OVIPOSITION RESPONSES OF 4 CHORISTONEURA (LEPIDOPTERA, TORTRICIDAE) SPECIES TO CHEMICAL AND PHYSICAL STIMULI ASSOCIATED WITH HOST AND NONHOST FOLIAGE

Oviposition responses of three conifer-feeding Choristoneura species (C. fumiferana [Clemens], C. occidentalis Freeman, and C. pinus Freeman) and one deciduous-feeding Choristoneura species (C. conflictana [Walker]) to host cues were studied in arenas containing filter paper as the main oviposition substrate. Generally, all species laid more eggs on filter paper treated with hexane extracts of host foliage than with hexane alone, but the number of eggs deposited per egg mass was not significantly different. For the conifer-feeding species, the stimulating effect of host chemicals was independent of physical stimuli associated with host foliage. Oviposition by C. fumiferana females was also stimulated by extracts of nonhost conifers and trembling aspen, a deciduous species. C. pinus and C. occidentalis were stimulated by some nonhost coniferous extracts but not by extracts of trembling aspen. C. conflictana females were not stimulated by coniferous extracts. Oviposition responses to host physical stimuli were evaluated with artificial (plastic) coniferous twigs with needle lengths of 1.25, 2.5, or 3.5 cm. In most cases, females of the conifer-feeding species preferred the artificial twigs to the filter-paper substrate. Needle lengths of the preferred twigs corresponded to the range of needle lengths found on the hosts of each species. C. conflictana oviposited exclusively on the filter-paper substrate, which corresponds to the flat surface of aspen leaves. When given a choice between ovipositing on surrogate twigs or on filter paper treated with host extract, C. fumiferana females preferred the surrogate twigs, suggesting that the effects of tactile cues predominated over close-range chemical cues.