There are many interactions and it is exetremely difficult to predict the impact of climate change on insect pests in the future, but we may expect an increase of certain primary pests as well as secondary pests and invasive specie

Jagers op Akkerhuis, G.A.J.M.

Jagers op Akkerhuis, L.

Moraal, L.G.

English

NARCIS 

Impact of climate change on insect pests of trees

Wageningen Yield 

Pagina 239Gewasbescherming  jaargang 39, nummer 6, november 2008
Mededelingenblad van de Koninklijke Nederlandse Plantenziektekundige Vereniging
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the Dickeya biovar 3 variant is taking over from 
D. dianthicola. 
In contrast to a biovar 7 D. dianthicola strain, the 
biovar 3 variant efficiently colonizes plant mate-
rial. Soil infestation with a GFP-tagged strain re-
sulted in a systemic colonization of potato plants 
within 30 days after inoculation. The biovar 3 
variant was also able to colonize roots, stolons 
and progeny tubers from infected stems.
Spread within a crop may also occur during crop 
production if bacterial cells of Dickeya spp. are 
disseminated via free water in soil from rotten tu-
bers to tubers of neighbouring plants. We showed 
that plants adjacent to blackleg diseased plants 
both within a row and between rows became 
contaminated after heavy irrigation. Dickeya spp. 
was able to cause disease symptoms even when 
present in seed at low densities. In field experi-
ments with vacuum-inoculated tubers, a level of 
0 cells per gram of potato peel was sufficient to 
end up with 30 and 15% diseased plants in 2005 
and 2006, respectively. Such low levels of infec-
tion easily remain unnoticed during seed testing, 
even if sensitive detection methods are used. As 
for Pectobacterium spp., spread of contamination 
within and between seed stocks often occurs 
during harvesting and grading. In an experimen-
tal field, contamination with Dickeya spp. was 
spread by mechanical harvesting up to a distance 
of 80 m behind a zone with rotten tubers, with an 
average of 12 meter. Hand-harvested tubers from 
a disease-free crop remained clean.
Dickeya spp. seems to act like a biotrophic 
organism, which needs the host for long-term 
survival. D. dianthicola and the biovar 3 variant 
survived maximally for only three months in soil. 
Soil type, temperature and humidity only had a 
minor effect on survival. 
In conclusion, a Dickeya spp. has become the 
dominant blackleg pathogen, probably due to 
its higher optimal growth temperature and its 
ability to colonize plant tissue more efficiently 
compared to Pectobacterium spp. The increasing 
importance of Dickeya spp. may be related to 
the increasing average temperature during the 
growth season due to global warming.
Impact of climate change on 
insect pests of trees
Leen Moraal and Gerard Jagers op Akkerhuis
Wageningen UR, Alterra; e-mail: leen.moraal@wur.nl; gerard.
jagers@wur.nl
In The Netherlands, insect pests on trees and 
shrubs are being monitored continuously since 
196. During these years, almost all insect pest 
populations showed marked changes, which 
may be the result of climate change, arrival of 
new pests, changes in forest management, shifts 
in forest composition etc.
In an earlier study, we analyzed the number of 
observations for all pest species in the database 
on deciduous trees. The results showed that 
since 1985, pest insects hibernating in the egg 
stage, numerically exceed insects hibernating as 
larva, pupa or adult. During the last 2-3 decades, 
the winters in The Netherlands have become 
relatively warm and more humid. In litera-
ture, it is stated that mild winter temperatures 
can reduce winter survival of adult, larval and 
pupal stages more than of the eggs, presumably 
because the first stages are more vulnerable for 
entomopathogenic nematodes and fungal activ-
ity. This phenomenon may be the cause of our 
observed increase of egg hibernators (Moraal et 
al. 200).
In a later study, we have analyzed trends in 61 
years of population development of the 91 most 
abundant species in our database, in such a way 
that frequently observed species did not bias the 
results. Of the observed species, only a minor-
ity occurred regularly over the entire observa-
tion period of 61 years. The remaining species 
showed population fluctuations that varied 
from single short-term outbreaks to long-last-
ing increases or decreases. On coniferous trees, 
most insect species showed decreasing numbers, 
while increasing numbers were found most on 
deciduous trees. In the increasing trend-group of 
Lepidoptera, more egg hibernating species were 
observed compared with the decreasing trend-
group (Moraal & Jagers op Akkerhuis, in prep).
Future climate change models for our region, 
predict increasing temperatures, drought peri-
ods, and heat waves during the growing sea-
son. The European literature on pest outbreaks 
that followed after the exceptional drought of 
2003, give us some indications of the impacts 
of extreme climatic conditions. Primary pest 
insects, mostly leaf-consuming larvae, are not 
dependant on the vitality status of the host trees. 
Secondary pests, mostly bark-boring species, are 
dependant on weakened trees e.g. by drought. 
In literature, some generalized predictions were 
made, based on current pest distributions and 
the severity of insect outbreaks in individual 
regions after the summer drought of 2003. The 
predictions are that tree mortality due to secon-
Pagina 240 Gewasbescherming  jaargang 39, nummer 6, november 2008
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Mededelingenblad van de Koninklijke Nederlandse Plantenziektekundige Vereniging
dary pest insects may become more important 
in the future, because dry summers will reduce 
the resistance of trees. A combination of global 
trade and a changing climate makes it possible 
for new invasive species to establish in the EU 
and The Netherlands. In the absence of specific 
natural enemies, these species may cause tree 
mortality on a large scale (Moraal, in press). 
There are many interactions and it is extremely 
difficult to predict the impact of climate change 
on insect pests in the future, but we may expect 
an increase of certain primary pests as well as 
secondary pests and invasive species.
References
Moraal, L.G. Expected impact of climate change on insect pests of 
forest trees in The Netherlands. Wageningen, Alterra-report 1761. 
In press.
Moraal, L.G., Jagers op Akkerhuis, G.A.J.M., Siepel, H., Schelhaas 
M.J. & Martakis G.F.P., 200. Verschuivingen van insectenplagen 
bij bomen sinds 196 in relatie met klimaatverandering. Met 
aandacht voor de effecten van stikstofdepositie, vochtstress, 
bossamenstelling en bosbeheer. Wageningen, Alterra-rapport 
856. 52 pp.
Moraal, L.G. & Jagers op Akkerhuis, G.A.J.M. Population changes of 
insect pests on trees and shrubs in The Netherlands since 196 in 
relation with climate change, forest management and site factors. 
In prep.
are changes in the 
composition of the Fusarium 
Head Blight complex caused 
by climate change?
Cees Waalwijk1, Theo van der Lee1, Lijun Yang2, 
Ineke de Vries1, Andreas Görtz3 and Gert Kema1
1 Wageningen UR, Plant Research International, Wageningen; 
e-mail: cees.waalwijk@wur.nl
2 Institute for Plant Protection and Soil Sciences, Hubei 
Academy of Agricultural Sciences, 430064, Wuhan, China
3 Institute of Crop Science and Resource Conservation, 
University of Bonn, Germany
Fusarium Head Blight (FHB) of wheat and barley 
is caused by a complex of species. Apart from 
yield losses, this disease has attracted much 
attention due to the capacity of many of the spe-
cies in the complex to produce mycotoxins that 
are detrimental to humans and animals. In The 
Netherlands, until the late 1980s / early 1990s, 
Fusarium culmorum was the predominant spe-
cies on wheat, but since then F. graminearum be-
came the most important pathogen. This trend 
was first detected in 2000 and 2001 (Waalwijk et 
al., 2003) and was confirmed in other countries 
in Western Europe. This finding can be explained 
in several ways, including the expansion of the 
acreage of maize, which is a good host of F. gra-
minearum, but less for F. culmorum. Secondly, 
F. graminearum has the capacity to go through 
sexual development, resulting in airborne 
ascospores that can travel several hundreds of 
kilometers; a clear advantage in colonization 
of crops in virgin soils. Lastly, F. graminearum 
favors higher temperatures than F. culmorum 
and the observed shift might be an indication of 
changes in climate. 
In China, the population structure of FHB pa-
thogens occurring on barley was investigated by 
sampling at 23 counties along the Yangtze River. 
In contrast to the situation in Europe or North 
America, the vast majority of isolates belong to 
F. asiaticum. Analyses of the structure of this 
population showed a dramatic gradient in the 
trichothecene mycotoxins produced (Yang et al., 
2008). While the production of nivalenol (NIV) 
was primarily found among isolates collected in 
the western part of the country, deoxynivalenol 
(DON) producers were mainly from the eastern 
provinces. As NIV producers have been reported 
in Asia in the past, we hypothesized that NIV 
producers represent the ancient population that 
is being replaced in the lowlands in the east. The 
populations in the western parts of China are not 
(yet) replaced as these counties reside in moun-
tainous areas which are more difficult to become 
colonized by the DON producers. 
A similar gradient was observed in Canada, 
where populations from the FHB complex in 
the East appear to overtake the place of those 
in the West. Phenotypic analyses showed that 
the ‘invading’ population consisted of strains 
that produced more mycotoxin and were more 
vigorous (Ward et al., 2008). To verify whether 
a similar situation is currently taking place in 
China, we analyzed the diversity within and bet-
ween populations using neutral VNTR markers. 
Some alleles were observed exclusively in upper 
valleys of the Yangtze River (Zhang et al.) which 
is in agreement with the occurrence of genetic 
differentiation along environmental gradients.
These results will be discussed together with 
data from a novel survey performed in the Ne-
therlands in 2008, to underline the previously 
observed temporal shifts in the composition of 
the FHB complex. To put this in a broader per-
spective, this will be compared with results from 
surveys in France and Germany, where similar 
analyses were also performed on maize (Görtz et 
al.)


Expected impact of climate change on insect pests of forest trees in The Netherlands. Wageningen, Alterra-report 1761.

In contrast to the situation in Europe or North America, the vast majority of isolates belong to F. asiaticum. Analyses of the structure of this population showed a dramatic gradient in the trichothecene mycotoxins produced (Yang et al.,

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Impact of climate change on insect pests of trees

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