INTRODUCTION TO PEST RISK ANALYSIS
Eli Szandala
Office of the Chief Plant Protection Officer
Australian Government Department of Agriculture, Fisheries and Forestry
Introduction
Biologists have long recognised the risks posed by the international movement of animals
and plants and their products. Recognition of these risks is reflected in early legislation in
many countries to control the movement of goods as a way of protecting animal and plant
health.
All quarantine policy and risk management measures developed to prevent the movement
of pests and pathogens are based on analysis of risk. For many years Australia fumigated
timber and bananas using cyanide, and apple imports into Australia from New Zealand
were prohibited for 70 years because of fireblight.
In recent times the science underpinning risk analysis has improved, including our
understanding of the pests and pathogens, their biology, control and methods for
detection. Driven by the disciplines applied by the SPS Agreement and obligations of
members of the WTO to make the process more transparent, quarantine risk analysis has
been given a formal structure by bodies such as the International Plant Protection
Convention (IPPC). Risk analysis is now based on sound science, is a structured and
transparent process that is, theoretically, consistent and repeatable.
Pest Risk Analysis
The purpose of Pest Risk Analysis (PRA) is to estimate the likelihood of successful
invasions by plant pests (including pathogens and weeds) that may occur as a result of a
pest entering, establishing and spreading into a new area. The PRA also assesses potential
impacts, severity of impact and options to mitigate pest risk.
There are two main approaches to conducting a PRA, one based on a commodity, the
other on a particular pest associated with various commodities. The majority of risk
analyses are conducted in response to a market access request (an application by an
exporting country to import a particular commodity) and are therefore commodity-based.
The IPPC has set standards for risk analysis as outlined in the International Standard for
Phytosanitary Measures (ISPM) No. 11 Pest Risk Analysis for Quarantine Pests,
including analysis of environmental risks and living modified organisms. The standard
recognises three main stages in a PRA:

Stage 1:
Initiation of the analysis;
1

Stage 2:
Risk assessment -the scientific evaluation of the biological risk and
potential consequences; and

Stage 3:
Risk management - a process of determining appropriate measures to
reduce risk.
With internationally agreed standards and procedures for PRA, the process is relatively
straight forward but requires reliable data to achieve an accurate assessment of risk. In
many instances there is not enough information available on some pests in the exporting
and importing countries to be certain of the pest’s status. This is particularly true for
countries that do not have adequate collections of pests and diseases to draw information
on pest biology and distribution.
Risk communication with stakeholders, which forms part of Article 5 of the Sanitary and
Phytosanitary (SPS) Agreement, is an important component of PRA. The process
requires frequent consultation and communication with stakeholders including the
applicant, scientists, government agencies and industry. Figure 1 illustrates the process of
plant PRA.
Risk Communication
Stage 1: Initiation
Stage 2: Risk assessment
1.
2.
3.
4.
5.
6.
Figure 1.
Stage 3: Risk
Management
Pest categorisation
Probability of entry
Probability of establishment
Probability of spread
Assessment of consequences
Conclusions: risk assessment
IPPC Approach to Pest Risk Analysis
Stage 1: Initiation of the analysis
Initiation is the first step in a plant pest risk analysis (PRA). The aim of this step is to
identify the pest or pests that are of quarantine concern, and should therefore be
considered for risk analysis. Such pests are referred to as quarantine pests. The IPPC
defines a quarantine pest as a pest of potential economic importance to the area
2
endangered thereby and not yet present there, or present but not widely distributed and
being officially controlled.
A PRA may be initiated as a result of:

identification of a pathway that presents a potential pest hazard;

identification of a pest that may require phytosanitary measures; and

review or revision of existing phytosanitary policies and priorities.
The majority of risk analyses are initiated in response to an application for market access
and are therefore commodity-based.
A list of pests likely to be associated with the pathway (e.g. carried by the commodity)
can be generated and the pests prioritised. If no potential quarantine pests are identified
as likely to follow a particular pathway, the PRA may stop at this point. However, if a
quarantine pest is identified, the PRA continues, into Stage 2: Risk Assessment.
Stage 2: Risk Assessment
Plant pest risk assessment is the second stage in a pest risk analysis (PRA). It follows the
initiation stage and precedes the risk management stage. The risk assessment should be
based on sound science, be structured and transparent, internally consistent and able to be
repeated by another operator using the same framework and data. An accurate assessment
of risk is dependant on the availability of adequate information on pest status and
biology, environmental conditions in the exporting country and PRA area combined with
expert judgement.
ISPM 11 divides the process of pest risk assessment into three interrelated steps:

Step 1 — Pest categorisation;

Step 2 — Assessment of the probability of introduction (entry and establishment)
and spread; and

Step 3 — Assessment of potential economic consequences (including
environmental impacts).
The results of steps 2 and 3 are combined to provide an overall estimate of risk, which
can then be assessed against the importing country’s appropriate level of protection
(ALOP) (See Table 7). The SPS Agreement defines ‘appropriate level of sanitary and
phytosanitary protection’ as ... the level of protection deemed appropriate by the member
establishing a sanitary and phytosanitary measure to protect human, animal and plant
life or health within its territory. Each country determines its own ALOP, by establishing
certain sanitary and phytosanitary measures, and application of the ALOP should be
consistent.
Step 1 — Pest categorisation
At the outset, it may not be clear which pest or pests identified at the initiation stage
require a plant PRA. The purpose of categorisation is to consider each pest to determine
3
whether it satisfies the criteria for a quarantine pest. ISPM 11 lists the following main
elements of categorisation of a pest as a quarantine pest:

identity of the pest is well understood and recognisable;

presence or absence in the PRA area;

regulatory status;

potential for establishment and spread in PRA area; and

potential for economic consequences (including environmental consequences) in
the PRA area.
Where an organism does not meet the criteria for a quarantine pest, the PRA for that
particular organism stops. Thus, pest categorisation provides an opportunity to eliminate
organisms at an early stage in the PRA, removing the need for in-depth examination.
Although pest data sheets are not prescribed by international standards, many countries
develop these as a way to document and arrange information on quarantine pests, because
they are a useful tool for carrying out a detailed risk assessment. Figure 2 illustrates a
possible template for a pest data sheet. Data sheets are generally not published because
these need to be kept current and updated whenever additional information becomes
available.
{Quarantine Pest Name}
Species:
Synonyms:
Common name(s):
Hosts:
Plant part(s) affected:
Distribution:
Biology (life cycle):
Epidemiology:
Control:
References:
Figure 2. Pest Data Sheet Template
Pest categorisation requires reliable information to determine the status of a pest in a
country or particular area. Table 1 illustrates one of the methods that can be used to
organise and present pest categorisation data, using the example of some of the pests
identified for an import risk analysis carried out by Biosecurity Australia, for the
importation of fresh citrus fruit from Florida, USA.
4
Table 1. Example of Categorisation of Certain Pests for a Risk Analysis of Fresh
Citrus Fruit from Florida (USA)
Scientific
Name
Present in
importing
country
(Yes/No)
Present in the pathway
(Yes/No)
Conside
r further
(Yes/No
)
Yes
(APHIS
1991)
Pink citrus Yes
rust mite
(Childers
(PCRM)
et al 2000)
Yes
(CSIRO
2001)
No
N/A
No
Eutetranychus
bankzi
McGregor
Texas
citrus mite
Yes
(APHIS
1991)
No
Pathogens
Elsinoe
fawcetti
Bitancourt &
Jenkins
Citrus
scab
Yes
(APHIS
1991)
Yes (some
pathotypes
) (Tan et
al 1996,
APPD
2002
Dead twig
Yes
(APHIS
1991)
No
Arthropod Pests
Aceria
sheldoni
(Ewing)
Aculops
pelekassi
Eutypella
citricola
Common
Name
Present in
exporting
country
(Yes/No)
Citrus bud
mite
Yes
(Feeds on green stems,
leaves and fruits.
Childers et al 2000)
Yes
(Feeds primarily on
upper leaf surface,
rarely found on fruit
except at high levels of
infestation. Childers &
Fasulo 1995)
Yes
(Infects fruit, leaves
and twigs, and scab
lesions appear as wartlike growths or as flat
scars on fruit and
leaves. Simone 1999)
No
(Recorded on dead
twigs. APHIS 1991)
Yes
Yes
No
N/A - Not applicable
Table 1 shows that, when assessing risks associated with importing a fruit commodity, a
pathogen associated with the roots of the fruit tree (e.g. Eutypella citricola, which causes
dead twig) is unlikely to require further consideration because it is not associated with the
fruit and is thus not on a distribution pathway. Where the association with a pathway is
not clear at this preliminary stage, the pest could be retained on the list for further
detailed risk assessment.
If a pest has the potential to be a quarantine pest, the PRA for that pest continues; if the
pest does not fulfil the criteria for a quarantine pest, the PRA for that pest stops.
5
Step 2 — Assessment of the probability of introduction and spread
Evidence should be available to support the conclusion that the pest could become
established and spread in the PRA area. ISPM 11 explains that introduction of a pest
involves both entry and establishment. Assessing the probability of introduction requires
analysis of each of the distribution pathways with which a pest may be associated, from
the origin of the pathway to the pest’s establishment in the PRA area.
The PRA area should have ecological or climatic conditions suitable for the
establishment and spread of the pest. Where relevant, host species (or near relatives),
alternate hosts and vectors should be present in the PRA area.
In a PRA initiated by a specific initiation pathway (usually an imported commodity), the
probability of pest entry is evaluated both for that specific pathway and for other possible
distribution pathways.
Probability of entry of a pest
The probability of entry of a pest depends on the pathways from the exporting country to
the destination, and the frequency and quantity of pests associated with these pathways.
The higher the number of pathways, the greater the probability of the pest entering the
PRA area.
Documented pathways for the pest to enter new areas should be noted, and potential
pathways should be assessed, whether or not these exist at the time of the PRA. Pest
interception data may provide evidence of the ability of a pest to be associated with a
pathway and to survive in transport to storage.
Table 2 shows the factors that ISPM 11 lists as needing to be taken into account when
considering the probability of the pest entering an area with a specific commodity.
6
Table 2. Factors for Consideration in Determining Probability of Entry of a Pest
Probability of the pest being associated with the pathway at origin:

Prevalence of the pest in the source area

Occurrence of the pest in a life stage that would be associated with the
commodity

Volume and frequency of movement along the pathway

Seasonal timing

Pest management, cultural and commercial procedures applied at the place of
origin
Probability of pest surviving during transport or storage:

Speed and condition of transport and duration of the life cycle of the pest in
relation to time in transport and storage

Vulnerability of the life-stages during transport or storage

Prevalence of the pest likely to be associated with a consignment

Commercial procedures (e.g. refrigeration) applied to consignments in the
country of origin, country of destination, or in transport or storage
Probability of pest surviving existing pest management procedures:


Effectiveness against the pest in question of measures (including phytosanitary
procedures) applied to consignments against other pests from origin to end-use
The probability that the pest will go undetected during inspection or survive
other existing phytosanitary procedures
Probability of transfer to a suitable host:






Dispersal mechanisms, including vectors
Whether the imported commodity is sent to few or many destination points in
the PRA area
Proximity of entry, transit and destination points to suitable hosts
Time of year at which import takes place
Intended use of the commodity (e.g. planting, processing or consumption)
Risks from by-products and waste
Probability of establishment of a pest
To estimate the probability of establishment of a pest, reliable biological information
(e.g. life cycle, host range, epidemiology and survival) should be obtained from the areas
where the pest currently occurs and the PRA area. Most of this information will have
already been collated in the pest categorisation step when the pest data sheet is
developed. The situation in the PRA area can then be compared with that in the areas
where the pest currently occurs, and expert judgement used to assess the probability of
establishment. Case histories concerning comparable pests can be considered. ISPM 11
provides examples of a range of factors to consider in determining the probability of
establishment of a pest. These factors are summarised in Table 3.
7
Table 3. Factors for Consideration in Determining Probability of Establishment of a
Pest
Availability of suitable hosts, alternate hosts and vectors in the PRA area:

Hosts and alternate hosts are present and how abundant or widely distributed
they may be

Hosts and alternate hosts occur within sufficient geographic proximity to
allow the pest to complete its life cycle

There are other plant species, which could prove to be suitable hosts in the
absence of the usual host species

A vector, if needed for pest dispersal, is already present in the PRA area or
likely to be introduced

Another vector species occurs in the PRA area
Suitability of environment:

Environmental factors (e.g. suitability of climate, soil, pest and host
competition) that are critical to the development of the pest and its host (and
vector, if applicable), and to their ability to survive periods of climatic stress
and complete their life cycles

Probability of establishment in a protected environment (e.g. glasshouses)
Cultural practice and control measures:



Where applicable, a comparison of practices employed during the
cultivation/production of the host crops in the PRA area and the origin of the
pest that may influence its ability to establish
Pest control programs or natural enemies already in the PRA area which
reduce the probability of establishment
Availability (or lack) of suitable methods for pest control or eradication
Reproductive strategy of the pest:

Characteristics that enable the pest to reproduce effectively in the new
environment, such as parthenogenesis/self-crossing, duration of the life cycle,
number of generations per year, resting stage etc
Genetic adaptability:

Whether the species is polymorphic and the degree to which it has
demonstrated the ability to conditions like those in the PRA area (e.g. hostspecific races or races adapted to a wider range of habitats or new hosts).
Genotypic variability facilitates a pest’s ability to withstand environmental
fluctuations, to adapt to a wider range of habitats, to develop pesticide
resistance and to overcome host resistance
Minimum population needed for establishment:

The threshold population that is required for establishment
8
Probability of spread of a pest after establishment
A pest with a high probability of spreading may also have a high probability of
establishment, limiting possibilities for its successful containment or eradication. To
estimate the probability of a pest spreading, it is useful to obtain reliable biological
information from areas where the pest currently occurs and compare that with the
situation in the PRA area. Case histories concerning comparable pests can also be useful.
Some of the factors that might be involved in the assessment of spread probability
include:

suitability of the natural and/or managed environment for natural spread of the
pest

presence of natural barriers

the potential for movement with commodities or conveyances

intended use of the commodity

potential vectors of the pest in the PRA area

potential natural enemies of the pest in the PRA area.
Conclusion on the probability of introduction and spread
The overall probability of introduction should be expressed in terms most suitable for the
data, the methods used for analysis and the intended audience. The overall probability
may be expressed qualitatively or quantitatively, and may be expressed as a comparison
with that obtained from PRAs on other pests. Table 5 is a matrix of rules used by
Biosecurity Australia for combining descriptive likelihoods, i.e. to determine the
likelihood of introduction of a pest the likelihoods of entry and establishment are
combined.
Table 5. Matrix of Rules for Combining Descriptive Likelihoods – Biosecurity
Australia
High
Likelihood of
introduction
High
Moderate
Low
Very low
Moderate
High
Moderate
Low
Low
V. Low
E. Low
Negligible
Low
V. Low
E. Low
Negligible
Low
V. Low
E. Low
Negligible
V. Low
V. Low
E. Low
Negligible
E. Low
E. Low
Negligible
Negligible
Negligible
E. low
Negligible
Negligible
Likelihood of establishment
9
Figure 3 outlines Biosecurity Australia’s approach to establishing the probability of
introduction and spread of a plant pest.
Establishing the probability of introduction and spread — Biosecurity Australia Approach
The following text is based on Biosecurity Australia’s Draft Guidelines for Import Risk Analysis. For qualitative
evaluation, likelihoods assigned to steps in the scenarios are categorised according to a descriptive scale (e.g.
‘low’, ‘moderate’, ‘high’ etc), with no attempt to equate descriptors with numeric values or scores. Likelihood can
be evaluated and reported qualitatively using the following terms:
Likelihood Descriptive definition
High
The event would be very likely to occur
Moderate
The event would occur with an even probability
Low
The event would be unlikely to occur
Very low
The event would be very unlikely to occur
Extremely low The event would be extremely unlikely to occur
Negligible
The event would almost certainly not occur
In this import risk analysis, qualitative likelihoods were assigned to the probability of entry (comprising an
importation step and a distribution step), the probability of establishment and the probability of spread. In other
analyses, it may be considered relevant to assign qualitative likelihoods to additional steps. This would depend on
the complexity of the issue and the information that was available. For example, within the importation step,
separate qualitative likelihoods could be assigned to the probabilities that source fruit is infested, that the pest
survives packinghouse procedures and that it survives storage and transport.
The stepwise procedure for combining likelihoods is as follows.
• Step 1 — Assign likelihoods to the probability of importation (e.g. ‘low’) and distribution (e.g. ‘moderate’)
• Step 2 — Combine these probabilities to give the probability of entry (e.g. ‘low’ × ‘moderate’ = ‘low’), using
the ‘rules’ provided in Table 4.
• Step 3 — Assign a likelihood to the probability of establishment (e.g. ‘high’)
• Step 4 — Combine probability of establishment with probability of entry to give the probability of
establishment (e.g. ‘high’ × ‘low’ = ‘low’)
• Step 5 — Assign a likelihood to the probability of spread (e.g. ‘very low’)
• Step 6 — Combine probability of establishment and likelihood of spread to give the overall likelihood of entry,
establishment and spread (e.g. ‘low’ × ‘very low’ = ‘very low’)
Step Qualitative descriptor Product of likelihoods
1. Probability of importation Low
2. Probability of distribution Moderate
3. Probability of entry Low (low × moderate)
4. Probability of establishment High Low (high × low)
5. Probability of spread Very low
6. Probability of entry, establishment and spread High (low × very low)
Figure 3. Biosecurity Australia’s Approach to Establishing the Probability of
Introduction and Establishment of a Pest
10
Step 3 — Assessment of potential economic consequences
Article 5.3 of the SPS Agreement states that:
“ … Members shall take into account as relevant economic factors: the potential damage
in terms of loss of production or sales in the event of entry, establishment or spread of a
pest or disease: the costs of control or eradication in the territory of the importing
Member: and the relative cost-effectiveness of alternative approaches to limiting risks.”
ISPM 11 provides guidance on factors to consider when assessing potential economic
consequences, including environmental consequences. It states that, after obtaining
information on areas where the pest currently occurs, ‘the information should be
compared with the situation in the PRA area. Case histories concerning comparable pests
can usefully be considered.’
There should be clear indications that the pest is likely to have an unacceptable economic
impact (including environmental impact) in the PRA area. Where possible, it is useful to
describe the output of the assessment of economic consequences in monetary terms.
Qualitative or quantitative measures without monetary terms can also be used. It is
important to specify sources of information, assumptions and methods of analysis.
Wherever appropriate, the part of the PRA area where presence of the pest will result in
economically important loss should also be identified.
The effects of the pest considered may be direct or indirect. Aspects that could be
considered in assessing direct and indirect pest effects, as provided in ISPM 11, are listed
in Table 6.
11
Table 6. Direct and Indirect Pest Effects
Direct Pest Effects










known or potential host plants
types, amount and frequency of
damage
crop losses, in yield and quality
biotic factors (e.g. adaptability
and virulence of the pest)
affecting damage and losses
abiotic factors (e.g. climate)
affecting damage and losses
rate of spread
rate of reproduction
control measures (including
existing measures), their efficacy
and cost
effect of existing production
practices
environmental effects
Indirect Pest Effects








effects on domestic and export
markets, including effects on
export market access
changes to producer costs or input
demands
changes to domestic or foreign
consumer demand for a product
resulting from quality changes
environmental and other
undesired effects of control
measures
feasibility and cost of eradication
and containment
capacity to act as a vector for
other pests
resources needed for additional
research and advice
social and other effects (e.g.
tourism)
ISPM 11 provides guidance on factors to consider when assessing potential economic
consequences, including environmental consequences. It states that, after obtaining
information on areas where the pest currently occurs, ‘the information should be
compared with the situation in the PRA area. Case histories concerning comparable pests
can usefully be considered. These points from ISPM 11 are summarised in Table 7.
Table 7. Factors for Consideration in Analysing Economic Consequences
Time and place factors

economic consequences are expressed with time and may concern one year,
several years or an indeterminate period

other scenarios could concern whether the pest occurs at one, few or many
points in the PRA area and the expression of potential economic consequences
will depend on the rate (e.g. slow or rapid) and manner of spread in the PRA
area

appropriate analysis may be used to estimate potential economic consequences
over the period of time when a pest is spreading in the PRA area

many of the pest effects outlined above could be expected to change over time

expert judgement and estimations are required
12
Analysis of commercial consequences

Many direct and indirect effects of a pest will be of a commercial nature.

It is useful to identify and quantify these effects (which may be positive or
negative), taking account of the

impact of pest-induced changes on:
– producer profits resulting from changes in production costs, yields or
prices
– quantities demanded or prices paid for commodities by domestic and
international consumers
– crop losses
Analytical techniques

The use of analytical techniques is often limited by lack of data, uncertainties
in available data and by
difficulties in expressing some effects in monetary terms (i.e. only qualitative
information can be provided). Approaches that can be used in consultation
with economists to make a more detailed analysis of the potential economic
effects of a quarantine pest include:
– partial budgeting — this approach will be adequate if the economic
effects of the pest on producer profits are generally limited to producers
and are considered to be relatively minor
– partial equilibrium — this is recommended if there is a significant
change in producer profits or consumer demand
– general equilibrium — this approach is used if the economic changes
are significant to a national economy and could cause changes to factors
such as wages and interest rates
Non-commercial and environmental consequences

Some of the direct and indirect effects of the introduction of a pest will be of
an economic nature, or affect some type of value, but not have an existing
market which can be easily identified. As a result, the effects may not be
adequately measured in terms of prices in established product or service
markets. Examples include:
– environmental effects (such as ecosystem stability, biodiversity and
amenity values)
– social effects (such as employment and tourism)

If quantitative measurement of such consequences is not feasible, qualitative
information about the consequences may be provided (also include an
explanation of how this information has been incorporated into decisions)
Where possible, it is useful to describe the output of the assessment of economic
consequences in monetary terms. Qualitative or quantitative measures without monetary
terms can also be used. It is important to specify sources of information, assumptions and
methods of analysis. Wherever appropriate, the part of the PRA area where presence of
the pest will result in economically important loss should also be identified.
13
Overall assessment of risk
The conclusions from pest risk assessment are used to decide whether risk management is
required.
The risk estimation matrix (Table 7) is used to combine the likelihood of an event
occurring and the consequences if it did occur. From this matrix, a level of risk is
determined and this is compared to the appropriate level of protection (ALOP) that has
been set. By comparing the risk against the ALOP it is possible to determine which pests
need risk management measures. The band of cells marked ‘very low risk’ represents
Australia's ALOP, or tolerance of loss.
Likelihood of entry,
establishment and spread
Table 7. Risk Estimation Matrix Used For PRA by Biosecurity Australia
High
likelihood
Negligible
risk
Very low
risk
Low risk
Moderate
risk
High risk
Extreme
risk
Moderate
Negligible
risk
Very low
risk
Low risk
Moderate
risk
High risk
Extreme
risk
Low
Negligible
risk
Negligible
risk
Very low
risk
Low risk
Moderate
risk
High risk
Very low
Negligible
risk
Negligible
risk
Negligible
risk
Very low
risk
Low risk
Moderate
risk
Extremely
low
Negligible
risk
Negligible
risk
Negligible
risk
Negligible
risk
Very low
risk
Low risk
Negligible
likelihood
Negligible
risk
Negligible
risk
Negligible
risk
Negligible
risk
Negligible
risk
Very low
risk
Negligible
impact
Very low
Low
Moderate
High
Extreme
impact
Consequences of entry, establishment and spread
According to ISPM 11, as a result of the pest risk assessment stage:

all or some of the categorised pests may be considered appropriate for risk
management

for each pest, all or part of the PRA area may be identified as an endangered area

a quantitative or qualitative estimate of the probability of introduction of a pest(s),
and a corresponding estimate of the economic consequences, will have been
obtained and documented, or an overall rating could have been assigned.
14
Degree of uncertainty
According to ISPM 11, estimation of the probability of introduction of a pest and of its
consequences involves many uncertainties. In particular, this estimation extrapolates
from the situation where the pest actually occurs to the hypothetical situation in the PRA
area. It is important to document the area of uncertainty and the degree of uncertainty in
the assessment, and to indicate where expert judgement has been used.
This is necessary for transparency and may also be useful for identifying and prioritising
research needs.
Resources and further reading
The information and much of the text for this section is taken directly from the following
documents:

ISPM 11 Pest risk analysis for quarantine pests including analysis of
environmental
risks
and
living
modified
organisms
<http://www.ippc.int/IPP/En/ispm.htm>

ISPM
8
Determination
of
<http://www.ippc.int/IPP/En/ispm.htm>

WTO 1995, Agreement on the Application of Sanitary and Phytosanitary
Measures

Biosecurity Australia, September 2001. Draft guidelines for Import Risk Analysis
(Draft).

Devorshak, C. and Griffin, R. (2002). Role and relationship of official and
scientific information concerning pest status. In G.J. Hallman and C.P. Scwalbe
(eds.) Invasive arthropods in agriculture: problems and solutions. Scientific
Publishers, Enfield, NH.
pest
status
in
an
area
15