MEALYBUGS (HEMIPTERA: PSEUDOCOCCIDAE)
AND ARGENTINE ANTS (HYMENOPTERA: FORMICIDAE)
IN 19th CENTURY MADEIRA
By A. M. F RANQUINHO A GUIAR 1 & J AMES K. W ETTERER 2
ABSTRACT. The Argentine ant (Linepithema humile) arrived on the Atlantic
islands of Madeira sometime before 1858. More than thirty years later, in the
1890s, Madeira experienced a plague of L. humile. We propose that this delayed
population explosion of L. humile may have been triggered by the arrival of a
new exotic species of mutualistic Hemiptera. Alternatively, a new crop variety
that was better suited as a host for a mutualistic Hemiptera already resident in
Madeira may have been responsible for the sudden outbreak of L. humile.
K EY
WORDS :
Linepithema humile, Argentine ant, mealybugs, Madeira.
RESUMO. Na década de 90 do século 19, a formiga Argentina, que tinha sido
introduzida na Madeira cerca de trinta anos antes, sofreu um tremendo aumento
da sua população na ilha. Neste trabalho os autores exploram a possibilidade
deste facto ter sido despoletado pela chegada de uma nova espécie exótica de
um Hemíptero mutualista ou da introdução de uma nova variedade de cultura, a
qual poderia ter constituído um melhor hospedeiro para um Hemíptero mutualista
já residente na ilha.
PALAVRAS-CHAVE: Linepithema humile, formiga Argentina, cochonilhas algodão,
Madeira.
Laboratório de Qualidade Agrícola, Caminho Municipal dos Caboucos, 61, 9135-372 Camacha,
Madeira, Portugal. E-mail: antonioaguiar.sra@gov-madeira.pt
2
Wilkes Honors College, Florida Atlantic University, Jupiter, FL 33458, USA.
1
Bol. Mus. Mun. Funchal, 57 (317): 29-33, 2006
ISSN 0870-3876
30
Boletim do Museu Municipal do Funchal (História Natural)
No. LVII, Art. 326
In 1890s, the Argentine ant, Linepithema humile (Mayr), underwent a
tremendous population explosion in Madeira (FOREL, 1895; SCHMITZ 1896; GRABHAM,
1919, 1924). FOREL (1895) first reported L. humile in Madeira based on specimens
sent to him by Ernst Schmitz, who thought the ant was the big-headed ant, Pheidole
megacephala (Fabricius), a pest ant first reported in Madeira by HEER (1852). SCHMITZ
(1896) described the L. humile outbreak in Madeira: “In Funchal and its outskirts, ants
have become, in the past few years, a true plague and public calamity... They were ants
that in recent years were introduced from Demerara [now Guyana], or before that Brazil”.
Subsequent reports of this plague of L. humile in Madeira also presumed that L. humile
was a very recent arrival in Madeira. For example, GRABHAM (1919) asserted that L.
humile arrived in Madeira about 1892. Recently, however, we found a specimen of L.
humile dating from before 1858 in the Natural History Museum in London (WETTERER
et al., 2006). We wondered why L. humile apparently remained uncommon in Madeira
from 1858 until the 1890s, but then suddenly greatly increased in population.
Large populations of L. humile invariably depend heavily on honeydew produced
by large populations of phloem-feeding Hemiptera, such as mealybugs, aphids, and scale
insects. Therefore, the population explosion of L. humile in Madeira may have been
triggered by a population explosion of a newly arrived exotic Hemiptera that acted as a
mutualist (see WILSON, 2005). Alternatively, a mutualist Hemiptera already present may
have increased greatly due to the arrival of a new strain of crop plant.
In the 19th century, the dominant cash crop of Madeira alternated between
grapevine and sugarcane. GRABHAM (1924) wrote that “from time to time a blight or
other cause would obliterate the vine, and sugar-cane would become predominant: and
again in like manner the cane would periodically fail. Thus in regard to the vine, the
vineyards were completely destroyed in 1852 by the fungoid Oilium [now Oidium
tuckeri], and again in 1877 by the underground apterous Aphis Phylloxera vastatrix
[now Viteus vitifolii]”. From 1884-1886, all sugarcane in Madeira failed due to fungus
attack (da SILVA & MENESES, 1946). GRABHAM (1924) speculated that the pink sugarcane
mealybug Saccharicoccus sacchari (formerly Pseudococcus sacchari; sometimes
called the gray sugarcane mealybug) “was largely responsible for the introduction of
the fungus through its many punctures into the substance of the sugar-cane”. GRABHAM
(1924) reported “no attempt was made to replant sugar-cane after that dire destruction
and the ground was occupied for several years by the vine, sweet potato and general
food produce”. Soon after this, however, Madeira was replanted with new strains of
sugarcane, including the “Yuba” variety. GRABHAM (1924) wrote “The Argentine ant found
its way to Madeira 30 years ago when the Yuba cane was already well-established, and
the response of the Pseudococcus to the fostering influence of the new pest became at
once manifest in the startling increase and activity of the new cane parasite. The ground
was honeycombed with formicaries among the cane roots, and during the fortnightly
irrigation of the cane the legs of my men were black with myriads of ants seeking
2006
Aguiar & Wetterer, Mealybugs and Argentine ants in 19th century Madeira
31
shelter from the running stream of water among their nests”. GRABHAM (1924) reported
“The Pseudococcus is now found abundantly in every cane plantation in Madeira... The
Pseudococcus sacchari has no restraining enemy in Madeira. It is jealously protected
and fostered by the Argentine ant”.
GREEN (1923) listed 46 species of scale insects from Madeira, including the
pink sugarcane mealybug S. sacchari from sugar-cane, and described a new species,
Pseudococcus heterospinus Green, from the roots of grasses. BALACHOWSKY (1938)
reported only one species of mealybug on sugarcane in Madeira, the gray sugarcane
mealybug, Dysmicoccus boninsis (Kuwana), and determined P. heterospinus to be a
junior synonym of this species. BALACHOWSKY (1938) dismissed earlier records of S.
sacchari in Madeira as misidentifications; both species feed on the stalk under leaf
sheaths and, though not closely related (DOWNIE & GULLAN, 2004), they are superficially
similar in appearance. VIEIRA et al. (1983) confirmed that D. boninsis was the most
common mealybug on sugar-cane in Madeira, but retained S. sacchari in the list of
mealybugs of Madeira as very rare.
The reports that in 19th century Madeira S. sacchari was an important pest, but
later reports indicating that it was rare or absent suggest the intriguing possibility that
D. boninsis replaced the previously common S. sacchari and perhaps this replacement
was related to the L. humile population explosion.
We have been searching for 19th century mealybug specimens from Madeira
to test our hypothesis. We also have been looking for 19th century herbarium specimens
of sugarcane. Because P. sacchari and D. boninsis both feed on the sugarcane stalk
under leaf sheaths, intact dried sugarcane specimens may have mealybugs present.
Unfortunately, we have so far been unable to test this hypothesis. We found no
19th century specimens of mealybugs nor sugarcane in Madeira. Jon Martin at the
Natural History Museum in London, reported “we seem to have no material of
Saccharicoccus from Madeira. We do have a small series of Dysmicoccus boninsis,
under the name Pseudococcus heterospinus cockerell (now a junior synonym), part of
the type series of that species. The data are “roots of grasses” and “sugar cane”, and the
former have the date “i. 1921”. No localities given”.
ACKNOWLEDGEMENTS
We thank A. Wetterer and M. Wetterer for comments on this manuscript; the
National Geographic Society, the Laboratório de Qualidade Agrícola, and Florida
Atlantic University for financial support.
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Boletim do Museu Municipal do Funchal (História Natural)
No. LVII, Art. 326
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