Oviposition preference of Plutella xylostella (L.) (Lepidoptera: Plutellidae) on kale and rocket

The objective of this study was to compare the oviposition preference of Plutella xylostella on 2 varieties of crucifers, kale ‘HS20’ (Brassica oleracea var. acephala) and rocket ‘folha larga’ (Eruca sativa). We performed 5 replicates; each replicate was 1 plastic cage (diameter, 6 cm; height, 10 cm) containing one 8-cm-diameter leaf disc for the oviposition of adults. Each leaf disc was divided into 4 alternating segments: 2 parts of kale and 2 parts of rocket. In each cage, we placed 2 pairs of adult male and female. To evaluate the oviposition preference, we reared P. xylostella larvae on the leaves of kale or rocket for 4 generations. The second generation of P. xylostella reared on kale (8.5% of eggs on kale and 91.5% on rocket) and rocket (15.3% of eggs on kale and 84.7% on rocket) showed a clear preference; in the third generation again showed a clear preference (20.4% of eggs on kale and 79.6% on rocket), as did P. xylostella reared on rocket (9.4% of eggs on kale and 90.6% on rocket); in the fourth generation one again showed a clear preference (11.5% of eggs on kale and 88.5% on rocket), as did P. xylostella reared on rocket (17.0% of eggs on kale and 83.0% on rocket). P. xylostella reared on both kale and rocket leaves thus showed a clear preference for oviposition on rocket. Therefore, planting rocket on the borders of kale crops could potentially serve as a trap by attracting ovipositing females of the pest.