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137. Derived from: Legner, E. F. 1975.
Ethology of Host Selection by Entomophagous Insects: Effect on successful importation of
entomophagous insects. Proc. Workshop
Ethology of Host Selection by Entomophagous Insects, Tifton, Georgia, March
1975. pp. 14-18. Summary Importation activities for natural
enemies stresses a consideration of certain fundamental principles and
procedures derived from years of experience by investigators in classical
biological pest control.
Considerations that serve in the formulation of an importation program
are included. - - - - - - - -
- - - - - - - - The native habitat of a pest is the most likely source of
its effective natural enemies. If
natural enemies maintain the density of the pest species in its original
habitat at non-economic levels, then the restoration of such a balance in the
country or area of its importation may be expected. Foreign entomophagous arthropods should be secured from regions
most similar ecologically to the region in which they are to be
colonized. However, biological
control work to date indicates that species imported into subtropical or
tropical regions from the temperate zone are more likely to become
established than when importations are made in the reverse manner. If the pest populations in the foreign
country occur generally at low densities in habitats that are apparently
favorable for its reproduction, the natural enemies of the pest are probably
responsible for its scarcity. The
dominant species of natural enemy at minimum host densities is likely to be
the most effective species. In
regions of pest scarcity the natural enemy responsible for such scarcity may
be ascertained by the exposure of protected pest populations. The capacity of an entomophagous insect to control its
host in the country of its importation cannot be definitely predicted prior
to its actual introduction. The
evidence of effectiveness in the country of origin is of value only in
determining the priority and sequence of collecting. Natural enemies of phytophagous insects
should be collected from the species (or varieties) of host plants on which
they are to be established in the country of destination. This is because the probability of
attraction to certain host plants, as a habitat, is a first step in host
finding, and because the phytophagous species may consist of two or more biological
races or siblings characterized by specific host plants and specific
parasites as with Pseudococcus maritimus, which includes a form that
infests only the grape and which is specifically parasitized by Acerophagus
natativentris (S. S. Flanders, pers. commun.). The importation of an entomophagous species from one
geographical area should not preclude its importation from a different area,
since it has been demonstrated that a species may consist of two or more
geographical forms differing in seasonal occurrence, reproduction capacity,
and in kinds of hosts. Importation
work is not completed until all geographical races have been discovered,
collected, and shipped to the new country.
There is also the possibility that natural enemies might adapt to a
more significant population dampening role in the country of destination
through gradual genetic change. Although one principal species may give effective
control, such control may not be general until additional species that occupy
niches outside the range of the principal species are imported. The number of species in the natural enemy
complex of a plant insect in its country of origin may be very large. The number known to attack the oriental
fruit moth, Grapholitha molesta Busck, in Japan and Korea is over 50
species of which half are primary in habit. In searching for entomophagous species it should be
constantly borne in mine that host habitat finding is important to the success
or failure of natural enemies in finding their hosts. In the case of certain medically important
pests the degree of synanthropy is important. During host searching parasites often search first for the
environment frequented by the host.
Odor associated with these habitats is usually the attracting
force. Host visibility only aids the
parasite in pinpointing an object that has already exerted an
attraction. Many parasitic
Hymenoptera will oviposit in any suitable insect located in its preferred
habitat, the host plant occasionally being more attractive to the parasite
than the host itself. Honeydew
produced by aphids and coccids also can attract parasites; moisture in the
form of dew is required by many parasitic species. Locomotion of the parasite may determine the extent to which
the host habitat is selected and frequented.
Phytophagous hosts are sometimes rendered immune to successful
parasitization by certain plants upon which they feed. The plant on which the host is feeding may
affect host selection, fecundity, and longevity of the parasite. Askey, R. R. 1971. Parasitic Insects. Amer. Elsevier Publ. Co., Inc., New
York. 316 p. DeBach, P. 1964 (editor
and contributor). Biological Control
of Insect Pests and Weeds. Reinhold
Publ. Co., New York. 844 p. DeBach, P. 1974. Biological control by Natural
Enemies. Cambridge Univ. Press. 323 p. Flanders, S. E. 1937. Habitat selection by Trichogramma. Ann. Entomol. Soc. Amer. 30: 208-210. Laing, J. 1937. Host-finding by
insect parasites. 1. Observations of the finding of host by Alysia
manducator, Mormoniella vitripennis and Trichogramma
evanescens. J. Anim. Ecol. 6:
298-317. Legner, E. F. 1967. The status of Nasonia vitripennis
as a natural parasite of the housefly, Musca domestica. Canad. Entomol. 99(3): 308-09. Legner, E. F., R. D. Sjogren and I. M.
Hall. 1974. The biological control of medically important arthropods. Crit. Rev. Environ. Contr. 4(1): 85-113. Remington, C. L. 1968.
The population genetics of insect introduction. Ann. Rev. Entomology 13: 415-426. Salt, G. 1958. Parasitic
behaviour and the control of insect pests.
Endeavour 17: 145-148. Simmonds, F. J. 1972.
Approaches to biological control problems. Entomophaga 17(3):
251-264. |
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