How do Pieris rapae search for Brassicaceae host plants?

Pieris rapae curucivora Boisduval is a major cause of damage to important Brassicaceae vegetable crops. The method of host landing plant selection by adult females was investigated by covering cabbage (host) and lettuce (non-host) plants to block visual and/or olfactory signals, and also by using volatile extracts of both plants. Numbers of plant landings by pre-mating adult females was much lower than for post-mating females. In addition, the pre-mating females showed no clear preference for the host or non-host plants. These findings suggest that pre-mating females do not actively search for host plants. In contrast numbers of landings increased in post-mating females, immediately after mating, and there was a markedly higher preference for cabbage than lettuce. When plant odors were blocked by covering the plants with transparent or black polyethylene bags there was no difference in the landing preference of adult post-mating females, indicating that the adult females were unable to distinguish between cabbage and lettuce when their olfactory sense was blocked. The greater number of adult females landing on the plants covered with transparent polyethylene bags than those covered with black bags indicated that the females recognize the plants visually. When the transparent and black polyethylene bags had holes that enabled olfactory signals to reach the females, there was a clear preference for cabbage over lettuce. These results together with a preference for lettuce plants treated with cabbage volatile extracts than lettuce plants treated with lettuce volatile extracts indicate that the adult females detect host plants using their olfactory sense. (C) 2010 Elsevier Ltd. All rights reserved.