Attract, reward and disrupt: combining habitat manipulation and semiochemicals to enhance pest control in apple orchards

Abstract: Agricultural intensification entails negative effects on natural enemy populations and the pest regulation services they provide. Habitat manipulation holds potential to control pests with less negative effects on the environment than conventional methods. This can be achieved by the establishment of non-crop vegetation to support natural enemies and disfavour pests. Synthetic semiochemicals possess the capability of affecting arthropods behaviour and can be combined with habitat manipulation to increase pest control. In this thesis I examine how biological control is affected in high (conventional) and low (organic) intensity apple production systems and how habitat manipulation with and without semiochemicals can be used to enhance biological pest control. The intensity of management had a strong effect on the natural enemy community and their pest control potential. Organic apple orchards were able to support a higher number and diversity of natural enemies and presented a higher suppression of sentinel Dysaphis plantaginea colonies than integrated pest management orchards. The natural enemies which were most affected by management were predatory heteroptera with many species almost exclusively found in organic orchards. D. plantaginea, establishes a mutualism with ants as a protection strategy against natural enemies. By introducing bean plants infested with Aphis fabae, ants (Lasius niger) were diverted from D. plantaginea colonies, leaving them exposed to predation. The possibility to attract natural enemies with synthetic herbivore induced plant volatiles (HIPVs) was tested in apple and barley. In both crops the HIPVs were able to attract green lacewings (Chrysoperla carnea s.l.) over four weeks. Significant increases in oviposition and larval abundance was recorded compared to the control as well as a higher reduction in two species of cereal aphids. When HIPVs were deployed along flower strips, the attraction of natural enemies including Miridae was enhanced. The combination of HIPVs, flower strips and mating disruption suppressed populations of lepidopteran pests below that of flower strips + mating disruption or mating disruption alone under a three-year study.