realized in Iran (Rakhshani et al. 2000, 2004b, 2009; Monajemi and Esmaili 1981;
Amini et al. 2012). Usually the population of both narrow and broadly oligophagous
parasitoids fluctuate with their host aphid, where they are living in. Specific parasitoids are generally more adapted to the seasonal dynamics in the population of their
host to reduce the risk of starvation. They need also the same preferred host for
summer hibernating and overwintering within its empty body, as mature larva or
pupa. The local survey on the seasonal occurrence of Trioxys pallidus on walnut
orchards (Rakhshani et al. 2004b) is a good representative for the adaptation of the
specific aphid parasitoids. The general scheme of seasonal activity for this species is
an early emergence in the spring together with its host aphid, Chromaphis
juglandicola, which sharply declined in early summer, so that no aphids and
parasitoids were observed during the summer. Rearing the mummies collected in
early summer did not give adults in subsequent weeks, indicating existence of an
aestival diapause, which is expected to prolong until next spring. On the other hand,
the weak resurgence of aphid population in early autumn led to appearance of few
parasitoids, which successfully parasitized even the sexual form of C. juglandicola.
There is no evidence explained, what was happened for the mummies went into the
aestival diapause, and led to emergence in autumn, partly. Preservation of the
mummies collected during autumn in natural condition confirmed existence of an
adaptive diapause, which synchronize the emergence of the parasitoids with its
specific host in walnut orchards. The mid-season crash in the host aphid populations
is believed to be the consequence of some natural phenomena including decline in
plant nutritional quality, increased natural enemy pressure and extreme temperature
(Karley et al. 2004) directly affecting the population of the specific parasitoids.
Similar adaptation can be found in the complex environments as in alfalfa field,
where each parasitoid allocated a specified niche including the preferred ecological
or physiological host aphids. There is a well-known group of aphids associated with
alfalfa including, Acyrthosiphon kondoi Shinji, A. pisum (Harris), Therioaphis
trifolii (Buckton) and Aphis craccivora in many parts of Iran. Each aphid species
manifests a specific parasitoid complex, which seems not to have interference on
each other. Among the parasitoid of the alfalfa aphids, two species, Aphidius ervi
and Lysiphlebus fabarum are known as broadly oligophagous species, but they act as
locally specific parasitoids in alfalfa ecosystem, associating only with their preferred
hosts, Acyrthosiphon pisum (A. kondoi, as well) and Aphis craccivora, exclusively.
Praon volucre was also found commonly in association with Acyrthosiphon aphids
and very rarely on Aphis craccivora (Rakhshani et al. 2006a). The general trend of
the seasonal dynamics of the parasitoid species is well representative of their host
aphid, while the maximum rate of parasitism and occurrence of summer decline
differ according to the climatic adaptation of the aphid/parasitoid species (Rakhshani
et al. 2010). In the case of Therioaphis trifolii, two parasitoid species, Praon
exsoletum Nees and Trioxys complanatus Quilis occurred simultaneously in major
parts of the country, except few desertic areas in early summer. High populations of
both species are generally active during spring, but Trioxys complanatus showed
more activities in early summer, when Praon exsoletum disappeared. These observations need supplementary investigation to be confirmed and clarified. It is also
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E. Rakhshani and P. Starý
Amini et al. 2012). Usually the population of both narrow and broadly oligophagous
parasitoids fluctuate with their host aphid, where they are living in. Specific parasitoids are generally more adapted to the seasonal dynamics in the population of their
host to reduce the risk of starvation. They need also the same preferred host for
summer hibernating and overwintering within its empty body, as mature larva or
pupa. The local survey on the seasonal occurrence of Trioxys pallidus on walnut
orchards (Rakhshani et al. 2004b) is a good representative for the adaptation of the
specific aphid parasitoids. The general scheme of seasonal activity for this species is
an early emergence in the spring together with its host aphid, Chromaphis
juglandicola, which sharply declined in early summer, so that no aphids and
parasitoids were observed during the summer. Rearing the mummies collected in
early summer did not give adults in subsequent weeks, indicating existence of an
aestival diapause, which is expected to prolong until next spring. On the other hand,
the weak resurgence of aphid population in early autumn led to appearance of few
parasitoids, which successfully parasitized even the sexual form of C. juglandicola.
There is no evidence explained, what was happened for the mummies went into the
aestival diapause, and led to emergence in autumn, partly. Preservation of the
mummies collected during autumn in natural condition confirmed existence of an
adaptive diapause, which synchronize the emergence of the parasitoids with its
specific host in walnut orchards. The mid-season crash in the host aphid populations
is believed to be the consequence of some natural phenomena including decline in
plant nutritional quality, increased natural enemy pressure and extreme temperature
(Karley et al. 2004) directly affecting the population of the specific parasitoids.
Similar adaptation can be found in the complex environments as in alfalfa field,
where each parasitoid allocated a specified niche including the preferred ecological
or physiological host aphids. There is a well-known group of aphids associated with
alfalfa including, Acyrthosiphon kondoi Shinji, A. pisum (Harris), Therioaphis
trifolii (Buckton) and Aphis craccivora in many parts of Iran. Each aphid species
manifests a specific parasitoid complex, which seems not to have interference on
each other. Among the parasitoid of the alfalfa aphids, two species, Aphidius ervi
and Lysiphlebus fabarum are known as broadly oligophagous species, but they act as
locally specific parasitoids in alfalfa ecosystem, associating only with their preferred
hosts, Acyrthosiphon pisum (A. kondoi, as well) and Aphis craccivora, exclusively.
Praon volucre was also found commonly in association with Acyrthosiphon aphids
and very rarely on Aphis craccivora (Rakhshani et al. 2006a). The general trend of
the seasonal dynamics of the parasitoid species is well representative of their host
aphid, while the maximum rate of parasitism and occurrence of summer decline
differ according to the climatic adaptation of the aphid/parasitoid species (Rakhshani
et al. 2010). In the case of Therioaphis trifolii, two parasitoid species, Praon
exsoletum Nees and Trioxys complanatus Quilis occurred simultaneously in major
parts of the country, except few desertic areas in early summer. High populations of
both species are generally active during spring, but Trioxys complanatus showed
more activities in early summer, when Praon exsoletum disappeared. These observations need supplementary investigation to be confirmed and clarified. It is also
344
E. Rakhshani and P. Starý