They showed that prey type did not have any impact on searching rate and handling
time of fourth instar larvae but did on third instar larvae and females. They postulated the fourth instar larvae is the most voracious stage of this predator and in
addition to females it could be considered as releasing stages in an inundative
biocontrol project against cotton aphid. This speculation was confirmed again by
using Russian wheat aphid (RWA) as prey for H. variegata (Behnazar and Madadi
2015). Their results supported that fourth instar larvae and female adults had the
highest searching efficiency on Sardari c.v. of wheat, but instead, male adults was the
most voracious stage on Back cross c.v. of wheat (Table 2.3).
Virtually all of these F.R. studies on Coccinellids used the two-step analysis
method developed by Juliano (2001). This method determines the type of response
precisely and produces acceptable estimates of attack constant and handling time.
Collectively, studies conducted on functional response of H. variegata in Iran
showed different values for attack constant and handling time that makes comparison difficult. The first point is that most of these studies (except three cases) have
been done on small artificial arenas like leaf disc or even more simple medium like
Petri dish that increases predator-prey encounter rate and therefore type II functional
response has been reported. However, large-scale experiments did not change the
response type (Madadi et al. 2011; Davoodi Dehkordi and Sahragard 2013a).
Indeed, small scale experiment only gives an insight into the predator’s maximum
predation potential and does not produce actual value of predation rate. Additionally,
extrapolating the results of these studies to real conditions is difficult. This point is
one issue that should be considered in future experiments and as possible as Petri
dish experiments should be discarded. Most of these studies exhibited no difference
in F.R. response type. Furthermore, searching efficiency and handling time did not
deviate from corresponding values of other studies substantially. Although, as a
novelty, Davoodi Dehkordi and Sahragad (2013a) used an open patch design to
study the functional response of H. variegata to the cotton aphid. The design
included the black eyed bean leaf’s petiole wrapped with a wet cotton wool and
was placed in an open larger plastic box (18 Â 23 Â 5 cm) which unlike Petri dish
arena allow the lady beetles to freely move across the experimental unit. Another
point is that many F.R. studies have been done with only one prey stage (mostly
fourth instar nymphs), while it is obvious that predators usually encounter with a
mixture of prey stages simultaneously while searching in nature. This deficiency
might be attributed to difficulties in data analysis that the number of killed prey from
different stages could not be incorporated in the analysis. The development of
multistage functional response models could be useful for analyzing this kind of
data. Similar to life table studies, among aphids, only five species have been used in
F.R. evaluations and cotton aphid was used more than other preys (Table 2.3),
meanwhile few fruit tree aphid species have been used as prey. This might be due
to difficulties in rearing fruit tree aphid pests under laboratory conditions, but
certainly, this is an apparent defect of F.R. studies of H. variegata conducted to
date in Iran.
All life stages of H. variegata have predatory habits and kill their prey, but in
many of F.R. studies, only a single life stage of H. variegata has been used
62
H. Madadi
time of fourth instar larvae but did on third instar larvae and females. They postulated the fourth instar larvae is the most voracious stage of this predator and in
addition to females it could be considered as releasing stages in an inundative
biocontrol project against cotton aphid. This speculation was confirmed again by
using Russian wheat aphid (RWA) as prey for H. variegata (Behnazar and Madadi
2015). Their results supported that fourth instar larvae and female adults had the
highest searching efficiency on Sardari c.v. of wheat, but instead, male adults was the
most voracious stage on Back cross c.v. of wheat (Table 2.3).
Virtually all of these F.R. studies on Coccinellids used the two-step analysis
method developed by Juliano (2001). This method determines the type of response
precisely and produces acceptable estimates of attack constant and handling time.
Collectively, studies conducted on functional response of H. variegata in Iran
showed different values for attack constant and handling time that makes comparison difficult. The first point is that most of these studies (except three cases) have
been done on small artificial arenas like leaf disc or even more simple medium like
Petri dish that increases predator-prey encounter rate and therefore type II functional
response has been reported. However, large-scale experiments did not change the
response type (Madadi et al. 2011; Davoodi Dehkordi and Sahragard 2013a).
Indeed, small scale experiment only gives an insight into the predator’s maximum
predation potential and does not produce actual value of predation rate. Additionally,
extrapolating the results of these studies to real conditions is difficult. This point is
one issue that should be considered in future experiments and as possible as Petri
dish experiments should be discarded. Most of these studies exhibited no difference
in F.R. response type. Furthermore, searching efficiency and handling time did not
deviate from corresponding values of other studies substantially. Although, as a
novelty, Davoodi Dehkordi and Sahragad (2013a) used an open patch design to
study the functional response of H. variegata to the cotton aphid. The design
included the black eyed bean leaf’s petiole wrapped with a wet cotton wool and
was placed in an open larger plastic box (18 Â 23 Â 5 cm) which unlike Petri dish
arena allow the lady beetles to freely move across the experimental unit. Another
point is that many F.R. studies have been done with only one prey stage (mostly
fourth instar nymphs), while it is obvious that predators usually encounter with a
mixture of prey stages simultaneously while searching in nature. This deficiency
might be attributed to difficulties in data analysis that the number of killed prey from
different stages could not be incorporated in the analysis. The development of
multistage functional response models could be useful for analyzing this kind of
data. Similar to life table studies, among aphids, only five species have been used in
F.R. evaluations and cotton aphid was used more than other preys (Table 2.3),
meanwhile few fruit tree aphid species have been used as prey. This might be due
to difficulties in rearing fruit tree aphid pests under laboratory conditions, but
certainly, this is an apparent defect of F.R. studies of H. variegata conducted to
date in Iran.
All life stages of H. variegata have predatory habits and kill their prey, but in
many of F.R. studies, only a single life stage of H. variegata has been used
62
H. Madadi