Migration and dispersal of Anthonomus grandis (Coleoptera: Curculionidae) in South America

2007·0.61 MB·

by  Stadler, Teodoro

ISSN 0373-5680 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007 205
Migration and dispersal of Anthonomus grandis
(Coleoptera: Curculionidae) in South America
STADLER, Teodoro* and Micaela BUTELER**
*Laboratorio de Investigaciones y Servicios Ambientales Mendoza (LISAMEN)
Centro Regional de Investigaciones Científicas y Tecnológicas (CRICYT - CONICET)
Av. Ruiz Leal S/N Parque General San Martin, CC. 131, M 5500 IRA, Mendoza,
Argentina; e-mail: [email protected]
**Department of Land Resources and Environmental Sciences, Montana State University,
334 Leon Johnson Hall, Bozeman 59717, Montana, USA; e-mail:
[email protected]
Migración y dispersión de Anthonomus grandis (Coleoptera:
Curculionidae) en América del Sur
(cid:132)(cid:132)(cid:132)(cid:132)(cid:132) RESUMEN. El presente estudio sobre la dispersión de Anthonomus
grandis Boheman, el picudo del algodonero, en Argentina, Brasil,
Paraguay y Bolivia, explora las características ecológicas y fisiológicas
que han permitido a este insecto dispersarse y establecerse exitosamente
en América del Sur. La plasticidad fenotípica de A. grandis se caracteriza
por un tiempo de desarrollo flexible, ciclo de vida multivoltino con
generaciones superpuestas, la capacidad de alimentarse con polen de
diversas familias botánicas así como de otras fuentes de alimento y por
su habilidad para migrar y dispersarse con la ayuda del viento. Todo esto
hace de esta especie una plaga clave para el cultivo del algodón. Los
cultivos de cítricos en Misiones, Argentina, son posibles sitios para la
hibernación de esta especie. En esta región fueron capturadas grandes
cantidades de individuos prediapausantes, provenientes de algodonales
en post-cosecha en Paraguay, atraídos probablemente por compuestos
volátiles de cítricos cultivados en la zona. La quiescencia facultativa que
atraviesan los adultos ante condiciones adversas, conlleva a un retraso
en el desarrollo que se relaciona con las condiciones desfavorables. Esto
sugiere que la hibernación en A. grandis puede ser definida como
«oligopausa», una forma intermedia de diapausa. Desde su introducción
en Brasil en 1983 y hasta el 2006, el picudo se ha dispersado en dirección
sudoeste hacia Argentina, a una velocidad promedio de 61 km año-1. Sin
embargo, le ha insumido aproximadamente diez años cruzar 250 km,
desde Paraguay hacia el centro de la zona algodonera de Argentina. Este
progreso más lento se debe probablemente a las acciones llevadas a cabo
en el marco del programa de erradicación del picudo del algodonero,
por parte del gobierno de Argentina. La llegada del picudo al área central
de cultivo de algodón en la Argentina, así como a otras áreas de cultivo
en Paraguay y Argentina, confirma el hecho de que el picudo debería
finalmente incluirse en un programa único de manejo integrado de plagas
del algodón.
PALABRAS CLAVE. Picudo del algodonero. Manejo integrado de plagas.
Plaga clave.
Recibido: 7-IX-2007; aceptado: 2-X-2007
206 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007
(cid:132)(cid:132)(cid:132)(cid:132)(cid:132) ABSTRACT. This study discusses the dispersal of Anthonomus
grandis Boheman, the cotton boll weevil, in Argentina, Brazil, Paraguay
and Bolivia, exploring the ecological and physiological factors that have
made the dispersal and establishment of this insect in South America so
successful. The boll weevil’s phenotypic plasticity is represented by its
flexible developmental time, its multivoltine life cycle with several
overlapping generations, its capacity to feed on pollen from diverse
botanical families as well as from non pollen food sources and its ability
to migrate and disperse aided by winds. These characteristics make it a
key pest for cotton. Probable overwintering «hot spots» for the boll weevil
were identified in Misiones-Argentina, where large numbers of
prediapausing weevils concentrate after arrival from newly harvested
cotton fields in Paraguay, probably attracted by citrus orchards volatiles.
The boll weevil’s facultative quiescence is always relative to
environmental adverse conditions. This suggests that overwintering in
the boll weevil can be defined as «oligopause», an intermediate form of
diapause. Since its introduction to Brazil in 1983, until 2006, it has spread
southwest at an average of 61 km year-1 towards Argentina. However, it
took the boll weevil approximately ten years to move 250 km between
Paraguay and the main cotton growing area in Argentina. This slower
progress is probably due to the actions taken by the Argentine government
through the boll weevil eradication program. The arrival of the boll weevil
at the cotton cropping areas in Paraguay and Argentina reinforces the
fact that the boll weevil should finally be included in an integrated cotton
pest management program jointly with other major cotton pests.
KEY WORDS. Cotton boll weevil. Integrated Pest Management. Cotton
key pest.
INTRODUCTION predators and parasites that attack the BW,
these do not effectively control the pest
The «cotton boll weevil» Anthonomus populations. The BW is also susceptible to
grandis Boheman (Coleoptera: protozoan and fungal pathogens, but effective
Curculionidae) (BW) is considered the most control has not been achieved so far,
destructive cotton [Gossipium hirsutum L. primarily because the pathogens do not act
(Malvaceae)] pest in America, due to its fast enough (Bell, 1983). This fact is consistent
behavioural characteristics that allow with the concept that there are in principle,
migration and dispersal, its biological no effective control agents found in the
characteristics such as high reproductive habitat of newly introduced pests (Ables et
capacity, multivoltine life cycle, and the fact al., 1983).
that predation and parasitism by natural In South America, the BW has invaded
enemies provide poor control of its Brazil, Paraguay, Argentina and Bolivia (dos
populations. From moderate numbers of Santos, 2000; Gomez et al., 2000; Cosenzo
overwintered adults the pest may develop et al., 2001; Duran Parada, 2000). Cotton
into yield-damaging populations within the production in these countries is mainly
span of a single generation. Any insect species represented by two opposite situations: large
that exhibit these attributes has the potential cotton fields of over 50 ha and farmers with
of being a dangerous economic pest (Walker less than 3 ha, where smallholders rely on
& Niles, 1971). cotton as a cash crop. Cotton-growing areas
In the Northern and Southern American in Paraguay and Argentina are scattered
cotton growing areas, even though there are among the region and represented mainly by
over 50 recorded beneficial species of smallholders. This fact makes the cotton pest
STADLER, T. and M. BUTELER. Migration and dispersal of Anthonomus grandis in South America 207
complex situation quite different from the one advances in the knowledge of the interaction
in the US or in Australia, two countries with between the BW and its host-plant as well as
modern and technically advanced its feeding habits, offer an opportunity to
agricultural industries. understand the dispersal of the BW in Brazil,
As shown by the US Boll Weevil Paraguay, Argentina and Bolivia. Based on
Eradication Program (http:// the knowledge obtained we present a review
permanent.access.gpo.gov/lps3025/ of the ecological and physiological factors
weevil.html), the only effective way thus far, that have made the dispersal and
to reduce BW populations to levels below establishment of the BW in South America
economic significance is the use of intensive so successful, and discuss its implications.
pheromone mass trapping, pin-head
applications based on pheromone trapping, Natural history of the cotton boll weevil
in-season insecticide applications and
intensive «diapause-control programs». Such As described by West-Eberhard (2005),
an intensive, high input approach makes variability in responsiveness in an organism
cotton growing unprofitable for small farmers. is due partly to genetic variation and partly
Moreover, insecticides pose a serious to variations in the developmental plasticity
drawback on populations of beneficial of phenotype structure, physiology, and
organisms that regulate other cotton pests, behaviour that arise during development and
such as Pectinophora sp. (Lepidoptera: may be influenced by inputs from the
Gelechiidae), and Heliothis sp. (Lepidoptera: environment, like temperature, photoperiod
Noctuidae). Therefore, the use of pesticides and food availability. Survival and
to manage the BW impacts the whole insect reproduction of an individual strongly
pest management of the crop, and augments depend on its phenotypic plasticity (Caswell,
production costs. Thus, the arrival of the boll 1983; Ishihara, 1999).
weevil, has had severe social consequences The phenotypic plasticity of the BW has
because although damage by this insect pest been demonstrated by the high variability in
has reduced yields and profits drastically (e.g. time required by this species to develop from
Paraguay), smallholders are not expected to egg to adult even for eggs laid on the same
abandon cotton in the short term, since day. This developmental time range may be
historically there have been no other as short as three days and as long as thirty six
alternatives to cotton for a cash crop (Cosenzo days for weevils developing in squares and
et al., 2001). up to fifty one days for weevils developing in
The BW has been an issue of interest since bolls. Moreover, the BW is a multivoltine
the species first became known as a pest in species with eight to ten generations during
USA in the early 1890’s and considerable the normal season, and this is a critical
work has been published on the subject. attribute that makes it a dangerous economic
However, in South America, the BW has only pest (Coad, 1915; Horton & Ellis, 1997).
recently become a key pest, and many Different authors report that spring-emerging
questions regarding its biology, dispersal and BWs search for the nearest cotton plants
host relationships still remain unanswered in (Cushman, 1911; Grossman, 1928) to feed
this singular South American-scenario. on. Those weevils emerging before squares
Recent advances in the knowledge of the are available may feed on the terminals of
BW in the framework of a project titled cotton seedlings or on pollen from flowering
Integrated Pest Management of the Cotton plants near the cotton fields. The BW,
Boll Weevil in Argentina, Brazil and Paraguay however, needs cotton pollen to successfully
(CFC-ICAC/04), present an opportunity to mate, and oviposition does not occur until
review the origin, dispersal, host relationships squares are present (Pierozzi Jr., 1985). After
and natural enemies of the pest in South cotton square formation, BWs are attracted
America (Stadler, 2001). The new discovery to cotton fields by plant volatiles. They
of the BW at the southern limit of the cotton respond to the host plant volatiles as well as
cropping area in Argentina and the latest to aggregation pheromones from other
208 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007
individuals present in the field (Tumlinson et and feeds on pollen of other plants apart from
al., 1969; White & Rummel, 1978). Later, Malvales in North and South America
they mate and lay eggs when squares reach (Benedict et al., 1991; Jones et al., 1993). In
approximately 0.6 mm in diameter. BW Argentina and in Paraguay, adult BWs feed
oviposition has been well described by on native flora in the absence of cotton. This
several authors (Cushman, 1911; Hunter & was shown by different authors studying BW
Price, 1912; Bottrell, 1983). The BW female populations from Formosa and Misiones
scouts the flower or fruit bud tapping it with (Argentina), where 37 pollen types were
her antennae before laying an egg. Upon found in the digestive tract of trapped
selecting a suitable site the insect begins to individuals. Pollen found belonged to
bore a hole into it with its mouthparts, after Malvaceae, Compositae (Asteraceae),
pulling out a piece of the epidermis and lays Solanaceae, Euphorbiaceae, Amaranthaceae,
an egg. Females prefer to oviposit on squares Leguminosae (Fabaceae), and Polygonaceae
rather than on bolls (Isley, 1932; Habib & (Cuadrado & Garralla, 2000; Cuadrado,
Fernandes, 1983) unless the squares are too 2002). In the winter, pheromone trapped BWs
big (Showler, 2004). Usually, females lay one showed pollen from different species of
egg per square but each female may lay about Solanaceae, Leguminosae, Malvaceae, and
two hundred eggs during a ten to twelve day Compositae in their digestive tract (Cuadrado,
period. Eggs hatch in three to five days and 2002). Finally, Showler & Abrigo (2007)
newly emerged larvae feed within the squares showed that adult BWs can be sustained on
for eight to ten days. The pupal stage lasts non pollen food sources from plant species
from five to seven days. Generation time from common in the south tropics and
egg to egg averages about eighteen to twenty Mesoamerica. These authors demonstrated
one days, depending on environmental that the BW is able to feed on endocarps of
conditions (Horton & Ellis, 1997). Toward the prickly pear, grapefruit and orange, and
end of summer, most emerging adult weevils survive up to three and a half months.
enter a «pre-diapause» state, where they don’t Moreover, BWs seem to have a higher
mate and spend a great part of the time survival rate during the winter in citrus
feeding to build up reserves for the winter. In orchards than in other habitats, and Showler
semiarid regions (e.g. Rolling plains of Texas), (2006) calls these «overwintering hot spots»
adults generally spend the winter sheltered for the BW. Pollen as well as non pollen food
under leaf litter in wooded areas near cotton sources other than cotton are called «feeding
fields, in fence rows and grass banks hosts» and do not induce reproduction.
surrounding cotton fields (Sterling & Nevertheless, feeding hosts allow the survival
Adkisson, 1971). The BWs remain in these of weevils during the cotton-free months and
overwintering sites until temperatures represent an important energy supply for pre-
become warmer and days lengthen (Horton diapausal, migratory and post-diapausal
& Ellis, 1997). activities.
Cate & Skinner (1978) state that BWs are Recent findings present Hampea sp.
primarily pollen feeders and their populations (Malvaceae) as an original reproductive host
can be sustained by pollen when cotton is for the BW. However the BW has adopted
unavailable. Work conducted in the northern other reproductive hosts such as Gossypium
hemisphere and in Paraguay and Brazil, has hirsutum, Cienfuegosia sp. (Malvaceae) and
shown that the BW feeds on pollen from a pantropical species of Hibiscus
Malvaceae when reproductive hosts are (Malvaceae), Hibiscus pernambucensis (Cate,
lacking (Cross et al., 1975; Lukefahr et al., 1996).
1986; Marengo Lozada et al., 1987). The tribe Gossypiae (Malvaceae) in
Diversification in foraging in the BW is a America embraces four genera: Gossypium,
product of its phenotypic plasticity as part of Hampea, Thespesia and Cienfuegosia, and
the survival strategy in adults during periods BWs have been observed on all them.
when cotton is not available. It has been Hampea occurs mainly in Mexico and
shown that the BW is a polyphagous species Central America and south of the Amazon
STADLER, T. and M. BUTELER. Migration and dispersal of Anthonomus grandis in South America 209
only the genus Cienfuegosia occurs wild and The literature reports on BW diapause are
Thespesia populnea (L.) is often commercially diverse and in most cases, rather confusing
grown. The BW’s reproductive hosts in South (in Rankin et al., 1994). Most literature reports
America have not been experimentally on BW diapause (Earle & Newston, 1964;
determined so far, but according to Keeley et al., 1977; Wolfenbarger et al., 1978;
Krapovickas (2000) the genus Cienfuegosia Graham et al., 1979; Guerra et al., 1982;
seems to be the most probable reproductive Braga Sobrino & Lukefahr, 1984; Rankin et
host for the BW and its geographic al., 1994) match Müller’s (1970) definition
distribution in Argentina overlaps with the of oligopause: a «facultative response to
cotton-cultivated areas in this country. unpredictable exigencies on an irregular
Cienfuegosia is endemic from the province basis, induced by adverse environmental
of Chaco (Argentina) and Paraguay and it can conditions» and this particular response
be found up to latitudes of 33° S. Therefore, appears and ends with a delay relative to
knowledge of the species and its possible role unfavourable conditions.
as alternative host for the BW is of great According to Müller’s (1970)
importance, especially considering that its classification, some populations in the US as
blooming period extends from September to well as in north-eastern Brazil show an
June in Paraguay, providing an alternative oligopause (Braga Sobrino & Lukefahr, 1984).
food source for the BW in the off season On the other hand, the «diapause syndrome»
(Krapovickas, 2000). described in the BW by Rankin et al. (1994),
The BW faces different seasonal consists of a set of behavioural and
challenges during its life cycle, such as physiological species-specific markers of pre-
absence of its reproductive host, harsh winter diapause, diapause and post- diapause
conditions, and shortening of daylight. processes to seasonal changes (Tauber et al.,
Phenotypic plasticity allows the BW to adapt 1986).
to adverse factors through migration, Graham et al. (1979) suggest that the
dormancy and seasonal phenotypic variation. incidence of diapause in BW may vary
considerably from year to year. Earle &
Cotton boll weevil dormancy Newston (1964) describe differences in BW
diapause between individuals as a
Dormancy is a genetically based consequence of overwintering strategies other
arrestment in insect development through than diapause that occurs in response to an
behavioral adaptation to a seasonally array of environmental factors or diet.
changing environment. Stimuli like food Differences in responses to overwintering
quality and abundance can influence cues among insects of the same species from
dormancy through interaction with different geographical areas are common, and
photoperiod and temperature (Dingle, 1972; critical photoperiods for diapause induction
Beck, 1980). Dormancy also allows often appear related to latitude (Tauber et al.,
synchronization of insect lifecycles 1986; Leather et al., 1993). For example,
interacting with development rates and there are significant differences in BW
determining patterns of voltinism (Tauber & diapause (Keeley et al., 1977; Wolfenbarger
Tauber, 1976). Quiescence and diapause are et al., 1976; Guerra et al., 1982), as well as
the two types of dormancy usually identified in winter time reproduction (Showler, 2006)
in insects although diapause shows several between subtropical and temperate
intermediate forms (Müller, 1970; Beck, environments. Guerra et al. (1982) reported
1980; Tauber et al., 1986). that in the subtropical regions in the US,
Overwintering in the BW occurs in the diapause is best distinguished by interruption
adult stage, which may provide the greatest of sexual functions, which is only temporary
flexibility for location of, and movement and can be easily altered through feeding on
within overwintering sites, as well as cotton flower buds.
movement towards food and reproductive The regulation of diapause in the BW is
resources in spring. complex and dynamic. Both early and late
210 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007
life stages are sensitive to dynamic direction play primary roles in displacement
photoperiods and temperatures, individuals as decisive factors determining the direction
remain sensitive to these cues for different and distance travelled. Rainey (1977)
durations, and the cues have a cumulative highlighted the enormous survival rate of
effect on diapause induction over part or all insects using kinetic energy of atmospheric
of the life cycle (Wagner et al., 1999). This circulation through downwind movement to
adaptation would provide the species with locate and exploit ephemeral vegetation.
flexibility to allocate portions of its population In South America, the BW tends to
to reproduction or diapause as conditions disperse during late summer and early fall
dictate during development. matching the end of the cotton season, and
favored by high wind speeds. The average
Migration of the cotton boll weevil highest wind speeds observed in Argentina,
Brazil and Paraguay are from the NE and N
Migration in insects is a persistent, directions and they can have a significant
directed movement dependent upon an influence on BW dispersal from infested areas
inhibition of response to physiological stimuli (Ravelo et al., 2001). As described by several
(i.e. mating, food), that could eventually arrest authors (Gomez et al., 2000; Cosenzo et al.,
movement Kennedy (1961). This definition 2001), the highest BW trapping catches in
has shown to be useful in distinguishing Misiones were observed after cotton harvest,
migratory and trivial flight in insects (Rankin which is coincident with the massive
et al., 1994). The BW, like other insect migration of BW from southern Paraguay to
species, uses migration not only to escape NE Argentina (Misiones and Formosa
from old habitats and/or adverse conditions provinces) in the fall (Gomez et al., 1996;
but also for colonization and active dos Santos, 2000; Gomez et al., 2000). Young
exploitation of temporary habitats weevils emerged in the fall, will migrate after
(Southwood, 1962). cotton harvest mainly as a result of food
Migration in the BW occurs in the fall, scarcity as shown by different authors in
when the major portion of the BW population Brazil, Paraguay and Argentina (Gomez et al.,
moves from cotton fields into a winter habitat 1996; Gomez et al., 2000; dos Santos, W. J.,
relatively near the source field. According to 2001; Cosenzo et al., 2001). On the other
Moody et al. (1993), the early progeny of hand, spring-emerging early reproductive
these migrants will probably enhance the BWs will migrate in absence of reproductive
effective dispersal from the point of origin. hosts, and feed on feeding hosts until a
These authors also consider the reproductive reproductive host becomes available. Spring-
BWs dispersing from infested fields in the fall emerging BWs reproduce after reaching the
to play an indirect but major role in the limits of their dispersal flight. During this
establishment of overwintered adults in new phase, BWs could travel great distances
areas. Showler (2006) reports that (Rankin et al., 1994). Studies conducted by
curculionids are not known to migrate Rankin (1974) indicate that juvenile hormone
between specific locations and that the long (JH) controls the timing and coordination of
range movements of BWs are passive and flight and reproduction through its response
accidental relying on wind currents. So, the to photoperiod, temperature and food quality
BW might spread randomly to favorable and in Oncopeltus fasciatus (Dallas) (Heteroptera:
unfavorable habitats like plant seeds do. Early Lygaeidae). In this species, intermediate JH
workers recognized that the BW did not rely titers stimulate migratory behavior, allowing
totally on its flying ability to cover great rapid colonization by young adults at their
distances because it is a slow flyer with a non- highest reproductive potential, maximizing
aerodynamic body design, reaching the utilization of the new habitat. This
unassisted flight speeds of < 4,8 km h-1 phenomenon is termed «oogenesis flight
(McKibben et al., 1988). For BWs lifted by syndrome» (Dingle, 1974). During starvation,
convective currents to higher altitudes where JH titers continue to decline until the
wind velocities are greater, wind velocity and individual settles down to survive on its
STADLER, T. and M. BUTELER. Migration and dispersal of Anthonomus grandis in South America 211
reserves to maximize the chance of finding a (Burke et al., 1986). The rapid expansion of
more favorable environment (Rankin & the BW in the cotton growing areas in North
Riddiford, 1977). A similar efficient strategy and Central America and its high impact on
is employed to some extent by other species the crop yield are an evidence of the fast
as the (e.g.) Colorado potato beetle dispersal rate and high reproductive capacity
[Leptinotarsa decemlineata (Say) (Coleoptera: of this pest.
Chrysomelidae)] and the common cockchafer The Amazon was thought to be an
[Melolontha melolontha L. (Coleoptera: adequate barrier that would restrain the BW
Melolonthidae)] (Stengel & Schubert, 1970). from moving southwards. However, in
Very little is known about the reproductive February of 1983 the Department of
physiology of the BW, oogenesis, or adult Entomology of the Agricultural School in
diapause in this species. However, in a study Piracaba-Sao Paulo reported the presence of
conducted by Taub-Montemayor et al. (1997) the pest in cotton fields in Campinas Sao
elevated levels of hemolymph juvenile Paulo (Braga Sobrinho, 2000) (Fig. 1),
hormone esterase (JHE) were found to be although it is possible that the appearance of
positively correlated with survival throughout the BW in Brazil was due to an accidental
the winter in South Texas population of introduction other than because of natural
weevils. According to these authors JH seems dispersal (dos Santos & Meneguim, 1996). In
to control vitelogenesis in the pre- June 1983, probably disseminated through
reproductive female weevil and high JHE cottonseed trade, the BW infested the cotton
levels are correlated with diapause onset and growing areas of the northeast of Brazil
overwinter survival. Boll weevils with (Paraiba and Pernambuco). In March 1985,
relatively large fat bodies and incompletely 350 000 ha of cultivated cotton in the states
or partially developed ovaries show a of San Pablo, Paraiba, Pernambuco and Rio
tendency to make long duration flights Grande do Norte were affected by the pest
(Rankin et al., 1994). This condition is typical (dos Santos & Meneguim, 1996; Degrande,
of the «oogenesis flight syndrome» in which 1991). The first infestation in Parana was
migration occurs prior to the onset of found in 1987. Less than five years later, the
reproduction (Dingle, 1974). pest had infested more than 90% of the cotton
producing area of the country. It was
Dispersal of the cotton boll weevil in especially appalling for smallholders, who
Latin America couldn’t afford new technological advances
to control the pest (Gomez et al., 2000).
The BW may move more than 60 km in The appearance of the BW in Brazil put
search of food or overwintering habitats. Paraguay on the alert, where cotton is the
Johnson et al. (1975) recaptured marked BWs main crop. Traps to monitor the pest were
at distances ranging from 2 to 66 km from installed in Paraguay and as a measure to
the release point and Guerra (1988) reported restrain the advance of the pest into the
that several marked BWs were recovered at country, the entrance of cottonseeds from
a flight distance of approximately 320 km. Brazil was banned and cotton cultivated with
Other authors reported that an advance of seeds coming from that country were
approximately 80 km year -1 was normal for destroyed. In spite of all these efforts, BWs
this insect as it spread north and eastward were captured in pheromone traps for the first
(Hunter & Coad, 1923). The BW dispersal time in Paraguay in 1991, in the district of
stochastic models developed by McKibben Saltos del Guayrá (Gomez et al., 1996).
et al. (1991), show that maximum dispersal In 1993, the BW was reported in the
distances can be greater than 100 km for province of Misiones (Fig. 1), restricted to
some individuals of a migrant population. non-cultivated areas. In June 1994, BWs were
In the USA, the BW was firstly found in captured in San Ignacio de Loyola
Texas in 1892. In the subsequent thirty years, (Argentina), on the border with Paraguay, near
it infested the USA cotton belt and spread to cotton fields. At the same time BWs appeared
Venezuela in 1949 and to Colombia in 1950 in pheromone traps in the department of
212 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007
Fig. 1. Dispersal of Anthonomus grandis in Brazil, Paraguay, Argentina and Bolivia from 1983 until
2006 (schematic). * Dispersal of A. grandis in Brazil, Paraguay after Gomez et al. (2000).
Pilcomayo and then Pilagas (Formosa BW infested areas in Paraguay (Fig. 2): the
province). In 1996, BWs were captured 60 northern area where BW populations are high
km southwest of the cultivated area (Cosenzo (A), the central area where pest populations
et al., 2001), and finally in August 2006 BW are moderate to high (B) and the southern
was reported in Cte. Fernandez (Chaco), the area (C), dispersal front of the BW, with
main argentine cotton cropping area (http:// intermediate levels of infestation (Gomez et
www.inta.gov.ar/saenzpe/actual/06/abril/ al., 2000). As shown in the figure, BW
noticia1.htm) (Fig. 1). In 1999 the presence dispersion has been precisely followed in
of the BW was reported in Bolivia, and it is Paraguay through trapping programs
suspected that it was introduced from Brazil developed by the Ministry of Agriculture of
(Duran Parada, 2000). this country (Gomez et al., 2000),
At present the occurrence of the BW in demonstrating that the BW disperses
the Paraná state (Brazil), not only constitutes downwind at a rate of 60 to 100 km in a year.
a problem by reducing cotton profitability, In an attempt to eradicate the BW from
but it also creates dispersal sources that move Argentina, and to prevent infestation of the
to Argentina. The pest has been restrained main cotton cropping areas of the Chaco and
from the main cotton growing area in Formosa provinces, the Argentine authorities
Argentina although sporadic re-infestations decided to destroy all cotton planted in the
occur due to migrating insects from Paraguay province of Misiones (Fig. 1), close to the
(Cosenzo et al., 2001). border of Paraguay and Brazil. Surprisingly,
In Paraguay the BW affected even when cotton was eradicated in the
approximately 95% of the cotton growing province of Misiones, trap captures
areas in 1996, migrating in a windward established since 1996, show a trend of BW
direction (NE) at a speed of 60 km a year populations migrating upwind in northeast
(Gomez et al., 2000). There are three distinct direction in the fall from Paraguay into
STADLER, T. and M. BUTELER. Migration and dispersal of Anthonomus grandis in South America 213
Fig. 2. Migration and dispersal of Anthonomus grandis in Paraguay (schematic - after Gomez et al.,
2000). SW windward movement into Argentina and E-NE upwind movement into the main citrus
cropping area in Misiones-Argentina.
Misiones and further into Corrientes province Gomez et al., 2000). The unusual behavior
(Argentina) (Retzlaff, 1998), two provinces of upwind movement, over short distances,
where citrus are among the main crops. of large numbers of weevils from Paraguay
Remarkably, the results of the Argentine BW into non-cotton areas into Misiones (Fig. 2)
trapping program show that the BWs’ since 1996, can be understood under the light
southwestern (downwind) migration in of Showler´s (2006) work. This author showed
direction to the main Argentine cotton that BWs survive better in citrus orchards than
cropping area was always lower than in other habitats during the winter and that
expected (E. Cosenzo pers. comm.). such habitats are examples of overwintering
In South America, the BW tends to «hot spots» in the sub-tropical Lower Rio
disperse during late summer and early fall Grande Valley of Texas. Cotton harvest in
matching the end of the cotton season, and Paraguay (March, April) causes BWs to search
is favored by high wind speeds. The average for alternative food sources (Guerra, 1986),
highest wind speeds observed in Argentina, as well as for overwintering refuges. Also,
Brazil and Paraguay are from the NE and N cotton harvest overlaps with late citrus
directions and they’ve had a significant orchard ripening in Misiones and Corrientes
influence on BW dispersal from infested areas (Argentina). Therefore, the atypical upwind
(Ravelo et al., 2001). As described by several (northeast) movement of weevils from
authors, the highest BW trapping catches harvested cotton fields in Paraguay observed
where reached after cotton harvest, which is since 1996, reinforces Showler´s (2006)
coincident with the massive migration of BWs statement on the attractiveness of citrus
from southern Paraguay to Argentina orchards volatiles to the BW.
(Misiones and Formosa provinces) in the fall
(Gomez et al., 1996; dos Santos, W. J., 2000;
214 Rev. Soc. Entomol. Argent. 66 (3-4): 205-217, 2007
CONCLUSIONS if Cienfuegosia is a reproductive host for the
BW experimentally in order to establish if
The BW invaded Brazil in 1983, from BWs migrating great distances between
where it moved southwest and arrived in cotton cropping sites, do reproduce on wild
Paraguay in 1991, in Argentina in 1993 and hosts or if they do so exclusively on cotton.
finally in Bolivia in 1999. In August 2006, Determined efforts were made by various
the BW reached the epicenter of the argentine investigators to establish principles and
cotton cropping area (27º S) (Fig. 1). Since its techniques to control the BW. Experience has
introduction in Sao Paulo in 1983, the BW shown that no efficient biocontrol agents are
has moved approximately 1400 km available at the moment and total
southwest. The remarkable upwind (North- dependence on insecticides is a non effective
East) movement of weevils from harvested and expensive form of BW control. Also,
cotton fields in Paraguay to Misiones- erradication technologies as those utilized in
Argentina (Fig. 2), where no cotton is grown, the US BW eradication program are not
suggests that BWs are attracted to citrus feasible in Paraguay and Argentina due to the
orchards volatiles and that such habitats are large number of smallholders with less than
probably overwintering areas. 3 ha plots, distributed erratically in the forest,
The variability in responsiveness of the producing cotton as a cash crop, and based
BW to environmental factors is due partly to on rudimentary technology. In this scenario
genetic variation and partly to variations in only an integration of cultural and chemical
the developmental plasticity of phenotype tactics will provide effective control. These
structure that arise during individual cultural methods involve the management of
development influenced by inputs from the overwintering habitat, stalk destruction,
environment, like temperature, photoperiod uniformly delayed cotton planting, early crop
and food availability (West-Eberhard, 2005). termination, the use of resistant cotton varieties
Variability in responsiveness to environmental and chemical control of diapausing BWs. The
cues permits the BW to go through several arrival of the BW to the epicenter of the
overlapping generations during the cotton argentine cotton cropping area in August
growing season, to develop in squares as well 2006, reinforced the fact that the BW should
as in bolls, to adjust its developmental time finally be included in an integrated cotton pest
from egg to adult to a broad time range, to management program jointly with other major
migrate and disperse when the conditions are cotton pests common in Argentina and
unfavorable, to feed on pollen from different Paraguay such as the pink boll worm
botanical families as well as from non pollen [(Pectinophora gossypiella (Saunders)
food sources. External factors have a major (Lepidoptera: Gelechiidae)], the boll worm
developmental effect on the BW, which complex (Spodoptera - Heliothis) and the leaf
allows for variable life spans. Thanks to this, worm [Alabama argillacea (Hübner)
this insect is able to thrive in various (Lepidoptera: Noctuidae)].
environments differing in food availability After its introduction to Sao Paulo-Brazil
and climate. These are all critical attributes in 1983, the BW has moved approximately
that make the BW a great survivor, and a 1400 km southwest reaching the centre of
dangerous economic pest (Coad, 1915; the Argentine cotton cropping area (27º S) in
Horton and Ellis, 1997). August 2006. From there, the BW has spread
Because the BW can profit in an towards the southwest at an average of 61
opportunistic way from pollen of very km year-1 between Sao Paulo and Cte.
different botanical families as well as from Fernández, Chaco-Argentina. The same
other plant structures like endocarps of speed was observed during the dispersal of
prickly pear, grape fruit and oranges, BW the pest from the north to the south of
migration routes seem to be independent of Paraguay. However, the BW didn’t move as
possible «floristic corridors» connecting fast as expected from SW Paraguay to the
different cotton cropping areas in South centre of the Argentine cotton cropping area
America. It remains necessary to determine (Cte. Fernández-Chaco) between 1995 and