certain trophic association in an environment, even at very low population level.
Thus, aphid-parasitoid conservation reflects the conservations of both the insect
groups. There are explicit, but small-scale evidences indicating that parasitoids
benefit from the resources in non-crop habitats and then spill over into adjacent
agricultural areas to parasitize their host insects (Starý 1975; Rand et al. 2006). Such
situations have become common today in the cultivated landscape, from the fields,
meadows, orchards, up to the urban ecosystems. A special attention also represents
so-called non-cultivated habitats such as wastelands, hedges and fallows as well as
their interactions with the nearby occurring forests. However, some crops and their
respective management may themselves also represent refugia of natural enemies
(parasitoids). The occurrence of a particular refugium can be short- or long-termed,
respectively, as well as its environmental interactions. There are different refugiums
derivable from the target enemies. For the aphidiine parasitoids, the host spectrum
and associations are important.
A target aphid-parasitoid association works also in the refugium, but sometimes
there are differences between the aphids and parasitoids. The aphids are generally
followed by the parasitoids in all the environments, but, on the other hand, the
parasitoids manifest also more or less other interactions derivable from their host
range, i.e. attacking other aphid/plant associations, apart from the target pest species.
These situations are perhaps best to be exemplified, as follows: Alfalfa is attacked by
Acyrthosiphon pisum throughout the season, with respective seasonal population
fluctuation. There is an almost obligate association with Aphidius ervi (Rakhshani
et al. 2006a), thus alfalfa works as a semi-perennial seasonal refugium of this
parasitoid, which can disperse through the other preferred host in favourable condition. However, alfalfa may be cut off- and the population association are temporarily
more or less broken until the autumn. Acyrthosiphon pisum looks for the legumes
(other alfalfa fields, peas), the parasitoid (Aphidius ervi) may find also other hosts but
both in other legumes fields or in the cereals (cereal aphids). In the annual cereals,
which are temporary refugia, the population of cereal aphids and their parasitoids
colonize on the crop (Rakhshani et al. 2008b; Tomanović et al. 2009), but seasonally
affected by crop ripening causing subsequent leave of the parasitoids and aphids into
the surrounding environment including alfalfa fields, where merely Aphidius ervi
can survive on A. pisum.
However, the situation is different for Therioaphis trifolii, another pest aphid on
alfalfa. The aphid is holocyclic on alfalfa, manifesting a different seasonal population peak than A. pisum, both the parasitoids, P. exsoletum and T. complanatus are
specific to Therioaphis, and cannot find other host species on nearby cereals. The
only refugium are alfalfa fields in nearby areas or possible associated with same host
aphid the weeds. Strip-harvesting system is a conservation method that provided two
separate stages of alfalfa in the same field throughout the growing season (Stern et al.
1964). The more stable environment prevents emigration of the natural enemies
(Summers 1976) and provide a local refugium as expected (Hossain et al. 2000;
Rakhshani et al. 2010). In a refugium, there may be a set of other plant-aphid
associations which may be but economically indifferent if related to a target pest
aphid., i.e. wild grasses related to alfalfa like Melilotus spp.. The effect of a refugium
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
373
Thus, aphid-parasitoid conservation reflects the conservations of both the insect
groups. There are explicit, but small-scale evidences indicating that parasitoids
benefit from the resources in non-crop habitats and then spill over into adjacent
agricultural areas to parasitize their host insects (Starý 1975; Rand et al. 2006). Such
situations have become common today in the cultivated landscape, from the fields,
meadows, orchards, up to the urban ecosystems. A special attention also represents
so-called non-cultivated habitats such as wastelands, hedges and fallows as well as
their interactions with the nearby occurring forests. However, some crops and their
respective management may themselves also represent refugia of natural enemies
(parasitoids). The occurrence of a particular refugium can be short- or long-termed,
respectively, as well as its environmental interactions. There are different refugiums
derivable from the target enemies. For the aphidiine parasitoids, the host spectrum
and associations are important.
A target aphid-parasitoid association works also in the refugium, but sometimes
there are differences between the aphids and parasitoids. The aphids are generally
followed by the parasitoids in all the environments, but, on the other hand, the
parasitoids manifest also more or less other interactions derivable from their host
range, i.e. attacking other aphid/plant associations, apart from the target pest species.
These situations are perhaps best to be exemplified, as follows: Alfalfa is attacked by
Acyrthosiphon pisum throughout the season, with respective seasonal population
fluctuation. There is an almost obligate association with Aphidius ervi (Rakhshani
et al. 2006a), thus alfalfa works as a semi-perennial seasonal refugium of this
parasitoid, which can disperse through the other preferred host in favourable condition. However, alfalfa may be cut off- and the population association are temporarily
more or less broken until the autumn. Acyrthosiphon pisum looks for the legumes
(other alfalfa fields, peas), the parasitoid (Aphidius ervi) may find also other hosts but
both in other legumes fields or in the cereals (cereal aphids). In the annual cereals,
which are temporary refugia, the population of cereal aphids and their parasitoids
colonize on the crop (Rakhshani et al. 2008b; Tomanović et al. 2009), but seasonally
affected by crop ripening causing subsequent leave of the parasitoids and aphids into
the surrounding environment including alfalfa fields, where merely Aphidius ervi
can survive on A. pisum.
However, the situation is different for Therioaphis trifolii, another pest aphid on
alfalfa. The aphid is holocyclic on alfalfa, manifesting a different seasonal population peak than A. pisum, both the parasitoids, P. exsoletum and T. complanatus are
specific to Therioaphis, and cannot find other host species on nearby cereals. The
only refugium are alfalfa fields in nearby areas or possible associated with same host
aphid the weeds. Strip-harvesting system is a conservation method that provided two
separate stages of alfalfa in the same field throughout the growing season (Stern et al.
1964). The more stable environment prevents emigration of the natural enemies
(Summers 1976) and provide a local refugium as expected (Hossain et al. 2000;
Rakhshani et al. 2010). In a refugium, there may be a set of other plant-aphid
associations which may be but economically indifferent if related to a target pest
aphid., i.e. wild grasses related to alfalfa like Melilotus spp.. The effect of a refugium
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
373