and searching rate of this species enhanced compared to equal numbers of conspecifics in a single species arena. In contrast, T. vassilievi could not handle more than ¼
of the total parasitized eggs. This may imply that T. grandis is more aggressive than
T. vassilievi, however, in muti-species situations, it neglecs presence of conspecific
more frequently than the other species. Larval competition between the two species
was studied by Najafipour et al. (2018). Overall, first invador will be win the contest
disregarding species and interval between attacks (3–48 h), however success rate of
T. vassilivi decreases as second attack delays.
8.5.3 Effect of External Factors – II. Abiotic Factors
Temperature
Among abiotic factors, the temperature is the most influencing one. Insects are
poikilothermic animals and their body temperature is the function of their environment. Body temperature determines the speed of biochemical reactions and activity
of enzymes. Temperatures in which development occur can be wider than temperatures within which reproduction realizes. There is a thermal threshold for development above which development and biochemical reactions accelerate up to an
optimal temperature. In colder temperatures, all activities stop. Beyond optimal
temperature, reactions slow down. This range of temperature may determine the
fundamental niche and distribution pattern of an insect. In optimum temperature,
speed of reactions is the maximum and hence handling time is the shortest, the
searching rate is highest, development is most rapidly and reproduction occurs in the
shortest interval. Both in colder and warmer temperatures speed of these events
decreases. Parasitoids often experience colder than optimum temperatures in fields.
In this condition, daily attack rate reduces. Total fecundity is lower and parasitism
occurs with a lower daily rate but in a longer period. Lower parasitism rates in colder
regions were reported (Haghshenas 2004; Nozad-Bonab and Iranipour 2010). On the
other hand, cold springs can limit the activity of some species with higher thermal
threshold and heat requirements such as T. vassilievi in colder provinces (Iranipour
et al. 2015). The main problem in natural biological control of sunn pest complex is
early season low parasitism due to higher reproductive requirements of parasitoids
compare to hosts (Salavatian 1991). In previous sections, detailed effects of temperature were discussed.
Effect of low temperatures on survival of T. grandis and T. vassilievi was studied by
Iranipour et al. (2018b). Females of both species were introduced to 4
C after a
10 day acclimatization in 10
C. They were confined individually or in batches of
3–30 individuals among shelters constructed from the paper balls. Their mortality
then was monitored weekly in room air. In all duration of the experiment, mortality
of T. vassilievi was higher than T. grandis. On the other hand, aggregation in higher
numbers protected females from higher mortalities observed in lower batches. An
advantage of 1.35, 3.04 and 6.24 times more T. grandis survivors was predicted by
322
S. Iranipour
of the total parasitized eggs. This may imply that T. grandis is more aggressive than
T. vassilievi, however, in muti-species situations, it neglecs presence of conspecific
more frequently than the other species. Larval competition between the two species
was studied by Najafipour et al. (2018). Overall, first invador will be win the contest
disregarding species and interval between attacks (3–48 h), however success rate of
T. vassilivi decreases as second attack delays.
8.5.3 Effect of External Factors – II. Abiotic Factors
Temperature
Among abiotic factors, the temperature is the most influencing one. Insects are
poikilothermic animals and their body temperature is the function of their environment. Body temperature determines the speed of biochemical reactions and activity
of enzymes. Temperatures in which development occur can be wider than temperatures within which reproduction realizes. There is a thermal threshold for development above which development and biochemical reactions accelerate up to an
optimal temperature. In colder temperatures, all activities stop. Beyond optimal
temperature, reactions slow down. This range of temperature may determine the
fundamental niche and distribution pattern of an insect. In optimum temperature,
speed of reactions is the maximum and hence handling time is the shortest, the
searching rate is highest, development is most rapidly and reproduction occurs in the
shortest interval. Both in colder and warmer temperatures speed of these events
decreases. Parasitoids often experience colder than optimum temperatures in fields.
In this condition, daily attack rate reduces. Total fecundity is lower and parasitism
occurs with a lower daily rate but in a longer period. Lower parasitism rates in colder
regions were reported (Haghshenas 2004; Nozad-Bonab and Iranipour 2010). On the
other hand, cold springs can limit the activity of some species with higher thermal
threshold and heat requirements such as T. vassilievi in colder provinces (Iranipour
et al. 2015). The main problem in natural biological control of sunn pest complex is
early season low parasitism due to higher reproductive requirements of parasitoids
compare to hosts (Salavatian 1991). In previous sections, detailed effects of temperature were discussed.
Effect of low temperatures on survival of T. grandis and T. vassilievi was studied by
Iranipour et al. (2018b). Females of both species were introduced to 4
C after a
10 day acclimatization in 10
C. They were confined individually or in batches of
3–30 individuals among shelters constructed from the paper balls. Their mortality
then was monitored weekly in room air. In all duration of the experiment, mortality
of T. vassilievi was higher than T. grandis. On the other hand, aggregation in higher
numbers protected females from higher mortalities observed in lower batches. An
advantage of 1.35, 3.04 and 6.24 times more T. grandis survivors was predicted by
322
S. Iranipour