However, just three species of T. grandis, T. semistriatus and T. vassilievi are
considered as main candidates for biological control of the sunn-pest complex.
8.3.1 Factors Influencing Species Richness and Distribution
Weather condition is the most important factor that influences geographical distribution and the parasitism rate. For example, the parasitism rate is very low in dry
regions and increases around water resources like irrigation channels. In addition,
parasitism rate is always lower in rain-fed fields (Martin et al. 1969; Radjabi 2000).
On the other hand, lower parasitism was recorded in colder regions like
Chaharmahal-o-Bakhtiari and East Azarbaijan provinces (Haghshenas 2004;
Nozad-Bonab and Iranipour 2010). In a laboratory study, an equal number of three
species of T. grandis, T. semistriatus and T. vassilievi was released on E. integriceps
eggs at 25, 30 and 34
C and 10, 33, 55 and 85% RH regimes. T. semistriatus
preceded other species just at 30
C and 85% RH, while it declined to zero at 34
C.
In other RH regimes at 30
C T. vassilievi preceded the others and T. grandis
preceded at all RH regimes at extreme temperatures (Radjabi 2000). This may
imply a wider thermal range of the recent species. In fact, T. grandis is a prevalent
species in many regions in Iran. It can found equally in cold and warm conditions or
dry and humid ones. This species recorded as prevalent species in Golestan province
on E. maura (Iranipour et al. 1998a), which is one of the most humid regions of the
distribution of sunn pest in Iran. It is also dominant species in cold regions such as
northwestern provinces (Shafaei et al. 2011; Nozad-Bonab and Iranipour 2013) as
well as warmer and drier region such as Varamin (Iranipour et al. 2011). In recent
place, however, T. vassilievi and T. grandis precede the other species at different
years. This is mainly due to temporal density dependence of T. vassilievi that led this
species to exceed T. grandis in those years that outbreak occurs. T. grandis caused
density independently 19.5–29.2% egg mortality, while T. vassilievi killed density
dependently 0–59.7% at different place-years. Although Iranipour et al. (2011)
observed no temporal reaction of T. grandis in this study, spatial density dependence
was recorded in another study (Amir-Maafi and Parker 2002). T. vassilievi was the
second key factor with a very weaker impact on host population compared to adult
mortality in diapause phase, which was the first key factor in population dynamics of
the sunn pest in Varamin fields (Iranipour et al. 2011).
Safavi (1973) believes that T. vassilievi is prevalent species of southern provinces
of Iran and has a tendency toward the dry and warm condition. However, In Isfahan
with a similar climate to Varamin, T. vassilievi has not reported yet. On the other
hand, in colder provinces such as East and West Azarbaijan, this species is an
occasional parasitoid of sunn pest (Shafaei et al. 2011; Nozad-Bonab and
Iranipour 2010).
Hence, different combinations of species are active in different regions. For
example, in Alborz wheat fields, T. grandis reported as prevalent species and
seven other species (T. semistriatus, T. vassilievi, T. basalis, T. rufiventris,
308
S. Iranipour
considered as main candidates for biological control of the sunn-pest complex.
8.3.1 Factors Influencing Species Richness and Distribution
Weather condition is the most important factor that influences geographical distribution and the parasitism rate. For example, the parasitism rate is very low in dry
regions and increases around water resources like irrigation channels. In addition,
parasitism rate is always lower in rain-fed fields (Martin et al. 1969; Radjabi 2000).
On the other hand, lower parasitism was recorded in colder regions like
Chaharmahal-o-Bakhtiari and East Azarbaijan provinces (Haghshenas 2004;
Nozad-Bonab and Iranipour 2010). In a laboratory study, an equal number of three
species of T. grandis, T. semistriatus and T. vassilievi was released on E. integriceps
eggs at 25, 30 and 34
C and 10, 33, 55 and 85% RH regimes. T. semistriatus
preceded other species just at 30
C and 85% RH, while it declined to zero at 34
C.
In other RH regimes at 30
C T. vassilievi preceded the others and T. grandis
preceded at all RH regimes at extreme temperatures (Radjabi 2000). This may
imply a wider thermal range of the recent species. In fact, T. grandis is a prevalent
species in many regions in Iran. It can found equally in cold and warm conditions or
dry and humid ones. This species recorded as prevalent species in Golestan province
on E. maura (Iranipour et al. 1998a), which is one of the most humid regions of the
distribution of sunn pest in Iran. It is also dominant species in cold regions such as
northwestern provinces (Shafaei et al. 2011; Nozad-Bonab and Iranipour 2013) as
well as warmer and drier region such as Varamin (Iranipour et al. 2011). In recent
place, however, T. vassilievi and T. grandis precede the other species at different
years. This is mainly due to temporal density dependence of T. vassilievi that led this
species to exceed T. grandis in those years that outbreak occurs. T. grandis caused
density independently 19.5–29.2% egg mortality, while T. vassilievi killed density
dependently 0–59.7% at different place-years. Although Iranipour et al. (2011)
observed no temporal reaction of T. grandis in this study, spatial density dependence
was recorded in another study (Amir-Maafi and Parker 2002). T. vassilievi was the
second key factor with a very weaker impact on host population compared to adult
mortality in diapause phase, which was the first key factor in population dynamics of
the sunn pest in Varamin fields (Iranipour et al. 2011).
Safavi (1973) believes that T. vassilievi is prevalent species of southern provinces
of Iran and has a tendency toward the dry and warm condition. However, In Isfahan
with a similar climate to Varamin, T. vassilievi has not reported yet. On the other
hand, in colder provinces such as East and West Azarbaijan, this species is an
occasional parasitoid of sunn pest (Shafaei et al. 2011; Nozad-Bonab and
Iranipour 2010).
Hence, different combinations of species are active in different regions. For
example, in Alborz wheat fields, T. grandis reported as prevalent species and
seven other species (T. semistriatus, T. vassilievi, T. basalis, T. rufiventris,
308
S. Iranipour