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Special Terms (Hyperparasitism,
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Taxonomic Categories of Predaceous & Parasitic
Arthropods Detailed text and references of taxonomy are arranged according to
key predatory or parasitic groups in separate Master Text Files and
Illustration files as follows:
[e.g., <ANTHICID.TXT> = general text emphasizing behavior of
adults; <ANTHI1.ADU> = illustrations of adults; &
<ANTHI1.IMA> = text & illustrations of immatures] (References stored in Files
<BIOLOGY.A> thru= <BIOLOGY.Z>)
See <Taxnames> for texts & images. Insect Parasitoids The test for distinguishing parasitoids from predators is whether
they reach maturity by consuming but
a single host or several host individuals during the course of their
development. Exceptions are found in
some Scelionidae that develop individually in spider egg masses, yet consume
several eggs. They can be called
either egg predators or egg-mass parasitoids. In some cases an individual coccinellid
larva was reported to have reached maturity by feeding on single large
specimens of scale insects. Insect parasitoids differ in several ways from true
parasites: (a) a parasitoid usually destroys
its host as it develops to maturity; (b)
the host is usually of the same
taxonomic class as the parasitoid (Insecta); (c) insect parasitoids are large
relative to the size of their hosts; (d)
the adults are free-living; only
the immature stages are parasitic; (e)
there is no heteroecism =
passing through different stages on alternate hosts during development. Parasitoid activity as a parameter in population dynamics
resembles that of predators rather than true parasites. Groups of
Parasitoids A. Internal or endoparasitoid: develops within the host's body cavity. B. External or ectoparasitoid: feeds while immature from an external
position. C. Solitary: only one individual develops per host. D. Gregarious: several parasitoid progeny
of a single species habitually develop in or upon a single host individual. E. Various combinations of
these categories can be used to distinguish, e.g., solitary endoparasitoids, or gregarious ectoparasitoids. Because various
developmental stages of insects are parasitized, the parasitoids involved may
variously be called: A. egg parasitoids, larval
or nymphal parasitoids, adult parasitoids, etc., depending on the host stage attacked. B. intermediate categories are
used to distinguish, e.g., those cases where a parasitoid oviposits in a host
larva in which initial development occurs, but the parasitoid continues to
develop within and emerges from the host pupa (= a larval-pupal parasitoid). Other examples are an egg-larval
parasitoid, and a larval-adult parasitoid, etc. Special Terms Hyperparasitism is parasitization of a parasitoid by another parasitoid. Various degrees are primary, secondary,
and tertiary. As an example, if a parasitoid attacks a
phytophagous insect it is called primary; a parasitoid of the primary would
be the secondary. Degrees of
parasitism beyond secondary are uncommon.
Secondary parasitoids are generally polyphagous and individual species
tend to be geographically widely distributed on continents. Technically, phytophagous insects are
primary plant parasites and their primary parasitoids are
"hyperparasites" of the host plant. Substituting the word "parasitoid" avoids this
difficulty. Autoparasitism is found in several species of Aphelinidae. Females develop as primary parasitoids,
but males are hyperparasitic on female larvae of their own species. Indirect Hyperparasitism is that type of hyperparasitism in which a parasitoid attacks a
host insect upon which it itself is incapable of developing with the purpose
of encountering the primary parasitoid which the secondary host may
contain. It is the opposite of direct
hyperparasitism. This classification depends
on whether or not the hyperparasitoid can discriminate between parasitized
and unparasitized secondary hosts. A
direct hyperparasitoid will recognize parasitized secondary hosts and
restrict its oviposition to these; whereas, an indirect hyperparasitoid will
attack all secondary hosts it encounters, whether parasitized or unparasitized. Facultative Hyperparasitoids are hyperparasitoids which may also develop as primary
parasitoids. It is the opposite of
"obligate hyperparasitoid." Superparasitism is parasitization of an individual host by more larvae of a
single parasitoid species than can mature in or upon that host
individual. It results when a
parasitoid female or a succession of females of the same species, lay a
super-abundance of eggs in or upon a single host individual. Superparasitism results in a waste of
progeny through mortality generated by intraspecific competition, or it
results in stunted or weakened progeny, also as a result of such
competition. Many parasitoid species
are thought to exhibit superparasitism in nature, particularly when
ovipositional pressures are great and hosts are scarce. Multiple Parasitism is the simultaneous parasitization of a host individual by two or
more species of primary parasitoids. The Imago
or Adult Parasitoid This is critically important stage in the maintenance of any host-parasitoid
relationship, and of especially importance to biological control because the
female parasitoid finds and selects the host of her progeny. If an entomophagous insects is to act
usefully as a regulatory factor, the females of the species will display
certain characteristics of an effective natural enemy as follows: 1. demonstrate a high searching capacity = ability to
find the host a low host densities. 2. reasonably host-specific, not polyphagous. 3. possess a high potential for increase, largely
as a result of a high fecundity and a short period of development relative to
that of its host. 4. demonstrates the ability
to occupy and survive well in all ecological niches occupied by its host. 5. relative to biological
control practices, some workers feel that a good natural enemy should also be
easily cultured in the insectary,
so that adequate numbers can be reared to facilitate colonization and
distribution. However, C. P. Clausen
has stated that a truly effective parasitoid could be established with the
release of a single mated female. 6. the female should be
able to restrict oviposition to hosts suitable for the
development of her progeny; i.e., to recognize healthy hosts and to avoid
ovipositing in already parasitized hosts, thus avoiding superparasitism and
multiple parasitism. Mating
A premating period following adult emergence is generally not characteristic of
parasitoids. If the opposite sex is
present upon emergence, then mating usually proceeds immediately in most
parasitic Hymenoptera. There are a
few cases of a premating period of a few days to three weeks duration. Predators, on the other hand, generally exhibit a premating
period (few days to several months), particularly if a period of reproductive
diapause, hibernation, or aestivation is interposed between adult emergence
and mating. A single mating is often sufficient to
insure that a short-lived female can produce female offspring throughout her
reproductive life. Females with sperm
in their spermatheca
(sperm-storage organ) will usually resist the further attention of males.
Males, on the other hand, generally are prone to mate repeatedly; however,
females with sperm may not stimulate mating behavior in males. Some pteromalid parasitoids that attack
synanthropic Diptera go into a short dispersal phase prior to and after
mating. Mating occurs at the site of
female eclosion. Mating may influence the behavior of the female parasitoid. In the Aphelinidae, unmated autoparasitoids
oviposit only in coccid hosts already parasitized by the same or a closely
related species, and thus function as hyperparasitoids. Mated females, however, function both as
hyperparasitoids and as primary parasitoids, ovipositing in coccid hosts whether
these are parasitized or not. If at
the insertion of the ovipositor a primary parasitoid is located, she deposits
an unfertilized, haploid male egg.
But if the coccid host is not parasitized, she lays a fertilized,
diploid female egg. In Pteromalidae, mating may change the rate of oviposition,
longevity and gregarious behavior according to the particular male's genetic
make-up. Males are able to change a
female's oviposition phenotype upon mating, by transferring an unknown
substance with the seminal fluid (Legner 1989). This subject will be treated in greater
detail on the succeeding section on polygenes. Ovigenesis
Female parasitic Hymenoptera may be classified either as proovigenic
or synovigenic,
with regard to the duration of ovigenesis.
Proovigenic females reach the adult stage already having elaborated a
complete or nearly complete complement of mature eggs which they usually
oviposit in short order if hosts are available. They develop no further eggs, however, once oviposition
begins. Only the store of nutrients
carried over from the larva is drawn upon during ovigenesis. All proovigenic Hymenoptera are endoparasitoids. This is because their eggs are alithal, or
"yolk-free" and must be placed in the host's body fluids in order
to obtain nutrients through absorption. Synovigenic Hymenoptera continue to produce eggs throughout their
oviposition period and include the greater number of parasitic species. Feeding by the adult female provides the
nutrients necessary for the continuous elaboration of eggs. Protein requirements for ovigenesis are
satisfied in nature either by storage during larval development or by feeding
as adults on the blood of their hosts (host-feeding). The adults also may feed on honeydew,
plant exudates or tender plant tissues to obtain carbohydrates. Thus, the source of food available to
parasitoid adults is important to biological control since it affects
parasitoid distribution and effectiveness. Host-feeding and the accompanying host mutilation by adult
females are also important to biological control in that they constitute
forms of predation. Characteristics of Host-feeding Feeding occurs directly on the blood that exudes from
ovipositional wounds. When hosts are
found in cells, cocoons or puparia, the parasitoid female may construct a
kind of feeding
tube to obtain a blood meal.
The ovipositor is inserted into the "hidden" host and a waxy
secretion flows around the ovipositor, which hardens in the form of a tube or
"straw>" Once the
ovipositor is withdrawn, this feeding tube serves to connect the puncture in
the host's body with the outside. The
blood rises to the top through capillary action, internal pressure and
possibly by suction from the parasitoid's mouthparts. Host-feeding and oviposition may occur on
the same host individual. If the host
is badly mutilated, oviposition may not occur. Ovisorption
If there are no sites available to stimulate the deposition of
eggs, the ovarian eggs of a synovigenic female that has commenced oviposition
are absorbed into her blood stream.
This phenomenon is called ovisorption
or egg resorption. The process was apparently originally
described by Weyer (1927) working on ants.
Biological control workers related ovisorption to the effectiveness of
parasitoids in regulating their hosts (Flanders 1935). Insect physiologists also noted the
phenomenon almost simultaneously in other orders of insects (Pfeiffer 1939,
Wigglesworth 1936). The cyclic process of ovigenesis - ovisorption - ovigenesis,
permits the retention of metabolites and this is physiologically economical
in that it conserves materials used in ovigenesis. While
ovigenesis may require several days, the egg resorptive process may occur in
a few hours. This egg degeneration
apparently occurs only in the ovarioles, not in the oviduct. The phenomenon of ovisorption seems to be correlated with a high
searching capacity in parasitic Hymenoptera.
Those species possessing facultative oviposition generally are the
most effective biological control agents at low host densities. This effectiveness may result from the
conservation of egg-forming material and the resulting long reproductive life
of the female. Proovigenic parasitoids are generally more effective initially in
reducing host population densities.
This is because they have a greater number of eggs stored and ready
for deposition and can thus respond immediately to high host densities. Synovigenic parasitoids, however, are
potentially more effective at the lower host densities because they are able
to spend more time in host-searching, during which time ovisorption conserves
nutrients.. Exercises
Exercise 3.1-- How are true predators
distinguished from parasitoids? Exercise 3.2-- Name and describe
the several groups of parasitoids? Exercise 3.3-- Define autoparasitism, hyperparasitism, indirect
hyperparasitism, superparasitism, facultative hyperparasitism, multiple parasitism. Exercise 3.4-- What are
important attributes of an effective adult parasitoid? Exercise 3.5-- Discuss some of
the effects of mating on the behavior of parasitoids. Exercise 3.6-- Discuss
ovigenesis in parasitic insects. Exercise 3.7-- How is
host-feeding important in parasitic insects? Exercise 3.8-- Briefly describe
the ovisorption process in parasitoids. REFERENCES: [ Additional references may be found at MELVYL Library ] Bellows,
T. S., Jr. & T. W. Fisher, (eds)
1999. Handbook of Biological
Control: Principles and Applications. Academic Press, San Diego, CA. 1046 p. Clausen,
C. P. 1940. Entomophagous Insects,
McGraw-Hill Book Co., Inc. (reprinted by Hafner Publ., Co., Inc., New
York, 1962). 433 p. DeBach,
P. (ed.). 1964. Biological Control of Insect Pests and
Weeds. Reinhold Publ. Co., New
York. 844 p. 265. Gordh, G., E. F. Legner
& L. E. Caltagirone. 1999. Biology of parasitic Hymenoptera. In: T. W. Fisher & T. S. Bellows, Jr.
(eds.), Chapter 15, p. 355-381, Handbook
of Biological Control: Principles and
Applications. Academic Press, San
Diego, CA 1046 p. Hopkins,
C. R. & P. E. King. 1964. Egg resorption in Nasonia vitripennis
(Walker) (Hymenoptera, Pteromalidae).
Proc. Roy. Ent. Soc. London (A) 39:
101-07. Hopkins,
C. R. & P. E. King. 1966. An electron-microscopical and
histochemical study of the oocyte periphery in Bombus terrestris
during vitellogenesis. J. Cell Sci.
1: 201-16. King, P.
E. & J. G. Richards. 1968. Oosorption in Nasonia vitripennis
(Hymenoptera: Pteromalidae). J. Zool.
London 154: 495-516. 242. Legner, E. F. 1989.
Wary genes and accretive inheritance in Hymenoptera. Ann. Entomol. Soc. Amer. 82(3): 245-249. Telfer, W.
E. 1965. The mechanism and control of yolk formation. Ann. Rev. Ent. 10: 161-84. Waage, J.
& D. Greathead (eds.). 1986. Insect Parasitoids. 13th Symp. Roy. Ent. Soc., London. Academic Press, San Diego. 389 p. |
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FILE NAMES FOR ENTOMOPHAGOUS INSECTS
(Please see <taxnames.htm> for interactive list