parasitoid, readily (Meyhöfer and Klug 2002). Foraging female of Aphidius ervi
make patch leaving decisions according to both the relative requirements for oviposition and avoidance of intraguild predation, which may be adjusted by adult
experiences (Nakashima and Senoo 2003). The parasitoid is able to utilize indirect
cues of the predator, which has recently been removed (Taylor et al. 1998). This
might have a chemical basis that left either by the predator or even the alarm
pheromones of the reacting aphids. The spiders are group of generalist predators,
the adult parasitoids caught within their web, and even have been eaten as prey.
These interactions were studied in the case of some aphidiine, partly (Völkl and
Kraus 1996), but may have a large impact on the efficiency of parasitism, where the
spiders are rather common.
9.5.3 Agricultural Activities
The naturally heterogeneous and complex environments including grasslands, forests, hedgerows, and other semi-natural habitats are well-balanced in the proportions. The agricultural activities, transforming these habitats into homogeneous and
simple landscapes dominated with preferred field crops. Agro-technical activities
greatly change the insect community structure and may significantly interrupt the
population-relations between the aphid and parasitoids. The simplified agroecosystems cannot maintain high populations of the natural enemies (Perović et al.
2010; Jonsson et al. 2012), while common agricultural practices including application of pesticides, tillage, habitat isolation, and harvesting, require arthropods to
frequently recolonize crops (Wissinger 1997) and make severe reductions on their
population density. Disturbance caused by the agricultural activities by the human
and the habitat isolation resulting the significant decreases in biodiversity and disrupt
the structure of resident communities (Andrade et al. 2015). Aphid parasitoids are
very susceptible to environmental changes, and simply lose their natural habitat or
any transformation in the farmlands (Brewer et al. 2008; Lohaus et al. 2013).
Population of the aphid parasitoids sharply disappear after each harvesting step
and they can start with delays, after the successful establishment of their hosts.
Periodic harvesting of alfalfa affects adversely the aphid population as well as the
number of their parasitoids. Strip-cutting program might be adapted in
respective time.
The effects of fertilizers, as a common agricultural element on efficiency of the
aphid parasitoids surveyed partially (Garratt et al. 2010). Changes on the host plant
volatiles can affect the heterogeneity and size of the associated insect community
including aphid parasitoids (Krauss et al. 2007). Suitability of the host can also be
affected through fertilizer treatment and subsequently influences on fitness and
abundance of the aphid parasitoids. Results of the experiments conducted by Garratt
et al. (2010) indicated fertilizer treatments that improve fitness of the cereal-aphid
(Metopolophium dirhodum Walker) will also improve the fitness of parasitoid
(Aphidius ervi Haliday), measured by parasitoid size, but may not influence
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E. Rakhshani and P. Starý
make patch leaving decisions according to both the relative requirements for oviposition and avoidance of intraguild predation, which may be adjusted by adult
experiences (Nakashima and Senoo 2003). The parasitoid is able to utilize indirect
cues of the predator, which has recently been removed (Taylor et al. 1998). This
might have a chemical basis that left either by the predator or even the alarm
pheromones of the reacting aphids. The spiders are group of generalist predators,
the adult parasitoids caught within their web, and even have been eaten as prey.
These interactions were studied in the case of some aphidiine, partly (Völkl and
Kraus 1996), but may have a large impact on the efficiency of parasitism, where the
spiders are rather common.
9.5.3 Agricultural Activities
The naturally heterogeneous and complex environments including grasslands, forests, hedgerows, and other semi-natural habitats are well-balanced in the proportions. The agricultural activities, transforming these habitats into homogeneous and
simple landscapes dominated with preferred field crops. Agro-technical activities
greatly change the insect community structure and may significantly interrupt the
population-relations between the aphid and parasitoids. The simplified agroecosystems cannot maintain high populations of the natural enemies (Perović et al.
2010; Jonsson et al. 2012), while common agricultural practices including application of pesticides, tillage, habitat isolation, and harvesting, require arthropods to
frequently recolonize crops (Wissinger 1997) and make severe reductions on their
population density. Disturbance caused by the agricultural activities by the human
and the habitat isolation resulting the significant decreases in biodiversity and disrupt
the structure of resident communities (Andrade et al. 2015). Aphid parasitoids are
very susceptible to environmental changes, and simply lose their natural habitat or
any transformation in the farmlands (Brewer et al. 2008; Lohaus et al. 2013).
Population of the aphid parasitoids sharply disappear after each harvesting step
and they can start with delays, after the successful establishment of their hosts.
Periodic harvesting of alfalfa affects adversely the aphid population as well as the
number of their parasitoids. Strip-cutting program might be adapted in
respective time.
The effects of fertilizers, as a common agricultural element on efficiency of the
aphid parasitoids surveyed partially (Garratt et al. 2010). Changes on the host plant
volatiles can affect the heterogeneity and size of the associated insect community
including aphid parasitoids (Krauss et al. 2007). Suitability of the host can also be
affected through fertilizer treatment and subsequently influences on fitness and
abundance of the aphid parasitoids. Results of the experiments conducted by Garratt
et al. (2010) indicated fertilizer treatments that improve fitness of the cereal-aphid
(Metopolophium dirhodum Walker) will also improve the fitness of parasitoid
(Aphidius ervi Haliday), measured by parasitoid size, but may not influence
370
E. Rakhshani and P. Starý