A bioassay to test the ovipositional responses of the generalist herbivore, Epiphyas postvittana, was developed, and various non‐chemical factors that influenced the laying, and number of eggs laid, by females were tested. In choice experiments using various models, surface texture was found to be an important factor influencing ovipositional behaviour, with females preferring to lay on smoother rather than rougher surfaces. Another surface texture feature that influenced oviposition was a raised wax ridge on a smooth surface. The wax ridge stimulated more eggs to be laid within close proximity to the ridge. Observations of females showed that the increased numbers of eggs laid on models with a wax ridge resulted not from increased landing, time spent, or numbers of eggs laid per ovipositional bout, but rather through an increased probability of ovipositing after landing on models with a wax ridge compared to models without the ridge. Spatial features of the models were also found to influence egglaying by females. Females showed a tendency to lay on the upper rather than the lower surface of models, although this appeared to depend upon how stimulatory the upper surface of the model was. Females also laid more eggs on models with a dense array of leaves than on models with a more spread‐out array.

The polyphagous leafroller moth, Epiphyas postvittana, is a pest of many fruit crops in New Zealand. Since the larva is highly mobile, host selection in this insect may involve both the adult female and the larva. In order to test the relative importance of the adult female and the neonate larva in the selection of host plants, the ovipositional preferences of females, and the preferences or acceptances of neonate larvae towards 26 plant species, consisting of 15 plants considered hosts and 11 not considered hosts, were investigated. In the ovipositional tests, the mean preferences of females for hosts and non‐hosts were very similar. In contrast, larvae showed a significantly greater mean preference or acceptance towards hosts than to non‐hosts, in both choice and no‐choice bioassays, respectively. There were highly significant correlations between the preferences and acceptances of larvae for plants in the choice and no‐choice tests. In the no‐choice tests, there was a highly significant correlation between the acceptances of neonate larvae towards plants after one and three days (i.e., acceptances changed little over time). Moreover, in these no‐choice tests, there was a significant negative correlation between larval acceptance at 1 day and larval mortality after 3 days; that is, the less acceptable a given plant at 1 day, the more likely larvae would fail to establish, feed, and survive on it by three days. Female and larval preferences towards the various plants were also negatively correlated. Together, these data suggest that the selection of a plant for the neonate larva to feed on is largely governed by the preferences of the larva, rather than by the preferences of the female. However, selection of a plant for oviposition by the female, may be important in host selection for reasons unrelated to larval preferences, for example, by encouraging dispersal, perhaps to other plant species, of the neonate larvae and thereby decreasing intersibling competition.

The effects of mating, age at mating, the presence or absence of a plant leaf, and the deprivation of a suitable ovipositional substrate during when the first ovipositional bout after mating would normally take place, on the lifetime fecundity and fertility (percentage of fertile eggs laid) of female Epiphyas postvittana were investigated. Mating had a significant effect on lifetime fecundity, with mated females laying 2.5 times more eggs than virgin females. Age at mating had a significant effect on both fecundity and fertility, both declining with increasing age when the female was mated. In the presence of a leaf of C. japonica, mated females had a greater lifetime fecundity than when no leaf was present; females in the presence of a C. japonica leaf consistently laid more eggs each day during the first 4-6 days after mating than females without a leaf. When females were deprived of a suitable ovipositional substrate, for the first 22 h after mating, they were significantly less fecund over their lifetime than were control females. Finally, in no-choice tests with three plants of different acceptability to females, the fecundity of females differed in the order C. japonica > Urtica ferox > Tibouchina multiflora. This different fecundity appeared to be inversely related to the pubescence of the leaves, suggesting that leaf texture may be a suitable antixenotic resistance factor for crops to be protected from this insect. These results suggest that strategies whereby mating is delayed or oviposition reduced within a critical period after mating, may result in significant reductions in pest populations.

No abstract

Age-related changes in the reproductive characters, proportions, durations, and temporal patterning of copulation in females, mean sex pheromone titre of females, number of eggs laid in relation to age at first mating of female, and the flight responses of male moths, were studied in adults of four species of tortricid moths. Adults of the moth, Ctenopsenstis obliquana. showed few changes with age (over the age range tested, 1-11 days after emergence): mean copulation time decreased slightly as the age of the female increased; pheromone titre increased slightly until 3 days and then declined; and the number of eggs and egg masses iaid decreased and increased, respectively, with increasing age of first mating of the female. For the sibling species, C. herana. greater proportions of females copulated with increasing age. and copulation appeared to commence over a slightly broader time period during the scotophase for older than for younger females; pheromone titre peaked at 2 days and declined with increasing age: and the flight responses of males to synthetic sex pheromone were higher for the older (5-and 7-day-old) than for the younger (1-and 3-day-old) males. Planutortrix octo adults generally showed age-related changes in the various characters. Notably, none of the 1-day-old females that copulated had a spermatophore in their bursa copulatrix after copulation, pheromone titre increased until 3 days and then declined, and fewer 1-day-old males responded to sex pheromone than older males. Adults of the moth Epiphyas postvittana tended to show peaks in the characters studied around 2-3 days after emergence. Thus, the greatest proportion of copulations occurred for 3-day-old females, copulation tended to commence later in 1-day-old females than in older females, 2-day-old females had the highest sex pheromone titre, and 3-day-old males exhibited the greatest response to sex pheromone.