Open Life Sci. 2015; 10: 1–6
Research Article
Open Access
Peter Kaňuch, Anna Sliacka, Anton Krištín*
Habitat-conditioned feeding behaviour
in Barbitistes constrictus (Orthoptera: Tettigoniidae)
Abstract: Some insect herbivores can regulate their
nourishment intake by different feeding behaviour.
This mechanism allows them to persist with utilising
different food resources according to the composition of
the vegetation within their habitats. Using a two-choice
experiment, we analysed foraging behaviour in females
of the tree-dwelling bush-cricket Barbitistes constrictus
(Orthoptera), which originated from two different
forest habitats, spruce and beech forest. We found that
individuals from the spruce forest mainly foraged on
needle tips, and thus they nibbled more needles per day
than individuals from the beech forest (medians 106.0 vs.
42.5; p < 0.0001). However, when the contents of droppings
were dissected, the volume of consumed spruce was
similar in both groups of bush-crickets (median > 90%),
which is explained by the different feeding techniques of
bush-crickets from different habitats. We propose possible
scenarios for bush-cricket feeding adaptations to the
deleterious effects of the host plant chemical compounds
serving as a plant defence against herbivores.
Keywords: Diet, Bush-crickets, Phytophagy, Insect,
Choice, Woodland
DOI 10.1515/biol-2015-0001
Received March 4, 2014; accepted August 12, 2014
1 Introduction
Many herbivorous insects are consistent in their feeding
habits during their evolution, but some species may alter
their foraging behaviour as a response to changes within
*Corresponding author: Anton Krištín: Institute of Forest Ecology,
Slovak Academy of Sciences, 960 53 Zvolen, Slovakia, E-mail:
[email protected]
Peter Kaňuch, Anna Sliacka: Institute of Forest Ecology, Slovak
Academy of Sciences, 960 53 Zvolen, Slovakia
their host plants [1,2]. While strictly monophagous species
suffer from a deficiency of eating their preferred food and
are forced to migrate into new areas [e.g. 3,4], other species
are able to persist with utilising different food resources
according to the composition of the vegetation within
their habitats [5,6]. A balanced intake of nutrients is the
most limiting factor influencing the fitness of herbivores
[e.g. 7,8]. However, insect herbivores can actively regulate
protein-carbohydrate intake using both physiological and
behavioural mechanisms [reviewed by 9,10].
One such behavioural mechanism can be an insect’s
ability to adapt feeding behaviour in different habitats,
and is defined as a change in behaviour that comes with
experience [11]. It can facilitate host selection and feeding
strategy in herbivorous species and is often interpreted
as an adaptive consequence of natural selection [12-14].
This insect’s ability has been clearly documented
through artificial selection and conditioning over several
generations that produced populations with improved
behavioural responses [e.g. 15,16]. Therefore, some species
that are successfully introduced into new areas or habitats
may also attack plants that were not previously known to
be acceptable for them, which is very important for the
control of pests [17-19].
In order to investigate how a herbivorous insect can
alter its foraging behaviour, we used the tree-dwelling and
flightless bush-cricket, Barbitistes constrictus (Orthoptera:
Tettigoniidae). The range of the species closely matches
the distribution of coniferous and beech forests in Central
and Eastern Europe [e.g. 20,21,28]. However, besides
its primary habitat, it seldom also breeds (most likely
thanks to human-mediated introduction events, e.g. [2])
in non-characteristic areas including broadleaved forests.
Thus the availability of the most preferred coniferous
food [20,22,23] strongly differs in these habitats as it is
either superabundant (in spruce forests) or very limited
(in beech forests). In addition, such populations are
potentially long-term conditioned to overcome deleterious
effects of different secondary carbon-based compounds,
which are synthesised by available host plants to defend
against herbivores (monoterpenes in spruce versus
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2 P. Kaňuch et al.
phenols in beech) [24,25]. Therefore, one can hypothesise
that populations are subjected to natural selection on
account of differences in food plants and their different
parts [cf. 11,26]. In this experimental study, we analysed
the foraging behaviour of B. constrictus in relation to
the source environment from where these individuals
originated.
2 Experimental Procedures
2.1 Study species
The eastern saw-tailed bush-cricket, B. constrictus, is a treedwelling species occurring mainly in coniferous forests,
but some isolated populations can also be found in forests
where broadleaved trees (beech, oak, hornbeam) dominate
[22,27]. Although the species was found to be a pest among
the seedlings of conifers in the past, nowadays it is recorded
in very low abundance, probably because of the change in
forest management towards more nature-friendly practices
excluding monoculture plantations [20,21]. As a herbivorous
species, it can consume a wide variety of plants, but it
mainly feeds upon the needles of the Norway spruce (Picea
abies) and Scots pine (Pinus sylvestris) [20,21,29]. Eggs are
hatched after 1–3 years (winter diapauses) depending on
the local climatic conditions and five or six nymphal instars
precede adult moulting [21,23]). Adults that reach a body
length of 14–25 mm are short-winged, hence flightless,
with an average adult lifetime of about two months [29].
This species has two colour phenotypes – dark or light
green – with possible intermediate forms [20]. Though
dark-green are the most typical, light-green individuals
prevail in broadleaved forests (see below) where specific
environmental conditions can determine their body colour
[cf. 30].
2.2 Experimental design
For the lab experiment, we used bush-crickets hatched in
natural conditions; thus the sample size was limited by
the rare occurrence (especially in broadleaved forests)
and difficult field collection of the species [21]. Third
to fifth nymphal instars were collected from woody
vegetation by sweeping hand nets from May 25 until
June 8 (2010 and 2011) in Central and Northern Slovakia
(48°29´–49°09´N, 19°01´–19°55´E). We sampled bushcrickets in different source forest habitats regarding a
dominant tree species (i.e. >90% of cover in the canopy
layer) and pooled individuals from several independent
sites into two groups. Individuals from a ‘spruce forest’
(dominant tree species – P. abies) were collected at two
sites (1068–1658 m a.s.l.) while individuals from a ‘beech
forest’ (dominant tree species – European beech, Fagus
sylvatica) were collected at five sites (497–868 m a.s.l.).
After transporting the specimens into the lab, they
were reared (7–10 days) according to standard conditions
(air temperature 22–26 °C, relative humidity ~50%, natural
daylight) and fed leaves of European dewberry, Rubus
caesius, ad libitum. All individuals, before entering the
experiment (June 24 – July 10), were kept acclimatised
for at least one week or until they reached adulthood.
Finally, 22 adult females (2–5 days of adulthood) from the
spruce forest (91% of them were classified as dark-green
phenotype) and 23 (2–6 days of adulthood) from the beech
forest (74% light-green phenotype) were used for 10 days
in a parallel experiment (from both populations) that
involved a choice of two different diets. (No males were
involved in the experiment because of the low sample size.)
The standard daily fresh-food dose (twigs stored in a glass
of water) comprised one twig of spruce where one-year-old
needles had grown on 25 cm of its total length and one twig
of young beech (<5 years old) wearing three fresh leaves,
each with an average length of 6 cm. Both the offered host
plant materials were collected from plant individuals and
twigs of the same age at one site daily during the time of
the experiment. Each female was housed separately in a
glass container (volume 4 l) with air circulating through the
netting at the top (air temperature 22–26°C, relative humidity
~50%, natural daylight). Along with the replacement of
food and fresh water, the containers that they lived in were
cleaned each day from 06:00 to 06:30 CEST. We recorded
two parameters of foraging behaviour each day of the
experiment: 1) the number of needles that had signs of
being nibbled by bush-crickets according to the description
[29], and 2) the relative proportion of spruce droppings from
all of the droppings that were defecated. The consumed
needle area was noted (measured as % of needle length)
in both bush-cricket populations. A needle was considered
to be fully consumed when >90% of its length was missing
and as nibbled when only tip of the needle was consumed
(<10%). Less than 5% of beech leaves had traces of nibbling
(in positive cases a maximum 20% of the leaf surface), so
we did not compare the damage to beech leaves between
the two tested groups. All the droppings were dissected
under 30× magnification using a Motic SMZ-168 stereo
zoom microscope and the determination of their contents
was based on the structure of the plant tissue remains
[31]. These include observations of spruce having a light
fibrous structure and beech showing green fragments of
leaf nervation (Fig. 1). Before the experiment, the structure
of defecated remains was verified using independent
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Conditioned foraging of bush-crickets 3
individuals when only single plant species were provided;
thus, it was possible to easily classify each dropping as
either a spruce or beech dropping. This method allowed
the unambiguous classification of droppings into these two
categories and the proportion of some intermediate forms
(mixed spruce and beech plant material in one dropping)
was negligible.
2.3 Data analysis
The experiment was designed so that each individual was
tested repeatedly for ten days. Therefore, we analysed data
using a repeated-measures analysis of variance. We tested
for the source habitat as a between-groups effect (spruce
or beech forest) and for the day (day in the experiment)
and source habitat × day (interaction term) as withingroups effects. The number of needles that had signs of
being nibbled and the proportion of spruce droppings
from all of the droppings that were defecated did not have
normal distributions, thus we log-transformed data prior to
analysis. We used Mauchly’s test to control for the sphericity
assumption of univariate repeated-measures analysis. When
the data did not meet that assumption, degrees of freedom
and p-values were adjusted by using the Greenhouse-Geisser
correction for effects with more than two levels. The total
number of droppings per individual was compared between
the two groups by non-parametric Mann-Whitney U test.
Computations were performed in R 2.11.1 [32].
Figure 1: Determination of food consumed by the Barbitistes
constrictus females based on the structure of the plant tissue
remains; dissected droppings containing spruce needles (a) and
beech leaf fragments (b).
3 Results
In the experiment we found that the source habitat had
a highly significant effect on the number of needles
nibbled by adult bush-cricket females (p < 0.001; Table 1,
Fig. 3a). Individuals from the spruce forest mainly foraged
only on needle tips (<10% of the needle length) and
often tore off needles from the twig while eating (Fig. 2).
Figure 2: Spruce needles with tips nibbled by bush-crickets
originating from the spruce forest.
Table 1: Effects of the source habitat and the day with interaction term on the number of needles that had signs of being nibbled during the
10-day experiment (repeated-measures ANOVA)
Effect
Between groups
source habitat
Error
Within groups
day
source habitat × day
Error
df
dfa
1
43
9
9
387
5.7
5.7
245.4
MS
F
p
15.8
0.9
16.25
<0.001
0.1
0.2
0.3
0.53
0.96
0.850
0.477
pa
0.698
0.429
a
Since sphericity could not be assumed (Mauchly’s test, ε = 0.63, p < 0.05), degrees of freedom and p-values were adjusted by GreenhouseGeisser correction.
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4 P. Kaňuch et al.
In contrast to this, individuals from the beech forest had a
different strategy, since they almost consumed the entire
needle (>90% of the needle length). Hence, individuals
from the spruce forest nibbled more needles per day
than those from the beech forest (medians 106.0 vs. 42.5;
Fig. 3a). The day of the experiment did not have an effect
on this pattern.
Though they had different strategies when foraging
on needles, both groups of bush-crickets avoided beech
leaves as spruce droppings represented 93.6% (median) in
individuals from the spruce forest and 90.2% in individuals
from the beech forest (Fig. 3b). This composition of
droppings did not change significantly during the
experiment (Table 2). Nevertheless, the overall appetite of
the individuals was very similar regardless of the source
habitat. Individuals from both the spruce and beech
forest produced almost the same number of droppings,
7644 and 7621 respectively, i.e. 34 (33–35) droppings a day
(as a median and 95% CI; Z = 0.2, p = 0.842).
effects of their hosts [24,33]. When a population is exposed
to such an effect on individuals’ fitness over generations,
a selection process can alter foraging behaviour [16,26].
In our case, the bush-crickets from the spruce forest
adapted to consume only high-quality food, the needle
tips [24]. The observed variation in foraging behaviour
4 Discussion
Our experimental study showed that the foraging
behaviour of B. constrictus individuals may differ with
regard to the source habitat they come from [cf. 9,23].
Besides equal consumption of spruce mass (expressed
by the production of droppings) in both tested groups,
individuals from the spruce forest nibbled significantly
more needles which was the result of a different foraging
strategy. To our knowledge, this is the first report on
conditioned feeding strategy coming with experience
in needle eating insect. Specialised foraging on conifer
needles seems to be typical for all developmental stages
in our studied species and it is a very special diet among
orthopterans [22,23]. The consumption of both tested
plants is generally possible for specialised herbivores
only, which possess mechanisms to overcome the harmful
Figure 3: (a) The number of nibbled needles per day in females that
originated from different source habitats and (b) relative proportion
of spruce droppings from all droppings defecated per day (n = 23
females from beech forest, 22 from spruce forest). Box-plots represent medians (lines), 95% confidence intervals (notches), quartiles
(boxes) and non-outlier ranges (whiskers).
Table 2: Effects of the source habitat and the day with interaction term on the relative proportion of spruce droppings from all of the droppings that were defecated during the 10-day experiment (repeated-measures ANOVA)
Effect
Between groups
source habitat
Error
Within groups;
day
source habitat × day
Error
df
dfa
1
43
9
9
387
6.3
6.3
272.4
MS
F
p
1.1
0.9
1.21
0.277
0.1
0.2
0.3
0.22
1.23
0.992
0.277
pa
0.942
0.300
Since sphericity could not be assumed (Mauchly’s test, ε = 0.70, p < 0.05), degrees of freedom and p-values were adjusted by GreenhouseGeisser correction.
a
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when the bush-crickets consumed the generally preferred
spruce [20,22,23] supports this possibility.
Although our data set is limited due to methodological
constraints, we may suggest that differences in obtaining
nutrition from spruce needles have most likely evolved
through natural selection [15,16]. Here we briefly
propose possible scenarios of adaptations that are rather
remarkable in insect evolution.
What needs to be considered first is that coniferous
foliage has a characteristic increase in concentration
and amount of monoterpenes along the needle from tip
to base, which deters herbivore insects from feeding on
entire needles [24]. Preference for needle tips may also
be related to softer tissue or higher nutritional value
and can be demonstrated by individuals that originated
from spruce forests and preferred needle tips. Thanks
to this adaptation, bush-crickets from spruce forests
can effectively avoid harmful effects and maintain their
fitness or breeding success better than individuals from
beech forests [2,14,33]. This hypothesis is supported by
a significantly higher abundance of studied species in
coniferous than in broadleaved forests [20,21]. The other
consideration involves individuals that hatched in a beech
forest and artificial surplus of spruce needles as a valuable
food source could alter their behaviour [10]. Either that,
or bush-crickets are possibly adapted to worse beech
(phenolic) conditions, this encourages the feeding of
whole needles when available [23,25]. Both considerations
are quite plausible as conditioned behaviour appears to be
an adaptation mechanism when it comes to the foraging of
B. constrictus. However, multi-choice feeding experiments
with different host plants may shed more light on the diet
selection process of this herbivorous insect.
Acknowledgements: We would like to thank V. Badinková
for her assistance during the experiments and P. Tuček and
M. Mikuš for help in the field. This work was funded by the
Scientific Grant Agency (VEGA 2/0157/11, 2/0035/13) and the
Slovak Research and Development Agency (APVV-0497-10).
References
[1] Dethier V.G., Evolution of feeding preferences in phytophagous
insects, Evolution, 1954, 8, 33-54
[2] Bernays E.A., Chapman R.F., Host-plant selection by
phytophagous insects, Chapman & Hall, New York, 1994
[3] Singer M.C., Thomas C.D., Evolutionary responses of a butterfly
metapopulation to human- and climate-caused environmental
variation, Am. Nat., 1996, 148, 9-39
[4] Hanski I., Singer M.S., Extinction-colonization dynamics and
host-plant choice in butterfly metapopulation, Am. Nat., 2001,
158, 341-353
Conditioned foraging of bush-crickets 5
[5] Berner D., Blanckenhorn W.U., Korner C., Grasshoppers cope
with low host plant quality by compensatory feeding and food
selection: N limitation challenged, Oikos, 2005, 111, 525-533
[6] Franzke A., Unsicker S.B., Specht J., Köhler G., Weisser W.W.,
Being a generalist herbivore in a diverse world: how do diets
from different grasslands influence food plant selection and
fitness of the grasshopper Chorthippus parallelus? Ecol.
Entomol., 2010, 35, 126-138
[7] Behmer S.T., Joern A., Coexisting generalist herbivores occupy
unique nutritional feeding niches, P. Natl. Acad. Sci. USA,
2008, 105, 1977-1982
[8] Pearson R.E.G., Behmer S.T., Gruner D.S., Denno R.F., Effects
of diet quality on performance and nutrient regulation in an
omnivorous katydid, Ecol. Entomol., 2011, 36, 471-479
[9] Bernays E.A., Bright K.L., Mechanisms of dietary mixing in
grasshoppers: A review, Comp. Biochem. Phys. A, 1993, 104,
125-131
[10] Behmer S.T., Insect herbivore nutrient regulation, Annu. Rev.
Entomol., 2009, 54, 165-187
[11] Papaj D.R., Lewis A.C., Insect learning: Ecological and
evolutionary perspectives, Chapman & Hall, New York, 1993
[12] Papaj D.R., Prokopy R.J., Ecological and evolutionary aspects of
learning in phytophagous insects, Annu. Rev. Entomol., 1989,
34, 315-350
[13] Cunningham J.P., Jallow M.F.A., Wright D.J., Zalucki M.P.,
Learning in host selection in Helicoerpa armigera (Hübner)
(Lepidoptera: Noctuidae), Anim. Behav., 1998, 55, 227-234
[14] Dukas R., Bernays E.A., Learning improves growth rate in
grasshoppers, P. Natl. Acad. Sci. USA, 2000, 97, 2637-2640
[15] McGuire T.R., Hirsch J., Behavior-genetic analysis of Phormia
regina: conditioning, reliable individual differences, and
selection, P. Natl. Acad. Sci. USA, 1977, 74, 5193-5197
[16] Mery F., Kawecki T.J., Experimental evolution of learning ability
in fruit flies, P. Natl. Acad. Sci. USA, 2002, 99, 14274-14279
[17] Cox G.W., Alien species and evolution: The evolutionary
ecology of exotic plants, animals, microbes, and interacting
native species, Island Press, Washington DC, 2004
[18] Scriber J.M., Integrating ancient patterns and current dynamics
of insect-plant interactions: Taxonomic and geographic
variation in herbivore specialization, Insect Sci., 2010, 17,
471-507
[19] Cunningham J.P., Zalucki M.P., West S.A., Learning in
Helicoverpa armigera (Lepidoptera: Noctuidae): a new look at
the behaviour and control of a polyphagous pest, B. Entomol.
Res., 1999, 89, 201-207
[20] Detzel P., Die Heuschrecken Baden-Württembergs, Ulmer,
Stuttgart, 1998, (in German)
[21] Holuša J., Heralt P., Drápela K., Occurrence and bionomy of
Barbitistes constrictus (Orthoptera: Tettigoniidae) in the
eastern part of the Czech Republic, J. Forest Sci., 2006, 52,
61-73
[22] Ingrisch S., Köhler G., Die Heuschrecken Mitteleuropas,
Westarp Wissenschaften, Magdeburg, 1998, (in German)
[23] Gottwald J., Richter C., Wörner M., Habitatwahl, Nahrungswahl
und Entwicklung von B. serricauda (Fabricius, 1787) und B.
constrictus Brunner von Wattenwyl, 1878 (Phaneropterinae),
Articulata, 2002, 17, 51-78, (in German)
[24] Litvak M.E., Monson R.K., Patterns of induced and constitutive
monoterpene production in conifer needles in relation to insect
herbivory, Oecologia, 1998, 114, 531-540
Unauthenticated
Download Date | 6/17/17 4:36 PM
6 P. Kaňuch et al.
[25] Petrakis P.V., Spanos K., Feest A., Daskalakou E., Phenols in
leaves and bark of Fagus sylvatica as determinants of insect
occurrences, Int. J. Mol. Sci., 2011, 12, 2769-2782
[26] Dukas R., Evolutionary biology of insect learning, Annu. Rev.
Entomol., 2011, 53, 145-160
[27] Zuna-Kratky T., Karner-Ranner E., Lederer E., Braun B., Berg
H-M., Denner M., et al., Verbreitungsatlas der Heuschrecken
und Fangschrecken Ostösterreichs, Verlag Naturhistorisches
Museum, Wien, 2009, (in German)
[28] Krištín A., Kaňuch P. (eds), Distribution of Barbitistes
constrictus in Slovakia, http://www.orthoptera.sk, 2013
[29] Haber A., Opaślik sosnowiec Barbitistes constrictus Br. Watt.
(Locustidae Orth.), Państwowe wydawnictwo rolnicze i leśne,
Warszawa, 1953, (in Polish)
[30] Saglam I.K., Caglar S.S., Distribution and habitat characteristics of the color polymorphic bush-cricket Isophya rizeensis
Sevgili (Orthoptera: Tettigoniidae: Phaneropterinae) in Turkey,
Entomol. News, 2005, 116, 309-324
[31] Gangwere S.K., Monograph on food selection in Orthoptera, T.
Am. Entomol. Soc., 1961, 87: 67-230
[32] R Development Core Team, R: A language and environment for
statistical computing, R Foundation for Statistical Computing,
Vienna, 2010
[33]Nykänen H., Koricheva J., Damage-induced changes in woody
plants and their effects on insect herbivore performance: a
meta-analysis, Oikos, 2004, 104, 247-268
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