Increasing agrobiodiversity by crop intercropping and
application of plant essential oils in fields may provide
potential alternatives to those currently used to control
S. avenae. Intercropping garlic or related volatiles releasing
in wheat fields has potentially direct effects on
the aphids, such as repellent, toxic, masking host plant
odours, and masking visual orientation, or indirect
effect, such as stimulating natural enamies and inducing
resistance in host plant. The push-pull strategy is
an useful tool for integrating pest management
programs, reducing pesticide input (Cook et al. 2007),
and maximizing the efficacy of behavior manipulating
stimuli through the additive and synergistic effects of a
non-host crop. Our results indicated that the abundance
of S. avenae was lower, with both varieties, in the wheatgarlic
intercropping system than in wheat monoculture.
This may be due to two factors: (1) garlic is a stimulus
for push components to make wheat resources hard to
locate, unattractive, or unsuitable to aphids; and/or (2)
intercropping systems that increase crop diversity in the
agroecosystem significantly preserved and augment more
ladybeetles and mummified aphids than monoculture
wheat fields. Similar phenomenon was also observed in
wheat-garlic (Wang et al. 2008), wheat-alfalfa (Ma
et al. 2007) and maize-sorghum (Khan et al. 1997) intercropping
system. The results of this study further
demonstrated the effects of intercropping on aphids and
their natural enemies. Wheat varieties (Beijing 837) that
are susceptible to wheat aphid might reduce wheat aphids
more effectively than an aphid-resistant variety
(Zhengzhou 831) in the intercropping system. This may
occur by an attracting more ladybeetles to suppress cereal
aphids. There was no significant difference on mummified
aphids densities between the varieties.