I. Early explorers wrote in considerable detail their experiences abroad. Such experiences are also common to modern-
II. The importation of beneficial insects today remains the most widely practiced and potentially most rewarding
approach to biological control. The reasons given for the practice of importation have remained essentially
unchanged. It is assumed that exotic insects are pests as a result of their having escaped regulation by their natural
enemies after their accidental introduction into new regions. Importation is done to restore the natural balance,
so to speak.
III. Guidelines in Foreign Exploration
A. Certain concepts have arisen over the years as a result of accumulated experience on natural enemy
importations. These concepts serve, for better or worse, to guide foreign exploration. Exceptions exist,
of course, as with any generalizations; yet the concepts function as useful guidelines.
B. Experience suggests that exotic pests offer better prospects for successful biological control than
native pests. This discrepancy probably reflects the greater amount of work that has been done with
foreign pests. Biological control efforts against native pest have been few compared to alien pests.
1. the lack of attention to native pests is though to be due to the fact that they are already attacked
by a complex of natural enemies, and that their rise to pest status has resulted primarily from factors
other than a lack of parasitoids and predators.
2. for example, the establishment of vast crop monocultures greatly expanded the habitats of these
native pests, disrupting the formerly effective natural controls.
3. success begets success; thus, we find that many biological control projects have followed and will
continue to follow the lead of previously successful projects. Hence, experience suggests that considerable
future foreign exploration work will involve scale insects, white flies, mealybugs, aphids and probably
C. An important concept relative to foreign exploration is that natural enemies of an alien pest are best
sought in its native home.
1. this is still held to be the logical initial approach to foreign exploration, because it is in the native
home of a pest that the long standing host/natural enemy complexes are to be found. These furnish natural
enemy species capable of locating and regulating their hosts at low host densities.
2. it is generally believed that the first choice ought to be the dominant species occurring at low host
D. It is not conceded that the search for natural enemies should also extend to areas of similar climate
containing close relatives of the pest.
IV. Procedures in Planning and Preparation For Explorations
A. The first step is to insure the proper identification of the pest species. Once correctly identified, the
host-plant affinities and the probable country of origin can be ascertained. Such relationships are learned
from the literature, museum collections, and from consultation with world specialists.
B. Misidentification can result in wasted time and effort. Examples are:
1. Circulifer tenellus, the beet leafhopper, first came into prominence as a pest in the United States around
1905. This insect spreads the destructive "curly top" virus of sugar beets, tomatoes, melons and a number
of other crops:
A first this species was placed in the genus Eutettix and was thought to be native to the southwestern
United States. In 1917-18 two expeditions to Australia failed to uncover any effective natural enemies. In
1928, acting on a misidentification recorded in the literature, an expedition was sent to Argentina, but also
failed to find either the leafhopper or natural enemies.
In 1936, Dr. Paul Oman called attention to a close resemblance between the beet leafhopper and a species
described from Israel. He concluded that C. tenellus was incorrectly placed in the genus Eutettix, and
ought to belong to the genus Circulifer, which contained a number of species native to the arid regions of
the Mediterranean and Central Asia. Foreign exploration was redirected to these areas where the beet
leafhopper and its natural enemies were found. Although several parasitoids were introduced into California,
they were not economically effective, however.
2. The fern weevil, Syagrius fulvitarsus, was once a destructive pest of indigenous tree ferns in Hawaii.
When biological control was contemplated in the 1920's, no clue as to its country of origin was forthcoming.
While examining a private insect collection in Sydney, Australia, a noted Hawaiian entomologist, Pemberton,
discovered a single specimen of the fern weevil which had been collected in Australia in 1857. Subsequent
search of the area from which the specimen had been collected produced a braconid larval parasitoid of the
fern weevil. Successful biological control was achieved when the braconid was introduced into Hawaii.
Thus, the data borne on a collecting label attached to a single insect specimen in Australia contributed
directly to the successful biological control of the fern weevil in Hawaii some 65 years later!
C. The third step, following identification and location of the native home of the pest, is to choose the
appropriate season for the exploration. Timing of collection is also somewhat dictated by the periods
most suited to domestic culture and colonization efforts. Ideally, foreign exploration is undertaken during
the period of greatest seasonal availability of natural enemies.
V. Foreign exploration for natural enemies has been greatly simplified nowadays with the advent of rapid air
transportation. In the past, foreign collecting often involved arduous work in rearing, with a relatively small part
of the collector's time being spent on detection and collecting.
A. Some of the early accounts of foreign exploration explain the various hardships of the collector. For
example, Albert Koebele <PHOTO> who played an important role in the cottony-cushion scale project,
spent the last six months of 1902 in Central Mexico collecting natural enemies of the weed, Lantana camara.
Plagued by sickness and heat throughout this period, he wrote the following of his collecting trip:
"Alameda, California, December 26, 1902:
“ I am still unwell, not yet over my fever, but a rest may help me, and I am only too glad to be out of Mexico
and rid of the hardest work that I ever did."
B. Modern foreign explorers can spend a considerable portion of their time searching for effective natural
enemies, shipping them by air in almost any stage of development from practically any corner of the earth,
knowing that the odds favor their arrival within a week's time. Also, modern low weight and breakage
resistant plastics that can be variously screened for aeration offer ease for natural enemy manipulation
VI. Recognition of Promising Natural Enemies Abroad
A. Host scarcity during optimum seasons of abundance is a good sign. The collection of adequate numbers
of natural enemies in such areas is difficult with ordinary methods. The host-exposure method can be
employed to alleviate this problem.
B. A colonial or localized type of host distribution is commonly associated with a high degree of natural enemy
effectiveness. Under these conditions, localized host populations increase in number, only to be decimated
following their detection by natural enemies, the result being a numerically and spatially shifting mosaic of host
C. The appearance of localized outbreaks of the host species associated with pesticide usage, or differences in
host abundance on insecticide treated crops versus untreated wild hosts, often indicates a favorable collecting
D. An abnormal abundance of the host where it is protected from its natural enemies by ants, dust, litter, spider
webs, etc., is also a favorable indicator of effective natural control in the area of search.
VII. Many foreign collectors often confine their collecting to relatively accessible areas such as botanic and domestic
gardens, parks, roadsides and empty lots, because host plants of the insects being sought often become infested at
variable intervals in these isolated situations. This often results in the pest species temporarily evading detection
by natural enemies, which results in localized outbreaks and which ultimately attracts high populations of parasitoids
VIII. Certain precautions must be taken to insure against the introduction of injurious organisms, such as
hyperparasitoids, potential insect pests, weeds, and plant pathogens.
A. The foreign collector has the initial responsibility for excluding potentially dangerous foreign organisms.
B. Usually the material is sent only to scientific institutions, which maintain elaborate quarantine facilities
and where any injurious organisms that may have escaped the attention of the foreign collector are carefully
screened out and destroyed.
C. There is additionally the danger of establishing parasitoids which attack other beneficial insects, such as
useful predators or phytophagous insects introduced for biological weed control. Predators being considered
for importation should either be known to lack parasitoids or be freed from them by laboratory manipulation
prior to their importation.
Compere, H. 1961. The red scale and its natural enemies. Hilgardia 31(7): 173-278.
Compere, H. & H. S. Smith. 1932. The control of the citrophilus mealybug, Pseudococcus gahani, by Australian parasites.
Hilgardia 6: 585-618.
Legner, E. F. 1986. Importation of exotic natural enemies, p. 19-30. In: J. M. Franz (ed.), Biological Control of Plant Pests and
of Vectors of Human and Animal Diseases. Fortschritte der Zool. Bd. 32: 341 p.
Legner, E. F. & R. D. Goeden. 1987. Larval parasitism of Rhagoletis completa (Diptera: Tephritidae) on Juglans microcarpa
(Juglandaceae) in western Texas and southeastern New Mexico. Proc. Ent. Soc. Wash. 89: 739-43.
Legner, E. F. & C. W. McCoy. 1966. The housefly, Musca domestic Linnaeus, as an exotic species in the Western Hemisphere
incites biological control studies. Canad. Ent. 98: 243-48.
Legner, E. F. & R. A. Medved. 1979. Influence of parasitic Hymenoptera on the regulation of pink bollworm, Pectinophora
gossypiella, on cotton in the lower Colorado Desert. Environ. Ent. 8: 922-30.
Legner, E. F. & A. Silveira-Guido. 1983. Establishment of Goniozus emigratus and Goniozus legneri [Hym: Bethylidae] on
navel orangeworm, Amyelois transitella [Lep: Phycitidae] in California and biological control potential. Entomophaga 28: 97-106.
Muir, F., & O. H. Swezey. 1916. The cane borer beetle in Hawaii and its control by natural enemies. Rept. Hawaiian Sugar
Planters Expt. Sta. Bull. 13: 102 p.
Perkins, R. C. L. 1906. Leaf-hoppers and their natural enemies (Introduction). Rept. of the work of the Expt. Sta., Hawaiian
Sugar Planters Assoc. Bull. 1: 32 p.
Silvestri, F. 1914. Report of an expedition to Africa in search of the natural enemies of fruit flies (Trypaneidae). hawaii Bd.
Agric. & Forestry, Div. of Ent. Bull. 3. 176 p.
Zwölfer, H., M. A. Ghani & V. P. Rao. 1976. Foreign exploration and importation of natural enemies, p. 189-207. In: C. B.
Huffaker & P. S. Messenger (eds.), Theory and Practice of Biological Control. Academic Press, New York, San Francisco, London.