may have its own advantages in the variable environment with different host aphid
inhabited therein.
The surveys on the behavior of Lysiphlebus fabarum (Marshall) on the black bean
aphid, Aphis fabae Scopoli indicated different strategies under choice and no-choice
host accessibility (Najafpour et al. 2016). No preference for specific nymphal instar
was documented, when the female parasitoids were offered different host instars
separately, while host instar preference progressively decreased with host age. On
the other hand, the host stage preference in the aphid parasitoids are known as a
constitute in the network of host aphid – parasitoid interaction (Henry et al. 2005). It
means the generalist parasitoids may show a variable host stage preference on
different host aphid species. Preference for the older nymphal instars can normally
led to a greater reduction in the population growth rate of the host aphid (Lin and
Ives 2003), then the population will be stabilized with the rest non-preferred instars.
On the other hand, preference on the younger nymphal instars (Perdikis et al. 2004)
is also suggested as an advantage for the aphid parasitoids enabling them to control
the more numerous fraction (Kouame and Mackauer 1991) of the aphid populations
in early stages of their increase (Perdikis et al. 2004). Defensive behavior of the
aphid in late instars (third and fourth) may also result in the lower preference for
some parasitoids (Kouamé and Mackauer 1991; Kairo and Murphy 1999; Wyckhuys
et al. 2008), which increases the handling time of the foraging female (Kant et al.
2008). The parasitoids develop at a slower rate in the smaller aphid hosts (Henry
et al. 2005; Najafpour et al. 2016). This prolonged developmental time is necessary
in order to acquire additional resources while the host is developing. Theoretically, a
preference for the younger nymphal instars may increase the yield of mass rearing
efforts, since it is easier to provide a large number of first and second nymphal
instars. Najafpour et al. (2016) recommend a synchronous population of second
nymphal instar of Aphis fabae for mass rearing of Lysiphlebus fabarum. Rearing on
the younger nymphal instars may result to a significantly male –biased population,
since the female parasitoids have preferentially a sex allocation behavior through
which they lay the unfertilized eggs into the smallest aphids (Pandey and Singh
1999; Cloutier et al. 2000).
9.3.5 Ant Associations
The aphid colonies are frequently attracting the ants (Fig. 9.3), which may range
from an occasional encounter to highly evolved coexistence, as bilateral mutualism
(Starý 1966). Interactions between ants and aphids as common honeydew-producing
insects are widespread and abundant, but their ecological consequences are very
poorly known. One of the more advanced relationships is the transportation of the
aphid nymphs by ants into the suitable parts of the host plant, then achieving more
honeydew secretions. Some aphid species alter their feeding behavior and the
composition of their honeydew in the presence of the attending ants (Yao et al.
2000). The ants are known also protecting the aphid colonies from the natural
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
351
inhabited therein.
The surveys on the behavior of Lysiphlebus fabarum (Marshall) on the black bean
aphid, Aphis fabae Scopoli indicated different strategies under choice and no-choice
host accessibility (Najafpour et al. 2016). No preference for specific nymphal instar
was documented, when the female parasitoids were offered different host instars
separately, while host instar preference progressively decreased with host age. On
the other hand, the host stage preference in the aphid parasitoids are known as a
constitute in the network of host aphid – parasitoid interaction (Henry et al. 2005). It
means the generalist parasitoids may show a variable host stage preference on
different host aphid species. Preference for the older nymphal instars can normally
led to a greater reduction in the population growth rate of the host aphid (Lin and
Ives 2003), then the population will be stabilized with the rest non-preferred instars.
On the other hand, preference on the younger nymphal instars (Perdikis et al. 2004)
is also suggested as an advantage for the aphid parasitoids enabling them to control
the more numerous fraction (Kouame and Mackauer 1991) of the aphid populations
in early stages of their increase (Perdikis et al. 2004). Defensive behavior of the
aphid in late instars (third and fourth) may also result in the lower preference for
some parasitoids (Kouamé and Mackauer 1991; Kairo and Murphy 1999; Wyckhuys
et al. 2008), which increases the handling time of the foraging female (Kant et al.
2008). The parasitoids develop at a slower rate in the smaller aphid hosts (Henry
et al. 2005; Najafpour et al. 2016). This prolonged developmental time is necessary
in order to acquire additional resources while the host is developing. Theoretically, a
preference for the younger nymphal instars may increase the yield of mass rearing
efforts, since it is easier to provide a large number of first and second nymphal
instars. Najafpour et al. (2016) recommend a synchronous population of second
nymphal instar of Aphis fabae for mass rearing of Lysiphlebus fabarum. Rearing on
the younger nymphal instars may result to a significantly male –biased population,
since the female parasitoids have preferentially a sex allocation behavior through
which they lay the unfertilized eggs into the smallest aphids (Pandey and Singh
1999; Cloutier et al. 2000).
9.3.5 Ant Associations
The aphid colonies are frequently attracting the ants (Fig. 9.3), which may range
from an occasional encounter to highly evolved coexistence, as bilateral mutualism
(Starý 1966). Interactions between ants and aphids as common honeydew-producing
insects are widespread and abundant, but their ecological consequences are very
poorly known. One of the more advanced relationships is the transportation of the
aphid nymphs by ants into the suitable parts of the host plant, then achieving more
honeydew secretions. Some aphid species alter their feeding behavior and the
composition of their honeydew in the presence of the attending ants (Yao et al.
2000). The ants are known also protecting the aphid colonies from the natural
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
351