Entomologia Experimentaliset Applicata 74: 71-82, 1995. 71 (~) 1995 Kluwer AcademicPublishers. Printed in Belgium. Larval diet influence on oviposition behaviour in Spodoptera littoralis P. Anderson 1, M. Hilker 2 & J. LOfqvist 3 I University of Lund, Department of Ecology, Ecology Building, S-223 62 Lund, Sweden; 2University of Bayreuth, Institute of Animal Ecology II, P.O. Box 101251, D-95440 Bayreuth, Germany; 3Swedish University of Agriculture, Department of Plant Protection Sciences, Ecology Building, S-223 62 Lund, Sweden Accepted:May 26, 1994 Key words: Lepidoptera, Spodoptera littoralis, oviposition, deterrents, feeding, larval experience, induction, selection Abstract Females of Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae) with different feeding experiences during their larval development were tested for their ovipositional response to methanol extracts of larval frass and semi- synthetic diets. The effect of the following frass, diet and diet component extracts was tested: (a) frass from S. littoralis or Agrotis segetum larvae fed on a potato-based diet; (b) frass from S. littoralis larvae fed on a wheat germ-based diet; (c) potato and wheat germ-based diets; and (d) potatoes and wheat germ. Ovipositing females without prior experience of the potato diet were deterred by extracts of: (1) larval frass from either species fed on potato diet; (2) the potato-based diet; (3) potato. Also females with experience of the potato diet during only a part of their larval development were deterred from oviposition by frass of larvae reared on the potato diet and by the diet itself. However, for females reared on the potato diet for their entire larval development, oviposition was no longer deterred by either of the three extracts listed above. Extracts of: (1) frass from larvae of either species reared on wheat germ diet: (2) the wheat germ diet; or (3) wheat germ did not significantly affect oviposition. Females with ablated antennae were still deterred by frass extracts from larvae fed on potato diet, when they had been reared on the wheat germ diet. In feeding experiments, larvae of larval stage one and of larval stage three-four reared on either of the two diets preferred to feed on the wheat germ diet. However, the preference was significantly stronger for larvae with no prior contact with the potato diet. The effect of larval experience on the loss of oviposition-deterring activity by extracts of larval frass, diets and diet components is discussed in view of induction and selection. Introduction Choice of oviposition site in phytophagous insects is known to be directed by visual and/or chemi- cal cues. The acceptance of an oviposition site by olfactory and/or contact chemoreceptive recognition may be governed either by stimulating signals or by the absence of deterrents (e.g., Renwick & Radke, 1988). Oviposition deterrence has been studied in numer- ous phytophagous insects. Extracts of non-hosts and macerated host plant material, larval and adult frass, as well as conspecific eggs are known to act as ovipo- sition deterrents (Rothschild & Schoonhoven, 1977; Prokopy, 1981; Renwick & Radke, 1985). In sev- eral noctuid species larval frass deters oviposition in conspecific females (Renwick & Radke, 1980; Hilker, 1985). For example, the Egyptian cotton leaf worm, Spodoptera littoralis, is deterred from oviposition by frass from conspecific larvae feeding on cotton leaves (Hilker, 1985; Hilker & Klein, 1989). The chemical identity of oviposition deterrents is known only in a few species. The oviposition deterring compounds of larval frass have hitherto been identified only from S. littoralis (Klein et al., 1990; Anderson et al., 1993). Also semi-synthetic diets and frass of larvae feeding on such a diet may act as oviposition deterrents, as has been demonstrated in the noctuid moths S. frugiperda (Williams et al., 1986) and Agro- tis segetum (Anderson, unpubl.). In the S. frugiperda