Impacts on Nematode Pests - Climate Resilient Agriculture for Ensuring Food Security - page 184

Fig. 9.3 Average minimum monthly ambient temperatures in Davis, California, from November to February
1983-2010. The lower reproductive limit of stem nematode females is 41 °F

and nematode distribution. Based on this result,
the authors predicted that climate change could
result in increased nematode and virus problems
in Northern Europe; they estimated that a 1 °C
warming would allow the species in study to
migrate northwards by 160-200 km (Neilson and
Boag 1996 ). Although nematodes migrate very
slowly, humans are credited with effi ciently dis-
seminating them. Hence, nematode spread into
new regions could put a wide range of crops at
risk; additionally, introduction of new crops into
a region could also expose them to infestation by
nematode species already present. Changes in
precipitation, which were not considered in these
analyses, could infl uence nematode distribution
on a large scale, although previous fi ndings had
suggested that soil moisture would not affect
nematode distribution in most agricultural soils
in Northern Europe (Neilson and Boag 1996 ).
Studies have also demonstrated that the geo-
graphical distribution range of plant pathogenic
nematodes may expand with global warming
spreading nematode problems to newer areas.
The soybean cyst nematode ( Heterodera
glycines ) is the cause of great economic losses to
soybean producers in the USA. The pest has been
expanding since the early 1950s, but the increase
has been more dramatic since the early 1970s.
Before 1970, the soybean cyst nematode was

mainly distributed in the Mississippi River Delta
area, northern Arkansas, southern Missouri,
southern Illinois, and western Kentucky. It is now
distributed throughout the main soybean produc-
tion area and has become the number one soybean
pest in the USA (Rosenzweig et al. 2000 ). In
Iowa alone, it caused an estimated yield loss of
201 million bushels (worth about $1.2 billion)
during the 1998 growing season (USDA NCR-
137 1999 ). In the northern production region, the
nematode has up to three generations per year,
depending on planting and weather conditions
during the growing season. A longer growing
season, associated with a warmer climate, would
result in an increased risk of losses similar to the
ones reported during the 1998 year. This pest has
been monitored and mapped since the 1950s.
Ghini et al. ( 2008 ) compared climatological
norms from 1961 to 1990 with future scenarios
(A2 and B2) of the decades of 2020s, 2050s, and
2080s from fi ve general circulation models
(IPCC 2001 ) to predict the changes in spatial dis-
tribution of infestation levels based on number of
generations per month in Brazil. They predicted
that the nematode infestation will increase in the
future due to greater number of generations per
month. The number of generations of nematodes
will increase in both scenarios, but it will be
lower in B2 than A2 scenario.