Seasonal variation in larval host plants and consequences for Heliconius erato (Lepidoptera: Nymphalidae) adult body size

Abstract Adult body size, a key life history component, varies strongly within and between Heliconius erato phyllis (Lepidoptera: Nymphalidae) populations. In the present study, we determined whether seasonal variation in adult body size is temperature related and/or determined by seasonal changes of host plants (Passifloraceae) used by the larval stage. A population of H. erato phyllis located in a Eucalyptus plantation (Barba Negra Forest, Barra do Ribeiro County, Rio Grande do Sul State, Brazil) was sampled every 45 days from March 1997 to October 1998 to quantify seasonal variation in adult body size and use of larval host plants. In the laboratory, the effects of the following factors on adult body size were quantified: (i) host plant species (Passiflora misera or Passiflora suberosa); (ii) food quantity consumed by larvae (experimentally manipulated for each passion vine species); (iii) winter and summer temperatures (15 and 25°C, respectively); and (iv) the interaction between host plant species and temperature. Adults emerging during summer were larger than those emerging in other seasons. Female butterflies oviposited selectively on P. misera even when the dominant passion vine was P. suberosa. They only switched from using P. misera to P. suberosa during later autumn and winter, when P. misera vines were completely defoliated. The laboratory feeding trials with both passion vines showed a strong positive association between food quantity consumed by larvae and adult size. They also confirmed that adults are larger when their larvae are reared on P. misera than on P. suberosa. Temperature during larval development had no effect on H. erato phyllis adult size. Thus, seasonal variation of H. erato phyllis adult size in a given place is primarily determined by the availability and quality of host plant species used by the larval stage.     

Geographical variation in insect developmental period: effect of host plant phenology on the life cycle of the bruchid seed feeder shape Kytorhinus sharpianus

The voltinism of the bruchid Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) and the phenology of its host plant Sophora flavescens Aiton (Leguminosae) were observed at four latitudes: Aomori (40°46' N), Obanazawa (38°37' N), Kujiranami (37°21' N) and Mitsuma (36°05' N) in northeastern Honshu (Japan). Kytorhinus sharpianus life cycle ranged from bivoltine and partially trivoltine in the south to univoltine and partially bivoltine in the north. Sophora flavescens started growing later in spring at higher latitudes. However, the relative growth rate was higher in the north (Aomori) than in the south (Mitsuma). In parallel with this, the first-generation of adult K. sharpianus appeared later at higher latitudes. When the four local populations were reared at 24 °C, L16:D8 and 65% r.h., males developed faster than females. The mean developmental time showed a saw-toothed latitudinal cline. The reversion in the latitudinal trend of variation corresponded to the change in the major type of life cycles from univoltine to bivoltine. Two heat units throughout the year and post-fruiting period were calculated as the sums of degree-days above the developmental threshold (12 °C) of K. sharpianus. Both heat units decreased in parallel with each other with increasing latitude. The greater growth rate of hosts in the northern population compensated for the smaller heat units. In addition, when the heat units were divided by the degree-days needed to complete development, the numerical value was the approximate number of generations observed in each locality.     

Temporal host plant use in three polyphagous Heliothinae,with special reference to Helicoverpa punctigera (Wallengren) (Noctuidae: Lepidoptera)

Abstract Potential host plants of the polyphagous lepidopteran Helicoverpa punctigera (Wallengren) were surveyed in two ways. A broad survey, conducted in southern Queensland and northern New South Wales, indicated that H. punctigera larvae were present on relatively few plant species. A detailed survey of host plant use in a non-cropping area in which H. punctigera was numerous demonstrated restricted host plant use by this species. The density of H. punctigera on its principal host in the area, the indigenous daisy Ixiolaena brevicompta F. Muell., was much higher (as measured per unit of time searched) than on other plant species available. Also, I. brevicompta was used regularly by H. punctigera after rainfall events. Ixiolaena brevicompta represents a new host record and on the basis of the pattern of its use by H. punctigera should be considered a ‘primary host plant’ of this noctuid. In cropping areas sampled, usually more than one plant species hosted H. punctigera regularly and in large numbers. Usually a crop species was included (e.g. cotton and chick pea). Alternative hosts in cropping areas were Sonchus oleraceus L. (sowthistle) and possibly the native legume Sesbania cannabina (Retz.) Poiret. Our results imply that the polyphagy of H. punctigera is probably not as extensive as previously claimed. The criteria for inclusion of a plant species as a primary host for H. punctigera need to include the regularity of use of that species and the relative abundance of eggs and larvae on it. We suggest that an understanding of the host-searching mechanism of this species will be best achieved through study of the interaction of H. punctigera with its indigenous primary hosts. The surveys also yielded information on host plants of two other heliothine noctuids, H. armigera (Hübner) and Australothis rubrescens (Walker), and this is also presented.     

Genetic architecture of host use in a widely distributed, polyphagous butterfly (Lepidoptera: Papilionidae): adaptive inferences based on comparison of spatio-temporal populations

Genetic variance-covariance structure of larval performance within and among spatio-temporal populations of the widely distributed, polyphagous tiger swallowtail butterfly, Papilio glaucus , is described. Performance traits were assessed for full-sibling families on three host species: Liriodendron tulipifera, Magnolia virginiana and Prunus serotina . Mean performance varied across hosts, indicating these hosts present unique developmental environments. Although full-sibling families significantly differed in plasticity of across-hosts response in three of the five spatio-temporal populations, additive genetic variation was mostly associated with P. serotina or pupal mass. The relative lack of heritable variation in rate and length of larval development on L. tulipifera and M. virginiana was consistent with an earlier study that established host-associated geographic differentiation of P. glaucus populations. Performance appeared relatively independent across hosts and thus genetic constraints cannot be casually invoked to explain persistence of local adaptation and host specialization in the face of extensive gene flow. I promote the hypothesis that gene flow among geographically distant populations is relatively restricted and that previously established, allozyme-based estimates of panmixia are confounded by effects of Pleistocene glaciations. Significant heterogeneity of variance-covariance structure among spatio-temporal P. glaucus populations supports an interpretation of restricted gene flow and relative evolutionary independence. Despite low precision of estimates of genetic parameters, local variance-covariance structure was remarkably consistent with expectations given the presumed evolutionary history of regional populations.