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Distributional Patterns of Selected Western
North American Insects!
The Distribution of Diabroticites in Western North America
By
University
RAY
F.
SMITH
of California, Berkeley
The Diabroticites is a subtribe of the Galerucinae that
now includes an array of fifteen genera for the beetles
formerly included in the large neotropical genus Diabrotica Chevrolat. About 900 species have been described
and there are at least that many more undescribed. The
group is of rather recent origin and is still rapidly
evolving. The Diabroticites are almost entirely Neotropical in distribution and the greatest diversity of
species is reached in the tropical areas of South America.
A few species extend the distribution of the group into
temperate regions in both North and South America.
Seventeen species are found in the United States and only
nine species in the eleven Western States.
When animals of tropical origin invade temperate
regions, especially continental areas, they are faced with
the major hazard of cold winter temperatures.
Their
geographic limits can usually be explained in terms of
cold winter conditions. Those species which develop special behavioral or physiological adaptations to survive
low winter conditions can greatly extend their distributions. Others, less adapted, are often limited to seasonal
extensions of range or to the milder coastal areas. The
ability of a species to invade favorable areas made available seasonally is determined not only by the inherent
characteristics of the species but also by the patterns of
air movement that prevail at the time of dispersal. To a
lesser extent dry conditions or the limited distribution of
specific host plants can restrict the invasion of neotropical
elements. Finally, man's modifications of the environment as he has extended and modified his agro-ecosystems
has permitted great extensions of range. These several
factors may be seen in the distribution of the Diabroticites
invading Western North America.
AmPhelaslna cmmm vicintt11l (Jacoby) is the northernmost representative
of a genus that extends south to
Argentina.
It is a common species in Mexico where it
seems to be associated with species of mint. This subspecies is associated with the mesquite grassland biome
in the northern plateau region of Mexico. Records from
the United States are limited to four female specimens
collected in the Huachuca Mountains of Arizona.
Paranapiacaba tricincta (Say) is also the northernmost representative of its genus, but it has been more
successful in invading the Southwest than A. cavum. It
occurs abundantly on perennial grasses in the southern
parts of the short grassland and mesquite-grassland areas.
It does not extend as far north as its grass hosts and
presumably is limited by cold winter temperatures. ParalIapiacaba connexa (LeConte) has been found from southern Texas south to Vera Cruz.
The members of the genus Acalym11la are the most
successful of the Diabroticites as invaders of continental
areas with severe cold winter temperatures.
They have
developed physiological or behavioral means of becoming
cold hardy as adults and often aggregate in large numbers
in protected winter microhabitats.
Members of the genus
Acalymma are closely associated with their larval hosts,
the Cucurbitaceae and especially the genus Cuwrbita.
A. gouldi Barber is locally common in favored river
bottom areas on the annual cucurbits Echinocystis lobata
and Sicyos angulatus (Lammers 1964). It is found in
the Central and Northeastern States and over most of its
distribution is rare. A. vinctllm (LeConte)
is a rare
species of the Southeast where it is associated with CuCllrbita okeechobcensis.
It is the one species of the
Diabroticites that has invaded the United States from the
Caribbean area. A. percgrinum (Jacoby) occurs in southern Texas and south into Mexico on naturalized Cucll1nis
meta.
A. blandulltm (LeConte) is intimately associated with
Cuwrbita foetidissima and does not move over to cultivated Cltcurbita. However, its geographic distribution
does not extend to the limits of its host plant. Low summer precipitation (June to August) is correlated with
the western limits of its distribution in Arizona and New
Mexico, and the species does not occur where summer
precipitation is less than six inches. This phenomenon
does not explain the absence of A. blandulum in the
eastern part of the distribution of C. foetidissil1la (e.g.
eastern Kansas, Iowa, Missouri).
Low winter temperatures or the low populations of C. foctidissima may be
an explanation.
A. trhrittailt111 (Mannerheim),
the western striped cucumber beetle, and A. vittatum (F.), the striped cucumber beetle are important economic pests of cultivated
cucurbits. A. trivittatum occurs from the State of Washington south along the Pacific slope into Mexico and
thence south to Colombia. It is not able to overwinter in
cold areas (where the January mean is 32° F. or lower)
and does not invade the Great Basin area. A. vittotllm
is widely distributed in the United States east of the
Rocky Mountains and extends into southern Canada but
not into Mexico. Although these species are now abundant as economic pests of cucurbitaceous cultivars, it is
difficult to assess their original relationship to these
plants or their native antecedents (Whitaker and Bemis
1965). In any event, the cultivation of pumpkins and
squashes by man has certainly favored the increase in
population levels of these species and probably their
ranges as well. In California and Oregon A. trivittatl/n1
is often found associated with species of Marah (Stocking 1955). It may be that A. tri'vittatl/m in Western
United States was associated with these common native
noncultivated hosts prior to introduction of Cucl/rbita.
A. tri71ittatutn was collected by Tschernikh in northern
California no later than 1841 and prior to the time of
extensive plantings of cultivated cucurbits.
Diabrotica u. tmdecitnpullctata Mannerheim, the western spotted cucumber beetle, is another important eco-
I Invitational
paper presented in a symposium at the ?acific
Branch meeting, Monterey, California, June 21-24, 1965.
108
FIG.
I.-The
distribution
of the subspecies of Diabrotica
nomic insect. In dry Western areas, it is seriously
limited by moisture conditions. This species has a spring
generation in uncultivated grassland areas on grass and
legumes (Smith and Michelbacher 1949). Later generations develop on agricultural crops, e.g. alfalfa, potatoes.
FIG.
2.- The distribution
undecimpunctata
in the United States.
and cucurbits. The species cannot overwinter in areas
where the mean January temperature drops below 32"
F. Hence it does not occur in the Great Basin area, and
in the East it does not overwinter north of southern
Kansas and Missouri (Fig. 1). Each year the Eastern
of Diabrofica
109
ba/tcafa
III
the United States.
dorf 1947), but this host relationship is yet to be proven.
In recent years, man has greatly increased the range of
this species by the cultivation of corn, especially without
rotation, on river-bottom
land in the Great Plains
area. Within a IS-year period it has spread from western
Kansas to northeastern
1l1inois, and this extension of
range continues.
subspecies, D. IIl1decilllpllllctata, lzo1t'ardi Barber, the
southern corn rootworm or spotted cucumber beetle, reinvades northern United States and Canada (Smith and
Allen 1932). Occasionally it has been found as far north
as Port Harrison halfway up Hudson Bay. These migratory movements are greatly influenced by the wind
patterns in central United States and Canada. The
western subspecies, D. 1l. wldecimpunctata
(Mannerheim), has the same potential for seasonal spread into
the Great Basin area, but the pattern of prevailing winds
does not permit it to cross the Cascades and Sierra
Nevada.
D. balteata LeConte, the banded cucumber beetle, is an
economic pest of vegetables and legumes. For this species,
we have clear documentation of increased extension of
range as the result of man's activities. Similar increases
undoubtedly have occurred with other invading species as
barriers have been broken. D. balteata, prior to 1910,
occurred in the United States only in southern Arizona
and in southern Texas (Fig. 2). In the period from
1914 to 1923 it spread across the Southern States.
D. longicorllis (Say), the northern corn rollt\\"orm,
occurs most abundantly in the Corn Belt, but a southern
subspecies extends into northern Mexico. This species is
closely related to D. virgifera and it also overwinters in
the egg stage. Again, it is likely that Tripsacllffl was the
original native host, and that man has greatly favored
this species by the development and cultivation of extensive corn acreages. Three subspecies have developed, possibly in rather recent times in association with Indian
corn cultures of pre-Colombian times. Man's modern
corn culture has broken the barriers that isolated these
subspecies.
This
REFERENCES CITED
spread is correlated with the diversification of agriculture but the exact causal relationship is not known. It
has also reached Cuba in recent years. It spread into
California from Arizona in the period from 1924 to
1940 (Davis 1931) apparently as the result of increased
irrigation, agriculture, and transportation
bridging the
desert barrier. D. balteata extends its distribution southward into Colombia.
D. t,'bia/is Jacoby (= picticornis Horn) occurs from
southern Texas to Vera Cruz. D. lemniscata LeConte is
locally abundant on wild perennial grasses from the
Southwestern
United States south to Guatemala.
D.
cristata Harris (= atripennis Say) is associated with
wild grasses in the United States east of the Rocky
Mountains south onto the plateau of Mexico.
D. 1'irgifera LeConte, the western corn rootworm, in
contrast to the species here discussed, overwinters as an
egg. It is intimately associated with cultivated corn (a
manmade plant) and no other hosts are known. Its
original native host was probably Tripsacll11t (Mangels-
Davis, A. C. 1931. Diabrotica balteata Lec. J. Econ.
Entomo!. 24 (2) : 560.
Lammers, G. W. 1964. Biological notes on the leaf beetle Acalymma goltldi. Entomo!. News 75(7): 187-9.
Mangelsdorf, P. C. 1947. The origin and evolution of
maize. Adv. in Genetics 1: 167-207.
Smith, C. E. and N. Allen. 1932. The migratory habit
of the spotted cucumber beetle, ]. Econ. Entomo!.
25 (1) : 53-57.
Smith, Ray F. and A. E. Miche1bacher.
1949. The
development and behavior of populations of Diabrotica
ll-plUlctata in foothill areas of California. Ann. Entomol. Soc. Amer. 42 (4) : 497-510.
Stocking, K. M. 1955. Some taxonomic and ecological
considerations of the genus M arah. Madroii.o 13 (4) :
113-44.
Whitaker, T. W. and W. P. Bemis. 1965. Evolution in
the genus CI/cl/rbita. Evolution ]8(4): 553-9.
Distributional Patterns of Selected Western
North American Insects1
Problems of Bee Distribution in Western North America
By
University
PAUL
D. HURD}
JR.
of California, Berkeley
There are approximately 3,500 described species and
subspecies of bees in America north of Mexico. Nearly
two-thirds of these occur in the area west of the Mississippi River and are especially well represented in the
more arid regions of Western North America. For many
of these species there is already a reasonably sufficient
basis to determine the more prevalent patterns of distribution. One must remember, however, that for the majority of these species there is scarcely more than a frag1 Resume
of invitational
paper presented in a symposium
at the Pacific Branch meeting, Monterey, California, June 22-24,
1965.
mentary idea of their distribution. Even so, it is anticIpated that once the problem of incomplete data is overcome it seems unlikely that it will appreciably alter the
major patterns of distribution as we now understand
them.
Among the chief problems associated with bee distribution yet to be determined are the regulatory features of
the environment that produce the rather characteristic
distributional patterns so apparent in the studies thus far
undertaken. It is significant that the major patterns of
bee distribution are basically repetitive. This fact sllg-
110