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I. ONTOGENY
A. Eggs
1. Size
of eggs.
a. not correlated that large female parasitoids
deposit large eggs.
b. egg size is related to the number of
ovarioles and to the egg deposition rate.
(1). proovigenic females with large numbers of
ovarioles and a high deposition rate tend to
produce small eggs.
(2). e.g., females of all known species of
Trigonalidae (Hymenoptera) lay up to 10,000 eggs at the
rate of 5,000 per day!
2. Chorion
a. the majority of endoparasitoid Hymenoptera
have semi-transparent and unsculptured chorions.
b. among ectoparasitoid Hymenoptera, chorions
may be adorned with tubercles, spines or ridges.
3. Egg
Types
a. hymenopteriform egg
(1). ovoid to spindle-shaped in outline and are
smoothly rounded at both ends.
(2). chorion is either smooth or variously
sculptured.
(3). deposited internally, externally or apart
from the host.
(4). of general occurrence in parasitoid
Hymenoptera, but also found in some families of parasitoid
Diptera.
b. acuminate egg
(1). elongate, tapering to a sharp point at one
or both ends.
(2). chorion is smooth.
(3). found largely among Ichneumonidae and
Braconidae, parasitoids possessing long ovipositors
for reaching hidden hosts in galls, galleries,
wood tunnels, etc.
c. stalked egg
(1). tube-like extensions at one end.
(2). generally found in parasitoid Hymenoptera
and a few Diptera.
(3). may be deposited within, upon or apart from
the host.
d. encyrtiform egg
(1). dumbbell-shaped.
(2). deposited internally.
(3). one collapsed "bell" and a portion
of the stalk that connects the two, remain protruding from
the ovipositional puncture.
(4). the projecting structures bear a
longitudinal rib along one side called the aeroscopic plate that
functions in larval respiration.
(5). found in many genera of Encyrtidae.
e. pediculate egg
(1). one end penetrates the host integument and
is variously twisted, expanded or knotted to serve
as an anchor for the externally
projecting egg body.
(2). found in Agriotypidae, Ichneumonidae and
Eulophidae.
f. macrotype egg
(1). large, oblong and ventrally flattened.
(2). deposited externally.
(3). found
only in Tachinidae.
g. microtype egg
(1). minute, oval, ventrally flattened.
(2). deposited on foliage apart from hosts and hatch
only upon being eaten by the host.
(3). common in Tachinidae and Trigonalidae.
h. membranous egg
(1). chorion is extremely delicate.
(2). deposited either internally or externally.
(3). found in Tachinidae and Sarcophagidae.
i. acroceriform egg
(1). pear-shaped and darkly pigmented.
(2). the smaller end bears a well-defined
circular cap which is forced off at eclosion.
(3). found in Cyrtidae (Diptera).
4. Polyembryony
Usually only a single parasitoid is produced per
egg in monoembryony. Sometimes the egg
develops
polyembryonically.
a. has developed independently in four
hymenopterous families: Braconidae,
Encyrtidae,
Platygasteridae and Dryinidae.
b. also present in a few species of
Strepsiptera.
c. the number of individuals arising from each
egg is extremely variable, ranging from two to 2,000
as in the genus Litomastix (Platygasteridae). The number is apparently directly proportional
to the size of the mature host larva.
d. host preference is shown, as, e.g., the
polyembryonic Braconidae and Encyrtidae only parasitize
Lepidoptera; whereas polyembryonic
Platygasteridae parasitize hosts in the dipterous family
Cecidomyiidae.
e. restricted parasitoid genera: only in the Encyrtidae is more than one
genus in a family known to
be polyembryonic.
f. host stage attacked: all polyembryonic Encyrtidae and
Platygasteridae oviposit in the egg of their
hosts and complete their development
in the mature host larva or pupa. Thus,
they are all
either egg-larval or egg-pupal
parasitoids.
g. Sex:
the parasitoid brood from a single host may be all of one sex or mixed.
h. Distinction from Gregariousness
(1). polyembryonic species oviposit in the egg or
very young host larva, with parasitoid maturity
occurring in the mature host larva or
pupa.
(2). exceptionally large numbers of progeny
usually develop in a single host.
(3). simultaneous development and emergence of
the brood.
(4). a portion of the broods consist of one sex
only, and the mixed broods show widely varying
sex ratios.
i. Polyembryonic development results in an
increased reproductive capacity, but does not
necessarily confer a corresponding
increased efficiency as a natural enemy.
Polyembryony
may, instead, be viewed as an effort
on the part of the parasitoid to overcome certain
unfavorable factors in its
environment.
j. Relatively few polyembryonic species have
been known to function effectively as biological
control agents. However, as in the case of the navel
orangeworm, Amyleois transitella, they
may work in concert with other
parasitoids to produce effective biological control.
B. First-Instar
Larvae
The most distinctive and variable stage in the
life cycle of many entomophagous parasitoids and
predators.
a. Planidium-type larva
(1). Greek word meaning "diminutive
wanderer."
(2). all Eucharitidae and Perilampidae and males of
Aphelinidae; also dipterous Cyrtidae and many
Tachinidae.
(3). spindle-shaped, heavy sclerotized, possess
sensory organs and equipped for locomotion by
means of thoracic or caudal ambulatory
setae; or by vigorous twisting, jumping or looping
movements.
(4). can survive weeks or more without feeding.
(5). they arise from eggs that are deposited
apart from their hosts.
(6). upon hatching, they search for or otherwise
contact their hosts. They are strongly
attracted
to any moving object and attach
themselves to passing hosts or to nonhost carriers which
then carry them to their hosts.
b. Triungulinid-type larva
(1). the counterpart of the planidium larva but
found in Strepsiptera, and coleopterous Meloidae
and Rhipiphoridae.
(2). similar in all respects to planidium larvae,
with the exception that they possess segmented legs
for locomotion.
c. Sacciform-type larva
(1). body in bag-like form, lacking apparent
segmentation and lacking a tracheal system.
(2). develop only internally.
(3). found in certain Dryinidae,
Trichogrammatidae and Mymaridae.
d. Teleaform larva
(1). body segmentation also not apparent.
(2). cephalothorax and abdomen separated by a
deep constriction.
(3). mandibles are very large.
(4). abdomen sub-spherical and bears a long,
blade-like process posterio-ventrally.
(5). internal larval forms found in Scelionidae.
e. Mymariform larva
(1). spindle-shaped and indistinctly segmented.
(2). head conical.
(3). body segments ringed with long spines.
(4). last abdominal segment greatly elongated and
tail-like.
(5). internal larval forms found in certain
Mymaridae and Trichogrammatidae.
f. Cyclopiform larva
(1). cephalothorax larger than abdomen.
(2). mandibles very large.
(3). abdomen tapers posteriorally and its last
apparent segment is usually forked.
(4). the majority of Platygasteridae; all
internal.
g. Eucoiliform larva
(1). distinguished by the paired, fleshy ventral
processes on each thoracic segment.
Also, sharply
tapered, often tail-like abdomen.
(2). internal; found in certain Cynipidae.
h. Mandibulate larva
(1). distinct segmentation and large, broad,
somewhat flattened, heavily sclerotized heads that are
armed with large sickle-shaped
mandibles.
(2). internal forms; found in many Ichneumonidae,
Braconidae, Serphidae and Diapriidae.
i. Microtype larva
(1). minute in size.
(2). integument delicate.
(3). each thoracic segment bears a series of
heavy spines or hooks.
(4). internal.
(5). hatch from microtype eggs of the
Trigonalidae and many species of Tachinidae.
j. Muscoidiform larva
(1). commonly called "maggots."
(2). found in the suborder Cuyclorrhapha of the
Diptera.
k. Hymenopteriform larva
(1). larvae spindle-shaped to spherical in
outline.
(2). usually 12-13 body segments distinguishable.
(3). integument bare or studded with sensory
setae and cuticular spines.
(4). includes both internal and external forms
and is of general occurrence in the Hymenoptera.
l. Agriotypiform larva
(1). bodies of these larvae bear a transverse row
of long, heavy spines dorsally on each segment.
(2). last abdominal segment bears two, long and
slender, sharply-pointed and heavy sclerotized
spines.
(3). external forms found only in Agriotypidae.
m. Vesiculate larva
(1). similar to hymenopteriform type, except that
the hindgut protrudes posteriorly as an enlarged,
spherical sac.
(2). internal only.
(3). many Braconidae.
n. Caudate larva
(1). distinctly segmented, usually somewhat
elongate.
(2). last abdominal segment is modified into a
fleshy, tail-like organ.
(3). internal only.
(4). found only in many Ichneumonidae and
Chalcidoidea.
C. The
greatest variation in larval form occurs in the first instar. Development thereafter tends to
converge towards the hymenopteriform larva
in parasitoid Hymenoptera and towards the
muscoidiform larva in the
cyclorrhaphous Diptera.
The
intermediate and last-instar larvae of ectoparasitoid Hymenoptera generally do
not undergo great
changes in form as they progress towards maturity.
However, endoparasitoids, and those species in which the eggs or larvae
are deposited apart from their
hosts, usually undergo conspicuous modifications
during their larval development. These
changes in
larval
form may be completed by the second instar or the transition may be more
subtle, with progressively
more simplified larval forms interposed between
the first and last instar.
The
intermediate stages of both dipterous and hymenopterous parasitoids usually
resemble the last instar
in form.
The greatest change usually takes place at the first molt among
parasitoid species that possess
the most
highly specialized primary larvae, namely the planidium, cyclopiform,
teleaform, agriotypiform
and mandibulate types. Here, by the second instar the larvae are either hymenopteriform
or are very close
to the same.
D. Special Larval Types
1. In
certain Cynipoidea having eucoiliform primary larvae, the 2nd instar is called polypodieform. This
unique intermediate stage larva has a distinctly segmented body, several
anterior abdominal segments
of
which each bears a pair of ventrally-directed, fleshy lobes.
2. Another
distinctive 2nd instar larva is the histriobdellid type found among Mymaridae
egg parasitoids
that
have sacciform primary larvae. This
intermediate type has a cylindrical body that is interrupted
by 6
annular constrictions. The head bears a
pair of large, slender curved mandibles; and both the head and
the
last apparent body segment each bear a pair of fleshy lobes.
D. An
interesting phenomenon associated with the larvae of parasitoid Hymenoptera is
the fact that the
hindgut is not excretory in function until the prepupal molt is about to
occur. Until this time the hindgut
ends
blindly and may occupy much of the body cavity of the larva, serving as both an
organ of digestion
and
storage. At the time of the prepupal
molt, all fecal material accumulated and stored in the hindgut
during larval feeding is released at one time, forming what is called
the meconium.
II. SEX DETERMINATION AND
PARTHENOGENESIS
A. In
Hymenoptera, sex determination follows what is called Dzierzon's Law. Dzierzon was a
Silesian priest who lived around
1845.
1. males are derived from haploid, unfertilized
eggs; females from diploid, fertilized eggs.
2.
diploidy is
brought about in either of two ways:
a. as a modification of meiosis in the ovary.
b. by fertilization of the haploid egg at the
moment of oviposition, which changes the sex of the egg from
male to female.
B.
Genetics of Sex Determination
1.
History
a. originally thought to be like Drosophila (e.g., males = X;
females = XX)
b. Petrunkewitsch (1901) believed that gonads
were diploid even though the male body was
haploid.
c. Castle (1903) considered differential egg maturation.
d. Nachtsheim (1913) proposed differential egg
maturation directed by the presence or absence of
a sperm nucleus.
e. P. W. Whiting (1933) developed an early
theory of multiple alleles.
f. P. W. Whiting (1943) perfected the multiple
allele theory
xa,
xb, ..., xi -- any heterozygote (diploid), xa/xb, xc/xd, etc. is female.
xa,
xc, etc. -- any azygote (haploid) or homozygote, xa/xa, xb/xb, etc. is male.
g. Cunha and Kerr (1957) developed the theory
of a series of male-determining genes in balance with a series
of female-determining genes. The
female-determining (FD) genes would be additive in their effect, whereas
the male-determining (MD) would not.
C. In
most Hymenoptera, the spermatheca functions as a sex-changing organ. There are two principal ways
in
which this sex-changing process operates.
1. In Braconidae, Ichneumonidae and aculeate
Hymenoptera (bees and wasps), the process begins when
stimuli from the oviposition site activate
the sperm stored in the spermatheca.
Prior to this necessary stimulation
by
host contact, the stored sperm are inactive (incapable of locomotion). Once the sperm are activated, each
time
an egg passes down the oviduct, it stimulates several sperm to be emitted,
which enter the egg through
the
micropyle and fertilization results.
2. In Chalcidoidea, a secondary sex changing
mechanism is present following sperm activation. This is the
control of sperm emission from the sperm duct of the spermatheca. The passage of the egg down the oviduct
usually stimulates the emission of but a single sperm. However, another stimulation from the
oviposition
site
may secondarily stimulate a muscular contraction that closes the aperture of
the sperm duct, so the egg remains unfertilized and male at deposition.
D. Three
types of parthenogenetic reproduction
1. Thelytoky
a. obligatorily parthenogenetic.
b. each generation consists almost entirely of
females; males are rare.
c. the progeny of the virgin female are
necessarily uniparental.
2. Deuterotoky
a. both males and females are produced
parthenogenetically.
b. both males and females are uniparental.
c. the
same as thelytoky except that there are more males present in the population.
3. Arrhenotoky
a. the majority of parasitic Hymenoptera are
arrhenotokous.
b. females are derived from fertilized eggs as
a result of the spermatheca operating as a sex-
changing mechanism.
c. in species exhibiting arrhenotoky, the
females, therefore, are usually biparental and the males
uniparental.
III. HOST SELECTION
A.
Analyses of the manner in which entomophagous insects find their hosts
and the bases for their host
preferences, as with phytophagous insects, currently are subjects of
active entomological inquiry.
B. Host
parasitoids in nature attack several host species, although a few monophagous
species are known.
C. No
parasitoid appears to be completely indiscriminate, however, in its choice of
hosts. In nature only a
fraction of the species on which development is actually possible are
attacked by any one species.
D. Definite
host preferences are expressed by various groups of parasitoids.
1. most parasitoids of Scarabaeidae larvae are
in the hymenopteran families Scoliidae and Tiphiidae.
2. egg parasitoids are Trichogrammatidae,
Mymaridae and Scelionidae.
3. parasitoids of gall midges, Cecidomyiidae,
are Platygasteridae.
4. in the laboratory, however, spatial and
temporal barriers which separate parasitoids from their potential
hosts in nature can be removed.
Parasitoids can be bred in numbers on unnatural or factitious
hosts. This
is
actually practiced in the mass-rearing of beneficial parasitoids for biological
control.
Example: the oriental fruit moth parasitoid, Macrocentrus ancylivorous, can be mass-reared on potato
tuberworm larvae, although this host/parasitoid
relationship never occurs in nature.
Similarly, synanthropic
fly parasitoids in the genus Muscidifurax can be reared on Drosophila in the laboratory, which greatly
stunts the adults which emerge. In nature Drosophila have never been found parasitized by this genus.
5. In the mid-1930's, the steps involved in
host selection were discovered by Laing, Salt and Flanders.
a. Salt:
Step I = ecological selection, where the parasitoid is brought into
contact with its host; Step II =
psychological selection, where the host is accepted once contact is
made; Step III = physiological selection,
where the suitability of the host as a food source is determined.
b. Laing:
parasitoids find the environment of the host first, then the host
itself.
c. Flanders:
divided Salt's ecological selection into host-habitat finding and host-
finding. The third and
fourth steps are host acceptance (equivalent to Salt's psychological
selection) and host suitability (equivalent
to Salt's physiological selection).
(1). host-habitat finding = used to describe the
process by which entomophagous insects orient to various
environmental stimuli characteristic of the habitats frequented by their
prey.
(2). host-finding = describes the either random
or nonrandom encounter of the prey individuals by the
parasitoid within its host's habitat.
6. Summary
of Procedures in
Parasitization
a. Host habitat finding represents the initial
step in the chain-like series of events by which any host/parasitoid
relationship is maintained. A
parasitoid initially detects certain habitats as those more likely to be
frequented
by
its host, even though those habitats at that particular time may not contain
the host.
Example 1: an ichneumonid parasitoid Idechthis canescens is attracted by the odor of oatmeal, even though
its host, the larva of the Mediterranean flour moth, is not present.
Example 2: a chalcidid parasitoid of ant lion larvae, Stomatocerus rubrum, is attracted to sand and actively
explores any small depressions on the sand surface.
Example 3: Nasonia
vitripennis is attracted to
carrion that contains blowfly larvae.
Either carrion or blowflies
alone are not attractive.
Example 4: Spalangia
and Muscidifurax species are
attracted to accumulated garbage or animal wastes in
which they find muscoid puparia as hosts.
Example 5: plant species may also prove strongly
attractive to a species of parasitoid even though suitable
phytophagous hosts may not be present.
On the other hand, parasitoids may ignore suitable hosts feeding
on
plants which hold no attraction for the parasitoid. One notable example is exhibited by Pimpla ruficollis,
an
ichneumonid parasitoid of the European pine shoot moth. Here sexually immature females are
unresponsive
to
the odor of pines, but sexually mature females are strongly attracted by pine
odor.
b. Host-finding
Once a parasitoid has reached its host's habitat, it attempts to locate a
host individual. Considerable research
shows that various combinations of random and
directed movements (taxes) are involved.
Chemotactic,
phototactic, hydrotactic and geotactic responses,
among others, all seem to play a part in the host-finding
process. These responses are variously modified by
olfactory, visual and other physical stimuli that
characterize a parasitoid's prey.
c. Host-acceptance
Once physical contact has been made, only after receiving a proper
combination of stimuli will further
behavioral responses be triggered, resulting in
acceptance of the prey; i.e., host-feeding and/or oviposition.
The stimuli for attack are known to involve,
among other factors, host odor, host size, host location, host
shape and
even host motion.
It
is well known that many parasitoids have the ability to discriminate between
parasitized and healthy hosts
and thus
avoid superparasitism. This
differentiation may result from an odor left on the host by the parasitoid
that first contacted, the so-called spoor effect. The parasitic Hymenoptera, as a rule, are
more discriminatory
than the
parasitic Diptera in their selection of hosts.
Among predacious species, host specificities range
from those which are nearly monophagous (e.g., Rodolia) to those which are
highly polyphagous
(Geocoris
spp.). Relatively speaking, a greater
proportion of parasitoids than predators exhibit monophagy.
d. Host-suitability
The fact that a parasitoid has found a potential host within its
respective habitat and has oviposited in or
upon the same, is no assurance that all criteria
for maintaining a host-parasitoid relationship have been met.
The host individual selected may prove unsuitable
for parasitoid development. In other
words, oviposition
is no
assurance of host suitability if the host individual proves to be resistant or
otherwise unsuitable for
parasitoid development.
A host may be unsuitable as follows:
(1). for physical reasons (too small, too thick).
(2).
for nutritional reasons.
(3). biological reasons: the host may be killed by the ovipositing
female following host-feeding or mutilation
.
The host may move and dislodge externally-attached parasitoid eggs or
larvae. The host may molt and thus
shed parasitoid eggs attached externally to the cast exuvium. Also, internally laid eggs and
endoparasitoid
larvae may be encapsulated by phagocytes. Phagocytes are blood cells that gravitate to and either ingest
or surround foreign bodies that are introduced into the haemocoel of a
host insect. The process is called
phagocytosis.
Evidence exists that formerly susceptible host populations may become
resistant to parasitoid attack. Cases
are also known where otherwise normal hosts are
rendered unsuitable by the host plants on which the host develops.
e. Host-regulation
This fifth category in the host selection process was proposed by Dr.
Bradleigh Vinson of Texas A. & M.
University to account for cases in which
parasitism changes the host physiologically, causing it to behave
in a
different manner. It does not have
anything to do with regulation of host numbers.
7. Manner
and Place of Oviposition
a. Obviously, those species that oviposit merely
in the vicinity of hosts or randomly within their host's
general habitat, are not exercising as much discrimination as those
parasitoids in which host-selection behavior
is
developed to the degree where a specific host organ or location on a host
serves as the oviposition site.
b. Many species of Diptera and a few parasitic
Hymenoptera, oviposit in habitats frequented by their hosts,
but apart from any host individuals that may be present. These parasitoids may lay their eggs more or
less
at
random upon plant foliage or other plant parts, and host contact is made when
those eggs are subsequently
ingested by their plant-feeding hosts.
The eggs of some Hymenoptera hatch into small, motile larvae which
usually can live without food for long periods of time and which attach
themselves to passing host individuals.
Some dipterous parasitoids are viviparous with the eggs hatching within
the parasitoid female the subsequently
larviposit within the vicinity of, but apart from, their hosts.
c. The eggs of many species of dipterous and
hymenopterous parasitoids are deposited on the host. The
larvae, after hatching, variously feed either externally as
ectoparasitoids or enter the host and develop as
endoparasitoids. The eggs of
such parasitoids may either be glued to the host integument or anchored in
place by peg-like extensions of the chorion which penetrate the host's
integument.
d. It can generally be said that hosts living
in exposed situations, such as leaf-skeletonizing larvae, tend to
be
attacked by endoparasitoids; whereas, hosts living in protected situations,
such as galls, tunnels, galleries,
mines, or in puparia or cocoons, tend to be attacked by
ectoparasitoids. It follows that
parasitoids of exposed
hosts generally oviposit within their hosts. These eggs may simply be thrust into the host's haemocoel and
left to float free in the blood, or the eggs may be inserted into
specific host organs.
IV. POLYGENES AND EXTRANUCLEAR
INHERITANCE
It
is generally agreed that most, if not all, behavior in animals is governed by
polygenic loci. Yet, due to
inherent difficulties with studying polygenic
inheritance, data has been difficult to obtain. Considerable
progress
has been made with a parasitic hymenopteran genus Muscidifurax in the late 1980's. It was learned
that
quantitative behavior associated with gregarious oviposition (>one
individual developed per host)
and fecundity in the South American parasitoid Muscidifurax raptorellus Kogan & Legner was controled
by such polygenes (Legner 1987a, 1991). This system provides insights into the true
nature of polygenic
loci. Simply the data
derived suggest that even animals which do not show the particular trait (e.g.,
high
fecundity, gregarious development, aggressiveness,
tallness, shortness, integument color, etc.) may have
all loci present for the maximum expression of
such traits, but in some cases not all loci are turned on or
activated.
In hybrid cases only a certain number are turned on.
In
the M. raptorellus system, inheritance of polygenic traits is
accompanied by some unique extranuclear
influences which cause changes in the oviposition
phenotype of females (Legner 1987a,b; 1988a).
Males
are able
to change a female's oviposition phenotype upon mating, by transferring an
unknown substance
(Legner
1987a, 1988a,b). Females with a
solitary genotype produce larvae with gregarious development
after mating with males possessing the gregarious
genotype, and females with the gregarious genotype
produce
larvae with reduced gregarious behavior after mating with males of the solitary
genotype. The
intensity
of this response is different depending on the respective genetic composition
of the mating pair
(Legner 1989a).
Thus, the genes involved, by regulating phenotypic changes in the mated
female, cause
partial
expression of the traits they govern shortly after insemination, and before
being inherited by
resulting progeny (Legner 1987a, 1988a,
1989a).
Maternal inheritance of extranuclear substances as discussed by Legner
(1987a) and Corbet (1985)
seemed a possibility for the passage of traits to
offspring. However, observations of
linear additivity
of the traits and variance changes in hybrid
versus parental generations and relatively constant daily
expressions of behavior in F1 and
backcrossed populations, point to chromosomal inheritance (Legner
1987,
1988a, 1989a,c). Chromosomal
inheritance of gregarious behavior was substantiated further by
the
formation of recombinant males, thereby enabling estimations of the number of
active genetic loci
governing gregarious development (Legner
1991a,b).
The
inheritance scheme in Muscidifurax
is fundamentally important to an increased understanding of the
genetic
of Hymenoptera. Therefore, the kind of
genes and their mode of inheritance deserve distinction.
Genes of
this sort that are able to cause partial phenotypic changes in mated females
before being inherited
by their
progeny have been termed wary genes because they, or their precursors, are
tested in the
environment in an attenuated manner before being
inherited by the offspring (chromosomal inheritance).
Whether
such genes possess chemical precursors capable of changing the female's
phenotype, or are
inherited extranuclearly after mating is
unknown.
The
behavioral change after mating is permanent, and there is no switchback in
behavior following a
second mating with the opposite parental
male. This suggests that a relatively
stable molecule like DNA
may be present
and becomes permanently active after a first mating. Speculations also have considered
microorganisms, male accessory gland fluids, and
behavior-modifying chemicals, such as prostaglandins,
responsible for the behavioral changes after
mating. Nevertheless, signals are sent
to a female from the
male
within hours of mating, probably via the sperm or seminal fluid. These signals express the code of
the genes themselves. The genes present in the male are then inherited by the progeny
in a typical
polygenic inheritance. Because inheritance of such genes seems to occur in a stepwise
manner, the entire
process might be termed accretive inheritance
(Legner 1989a).
In
the process of hybridization, wary genes may serve to quicken the pace of
evolution by allowing natural
selection for nonlethal undesirable and desirable
characteristics to begin to act in the parental generation.
Wary genes detrimental to the hybrid population
might thus be more prone to elimination and beneficial ones
may be
expressed in the mother before the appearance of her active progeny. If wary genes occur more
generally in Hymenoptera, their presence might
account partially for the rapid evolution thought to occur i
n certain groups of Hymenoptera (Hartl 1972, Gordh
1975, 1979), and possibly the quick adaptation and spread
of Africanized honey bees in South America as
discussed by Taylor (1985) and Legner (1989d)
[Please
see Expanded Research on this subject].
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