Response of a Host‐Specific Herbivore to Resource Density, Relative Abundance, and Phenology

Abstract

Ovipositing females of the host—specific herbivorous moth Frumenta nundinella Zeller discriminated among horsenettle (Solanum carolinense L.) plants in the laboratory and at five field populations. In laboratory experiments, the number of larvae that developed in high—density plant groups was not significnatly greater than the number that developed in low—density groups. Consequently, individual plants in low—density groups were disproportionately affected; twice as many larvae developed on them as on individual plants in high—density groups. Moths also discriminated between groups of pure horsenettle (high relative abundance) and groups of horsenettle plus another naturally co—occurring species (low relative abundance). Individual plants in high relative abundance groups had a tenfold greater infestation than did plants in low relative abundance groups. Natural horsenettle populations varied in density, relative abundance, plant size, and fruit production. Plant size, fruit production, and population density were all positively correlated, so the populations with the greatest density had the largest plants, which produced the most fruits. Despite differences in these plant parameters among sites, the extent of infestation differed little, except for one site that lacked parasitoids that attack F. nundinella. Infestation within field sites was heterogeneous among plants. Virtually all large plants (those with @> 15 fruits), but only about half the small plants (those with < 15 fruits), became infested (one or more infested fruit per plant). However, a greater proportion of the fruit crop was infested on small plants than on large plants. Large plants remained in flower an average 2.5 wk longer than did small plants, so a smaller proportion of their flowers was available during the short period of high oviposition risk. Because of the short oviposition period, plants that flowered earlier or later than the mean flowering time of their populations appeared to have lower infestations than did plants that flowered close to the population means.

Insetos galhadores associados a duas espécies de plantas invasoras de áreas urbanas e peri-urbanas

“…A abundância do recurso planta sofre grandes variações em centros urbanos, e a limitação na disponibilidade de habitats pode resultar em densidade e/ou abundância relativa diferencial de plantas hospedeiras de insetos galhadores (em comparação a não-hospedeiras), diminuindo assim as chances de espécies adicionais destes insetos ocorrerem (ver Root 1973;Solomon 1981, Kennedy & Southwood 1984. Além disso, a "idade" do recurso planta, é possivelmente um dos fatores mais importantes a atuar nos padrões já observados.…”

Conspecific mimics and low host plant availability reduce egg laying by Heliconius erato phyllis (Fabricius) (Lepidoptera, Nymphalidae)

“…Parasitoid wasps, for example, alter their host-searching behavior, daily oviposition rates and offspring sex ratio, among other reproductive parameters, according to variation in host availability (see VINSON 1981;CHARNOV 1982;WELLINGS 1991). Some butterfly species are also known to alter use of preferred host-plants as a function of host-plant abundance (SOLOMON 1981;COURTNEY & FORSBERG 1988). Little is known, however, about the potential effects of variation in abundance of a given host-plant species upon other butterfly reproductive behavior, such as in relation to searching, choice and acceptance of host-plants for oviposition.…”

Size of and damage on shoots of Passiflora suberosa (Passifloraceae) influence oviposition site selection of Heliconius erato phyllis (Fabricius) (Lepidoptera, Nymphalidae)

“…It has been demonstrated that insect host plant use is influenced by at least three other major component, besides host suitability: insect host finding behavior and preference, and density of potential hosts (JAENIKE 1978(JAENIKE , 1990SOLOMON 1981;WIKLUND 1981;SINGER 1983SINGER , 1986COURTNEY & FORSBERG 1988;JONES 1991). It is showed experimentally in this study that H. erato phyllis lays eggs only on the terminal portion of P. suberosa shoots, and that intraspecific variation in host plant attributes, such as damage and size of shoots, influences host selection for oviposition.…”

“…Thus, it is suspected that use of P. suberosa over other more preferred or more suitable host plants for larvae (e.g. P. rnisera Humboldt, Bonpland & Kunth and P. elegans Masters) may be mediated at local basis by variation intrinsic to these host plant populations, such as their relative availability and phenology (see CATES 1980;SOLOMON 1981;COURTNEY & FORSBERG 1988), or due to variation in preference of females within populations (see WIKLUND 1981;PAPAJ & RAUSHER 1983;ARAUJO 1987;JONES 1991). In the present study, it is addressed this question by determining H. erato phyllis ovipositional response to variation in size of and damage to host plants, based upon samples taken in a natural population of P. suberosa and on ovipositional choice experiments carried out under insectary conditions.…”