percentage of parasitism. Applications of both fertilizers and pesticides is believed to
result in losses in the biodiversity and habitat degradation.
There is yet great debate about how the agricultural activities affect the species
diversity (Tylianakis et al. 2007; Vollhardt et al. 2008; Gagic et al. 2012). Currently
the definition of “Agricultural landscape” is largely accepted in the pest management
strategies. In such system, there are habitats that provide alternative food sources,
shelter and overwintering sites for the aphid parasitoids according to their composition (Landis et al. 2000; Roschewitz et al. 2005; Bianchi et al. 2006; Liu et al.
2013). In some cases, the positive effects of managed agricultural activity on the
species diversity have been evidenced (Hole et al. 2005). In the local survey by
Alikhani et al. (2013), greater values of species diversity for the aphid parasitoids
were found comparing the non-cultivated areas. In the small scale it was interpreted
as negative effects of the desertic climate in the non-cultivated areas (in Markazi
province), which is not favourable for the development of both plants and aphids.
The agricultural activities, on the other hand provide enough irrigated areas
favouring the environments for growth of many host plants the aphids and their
parasitoids.
Application of pesticides has also significant effect on the efficiency of the aphid
parasitoids, and other natural enemies, as well (Bacci et al. 2009). Conventional
insecticides readily kill majority of the foraging female parasitoids and reduce their
survival rate. Sub-lethal effects of the pesticides led to further changes in the life
history parameter of the aphid parasitoids including developmental time, fecundity,
longevity, egg viability, sex ratio, host selection, foraging behavior and habitat
preference (Desneux et al. 2004, 2006; Rezaei et al. 2014). Indirect exposure to
spray droplets, or through contact with residue of insecticides on the host plant
foliage, as well as feeding on contaminated honeydews are the common routes,
negatively affecting the foraging female aphid parasitoids. Feeding on the extrafloral nectars of the plants, which their seed was treated with insecticide was found
inducing some changes in sex ratios of the offspring (Moscardini et al. 2014). Adult
parasitoids migrate into the treated area or emerge from the mummies and they can
subsequently be exposed to the insecticides, because the parasitoids spend much of
their life time foraging for food and host aphids for oviposition on the contaminated
plants.
The residue of chemical insecticides may alter behavior of the parasitoids through
disrupting activity of the central nervous system even at very small doses (Haynes
1988; Elzen 1989). The low doses of lambda-cyhalothrin was found to impair the
orientation and oviposition behaviors of Aphidius ervi (Haliday), when allocating its
host aphid, Myzus persicae (Sulzer) (Desneux et al. 2004). A single application of
insecticide is enough to destroy the whole population of the adult parasitoids;
however, the immature stages are more protected inside the body of their host
aphid. It was believed that the late developmental stages of the aphid parasitoids
inside the mummified bodies of their aphid hosts have the least susceptibility to the
conventional insecticides (Starý 1970a, b). Considering the importance of ecological
selectivity (Ripper et al. 1951) for the broad–spectrum insecticides, this period can
be an opportunity of the pesticide applications, which should be timed so that the
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
371
result in losses in the biodiversity and habitat degradation.
There is yet great debate about how the agricultural activities affect the species
diversity (Tylianakis et al. 2007; Vollhardt et al. 2008; Gagic et al. 2012). Currently
the definition of “Agricultural landscape” is largely accepted in the pest management
strategies. In such system, there are habitats that provide alternative food sources,
shelter and overwintering sites for the aphid parasitoids according to their composition (Landis et al. 2000; Roschewitz et al. 2005; Bianchi et al. 2006; Liu et al.
2013). In some cases, the positive effects of managed agricultural activity on the
species diversity have been evidenced (Hole et al. 2005). In the local survey by
Alikhani et al. (2013), greater values of species diversity for the aphid parasitoids
were found comparing the non-cultivated areas. In the small scale it was interpreted
as negative effects of the desertic climate in the non-cultivated areas (in Markazi
province), which is not favourable for the development of both plants and aphids.
The agricultural activities, on the other hand provide enough irrigated areas
favouring the environments for growth of many host plants the aphids and their
parasitoids.
Application of pesticides has also significant effect on the efficiency of the aphid
parasitoids, and other natural enemies, as well (Bacci et al. 2009). Conventional
insecticides readily kill majority of the foraging female parasitoids and reduce their
survival rate. Sub-lethal effects of the pesticides led to further changes in the life
history parameter of the aphid parasitoids including developmental time, fecundity,
longevity, egg viability, sex ratio, host selection, foraging behavior and habitat
preference (Desneux et al. 2004, 2006; Rezaei et al. 2014). Indirect exposure to
spray droplets, or through contact with residue of insecticides on the host plant
foliage, as well as feeding on contaminated honeydews are the common routes,
negatively affecting the foraging female aphid parasitoids. Feeding on the extrafloral nectars of the plants, which their seed was treated with insecticide was found
inducing some changes in sex ratios of the offspring (Moscardini et al. 2014). Adult
parasitoids migrate into the treated area or emerge from the mummies and they can
subsequently be exposed to the insecticides, because the parasitoids spend much of
their life time foraging for food and host aphids for oviposition on the contaminated
plants.
The residue of chemical insecticides may alter behavior of the parasitoids through
disrupting activity of the central nervous system even at very small doses (Haynes
1988; Elzen 1989). The low doses of lambda-cyhalothrin was found to impair the
orientation and oviposition behaviors of Aphidius ervi (Haliday), when allocating its
host aphid, Myzus persicae (Sulzer) (Desneux et al. 2004). A single application of
insecticide is enough to destroy the whole population of the adult parasitoids;
however, the immature stages are more protected inside the body of their host
aphid. It was believed that the late developmental stages of the aphid parasitoids
inside the mummified bodies of their aphid hosts have the least susceptibility to the
conventional insecticides (Starý 1970a, b). Considering the importance of ecological
selectivity (Ripper et al. 1951) for the broad–spectrum insecticides, this period can
be an opportunity of the pesticide applications, which should be timed so that the
9 Aphid Parasitoids: Aphidiinae (Hym., Braconidae)
371