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HOST DEFENSE REACTIONS
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Overview A host may
ward off a parasitoid either externally before oviposition has occurred, or
internally after oviposition,
Examples of external defense reactions are given by Cole (1957, 1959)
and Hinton (1955). Pupae of certain Lepidoptera (e.g., Aglais urticae
and Pararge aegeria) may wiggle vigorously
when being attacked by female ichneumonids (Apechthus spp.), and succeed in throwing off the
parasitoid. Certain tortrix moth pupae (Cole 1959) avoid parasitism by Apechthus spp. by moving to
other parts of their cocoon when it is probed. The response
of the host to attack by the parasitoid can sometimes result in death of the
female parasitoids. This has been observed in Goniozus gordhi
attacking P. gossypiella (Gordh 1976) and G. emigratus attacking the same host species (Busck 1917). Nickels et al. (1950) reported that Goniozus
punctaticeps is often killed
by nut casebearer larvae, but rarely is injured by shuckworm larvae. Factors
which may contribute to parasitoid injury or death may be the size of other
physical features of the ost, the age or physiological condition of the
female parasitoid, and the site of attack or ineffectiveness of the venom
injected by the female parasitoid. Internal
defense reactions were recognized early by Salt (1941) when he stated,
"Far from being a purely passive victim, obliterated without a tract,
the host is often able to impress its mark, and a very clear mark at that,
upon the insect parasitoid that destroys it. Proof is already available of
effects of the host on the size, form, rate of development and behaviour of
its parasitoid; evidence can be found of influence on fecundity, longevity
and vigour; and it is likely that many other effects still await discovery
and description. There can be no doubt that the host may bequeath to its
parasitoid an important and sometimes striking legacy of morphological,
physiological and behavioristic characters." Salt
continued, "It follows that the host is one of the important factors
that must be considered and controlled in any critical, and especially any
quantitative study of insect parasitoids. Accounts of behaviour, data on rate
of reproduction and longevity, measurements of length, even descriptions of
structure--none of these have any absolute validity for the species, none of
them can be considered 'biological constants' of a parasitoid, unless the
host is known and recorded." Internal host
reactions involve cellular reactions (encapsulation and
melanization) and humoral reactions (Griffiths 1960, 1961, 1969) Encapsulation (or phagocytosis) is the formation of a cyst by host cells
around foreign objects. Encapsulation has been reported to occur in
epidermal, tracheal, gut, muscle and nervous tissue. Haemolymphic capsules
are formed by the haemocytes congregating and differentiating into two
layers; and the cells of the inner layer form connective tissue fibers.
Opinions differ whether these inner cells form a true syncitium or not, and
whether the connective fibers are formed directly from the cytoplasm of the
cells or are secreted by them (Bess 1939, Schneider 1950, 1951, Muldrew 1953,
Griffiths 1960, Petersen 1962, van den Bosch 1964, Nappi & Streams
1970).. Melanization in
relation to defense reactions involves the deposition of pigment around a
parasitoid. Many authors feel that melanization is associated with
encapsulation and is essentially a cellular phenomenon. The melanin formed is
derived from tyrosine by way of the phenolase reactions. It is thought that
the substrate and enzyme are physically separated within certain blood cells
normally, but injury causes the reaction to proceed. Humoral Reactions are poorly
understood. Reports suggest that Coccophagus
gurneyi female larvae
gradually disintegrate in the body fluids of Pseudococcus longispinus
without visible reactions. Much the same occurs for Leptomastix dactylopii
larvae in Phenacoccus solani and with Monoctonus paladum in the aphid Aulacorthrum
circumflexum. There are two viewpoints concerning the role
of encapsulation in defense. One holds that haemocytes play a primary role in
causing the death of living eggs and larvae of parasitoids; the other that
humoral phenomena cause immunity, and haemocytes merely act as scavengers. Viewpoint No. 1 is favored because living
parasitoids have been found encapsulated. Also, it has been shown that
encapsulated Nemeritis
developed normally when reinjected into the normal host, Ephestia. Suppression of host reactions in normal hosts
revealed that the properties of the surface of Nemeritis eggs and larvae largely determined the extent of
their encapsulation in Ephestia. The immune response varies with the species
of host and parasitoid involved. In general different hosts utilize different
defense mechanisms against the same parasitoid, and different parasitoids
cause similar defense reactions in the same host. Temperature,
superparasitism and multiple parasitism also affect immune responses (Salt
1968, van den Bosch 1964). Encumbered
Host Defenses Although some microorganisms are detrimental
to entomophages, Goodwin (1984) noted that entomophagous parasitoids may have
symbiotic microorganisms enabling them to successfully attck hosts. For
example, Stoltz & Vinson (1979) showed that viruses present in the
oviducts of braconids and ichneumonids suppressed the defensive hemocoelic
encapsulation process in their hosts. Exercise 22.1--How may a host defend itself from a natural enemy? Exercise 22.2--Distinguish between humoral and haemocytic action. Exercise 22.3--Describe the situation with the alfalfa weevil and
its 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 Bess,
H. A. 1939. Investigation on the resistance of mealybugs (Homoptera) to
parasitization by internal hymenopterous parasites, with special reference to
phagocytosis. Ann.
Ent. Soc. Amer.
32: 189-226. Cole, L. R. 1957. The
biology of four species of Ichneumonidae parasitic on Tortrix viridana
L. Proc. Roy. Ent. Soc. London 22(C): 48-49. Cole,
L. R. 1959. On the defenses of lepidopterous pupae in relation to the
oviposition behavior of certain Ichneumonidae. J. Lepidop. Soc. 13: 1-10. Goodwin,
R. H. 1984. REcognition and diagnosis of diseases in insectaries and the
effects of disease agents on insect biology, pp. 96-129. In: E. G. King & N. C. Leppla (eds.), Advances and
challenges in insect rearing. U. S. Govt Printing Office Gordh,
G. 1976. Goniozus gallicola Fouts, a parasite of
moth larvae, with notes on other bethylids (Hymenoptera: Bethylidae;
Lepidoptera: Gelechiidae). U. S. Dept. Agr. Tech. Bull. 1524. 27 p. Griffiths,
D. C. 1960. Immunity of aphids to insect parasites. Nature 187: 346. Griffiths,
D. C. 1961. The development of Monoctonus
paludum Marshall (Hym.,
Braconidae) in Nasonovia ribis-nigri on lettuce, and immunity reactions in other lettuce
aphids. Bull. Ent. Res. 52: 147-63. Hadorn,
E. & I. Walker. 1960. Drosophila
and Pseudeucoila. I.
Selection experiments on increasing the defense reaction of the host. Rev.
Suisse Zool. 67: 216-25. Hinton,
H. E. 1955. Protective devices of endopterygote pupae. Trans. Soc. Brit. Ent.
12: 49-92. Muldrew,
J. A. 1953. The natural immunity of the larch sawfly [Pristiphora erichsonii
(Htg.)] to the introduced parasite Mesoleius
tenthredinis Morley, in Manitoba
and Saskatchewan. Canad. J. Zool. 31: 314-22. Nappi,
A. J. & F. A. Streams. 1970. Abortive development of the cynipid parasite
Pseudeucoila bochei (Hymenoptera) in species
of the Drosophila melanica group. Ann. Ent. Soc. Amer. 63: 321-27. Petersen, G. 1962. Haemocytare
Abwehrreaktion des Wirtes gegen endoparasitische Insekten und ihre Bedeutung
für die Biologische Bekämpfung. Bericht über die Wandersammlung Deutscher
Entomologen 6-8 V, 1961, Berlin. p. 179-95. Salt, G. 1955a. Experimental
studies in insect parasitism. VII. Host reactions following artificial
parasitization. Proc. Roy. Soc. London 144(B): 380-98. Salt, G. 1955b. Experimental
studies in insect parasitism. IX. The reactions of a stick insect to an alien
parasite. Proc. Roy. Soc. London 146(B): 93-108. Salt,
G. 1957. Experimental studies in insect parasitism. X. The reactions of some
entopterygote insects to an alien parasite. Proc. Roy. Soc. London 147(B):
167-84. Salt,
G. 1960. Experimental studies in insect parasitism. XI. The haemocytic
reaction of a caterpillar under varied conditions. Proc. Boy. Soc. London
151(B): 446-67. Salt,
G. 1963a. The defense reactions of insects to metazoan parasites. Parasitology 53(3-4): 527-642. Salt, G. 1963b. Experimental
studies in insect parasitism. XII. The reactions of six exopterygote insects
to an alien parasite. J.
Ins. Physiol. 9: 647-69. Salt,
G. 1965. Experimental studies in insect parasitism. XIII. The haemocytic
reaction of a caterpillar to eggs of its habitual parasite. Proc. Roy. Soc.
London 162(B): 303-18. Salt,
G. 1966. Experimental studies in insect parasitism. XIV. The haemocytic
reaction of a caterpillar to larvae of its habitual parasite. Proc. Roy. Soc.
London 165(B): 155-78. Salt,
G. 1967. Cellular defense mechanisms in insects. Fed. Proc. 26: 1671-74. Salt,
G. 1968. The resistance of insect parasitoids to the defense reactions of
their hosts. Biol.
Rev. 43: 200-32. Salt, G. & R. van den Bosch. 1967.
The defense reactions of three species of Hypera
(Coleoptera, Curculionidae) to an ichneumon wasp. J. Invert. Pathol. 9: 164-77. Schneider, F. 1950. Die Abwehrreaktion
des Insektenblutes und ihre Beeinflüssung durch die Parasiten. Vjschr.
naturf. Ges. Zurich 95: 22-44. Schneider, F. 1951. Einige physiologische
beziehungen zwischen Syrphidenlarven und ihren Parasiten. Zeitschr. f. angew.
Ent. 3: 150-62. Stoltz,
D. B. & S. B. Vinson. 1979. Viruses and parasitism in Insects. Adv. Virus
Res. 24: 125-71. Streams,
F. A. 1968. Defense reactions of Drosophila
species (Diptera: Drosophilidae) to the parasite Pseudeucoila bochei
(Hymenoptera: Cynipidae). Ann.
Ent. Soc. Amer. 61: 158-64. Thompson,
W. R. 1930a. Entomophagous parasites and phagocytes. Nature (London) 125:
167. Thompson,
W. R. 1930b. Reaction of the phagocytes of arthropods to their internal
insect parasites. Nature (London) 125: 565-66. van
den Bosch, R. 1964. Encapsulation of the eggs of Bathyplectes curculionis
(Thomson) (Hymenoptera: Ichneumonidae) in larvae of Hypera brunneipennis
(Boheman) and Hypera postica (Gyllenhal)
(Coleoptera: Curculionidae). J. Insect Pathol. 6: 343-67. Walker, I. 1959. Die Absehrreaktion des
Wirtes Drosophila melanogaster gegen die zoophage
Cynipide Pseudeucoila bochei. Weld
Rev. Suisse Zool. 66: 569-632. |