affecting the sex ratio, the food plant on which the host aphids are propagating, is
also important (Prasad et al. 2005).
9.3.3 Functional Response and Foraging Behavior
The behavioral characteristics of the aphid parasitoids have certainly a great impact
on their efficiency for the successful aphid biocontrol (Berryman 1999). Assessing
the foraging behavior and functional response of the aphid parasitoids in one of the
important criteria for selecting the effective species. It generally indicated how the
parasitoid influence the population dynamics of its host species (Jervis and Kidd
1996). In the simplest definition, functional response is the number of hosts that
successfully attacked per each parasitoid, depending to the host density (Solomon
1949). Various models are developed for clarification of the functional response of
the parasitoids. The host exploitation by the aphid parasitoids may fall into Holling’s
type II or the type III with a sigmoid response (van Steenis and El-Khawass 1995).
Parasitoids with type II functional response are not density dependent and their
parasitism rate does not increase with host density (Hassell 1978). The parasitoids
with a type III functional response, can regulate the population of their host to a
definite density, since they can increase the rate of parasitism with increases in host
density increase (Holling 1959). This behavior maximizes the exploitation of dense
patches (Stilmant 1996). It was suggested that the parasitoids with a type II functional response are able to control the pest aphid more effectively on the protected
crops, where the parasitoid can reach its hosts even at low densities (Lopes et al.
2009). The parasitoids with type III functional response are likely more successful in
the field conditions, especially in classical biological control program, where such a
density dependent regulation provide a stable and long term control (FernandezArhex and Corley 2003).
In many cases, a type II functional response was recorded (Table 9.2), but few
species of the aphid parasitoids showed the type III functional response (Rakhshani
et al. 2004a; Jokar et al. 2012; Tazerouni et al. 2016, 2017). Various factors directly
affect the functional response or its attributed parameters (Jervis and Kidd 1996). It
has been shown that temperature has no effect on the type of functional response but
may change some of its parameters (Zamani et al. 2006; Farhad et al. 2011;
Tazerouni et al. 2012c; Moayeri et al. 2013; Hajrahmatollahi et al. 2015). Handling
time is defined as the time used for handling and parasitizing the host, including the
time for resting, feeding and cleaning (Jervis and Kidd 1996). Significantly higher
handling time was recorded at the lowest temperature, which is likely a result of
non-searching activities including resting (Moayeri et al. 2013; Hajrahmatollahi
et al. 2015). The higher temperatures were also found to negatively affect the
handling time (Farhad et al. 2011). The host plant can also change the foraging
behavior and functional response of the parasitoids (Price 1986). It was shown that
the host plant variety has also significant effect on the type of functional response in
aphid parasitoids (Bazyar et al. 2012).
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
347
also important (Prasad et al. 2005).
9.3.3 Functional Response and Foraging Behavior
The behavioral characteristics of the aphid parasitoids have certainly a great impact
on their efficiency for the successful aphid biocontrol (Berryman 1999). Assessing
the foraging behavior and functional response of the aphid parasitoids in one of the
important criteria for selecting the effective species. It generally indicated how the
parasitoid influence the population dynamics of its host species (Jervis and Kidd
1996). In the simplest definition, functional response is the number of hosts that
successfully attacked per each parasitoid, depending to the host density (Solomon
1949). Various models are developed for clarification of the functional response of
the parasitoids. The host exploitation by the aphid parasitoids may fall into Holling’s
type II or the type III with a sigmoid response (van Steenis and El-Khawass 1995).
Parasitoids with type II functional response are not density dependent and their
parasitism rate does not increase with host density (Hassell 1978). The parasitoids
with a type III functional response, can regulate the population of their host to a
definite density, since they can increase the rate of parasitism with increases in host
density increase (Holling 1959). This behavior maximizes the exploitation of dense
patches (Stilmant 1996). It was suggested that the parasitoids with a type II functional response are able to control the pest aphid more effectively on the protected
crops, where the parasitoid can reach its hosts even at low densities (Lopes et al.
2009). The parasitoids with type III functional response are likely more successful in
the field conditions, especially in classical biological control program, where such a
density dependent regulation provide a stable and long term control (FernandezArhex and Corley 2003).
In many cases, a type II functional response was recorded (Table 9.2), but few
species of the aphid parasitoids showed the type III functional response (Rakhshani
et al. 2004a; Jokar et al. 2012; Tazerouni et al. 2016, 2017). Various factors directly
affect the functional response or its attributed parameters (Jervis and Kidd 1996). It
has been shown that temperature has no effect on the type of functional response but
may change some of its parameters (Zamani et al. 2006; Farhad et al. 2011;
Tazerouni et al. 2012c; Moayeri et al. 2013; Hajrahmatollahi et al. 2015). Handling
time is defined as the time used for handling and parasitizing the host, including the
time for resting, feeding and cleaning (Jervis and Kidd 1996). Significantly higher
handling time was recorded at the lowest temperature, which is likely a result of
non-searching activities including resting (Moayeri et al. 2013; Hajrahmatollahi
et al. 2015). The higher temperatures were also found to negatively affect the
handling time (Farhad et al. 2011). The host plant can also change the foraging
behavior and functional response of the parasitoids (Price 1986). It was shown that
the host plant variety has also significant effect on the type of functional response in
aphid parasitoids (Bazyar et al. 2012).
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
347