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Journal ArticleDOI

Performance of moth larvae on birch in relation to altitude, climate, host quality and parasitoids

01 Jul 1999-Oecologia (Springer)-Vol. 120, Iss: 1, pp 92-101
TL;DR: If, as predicted, the climate gradually warms up, the effects of warmer summers on the outbreaks of E. autumnata suggest a decrease in outbreak intensity, the most important factor appeared to be egg mortality related to minimum winter temperature, followed by parasitism and, finally, the variation in food plant quality.
Abstract: We studied topographical and year-to-year variation in the performance (pupal weights, survival) and larval parasitism of Epirrita autumnata larvae feeding on mountain birch in northernmost Finland in 1993–1996. We found differences in both food plant quality and parasitism between sites ranging from 80 m to 320 m above sea level. Variation in food plant quality had particularly marked effects on larval survival. The advanced phenology of the birches in relation to the start of the larval period reduced pupal weights. Parasitism rates were different between years and between sites. The clearest site differences were in the proportions of different parasitoid species: Eulophus larvarum was most abundant at the lowest-altitude sites, and Cotesia jucunda at the highest. Differences in the performance of E. autumnata were related to temperature conditions: at higher temperatures, survival and the egg production index were lower, and larval parasitism was higher than at lower temperatures. The higher parasitism at higher temperatures was probably due to greater parasitoid activity during warmer days. In the comparison of different sources of spatial and annual variation in the performance of E. autumnata, the most important factor appeared to be egg mortality related to minimum winter temperature, followed by parasitism and, finally, the variation in food plant quality. If, as predicted, the climate gradually warms up, the effects of warmer summers on the outbreaks of E. autumnata suggest a decrease in outbreak intensity.

Summary (1 min read)

Jump to: [Introduction][Material and methods][Results] and [Discussion]

Introduction

  • It is generally accepted that the population dynamics of insect species showing regular cycles are driven by delayed negative feedbacks (Berryman et al. 1987; Berryman 1996).
  • In addition to abiotic factors, biotic factors can also contribute to this variation.
  • First, the authors test whether sites at altitudes ranging from 80 m to 320 m above sea level (a.s.l.) show di erences, and whether these di erences are consistent between years.
  • Second, the authors test whether the variation in E. autumnata performance and parasitism can be explained by altitude and/or temperature variation among sites and years.

Material and methods

  • The study was conducted near the Kevo Subarctic Research Station (69°45¢N, 27°E) in northern Finland.
  • Daily mean temperatures and e ective temperature sums were calculated for each site and year on the basis of measured (when available) or estimated eight daily temperatures.
  • The authors used the following response variables.
  • As parasitism probabilities were high in the study years, survival without the e ects of parasitism was calculated as the proportion (out of the number of enclosed eggs) of larvae found as full grown or parasitized at the end of the larval period.

Results

  • Variation among sites and years Total variation in the annual temperature sums at their study sites during the study years ranged from 695 dd5 to 427 dd5, which is comparable to roughly a 200-km latitudinal shift in Finnish Lapland (see Ritari and Nivala 1993).
  • There were di erences between both sites and years in the proportion of larvae found and the egg production index (Table 2).
  • The apparent parasitism probabilities were also di erent between the sites in di erent years (Table 2): they were highest at most of the sites in 1994 and 1995, but in the two altitudinally highest sites, in 1996.

Discussion

  • Local climate and birch quality for E. autumnata.
  • The authors found a positive correlation between high temperature during the last 2 larval weeks and the apparent parasitism probability.
  • Predation and/or parasitism by generalist parasitoids are also suggested to be the reasons for the lack of outbreaks in the southern parts of the distribution area of E. autumnata (Haukioja et al.
  • The authors results suggests that warmer summers may have opposite consequences for E. autumnata populations than warmer winters (cf. Virtanen et al. 1998).
  • The authors are grateful to Matt Ayres, Pekka Kaitaniemi, and Kai RuohomaÈ ki for providing access to their data.

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Performance of moth larvae on birch in relation to altitude,
climate, host quality and parasitoids
Virtanen, T.
Springer
1999
Virtanen, T. and Neuvonen, S. 1999. Performance of moth larvae on birch in relation to
altitude, climate, host quality and parasitoids.Oecologia 120: 92-101
http://hdl.handle.net/1975/278
Downloaded from Helda, University of Helsinki institutional repository.
This is an electronic reprint of the original article.
This reprint may differ from the original in pagination and typographic detail.
Please cite the original version.

Tarmo Virtanen á Seppo Neuvonen
Performance of moth larvae on birch in relation to altitude,
climate, host quality and parasitoids
Received: 4 January 1999 / Accepted: 22 March 1999
Abstract We studied topographical and year-to-year
variation in the performance (pupal weights, survival)
and larval parasitism of Epirrita autumnata larvae
feeding on mountain birch in northernmost Finland in
1993±1996. We found dierences in both food plant
quality and parasitism between sites ranging from 80 m
to 320 m above sea level. Variation in food plant quality
had particularly marked eects on larval survival. The
advanced phenology of the birches in relation to the
start of the larval period reduced pupal weights. Para-
sitism rates were dierent between years and between
sites. The clearest site dierences were in the proportions
of dierent parasitoid species: Eulophus larvarum was
most abundant at the lowest-altitude sites, and Cotesia
jucunda at the highest. Dierences in the performance of
E. autumnata were related to temperature conditions: at
higher temperatures, survival and the egg production
index were lower, and larval parasitism was higher than
at lower temperatures. The higher parasitism at higher
temperatures was probably due to greater parasitoid
activity during warmer days. In the comparison of
dierent sources of spatial and annual variation in the
performance of E. autumnata, the most important factor
appeared to be egg mortality related to minimum winter
temperature, followed by parasitism and, ®nally, the
variation in food plant quality. If, as predicted, the cli-
mate gradually warms up, the eects of warmer sum-
mers on the outbreaks of E. autumnata suggest a de-
crease in outbreak intensity.
Key words Epirrita autumnata á Lepidoptera:
Geometridae á Betula pubescens ssp. czrepanovii á
Insect outbreaks á Climate change
Introduction
It is generally accepted that the population dynamics of
insect species showing regular cycles are driven by de-
layed negative feedbacks (Berryman et al. 1987; Berry-
man 1996). Factors causing this kind of feedback are
biotic: predators, parasitoids, pathogens, or induced
changes in food quality. However, even in the case of
these cyclically ¯uctuating species, abiotic factors may
synchronise outbreaks over large areas (Myers 1998)
and/or determine the spatial distribution of forest
damage (Tenow 1975; Martinat 1987). There is often
large landscape-scale variation in insect densities during
an outbreak (Kallio and Lehtonen 1973; Tenow 1975;
Larsson and Tenow 1984; Broekhuizen et al. 1993;
Ruohoma
È
ki et al. 1997). In addition to abiotic factors,
biotic factors can also contribute to this variation. To
better understand the population dynamics of insect s,
both the direct eects of climate and those mediated via
biotic factors (host quality, natural enemies) should be
incorporated in spatially explicit population dynamic
models (cf. Hunter 1997; see also Lawton 1994) .
Epirrita autumnata (Bkh.) is a geometrid moth peri-
odically defoliating large areas of mountain birch (Bet-
ula pubescens ssp. czerepanovii) forest, sometimes
causing the widespread death of trees along the Scan-
dinavian mountain chain and in Northern Fennoscandia
(Tenow 1972; Kallio and Lehtonen 1973). E. autumnata
shows regular cycles with variable amplitude in some
parts of its outbreak range (Andersson and Jonasson
1980; Bylund 1995), while in continental areas, the
outbreaks are irregular or lacking (Tenow 1972, 1996;
Oecologia (1999) 120:92±101 Ó Springer-Verlag 1999
T. Virtanen (&)
1
Section of Ecology, Department of Biology,
University of Turku,
FIN-20014 Turku, Finland
e-mail: tarmo.virtanen@metla.®, Fax: +358-16-3364640
S. Neuvonen
Kevo Subarctic Research Institute,
University of Turku,
FIN-20014 Turku, Finland
Present address:
1
Finnish Forest Research Institute,
Rovaniemi Research Station, Box 16,
FIN-96301 Rovaniemi, Finland

Tenow and Holmg ren 1987; Ruohoma
È
ki et al. 1997). It
is well known that the mortality of overwint ering eggs of
E. autumnata caused by winter minimum temperatures is
the main factor determining the topographical distri-
bution of damage in mountain birch forests; tempera-
tures in the valleys are generally low enough to kill the
eggs, while (due to temperature inversion) the upper
slopes are warmer during cold winter periods and out-
breaks may occur (Tenow 1972, 1975; Kallio and Leh-
tonen 1973; Niemela
È
1979; Virtanen et al. 1998).
Topographical and year-to- year temperature varia-
tion provide an opportunity to test dierent hypotheses
concerning the relationships between temperature and
the risk of forest insect outbreaks. Niemela
È
(1980)
proposed that the outbreaks of E. autumnata are asso-
ciated with low summer temperatures. On the other
hand, Ayres (1993) suggested that increased summer
temperatures enhance the development of E. autumnata
larvae more than that of their host trees, an increase of
1°C potentially tripling the population growth rate of
the herbivore. Finally, a general ly warmer environment
may also allow ants, parasitoids, and other natural en-
emies to kill a higher proportion of moth larvae and/or
pupae (Laine and Niemela
È
1980; Neuvonen et al. 1996,
see also: Karhu and Neuvonen 1998; Tanhuanpa
È
a
È
et al.
1999).
In this paper, we study topographical and year-to-
year variation in the performance (pupal weights, sur-
vival) and parasitism of E. autumnata larvae. First, we
test whether sites at altitudes ranging from 80 m to
320 m above sea level (a.s.l.) show dierences, and
whether these dierences are consistent between years.
Second, we test whether the variation in E. autumnata
performance and parasitism can be explained by altitude
and/or temperature variation among sites and years. We
also compare the potential strength of the eects (food
plant quality, parasitism) causing summer spatial vari-
ation in E. autumnata performance with that due to
variation in minimum winter temperatures. Finally, we
discuss how the predicted warmer summ er climate may
aect the population dynamics of E. autumnata.
Material and methods
Study area and sites
The study was conducted near the Kevo Subarctic Research Sta-
tion (69°45¢N, 27°E) in northern Finland. Four study sites were
used in 1993±1996 and six additional sites in 1995±1996 (Fig. 1,
Table 1). At each site, eight dierent birches within a 50 ´ 50 m
area were selected as study trees each year. The birches were from 2
to 5 m high (mean 3.2 m).
E. autumnata and birches
Larval performance was measured by enclosing 20 E. autumnata
eggs (from 20 dierent broods; ready to hatch within some hours)
into a mesh bag that was placed over the distal part of a branch
(about 1.5 m height; one per birch). The experiments were started
on dierent days at dierent study sites and years (an attempt was
Table 1 Description of the study sites: altitude above sea level,
yearly temperature sums, mean of temperature during larval period
in study years, and vegetation types (see criteria for the classi®ca-
tions in the legend to Fig. 1). Sites 1, 3, 6 and 8 were used every
year, others only in 1995 and 1996
Fig. 1 Location of the Kevo Meterological Station, and our study
sites. The major vegetation types in the area are based on the map of
Seppa
È
la
È
and Rastas (1980). Criteria for vegetation type classes: Pine
forest, at least 20% of the area covered by Scots pine; Mixed forest,
mountain birch forest with scattered Scots pines, with less than 20%
of the area covered by pines; Birch forest, some parts were damaged
by Epirrita autumnata in the mid-sixties and are only partly recovered;
Open mire, mire without forest cover; Barren fell top, area above the
tree limit
Site Altitude above
sea level (m)
Mean yearly
degree-days
over 2°C
Mean yearly
degree-days
over 5°C
Mean temperature
during larval period (°C)
Vegetation type
1 85 1031.6 640.0 10.20 Mixed forest
2 100 988.3 619.0 10.46 Mixed forest
3 190 992.4 615.0 10.27 Birch forest
4 200 908.9 551.0 9.94 Birch forest
5 215 922.1 557.6 10.27 Birch forest (near old Epirrita damage)
6 230 938.2 570.2 10.04 Birch forest
7 240 883.5 533.0 9.95 Birch forest (near old Epirrita damage)
8 285 829.7 489.1 10.09 Birch forest (near old Epirrita damage)
9 305 872.9 514.8 10.25 Birch forest (near treeline)
10 310 791.1 441.9 9.65 Birch forest (near treeline)
93

made to match the start of the experiment with average bud-burst
of the birches at each site); all the bags at each site were set up on
the same day. At the same time, the state of bud emergence was
estimated for every birch (mean of 20 buds) by comparing the
length of unfurled leaves to that of the bud scales (see Sulkinoja
and Valanne 1987); the phenology scale varied from 1 (leaves still
enclosed within buds) to 4 (leaf blades fully emerged) with an ac-
curacy of 0.5 units.
During the early larval period, ®ne mesh bags (0.4-mm mesh,
holes 0.2 mm; length 30 cm) were used to ensure that the young
larvae could not escape from the bags. When the larvae were in their
third instar, the mesh bags were changed to larger ones with a larger
mesh size (1-mm mesh, holes 0.8 mm; length 60 cm). The smallest
parasitoid of E. autumnata found in our study, Eulophus larvarum
(L.), could pass through the larger mesh, while larger species could
parasitize E. autumnata larvae at least by sticking their ovipositor
through the bag. The larvae were left to feed in the bags until the end
of their larval period, and the bags containing the larvae were
transported to the laboratory when the larvae started to pupate. The
larvae were allowed to pupate solitarily in 50-ml plastic vials con-
taining Sphagnum moss. The pupae were sexed and weighed after
2 weeks; emerged parasitoids were determined and counted.
Temperature measurement and modelling
Temperature was recorded (30-min intervals) at the study sites
(1994±1995 at all sites, in 1996 at seven sites) with HamsterTM (El-
pro, Buchs, Switzerland) dataloggers at a height of 1.5 m on one
birch in the centre of each study area. The dataloggers were protected
from direct sunlight. As we did not record temperature at any of the
sites in 1993 nor at three sites in 1996, we developed regression models
based on temperatures recorded at Kevo Meteorological Station
(within the study area; Fig. 1) for estimating the missing data.
Temperature recorded (eight times daily; every 3 h from 3.00 a.m. to
12.00 p.m. GMT) at the Meteorological Station (T
stat
) was used as
the predictor variable. The site-speci®c temperatures at the respective
times were estimated using the model: T
ij
= a
ij
+b
ij
T
stat
. Separate
parameters (a
ij
and b
ij
; i = index of site, j = index of time) were
estimated for each site and the daily measurement time because ra-
diation conditions dier between the study sites and at dierent times
of the day due to topography. We used all the available site-speci®c
measurements from June to August for parameter estimation.
Daily mean temperatures and eective temperature sums were
calculated for each site and year on the basis of measured (when
available) or estimated eight daily temperatures. We calculated the
eective temperature sums using both +2°C and +5°C as the
threshold value (expressed as degree-days over +2°C or +5°C,
dd2 or dd5). Temperature sum calculations traditionally use +5°C
as the threshold (e.g. Sarvas 1972; Ayres and MacLean 1987;
Sulkinoja and Valanne 1987; Ayres 1993), but a threshold of +2°C
gives the best ®t when predicting the emergence of mountain birch
leaves as a function of the temperature sum (our unpublished data;
M. Kozlov, personal communication).
In 1994, we also studied the within-area temperature variation
by placing digital thermometers on the study birches at a height of
1.5 m. The thermometers recorded minimum and maximum tem-
peratures. In addition to these measurements, the temperature
values were recorded every time the thermometers were removed
from the ®eld. Measurements were made in the 24 birches within
every area (study birches for the years 1993, 1994 and 1995) on 5
separate days with 2-week intervals. The mean dierences between
the minimum, maximum and collection time temperatures and the
area means were calculated for the each birch.
Data treatment
We used the following response variables.
(1) Pupal weight (mg) of E. autumnata. To remove weight dier-
ences due to variable sex ratios, male weights were transformed
to female weights before calculating the bag speci®c means
using the following equation: female pupal weight = )7.94 +
1.16 ´ male pupal weight (Kaitaniemi et al. 1999).
(2) Proportion of larvae found. As parasitism probabilities were
high in the study years, survival without the eects of para-
sitism was calculated as the proportion (out of the number of
enclosed eggs) of larvae found as full grown or parasitized at
the end of the larval period. Thus, 1±(proportion of larvae
found) estimates the mortality during the early larval period
and that caused by factors other than parasitoids (e.g. birch
foliage quality, weather). Proportion of larvae found also in-
cludes those full-grown larvae (about 1%) which were found
dead in the mesh bags: some of which were predated through
the mesh bags by spiders or ants.
(3) Egg production index. An estimate of egg production per en-
closing female assuming no mortality from parasitism. Pupal
mass correlates strongly with the potential and realised fecun-
dity of E. autumnata (Haukioja and Neuvonen 1985; Tammaru
et al. 1996). We used the following equation: eggs/
female = )101.9 + 2.93 ´ female pupal weight (mg) (Tam-
maru et al. 1996). Thus, egg production index = [proportion
of larvae found ´ ()101.9 + 2.93 ´ pupal weight)]/2.
(4) The apparent parasitism probability was calculated as the
proportion of parasitized larvae out of all larvae found.
(5) Apparent parasitism caused by dierent parasitoid species;
E. larvarum (L.), Eulophidae; Cotesia jucunda (Marshall),
Braconidae; Zele deceptor (Wesmael), Braconidae.
Statistical analysis
We analysed the data in two dierent steps. First, we made analyses
based on the birch-speci®c values (when within-site variation could
also be taken into account). In these analyses, the explanatory
variables were site (class variable), year (class variable), and their
interaction, bud state at the start of the experiment (continuous
variable), and birch-speci®c local climate (dierences in minimum,
mean, and maximum temperatures from the site means). As some
bags were destroyed by wind or other factors, the number of the
observations in survival and parasitism analyses was 193. As we did
not obtain pupal weight estimates for all the birches due to high
parasitism and/or low survival, in pupal weight and egg production
index analyses, the number of the observations was 139.
In the second step, we made our analyses on the basis of site-
speci®c means. As the bud state at the start of the experiment
signi®cantly aected, in the birch-speci®c analysis, some of the
response variables (Table 2, Fig. 2a±c), we removed bud state ef-
fects from the site-speci®c values by using the bud state as a co-
variate when calculating the site-speci®c values for pupal weight,
survival and egg production index. The altitude of the site and the
mean temperatures for the whole or dierent parts of the larval
period (®rst 2 weeks, next 2 weeks, and last 2 weeks) were also used
as continuous explanatory variables. In addition, the study year
(class variable) was used as an explanatory variable. Due to the
destruction of many bags we could not take sites 4 and 7 from the
year 1995 into the analyses, so the number of observations in the
analyses was 26. We performed all the ANOVAs using Proc GLM
(SAS 1990). In the analysis shown in Table 2 we used type III sums
of squares. In the analyses in Tables 3 and 4, we have presented
type I sums of squares; this enabled us to take into account ®rst the
year-, then altitude-, and ®nally the temperature-related variation.
However, even if we had used type III sums of squares in these
analyses, the results would have been the same.
Results
Variation among sites and years
Total variation in the annual temperature sums at our
study sites during the study years ranged from 695 dd5
94

to 427 dd5, which is comparable to roughly a 200-km
latitudinal shift in Finnish Lapland (see Ritari and
Nivala 1993). Site-speci®c means of the temperature
sums and mean temperatures are presented in Table 1.
When the eective temperature sums (dd5) are com-
pared to the mean temperature sum during the last
34 years (1963±1996), summer 1993 was the 6th, 1996
was the 8th, 1995 the 14th, and 1994 the 20th coldest at
the Kevo meteorological station. The total variation in
mean temperature during the larval period of E. au-
tumnata was from +9.0°C to +11.3°C at our study
sites. The temperature variation and timing of the larval
period during our study are presented in Fig. 2a±d.
Pupal weight of E. autumnata showed little or no
variation between the sites or years (Table 2); site means
calculated over the study years ranged from 64.7 mg to
76.2 mg, and yearly means only from 70.8 mg in 1993 to
72.3 mg in 1995. There were dierences between both
sites and years in the proportion of larvae found and the
egg production index (Table 2). The proportion of lar-
vae found was 40%, 70%, 62%, and 56% in 1993, 1994,
1995 and 1996, respectively. Yearly means in the egg
production index ranged from 20.0 in 1993 to 37.7 in
1994. Site and year interactions were not found in the
analyses of pupal weight, proportion of larvae found or
egg production index (Table 2). The advanced phenol-
ogy of the birches in relation to the start of the larval
period reduced the pupal weight and egg production
index (Fig. 3a±c, Table 2).
There were dierences between the years in the total
apparent parasitism probability: 36%, 62%, 63% and
35% in 1993, 1994, 1995 and 1996, respectively
(Table 2). The apparent parasitism probabilities were
also dierent between the sites in dierent years (Ta-
ble 2): they were highest at most of the sites in 1994 and
1995, but in the two altitudinally highest sites, in 1996.
The dierences in the parasitism probabilities of the
individual parasitoid species were greatest between the
sites, although year eects and and site and year inter-
actions were also found (Table 2). The relative abun-
dances of the dierent parasitoids calculated over the
whole study period and all the sites were as follows: E.
larvarum 35%, Z. deceptor 38%, C. jucunda 27%, and
Campoletis varians (Thomson), Ichneumonidae 0.5%. C.
jucunda was not found in 1993 at all, and in 1994 its
abundance was low compared to that of E. larvarum and
Z. deceptor. The advanced phenology of the birches at
the start of the larval period had no eect on the para-
sitism of E. autumnata (Table 2).
Responses associated with altitude and/or
temperature variation among sites and years
The proportion of larvae found and the egg production
index were low at the highest mean temperatures
(+11°C), but were relatively similar in the temperature
range from +9 to +10.5°C (mean temperature of the
larval period; Fig. 4b, c, Table 3). When the eect of
temperature was studied in the analysis as a separate
variable for dierent parts of the larval period, the di-
rection of the eect was the same as in the mean tem-
perature analysis. Temperature had not signi®cant eect
on pupal weights (Fig. 4a, Table 3). Pupal weight, pro-
portion of larvae found and egg production index were
not related to the altitude of the sites (Table 3).
Fig. 2a±d Weekly mean tem-
peratures during our study
summers at the Kevo Meteoro-
logical Station. Error bars show
standard deviations of daily
values. Squares show the start-
ing and the ending times of the
larval periods at the earliest and
latest study site
95

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Cites background from "Performance of moth larvae on birch..."

  • ...…species, such as the moth Epirrita autumnata on mountain birch Betula pubescens, the phenological state of the buds reflecting topographic variation, rather than temperature linked to altitude per se, was the main determinant of reproductive success and larval growth (Virtanen & Neuvonen, 1999)....

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  • ...Similar tritrophic studies along altitudinal gradients include the moth Phyllonorycter sp. on Quercus gambelii (Preszler & Boecklen, 1996), the sawfly Neodiprion autumnalis on Pinus ponderosa (McMillin & Wagner, 1998) and the moth Epirrita autumnata on Betula pubescens (Virtanen & Neuvonen, 1999)....

    [...]

  • ...In some species, such as the moth Epirrita autumnata on birch in Finland, the dominant parasitoid differs with altitude : with Eulophus larvarum and Cotesia jucunda dominant at higher and lower sites, respectively (Virtanen & Neuvonen, 1999)....

    [...]

  • ...…insects include the timing of bud burst, leaf flushing, leaf maturity, leaf senescence and fall, flowering, seed set and seed maturity and dispersal (Watt & McFarlane, 1991; Hunter, 1992; Hill & Hodkinson, 1995; Hodkinson, 1997; Hill et al., 1998; Virtanen & Neuvonen, 1999; Hodkinson et al., 2001)....

    [...]

Journal ArticleDOI
TL;DR: A careful analysis on how host-parasitoid systems react to changes in temperature is needed so that researchers may predict and manage the consequences of global change at the ecosystem level.
Abstract: Parasitoids depend on a series of adaptations to the ecology and physiology of their hosts and host plants for survival and are thus likely highly susceptible to changes in environmental conditions. We analyze the effects of global warming and extreme temperatures on the life-history traits of parasitoids and interactions with their hosts. Adaptations of parasitoids to low temperatures are similar to those of most ectotherms, but these adaptations are constrained by the responses of their hosts. Life-history traits are affected by cold exposure, and extreme temperatures can reduce endosymbiont populations inside a parasitoid, eventually eliminating populations of endosymbionts that are susceptible to high temperatures. In several cases, divergences between the thermal preferences of the host and those of the parasitoid lead to a disruption of the temporal or geographical synchronization, increasing the risk of host outbreaks. A careful analysis on how host-parasitoid systems react to changes in temperature is needed so that researchers may predict and manage the consequences of global change at the ecosystem level.

589 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of the secheresse and the canicule on the populations of infra-forestiers in Europe was investigated. But, the authors only focused on the effect of the stress hydrique on the performance of the infra -forestiers, i.e., their ability to adapt to changes in the environment.
Abstract: Bien que la secheresse affecte directement la physiologie et la croissance des arbres, l'impact de facteurs secondaires (insectes ravageurs, pathogenes et feu) est souvent plus important que le stress original et peut conduire a la mortalite des arbres. En 2003, une secheresse et des vagues de chaleur ont provoque des degâts importants dans les forets d'Europe centrale et occidentale. Cet article rend compte de l'impact de la secheresse et de la canicule sur les populations d'insectes forestiers dans le contexte de cet evenement exceptionnel. Les observations des fluctuations de populations des principaux insectes ravageurs des forets europeennes sont presentees et discutees en regard des connaissances actuelles et des theories des interactions entre secheresse et insectes. Nous avons recherche les effets directs et indirects de la secheresse, respectivement sur les traits d'histoire de vie et au travers des modifications physiologiques induites chez les arbres hotes. Les insectes forestiers ont ete separes en 4 groupes : xylophages, phyllophages, mineuses et suceurs de seve. L'impact du stress hydrique a ete different selon la guilde consideree. Les xylophages ont ete positivement influences par le declin de la resistance de l'hote suite a un stress hydrique prolonge. Au contraire, les phyllophages ont mieux profite de l'augmentation de l'azote dans les tissus de la plante sous un stress hydrique modere ou intermittent. Des observations de terrains ont montre l'importance du statut hydrique du sol sur le niveau de resistance des arbres contre les attaques de ravageurs. En certains sites, la secheresse de 2003 a d'ailleurs mis en evidence des choix d'essences inappropries. Cette secheresse exceptionnelle peut nous donner des indications sur les impacts des evenements climatiques extremes. Cependant les observations des performances au niveau individuel ne permettent pas de predire a long terme les dynamiques des populations, lesquelles dependent d'interactions complexes au niveau local entre facteurs biotiques et abiotiques.

349 citations


Additional excerpts

  • ...[6, 7, 9, 15, 41, 86])....

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Journal ArticleDOI
TL;DR: Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases.
Abstract: The individual of a species is the basic unit which responds to climate and UV-B changes, and it responds over a wide range of time scales. The diversity of animal, plant and microbial species appears to be low in the Arctic, and decreases from the boreal forests to the polar deserts of the extreme North but primitive species are particularly abundant. This latitudinal decline is associated with an increase in super-dominant species that occupy a wide range of habitats. Climate warming is expected to reduce the abundance and restrict the ranges of such species and to affect species at their northern range boundaries more than in the South: some Arctic animal and plant specialists could face extinction. Species most likely to expand into tundra are boreal species that currently exist as outlier populations in the Arctic. Many plant species have characteristics that allow them to survive short snow-free growing seasons, low solar angles, permafrost and low soil temperatures, low nutrient availability and physical disturbance. Many of these characteristics are likely to limit species responses to climate warming, but mainly because of poor competitive ability compared with potential immigrant species. Terrestrial Arctic animals possess many adaptations that enable them to persist under a wide range of temperatures in the Arctic. Many escape unfavorable weather and resource shortage by winter dormancy or by migration. The biotic environment of Arctic animal species is relatively simple with few enemies, competitors, diseases, parasites and available food resources. Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases. Arctic microorganisms are also well adapted to the Arctics climate: some can metabolize at temperatures down to -39degreesC. Cyanobacteria and algae have a wide range of adaptive strategies that allow them to avoid, or at least minimize UV injury. Microorganisms can tolerate most environmental conditions and they have short generation times which can facilitate rapid adaptation to new environments. In contrast, Arctic plant and animal species are very likely to change their distributions rather than evolve significantly in response to warming.

263 citations

References
More filters
Book
01 Jun 1996
TL;DR: The most comprehensive and up-to-date assessment available for scientific understanding of human influences on the past present and future climate is "Climate Change 1995: The Science of Climate Change" as mentioned in this paper.
Abstract: This extensive report entitled “Climate Change 1995: The Science of Climate Change” is the most comprehensive and up-to-date assessment available for scientific understanding of human influences on the past present and future climate. Its aim is to provide objective information on which to base global climate change that will ultimately meet the aim of the UN Framework Convention on Climate Change. The report includes an overview of the factors governing climate and climate change and quantification of the sources of globally important greenhouse gases and other pollutants arising from human activities. A review of the chemical and biological processes governing their removal from the atmosphere is presented. Also included is an assessment of recent trends in climate during the industrial era which has witnessed the ever-growing impact of human activities on the global environment. The strengths and weaknesses of various climate mathematical models used by researchers for understanding the past and present climate and for calculating possible future climates are assessed. Furthermore the report discusses research aimed at the detection of human influence on the climate of the last century and presents future change projections in global climate and sea level based on a range of scenarios of future emissions of pollutants due to human activity. Finally a list of research and observational priorities needed to improve scientific understanding in key areas is presented.

4,397 citations


"Performance of moth larvae on birch..." refers background in this paper

  • ...The role of parasitoids and predators in the population dynamics of E. autumnata may change in the future if the predicted climate warming occurs (see Houghton et al. 1996)....

    [...]

Book
01 Jan 1993
TL;DR: This chapter discusses the constraints on foraging patterns of caterpillars and the consequences of evolutionary and ecological consequences, as well as adaptations reflecting sets of constraints.
Abstract: Part I: The constraints on foraging patterns of caterpillars. Phylogenetic constraints - J E Rawlings Foraging of caterpillars in relation to the physical environment - T M Casey Nutritional ecology: the fundamental quest for nutrients - F Slansky, Jr Body size as a constraint on foraging - D Reavey and J Lawton Foraging with finesse: caterpillar adaptations for circumventing plant defences - D Dussourd Avian predators as constraint on caterpillar foraging - B Heinrich Invertebrate predators: how they constrain caterpillar feeding strategies - E A Bernays and C B Montflor Effects of parasitoids on the foraging activities of caterpillars - R M Weseloh Effects of induced plant defences on herbivores and their pathogens - V Krischik Patterns of interaction among sedentary herbivores - H Damman. Part II: Ecological and evolutionary consequences. Transition. Caterpillar lifestyles: adaptations reflecting sets of constraints. Sociality - T D Fitzgerald. Mutualism - N Pierce Aposematism - M D Bowers. Crypsis - L Fink. Part III: Environmental variation in time and space: Transition: Sum of constraints and variation in space and time Effects of caterpillar foraging and predation on population dynamics of caterpillars - E Haukioja A tropical view - D Janzen. Temperate view - N E Stamp Biotic and abiotic constraints on foraging of arctic caterpillars - O Kukal. Part IV: Implications for pest management of foraging constraints. Transition. Synthesis of evolutionary and ecological consequences. Accounting for caterpillar foraging behaviour in forest pest management - J C Schultz. Consequences of herbivore foraging patterns on plants in agroecosystems - P Barbosa.

499 citations


"Performance of moth larvae on birch..." refers background in this paper

  • ...During cold periods, the activity of ectotherm parasitoids or predators may be suppressed when their herbivorous hosts or prey are still capable of feeding (Stamp 1993)....

    [...]

Journal ArticleDOI
TL;DR: The available data suggest that forest caterpillar cycles are more likely to be the result of interactions with insect parasitoids, an old argument that seems to have been neglected in recent years.
Abstract: Hypotheses for the causes of regular cycles in populations of forest Lepidoptera have invoked pathogen-insect or foliage-insect interactions. However, the available data suggest that forest caterpillar cycles are more likely to be the result of interactions with insect parasitoids, an old argument that seems to have been neglected in recent years.

271 citations


"Performance of moth larvae on birch..." refers background in this paper

  • ...It is generally accepted that the population dynamics of insect species showing regular cycles are driven by delayed negative feedbacks (Berryman et al. 1987; Berryman 1996)....

    [...]

Book ChapterDOI
TL;DR: The chapter then turns to the discussion of hypotheses to explain population cycles, wherein, it has described variation in insect quality, climatic release hypothesis, and variation in plant quality, disease susceptibility, and mathematical models.
Abstract: Publisher Summary In this chapter, the characteristics of population cycles of forest Lepidoptera is described and mechanisms proposed to explain them are evaluated. Evidence for population cycles in forest lepidoptera is also discussed in the chapter. Characteristics of cyclic populations of forest lepidoptera is reviewed, wherein, characteristics of cyclic species, patterns of population change, the beginning of the decline, insect fecundity and population fluctuations, parasitoids and population fluctuations, cyclic and non-cyclic populations, and the impact of forest defoliators on the forests are described. The chapter then turns to the discussion of hypotheses to explain population cycles, wherein, it has described variation in insect quality, climatic release hypothesis, and variation in plant quality, disease susceptibility, and mathematical models. Evaluation of hypotheses is also done in the chapter. Population cycles of other organisms are also summarized in the chapter. Finally, the chapter closes with conclusions and speculations.

257 citations


"Performance of moth larvae on birch..." refers background in this paper

  • ...Parasitoids can generally produce cycles in the population dynamics of their host if the parasitoids are so highly specialized that their populations collapse with declining host density (see Myers 1988)....

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11 Apr 1972

224 citations


"Performance of moth larvae on birch..." refers methods in this paper

  • ...Temperature sum calculations traditionally use +5°C as the threshold (e.g. Sarvas 1972; Ayres and MacLean 1987; Sulkinoja and Valanne 1987; Ayres 1993), but a threshold of +2°C gives the best ®t when predicting the emergence of mountain birch leaves as a function of the temperature sum (our…...

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Frequently Asked Questions (2)
Q1. What are the contributions in "Performance of moth larvae on birch in relation to altitude, climate, host quality and parasitoids" ?

The authors studied topographical and year-to-year variation in the performance ( pupal weights, survival ) and larval parasitism of Epirrita autumnata larvae feeding on mountain birch in northernmost Finland in 1993±1996. In the comparison of di€erent sources of spatial and annual variation in the performance of E. autumnata, the most important factor appeared to be egg mortality related to minimum winter temperature, followed by parasitism and, ®nally, the variation in food plant quality. If, as predicted, the climate gradually warms up, the e€ects of warmer summers on the outbreaks of E. autumnata suggest a decrease in outbreak intensity. 

The role of parasitoids and predators in the population dynamics of E. autumnata may change in the future if the predicted climate warming occurs ( see Houghton et al. 1996 ). In conclusion, their study indicates that if summers warm up as predicted, the intensity of E. autumnata outbreaks in the future will probably decrease. Their results suggests that warmer summers may have opposite consequences for E. autumnata populations than warmer winters ( cf. Virtanen et al. 1998 ). The potential strength of the e ects due to summertime temperature variation on E. autumnata densities seems to be clearly less than that due to the variation in minimum winter temperatures ( Table 5 ).