Host location and oviposition of lepidopteran herbivores in diversified broccoli cropping systems

摘要

1 Host location and oviposition are crucial steps in the life cycles of insect herbivores. A diversified cropping system may interfere with these processes, ultimately reducing pest colonization of crops and the need for chemical interventions. 2 In the present study, nonhost vegetation was added to a broccoli (Brassica oleracea var. italica) cropping system to determine the effect of plant diversification on host location and colonization of broccoli by Lepidopteran pests. The two diversification strategies applied consisted of a broccoli/potato (Solanum tuberosum) strip crop, made up of 1.65 m (tractor width) replications of two rows of potatoes and two rows of broccoli, and a cereal rye (Secale cereale) cover crop, which formed a sacrificial planting that was killed and rolled flat to minimize weed competition and improve the agronomic performance of the subsequent broccoli crop. 3 Diamondback moth Plutella xylostella eggs, and subsequent larvae and pupae, were less abundant on broccoli with the cover crop, probably due to interference with host location and oviposition processes. The strip crop had no effect. 4 Numbers of cabbage white butterflies Pieris rapae eggs and larvae did not differ among treatments, probably due to the superior ability of these Lepidoptera to visually locate hosts and their active egg-dispersing behaviour. 5 These results of the present study indicate that the success of crop diversification strategies are contingent on the relative ability of the target herbivore to locate its host plant and the scale of diversity (e.g. the distance between the host and the nonhost plants), rather than diversity itself.