Fourth International Bemisia Workshop International Whitefly ...

Journal of Insect Science | www.insectscience.org ISSN: 1536-2442
compatible organisms that produce viable offspring
would be considered the same species. Several lines of
evidence, including the results presented here, suggest
that B. tabaci constitutes a single group of related
variants, of which some are reproductively compatible
while others are not. Also, certain variants are
recognizable by definitive sets of (adaptive) behaviors,
and are referred to as biotypes, a designation that has
contributed to taxonomic confusion. Even so, results
indicate that gene flow occurs between three of these
B. tabaci variants, in this instance ‘biotypes’, which
have experienced prolonged physical separations
imposed by geography and/or host plant. It is not
known whether the A, B, Jat, or other biotypes and
haplotypes have hybridized in nature and/or if so,
whether they are naturalized. Hybridization may more
commonly be employed as a means of diversification
in this species than previously thought.
Survival of whiteflies during long-distance
transportation of agricultural products
Piero Caciagli
Istituto di Virologia Vegetale – CNR, Torino, Italy.
Correspondence: p.caciagli@ivv.cnr.it
Besides being pests of tropical and subtropical crops
and of protected crops in temperate regions, some
whitefly species are also vectors of many plant viruses.
Worries about their possible movements to new areas
are therefore justified. Although whitefly species are
known to have invaded new areas through natural
spread, in general whiteflies are poor fliers and their
long-distance movements are likely assisted by
humans. The high risk of moving pests from place to
place by human activity is one of the few agreed
reasons for imposing quarantine restrictions. Hence, it
is very important to know, besides other things, the
conditions that permit survival of the pest. Among the
abiotic factors influencing survival of whiteflies,
temperature and relative humidity are important,
particularly at extreme values. Temperature has two
limits for the survival of whiteflies. High transport
temperatures are not compatible with transportation of
fresh plant products, but may be compatible with other
types of goods that do not require cooling or controlled
conditions. At 30 to 40°C, survival of adult B. tabaci is
very poor after 6 hours, independently of RH. At the
lower limit, adult whiteflies are the least resistant
stage, but they can survive for long times at
temperatures often recommended for the transportation
of potted ornamental plants and florist green materials.
Other stages, like eggs and nymphs, are much more
resistant to cold. Within the ranges of temperature and
time that allow survival of the non-adult stages,
products can be moved substantial distances. There is
also a possibility that plant pathogenic viruses can be
moved together with whitefly immature stages. Among
the biotic factors that could influence survival, only the
osmotic pressure of the host leaves seems to have a
direct bearing. Variations in host leaf water content,
and its associated soluble sugar concentration, strongly
influence egg survival of T. vaporariorum. On the
other hand, 4th instar nymphs can survive desiccation
of the leaves they are attached to and emerge as adults
after a few days. Given that the risk of transporting
undesirable species is high, the imposition of
quarantine regulations is not a decision for scientists.
Biologists, though, should provide the rationale behind
decisions of this type: not only the basic knowledge of
pests (biology, taxonomy), but also risk analysis, in
order to establish the priorities for political decisions
and for future research, and instruments for making
regulations enforceable. Methods are available for
identifying the undesirable pests both at the species
(official diagnostic protocols, identification guides,
ELISA tests, multiplex real-time PCR assays) or
biotype level (analysis of esterase patterns, sequencing
of whitefly genes, RAPD-PCR, AFLP, PCR-RFLP).
The analysis of biotypes/races can be even more
detailed by microsatellite markers. Other more general
instruments for reducing the risk of exporting pests are
available or being developed, with the aim of
excluding pests. If exclusion fails, we can still use our
knowledge to confine, and hopefully eradicate, the
undesired “guest”. Agriculture operators and
international travelers should be made aware of the
existence of destructive, exotic (plant) pests
threatening to enter a country in which they are not
known to occur, because it is clear that the success of
plant quarantine programs greatly depends upon public
cooperation with quarantine legislation.
Controlling the Tobacco Whitefly Bemisia
tabaci (Genn.) (Hom.: Aleyrodidae) in
Horticultural Crops with the Predatory
Mite Amblyseius swirskii (Athias-Henriot)
Javier Calvo 1 , Karel Bolckmans 2 , José E. Belda 1
1 Departamento I+D, Koppert Biological Systems, Águilas (Murcia),
Spain.
Correspondence: jcalvo@koppert.es
2 Koppert Biological Systems, AD Berkel en Rodenrijs, The
Netherlands
The predatory mite Amblyseius swirskii has
demonstrated the potential to become a key biological
control agent in several horticultural crops in southern
Spain. However, actual implementation of A. swirskii
required clarification of such critical parameters such
as optimal release rates, and introduction times,
response of pest populations, adaptability to various
crops, and compatibility with different natural
enemies. The experiments described below were
intended to provide this information under simulated
Journal of Insect Science: Vol. 8 | Article 4 11