Aussie insects invade New Zealand to colonize their eucalypts

1
Aussie insects invade New Zealand to colonize
their eucalypts
Jesse Soric Department of Biological and
Physical Sciences, University of Southern
Queensland, Australia
Introduction Since the 1860s Australian insects
have steadily colonised eucalypts in New Zealand.
Over the last two decades the rate of
colonization has increased rapidly. Eucalypts
were brought from Australia to New Zealand around
160 years ago, initially used as shelter trees
and for firewood, they are now used as plantation
trees for durable timber and woodchip. Eucalypts
growing in New Zealand are a vacant niche
awaiting invasion by insects. Australian insects
are able to reach New Zealand by a number of
methods. As New Zealand is only 1800 km from
Australia, the prevailing winds can carry seeds,
spore, pollen and insects to the islands. Tourism
and trade are routes by which insects may also
enter the country. Up until 1999, untreated cut
eucalypt foliage for the cut flower industry was
imported from Australia. Cargo containers camping
and golfing equipmenthas also been found to be
contaminated with Australian plants and
associated insects. This project aims to
illustrate the ease in which insects are able to
colonise another country provided there are the
right conditions to do so.
Figure 3. The cumulative colonization of eucalypt
trees in New Zealand by Australian insects.
Methods The areas studied were in New Zealand, in
particular around Auckland, with the distance
relationship to Australia being noted (Figure
1.). Research concerning the types of Australian
insects and spread of these insects in New
Zealand has been carried out over the last
century. A database of the exotic insects found
in New Zealand has been maintained. The database
contains information on the types of insects,
preferred food source, method of feeding,
possible origins and their distribution within
New Zealand. A graph was produced to illustrate
the increase in insect numbers over time.
Eucalypt-specific insects and polyphagous
insects were analysed as proportions of the total
numbers of insects recorded according to their
orders. Graphs were produced to illustrate any
patterns. Case studies were carried out -
Cardiaspina fiscella (brown lace lerp or brown
basket lerp) (Figure 2.) was identified. The
spread of this insect was monitored and recorded
over 3 years. The effects of C. fiscella on the
growth of Eucalyptus saligna and E. botryoides
was investigated.
Figure 4. The proportion of Australian specialist
Eucalyptus insects that have colonized Eucalyptus
in New Zealand
Figure 5. The proportion of Australian
polyphagous insects that have colonized
Eucalyptus as well as other trees in New Zealand
Discussion Many Australian insects have been
successfully colonizing New Zealand since the
introduction of trees from the Eucalyptus genus
more than 150 years ago. Figure 3. shows the
gradual increase in numbers of insects during
early colonization with approximately one species
each 7 years. During the last 25 years there has
been a rapid increase in the number of insects
colonizing eucalypts in New Zealand with one new
species every 17 months being observed. The rapid
increase in the establishment of Australian
insects in New Zealand may be explained by the
increasing trade between the two countries and
the associated movement of cargo containers and
plant materials containing contaminants.
Although it likely that many insect types have
travelled from Australia to New Zealand via
natural means (wind, storm fronts) their survival
has been unlikely, especially in the case of
eucalypt-specialist insects. The introduction of
a number of Eucalyptus species into New Zealand
has provided these insects with a food source,
and quite likely, there has been a lack of
competion or predators. These conditions appear
to be ideal for the numbers of insects to develop
to pest levels. Cardiaspina fiscella was first
identified in New Zealand in early 1996 and was
found to have spread more than 200km either side
of its origins in Auckland by 1999. C. fiscella
was to be causing damage to plantation trees
(Eucalyptus saligna and E. botryoides) within 12
to 24 months after colonizing a new region. Host
trees suffered severe defoliation 2-3 times in a
growing season leading to slowed growth, branch
dieback and even the death of some trees. Figure
4. shows the dominance of sap-sucking bugs
(Hemiptera) and leaf feeders (Coleoptera) among
the Australian eucalypt-specialists. Figure 5.
shows the dominant orders of Australian
polyphagous insects to be Coleoptera and
Lepidoptera. None of the polyphgous insects have
been considered pests of eucalypts in New
Zealand.
Figure 1. Map showing relative positions of
Australia and New Zealand
Figure 2. Brown lace lerp (Cardiaspina fiscella),
cause defoliation and dieback of branches and
some trees.
Results Figure 3. Shows a steady increase in the
number of insects colonising New Zealand
eucalypts over the last 150 years. Insect orders
for eucalypt specific feeders were grouped and
graphed in Figure 4. Hemipterans were the largest
proportion (40) of the orders observed with
Hymenopterans being the smallest (12). Insect
orders for polyphagous feeders whose host plants
include Eucalyptus species were grouped and
graphed in Figure 5. Coleopterans were the
largest proportion (40) of the orders observed
with Hymenoptera, Thysanoptera and Orthoptera
being the smallest (2).
Conclusion The number of Australian insects
colonizing New Zealand has increased rapidly over
the last 25 years. This has been partly explained
by the large amount of trade and tourism between
the two countries. Due to the extent of eucalypts
grown in New Zealand eucalypt-specialist insects
have spread rapidly and caused damage to
plantations in many areas. Polyphagous insects
did not develop into pests of eucalypts in New
Zealand but eucalypt-specialists have done so, in
particular, some Hemipterans (eg. Cardiaspina
fiscella) and Coleopterans.
Acknowledgement Adapted from Withers, T.M. (2001)
Colonization of eucalypts in New Zealand by
Australian insects. Austral Ecology (2001) 26,
467-476