an invasion through the neighbouring countries (Iraq, Turkey). Further exploration is
needed to find the source and the reasons, which disclosed the expansion of this
opportunistic species into Iran. More than 500 parasitoid-aphid associations are
recorded in various regions of Iran (Barahoei et al. 2014; Farahani et al. 2016)
including the data about parasitoid complex of many pest aphids. Further investigations with emphasis on the natural habitat and especially on the area surrounding the
field crops and orchards is needed to realize the host range pattern of the known
species throughout the season, as well as to determine the rare parasitoids, which
strictly attack the aphids on their natural and intact environments.
9.2.3.1 Host Specific Aphid Parasitoids
There are many monophagous species of aphid parasitoids, which are mainly
considered as rare species with unknown significance in biological control. Host
specificity in the aphid parasitoids is believed to be a result of parallel evolution,
apart of their phylogeny. The host plant distribution has a signification attribution in
this respect (Žikić et al. 2017). Strict host specificity increased to cost of ecological
interaction for the parasitoid species and it needs to acquire additional adaptations,
which are not necessary for other species, in general. The well-known species is
Monoctonia vesicarii Tremblay which is specific parasitoid of Pemphigus species on
poplars (Rakhshani et al. 2015a). It has only one generation per year and spending
most of the year as diapausing pupa inside the mummified aphid (Tremblay 1991).
The term “monophagous” should be re-defined in the case of aphid parasitoids,
referring the species which are associated with aphids in less diverse genera or even
monotypic. So that the parasitoids have no chance to find an appropriate host among
the related aphid taxa. Beside this, there are groups of specialized parasitoids
evolved within the more diverse aphid taxa, which can parasitize the closely related
aphids within the small genera. The border of their host range seems to be defined
ecologically by the habitat properties and host plant diversity. It means the parasitoid
can find its specific hosts only on the host plants of the same family level. According
to this explanation, this group of parasitoids can be categorized in a group named as
“narrow oligophagous” species.
There are some species that are very specific or have a very narrow host range.
They are mainly targeted in classical biological control programs of the invasive
aphids of economically important. The list of species exported from Iran are shown
in Table 9.1, among them, the specific parasitoids are dominant. Trioxys pallidus
(Haliday) is a specific parasitoid of Chromaphis juglandicola (Kaltenbach), but it is
also recorded in association with closely related aphids on different host plants,
including Eucalipterus tiliae L., Myzocallis coryli (Goetze), Tuberculoides
annulatus (Hartig) (Starý 1978), Pterocallis alni (De Geer) (Babaee et al. 2000)
and some other species. So, how it can be a specific parasitoid? and why many other
similar cases have been considered as generalist?. Trioxys pallidus is native to Iran
and can be found with its host aphid throughout the country. The association with
others, but closely related aphids has been confirmed and discussed for this species
340
E. Rakhshani and P. Starý
needed to find the source and the reasons, which disclosed the expansion of this
opportunistic species into Iran. More than 500 parasitoid-aphid associations are
recorded in various regions of Iran (Barahoei et al. 2014; Farahani et al. 2016)
including the data about parasitoid complex of many pest aphids. Further investigations with emphasis on the natural habitat and especially on the area surrounding the
field crops and orchards is needed to realize the host range pattern of the known
species throughout the season, as well as to determine the rare parasitoids, which
strictly attack the aphids on their natural and intact environments.
9.2.3.1 Host Specific Aphid Parasitoids
There are many monophagous species of aphid parasitoids, which are mainly
considered as rare species with unknown significance in biological control. Host
specificity in the aphid parasitoids is believed to be a result of parallel evolution,
apart of their phylogeny. The host plant distribution has a signification attribution in
this respect (Žikić et al. 2017). Strict host specificity increased to cost of ecological
interaction for the parasitoid species and it needs to acquire additional adaptations,
which are not necessary for other species, in general. The well-known species is
Monoctonia vesicarii Tremblay which is specific parasitoid of Pemphigus species on
poplars (Rakhshani et al. 2015a). It has only one generation per year and spending
most of the year as diapausing pupa inside the mummified aphid (Tremblay 1991).
The term “monophagous” should be re-defined in the case of aphid parasitoids,
referring the species which are associated with aphids in less diverse genera or even
monotypic. So that the parasitoids have no chance to find an appropriate host among
the related aphid taxa. Beside this, there are groups of specialized parasitoids
evolved within the more diverse aphid taxa, which can parasitize the closely related
aphids within the small genera. The border of their host range seems to be defined
ecologically by the habitat properties and host plant diversity. It means the parasitoid
can find its specific hosts only on the host plants of the same family level. According
to this explanation, this group of parasitoids can be categorized in a group named as
“narrow oligophagous” species.
There are some species that are very specific or have a very narrow host range.
They are mainly targeted in classical biological control programs of the invasive
aphids of economically important. The list of species exported from Iran are shown
in Table 9.1, among them, the specific parasitoids are dominant. Trioxys pallidus
(Haliday) is a specific parasitoid of Chromaphis juglandicola (Kaltenbach), but it is
also recorded in association with closely related aphids on different host plants,
including Eucalipterus tiliae L., Myzocallis coryli (Goetze), Tuberculoides
annulatus (Hartig) (Starý 1978), Pterocallis alni (De Geer) (Babaee et al. 2000)
and some other species. So, how it can be a specific parasitoid? and why many other
similar cases have been considered as generalist?. Trioxys pallidus is native to Iran
and can be found with its host aphid throughout the country. The association with
others, but closely related aphids has been confirmed and discussed for this species
340
E. Rakhshani and P. Starý