Peter ANDERSON-1, Hans ALBORN-2 & Jan LÖFQVIST-1
1- Swedish University of Agricultural Sciences, Department of Chemical Ecology,
Box 44, S-230 53 Alnarp, Sweden
2- Gothenburg University, Department of Chemical Ecology, Carl Skottbergs gate
22, 413 19 Göterborg, Sweden
Several plants have been shown to emit characteristic odours in response to herbivore damage. This type of induced volatile odour could help to guide phytophagous insects to a host plant habitat. However, parasitic wasps also have been shown to be attracted to induced plants (Turlings et al. 1991). Thus, ovipositing on an earlier damaged plant increases the risk for the offspring of the moth to be parasitized. Furthermore, plants with prior herbivore damage have been shown to be of lower value as food for lepidoptera larvae (Alborn et al. 1996). Therefore it might be beneficial for the female moth to avoid earlier damaged plant rather than being attracted to them.
The oviposition preference of female S. littoralis moths was investigated in choice tests between induced and non-induced cotton plants. Plants in the sixleaf stage were induced by caging a 3rd instar conspecific larva on a lower leaf. The larva was removed when it had consumed approximately 20-30 % of the leaf's area.
Ovipositing females preferred to lay their eggs on the plants which had been fed upon by larvae. Up to 75 % of the total number of eggs laid on the two plants were laid on the plant with induced defence. Reasons for the female choice are discussed.
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