
08.05.2002
15.05.2002
22.05.2002
29.05.2002
05.06.2002
12.06.2002
19.06.2002
26.06.2002
03.07.2002
C. pleurosti gma
C.napi
C. obstric tus
C. pallidact ylus
0
10
20
30
40
50
60
70
80
90
100
110
120
number of adults /10 netstrokes
Figure 4. Swarming of Ceutorhynchus species in 2002
In order to study the egg laying and the average fertility of Ceutorhynchus females rape
plants were planted out into field isolators and the number of laid eggs and the length
of the developmental stages were observed every day. Owing to the various
meteorological conditions of years the length of developmental stages was different.
The values determined by us are the equivalent of the data in the scientific literature
(Table 1.).
Figure 5-6. Ceutorhynchus obstrictus & Ceutorhynchus pallidactylus
(taken by Zs. Marczali)
Figure 7-8. Ceutorhynchus pleurostigma & Ceutorhynchus napi
(taken by Zs. Marczali)

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Table 1. Average length of developmental stages of C. pallidactylus and C. obstrictus
C. pallidactylus Average of years 1999-2002
embryonic development (days)
9±2
larval stage (days)
35±3
pupation and appearance of new adults (days)
24±2
whole developmental period (days) 68±7
C. obstrictus
Average of years 1999-2002
embryonic development (days)
10±3
larval stage (days)
35±2
pupation and appearance of new adults (days) 25±2
whole developmental period (days) 70±7
CONCLUSIONS
Two species of the genus Ceutorhynchus were dominant within the whole collected
material: C. pallidactylus and C. obstrictus. Their frequency of occurrence was 88-90%
among the identified adults. We found that C. obstrictus was the last species to settle.
C. napi occurred in the trial plot every year but its percentage hung far behind the
dominant species; its frequency of occurrence was 7-10%. In the case of C.
pleurostigma we experienced the specific occurrence that some individuals could be
netted shortly after C. pallidactylus and C. napi but hereupon they came to collected
material only in May. The appearance of C. pleurostigma in early spring can be
ascribed to the adults of the spring-race of this species which never lays eggs in winter
canola. The individuals netted in early summer were however the adults of the
autumnal race of C. pleurostigma which had taken nourishment before their summer
aestivation. It is just possible that other Meligethes and Ceutorhynchus species occur in
different regions of Hungary. To make these questions clear it is suggested performing
further investigations.
ACKNOWLEDGEMENTS
We should like to express our thanks to the University of Pannonia, Georgikon Faculty
(Keszthely), Institute of Plant Protection, for placing the experimental area at our
disposal. The later identification work of collected weevil species was funded by the
„Liveable Environment and Healthier People – Bioinnovation and Green Technology
Research at the University of Pannonia, TÁMOP 4.2.2-08/1/2008-0018” research project
of the Hungarian Government. The project is being co-financed by European Social
Fund with the support of the European Union.
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I.H. (2003). Spatial distribution of pest insects in oilseed rape: implications for integrated pest
management. Agric. Ecosyst. Environ., 95: 509-521.
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