8.3.5 Host-Parasitoid Synchrony Problem
The wasps emerge when the temperature reaches to 13
C in spring, begin to feed on
wild flowers around fields, and then enter cereal fields. Up to three weeks later, their
hosts arrive (Şimşek 1986; Şimşek and Yaşarakinci 1990). Such a delay has a
negative impact on parasitoids. Effect of such a delay studied by Bazavar et al.
(2015; see Sect. 8.5.2). Discontinuous access may occur when the density of host is
scarce and female wasp has to spend some time to find an egg mass. Delayed access
followed by subsequent unlimited access is possible when the delay in host arrival
occurs. Salavatian (1991) also believed that pioneer eggs are not attacked due to
colder condition of early spring. In fact, early-season parasitism or parasitism in the
colder regions is always low (Amir-Maafi 2000; Haghshenas 2004; Nozad-Bonab
and Iranipour 2010; Iranipour and Kharrazi-Pakdel 2011). Unfortunately, pioneer
eggs have a more important role in crop damage compared to subsequent ones
(Radjabi 1995). Some other reasons also are present to explain the low rate of
parasitism early season. For example, a longer pre-oviposition period of host and
density dependence of parasitoid may decrease the attack rate. In a multi-patch
experiment, it was shown that a female T. vassilievi spent 4.3, 13.0, 19.1, 23.9,
and 18.4% of her time in patches with 1, 2, 4, 8 and 15 clutches and 21.3% out of
patches. Corresponding parasitism rate in those patches was 4.0, 13.3, 22.5, 34.2 and
25.9% respectively. When parasitoid was alone no one-clutch patch was met. Other
patches were met equally. This may suggest a threshold density of two clutches,
which parasitoid can detect chemical cues. Lower amount of signals are neglected
and thus parasitoid avoids exploitation in low-density patches except in random
encounters. Inclusion of additional foraging females in this experiment caused the
parasitoids disperse more severly among the patches and hence, the one-clutch patch
also was met. This is clearly due to mutual interference among foraging parasitoids.
Pseudo-interference had a stronger influence on per capita attack rate. Actual
interference had only a minor role in per capita exploitation. These results suggest
that interference is an unimportant force in sunn pest-egg parasitoid systems
(Iranipour et al. 2020). The parasitoids encounter other kinds of problems late
season. They will encounter low quality hosts (parasitized eggs or developed hostembryogenesis).
8.3.6 Indirect Effects of Parasitism
In addition to direct mortality, parasitic wasps can disturb synchrony between most
vulnerable stage of the crop (ripening seeds) and most injurious stage of the pest
(adults and higher instar nymphs). Radjabi (1995) showed that higher parasitism rate
disturbs this synchrony. In those years or places where parasitism is high, stagestructure of the pest tend to consist of younger stages at ripening. In this regards,
early-season parasitism is very crucial. So in the future, our attempts should be
8 Superfamily Platygastroidea: Natural Enemies of True Bugs, Moths, Other. . .
311
The wasps emerge when the temperature reaches to 13
C in spring, begin to feed on
wild flowers around fields, and then enter cereal fields. Up to three weeks later, their
hosts arrive (Şimşek 1986; Şimşek and Yaşarakinci 1990). Such a delay has a
negative impact on parasitoids. Effect of such a delay studied by Bazavar et al.
(2015; see Sect. 8.5.2). Discontinuous access may occur when the density of host is
scarce and female wasp has to spend some time to find an egg mass. Delayed access
followed by subsequent unlimited access is possible when the delay in host arrival
occurs. Salavatian (1991) also believed that pioneer eggs are not attacked due to
colder condition of early spring. In fact, early-season parasitism or parasitism in the
colder regions is always low (Amir-Maafi 2000; Haghshenas 2004; Nozad-Bonab
and Iranipour 2010; Iranipour and Kharrazi-Pakdel 2011). Unfortunately, pioneer
eggs have a more important role in crop damage compared to subsequent ones
(Radjabi 1995). Some other reasons also are present to explain the low rate of
parasitism early season. For example, a longer pre-oviposition period of host and
density dependence of parasitoid may decrease the attack rate. In a multi-patch
experiment, it was shown that a female T. vassilievi spent 4.3, 13.0, 19.1, 23.9,
and 18.4% of her time in patches with 1, 2, 4, 8 and 15 clutches and 21.3% out of
patches. Corresponding parasitism rate in those patches was 4.0, 13.3, 22.5, 34.2 and
25.9% respectively. When parasitoid was alone no one-clutch patch was met. Other
patches were met equally. This may suggest a threshold density of two clutches,
which parasitoid can detect chemical cues. Lower amount of signals are neglected
and thus parasitoid avoids exploitation in low-density patches except in random
encounters. Inclusion of additional foraging females in this experiment caused the
parasitoids disperse more severly among the patches and hence, the one-clutch patch
also was met. This is clearly due to mutual interference among foraging parasitoids.
Pseudo-interference had a stronger influence on per capita attack rate. Actual
interference had only a minor role in per capita exploitation. These results suggest
that interference is an unimportant force in sunn pest-egg parasitoid systems
(Iranipour et al. 2020). The parasitoids encounter other kinds of problems late
season. They will encounter low quality hosts (parasitized eggs or developed hostembryogenesis).
8.3.6 Indirect Effects of Parasitism
In addition to direct mortality, parasitic wasps can disturb synchrony between most
vulnerable stage of the crop (ripening seeds) and most injurious stage of the pest
(adults and higher instar nymphs). Radjabi (1995) showed that higher parasitism rate
disturbs this synchrony. In those years or places where parasitism is high, stagestructure of the pest tend to consist of younger stages at ripening. In this regards,
early-season parasitism is very crucial. So in the future, our attempts should be
8 Superfamily Platygastroidea: Natural Enemies of True Bugs, Moths, Other. . .
311