Vagility and Probability of Survival in

Two Weevils (Coleoptera, Curculionidae):

 the sugarcane rootstalk borer weevil

 (Diaprepes abbreviatus [L.]) and the

sweet potato weevil (Cylas formicaius [F.])

 ILonce Bonnefil, Ph.D.
 Inter American University of Puerto Rico
 243 Viena Street, College Park, Rio Piedras, PR 00921


 The sugarcane rootstalk weevil borer Diaprepes abbreiviatus
(L.) moves freely among numerous plant hosts within Puerto-
rican agroecosystems. The sweet potato weevil, on the con-
trary, appears circumscribed to the family Convolvulaceae.
The fecundity, life cycle and longevity of the two insects were
probed to unveil the biological nature of vagility. Diaprepes
fecundity was greatly enhanced by the shift from wild to


cultivated hosts, development was not influenced appreciably,
and longevity was greater in the sedentary species. It is assum-
ed that vagile populations are briefly boosted by host shifts
even ending in expansion thrusts though longevity is not
necessarily extended. Under sedentary conditions populations
are generally low but stable.


Historical Recount of Diaprepes and Cylas
as Agricultural Pests
 Beavers et al. (1978) have compiled an extensive bibliography
of the sugarcane rootstalk weevil borer Diaprepes abbreviatus
which spanned the period from 1903 to 1978. For about 30 years
there was a near-loss of interest in the insect pest. Interestingly
enough, this lapse coincides with the period between the release
of the organochlorine insecticides for use by the public and their
ultimate banning. These pesticides when applied to the soil af-
forded a perfect control of Diaprepes which thus became inconse-
quential.
 Around 1979, however, the absence of the chemicals started to
be felt through a recrudescense of the weevil borer. A survey by
the U.S. Department of Agriculture revealed that 82,000 of the
115,000 acres of sugarcane in Puerto Rico were infested by the in-
sect. The annual production of 1,000,000 metric tons/year was
reduced to an estimated 150,000 metric tons/year, representing a
loss of $73 million (Beavers et al., 1978).
 Diaprepes was accidentally introduced into the United States
presumably in 1964 and the infestation has risen steadily since
(Woodruff, 1964; Selhime and Beavers, 1972). The weevil is now
a serious problem in Florida where it inflicts considerable losses to
the ornamental plants industry of between $140 and $150
million/year. Emergency Federal regulations took effect in Puerto
Rico, making it compulsory that all exports of ornamental plants
to the United States be certified by the U.S. Department of
Agriculture. According to T. Dorney of the SanJuan Star (1970),
30 of the 47 growers of ornamentals were quarantined and could
not export their products. The $10 million-a-year business seem-
ed to be in serious jeopardy with 63% of the producers unable to
ship to the mainland plants, plant parts and cut flowers. It could
have been said that the law was too restrictive, but hundreds of
millions of dollars worth of sugarcane products, citrus plants and
fruits, vegetables and ornamentals, were at stake in Florida and it
was imperative to prevent the spread of the pest to other states of
northern United States.


VOL. XX-PROCEEDINGS of the CARIBBEAN FOOD CROPS SOCIETY


 An evaluation of the damage of the sweet potato weevil in
Puerto Rico could not be found. Generally Cylasformicarius in-
fests the vines, tubers and roots of sweet potato and is found occa-
sionally on morning glory (Ipomea learii (Pexton,) bay hops
(Ipomea pescapreae [L.]). In commercial plantings many tubers
were found to be tunnelled, even totally honey-combed, offering
a repulsive appearance, foul odor and bitter taste. But in Puerto
Rico, sweet potato is not of great economic importance and the
losses caused by Cylas may not be considered significant except
for such academic aspects as the one discussed hereafter.

Description of the Insect Pests
 The so-called sugarcane rootstalk borer weevil Diaprepes ab-
 breviatus (L.) is a fairly large otiorhynchid beetle (Coleoptera,
 Curculionidae). It has a stout abdomen, a trapezoidal thorax one
 quarter longer than wide, a narrow head with small arched com-
 pound eyes and clubbed antennae distinctly elbowed. The body
 is black but colored scales impart to the insect a whole variety of
 hues. Individuals collected or reared on different hosts did show
 some consistency in coloration but not enough to separate diet
 groups. Adult size was equally variable in both sexes, ranging
 from 0.85cm to 1.90cm.
 The genus Diaprepes is apparently indigenous to the Carib-
bean area with species occurring in Central America and most of
the West Indies. It does not appear to extend into South America
or the United States (Fennah, 1942). Abbreviatus appears to be
the main species occurring in Puerto Rico, Haiti and the Lesser
Antilles with a series of other species occurring on other islands.

The Life Cycles of the Two Weevils
 In its development, Diaprepes goes through a complete
metamorphosis. The oval elongate eggs are laid in clusters of
about 30 between leaves tightly held together by a sticky,
transparent, elastic film. The total number of eggs produced by
one female during her life is about 5,000 (Wolcott, 1936 and
1948). The incubation is fairly uniform, lasting an average of


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