ALBERT

Notes: Summary Hyalophora cecropia larvae were reared on leaves of wild cherry,Prunus serotina, which contained variable amounts of leaf water but otherwise did not differ in fiber, total nitrogen, and caloric content. Larvae which were fed leaves low in leaf water grew more slowly and were less efficient at utilizing plant biomass, energy, and nitrogen than those larvae fed leaves which were fully supplemented with water. Experiments were performed using excised leaves under different regimes of relative humidity and leaf water supplementation in climatic control chambers maintained at identical temperatures and photoperiod. Foodplant biomass utilization efficiencies were severely reduced by decreasing amounts of leaf water. Growth rates were halved and the efficiency of conversion of assimilated dry matter into larval biomass was reduced from 82% in the treatment with fully supplemented leaves to 34% in the driest treatment. The nitrogen utilization efficiency (N.U.E.) was reduced from 75–80% to 48%, and the relative accumulation rate of nitrogen (N.A.R.) was suppressed nearly 2-fold for larvae on low-water leaves. Relative maintenance costs (calories expended in respiration/mg tissue/day) of larvae were nearly five times higher on dry leaves than on fully supplemented leaves. Larvae on leaves which were low in water content were themselves more desiccated, and metabolized greater portions of assimilated energy, perhaps in an attempt to supplement body water with metabolic water derived from respiration. The larval rates of consumption of biomass, energy, and nitrogen were the same for all treatments, indicating that leaf water affected larval growth primarily by restricting the efficiency of utilizing these nutrients. Where water was limiting (as in tree leaves), an increased consumption rate did not appear to be a successful means of increasing growth rates. There were daily and seasonal differences in leaf water content between different trees of the same species. Although absolute differences in leaf water exist between different trees and between young and old (fully expanded) leaves of a single tree, these differences are proportional and parallel each other through daily and seasonal cycles. In spite of evolutionary adaptations of herbivores to acquire adequate water and avoid desiccation, the leaf water content naturally encountered by cecropia larvae on cherry leaves may limit their growth, especially if the R.H. is low.

Notes: Summary The eastern tiger swallowtail butterfly,Papilio glaucus, is the most polyphagous of all Papilionidae species. While diverse larval detoxication abilities are known for bothPapilio glaucus and the closely relatedP. canadensis, the factors affecting oviposition preferences in adult females are unknown. These congeneric species were studied to determine the extent of oviposition mistakes on toxic plants. We were also interested in comparing the geographic patterns of variation in oviposition preferences and the genetic basis of these differences. We conducted oviposition three-choice studies with the Canadian tiger swallowtail butterfly,Papilio canadensis, and the Eastern tiger swallowtail,Papilio glaucus, giving them the choice of (1) tuliptree,Liriodendron tulipifera, which is toxic to virtually all populations (P. canadensis) north of the Great Lakes Region of North America, (2) quaking aspen,Populus tremuloides, which is toxic to essentially all populations (P. glaucus) south of the Great Lakes, and (3) black cherry,Prunus serotina, which is an excellent foodplant for all members of thePapilio glaucus group, but which does not occur at latitudinal extremes of North America (in Alaska and most of Canada or the southern half of Florida). Handpaired interspecific hybrids were tested under the same experimental design to evaluate the possibility of sexlinked oviposition behavior. There was considerable variability in the choice of plants by individual butterflies, but a general trend suggesting that the females of each species had a lower preference for the plant toxic to their larvae. More than 6000 oviposition bouts were counted from 37 differentp. canadensis and 54p. glaucus females along a latitudinal transect of approximately 5000 km from Alaska south through the Great Lakes hybrid zone region to southern Florida. While not exceptionally high anywhere, the preference for aspen (Salicaceae) declined precipitously in central Michigan (45° N latitude) and remained very low (5–12%) in all locations southward to Florida, whereas we observed a reciprocal trend in preference for tuliptree (Magnoliaceae) which was greatest in Florida (87% of all eggs) and steadily declined northward across the Great Lakes region. Cherry was selected in these 3-choice tests at a relatively consistent and low frequency at all latitudes. Fixed allele differences in sex-linked (LDH and PGD) and autosomal (HK) electromorphs are known forP. glaucus andP. canadensis. Our electrophoretic data suggest that the preference of an individual female for aspen is not simply a characteristic of the northern species (P. canadensis) but can occur inP. glaucus females. The reciprocal situation is also evident in Northern Michigan and Wisconsin females (scored electrophoretically and morphologically asP. canadensis) which sometimes exhibit a clear preference for the toxic tuliptree. In fact, Alaskan populations ofP. canadensis chose tuliptree for about 52% of their eggs, even though none of their offspring has ever survived on this plant species in laboratory studies. We conclude that even with distinctive latitudinal trends, a considerable amount of local variation in relative oviposition preference exists among individuals of these polyphagous species. BothP. glaucus andP. canadensis will lay eggs on toxic plants. It appears that factors selecting against oviposition on toxic tuliptrees have been minimal (relative to other factors) in Alaska and somewhat stronger in the Great Lakes hybrid zone. It is in this zone of contact with tuliptree where selection against theP. canadensis populations ovipositing on tuliptree may be strong due to high larval mortality when such natural “mistakes” are made. We do not know whether behavioral preference changes evolutionarily preceded or followed the development of specific physiological detoxication abilities for tuliptree or quaking aspen. However, for bothP. canadensis andP. glaucus the occurrence of “oviposition mistakes” on toxic plants by adults extends geographically well beyond the larval detoxication abilities of their offspring. Hybrid female offspring of pairings with Michigancanadensis females andglaucus males show distinct preferences for tuliptree, suggesting that oviposition may be controlled by a factor (or factors) on the sex chromosome. Unfortunately we were unable to obtain reciprocal hybrids to evaluate the possibility of sex-linked aspen preference.

Notes: Summary The eastern tiger swallowtail butterfly, Papilio glaucus L. has been presumed to be comprised of three parapatric subspecies (P. g. canadensis R & J, across Canada and the northern U.S.; P. g. glaucus L., in the eastern half of the U.S.; and P. g. australis Maynard, in Florida). Populations from 27° north latitude in Florida to 50° north latitude in Manitoba, Canada and from 75° west longitude in Pennsylvania to 96° west longitide in Canada were tested by laboratory larval feeding studies at various constant temperatures ranging from 16°–28° C. These data indicate that populations of Papilio glaucus show generally similar developmental responses to temperature, regardless of their geographic origin. Limited differences do exist between some populations studied, involving such traits as upper threshold temperature and differences between individual developmental rate curves. No consistent differences were noted between the three putative subspecies in their developmental response under these experimental conditions. In Wisconsin, the twenty year average of total season degree day accumulations above a base temperature (developmental threshold) of 10° C delineates a relatively narrow geographical region across the center of the state for which the bivoltine potential reaches its northernmost limits. This zone also closely corresponds to the southernmost limit of the P. g. canadensis subspecies (generally believed to be obligately univoltine).

Notes: Summary The effects of tannins on survival, growth, and digestion were compared in two polyphagous species of Lepidoptera (one, the southern armyworm, a forb-feeder; and the other, the promethea silkmoth, a tree-feeder). Two different types of tannins (hydrolyzable and condensed) were incorporated into artificial basal diets in order to determine whether or not differential survival and growth would result between the forb feeder, which normally does not encounter tannins in its natural diet, and the tree-feeder, whose host species include many tanniniferous plants from several different families. Neonate larvae of the forb-feeding armyworms exhibited significantly suppressed 10-day growth rates at all tannin concentrations tested (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0% of wet weight) for both the hydrolyzable and the condensed tannin compared to the control diet, however no dose-effect was detectable. In contrast, there were no detectable differences in neonate survival or growth through the first 10 days for the tree-feeding promethea silkmoth larvae fed diets with either tannic acid or quebracho tree condensed tannin. In order to determine the physiological mechanisms of action of these tannins against armyworms, we conducted detailed physiological bioassays of biomass and nitrogen utilization by penultimate instar larvae. Standard gravimetric feeding studies with both tannic acid and the quebracho tree condensed tannin demonstrated that reduced relative growth rates (RGR's) of Spodoptera eridania Cram. were due to the suppressed relative consumption rates (RCR's) and decreased conversion efficiencies (ECD's) rather than due to digestibility-reduction (as reflected by approximate digestibility, AD). As with the neonate larval growth rate suppression, there were no detectable dose responses at the different concentrations of tannic acid (0.25, 0.50, 0.75, 1.00, 2.50, and 5.0 percent) and condensed tannins from quebracho (0.25, 0.50, 0.75, 1.0, and 2.5 percent) in our penultimate instar studies.

Notes: Summary As a species, the promethea silkmoth, Callosamia promethea (Saturniidae: Lepidoptera) exhibits a wide host range on 6–10 families of plants, although specific populations are known to have local foodplant favorites. We tested the hypothesis that larvae from a particular host plant lineage would show physiological adaptations to this host compared with larvae from other host plant lineages. We found no evidence that larval survival and growth was any better for larvae fed the natural plant of the parental population than for larvae from other host lineages. These natural host lineages include: black cherry (Prunus serotina Ehrh.), tuliptree (Liriodendron tulipifera L.), sassafras (Sassafras albidum (Nutt.) Nees) and spicebush (Lindera benzoin (L.) Blume). The only apparent manifestation of physiological specialization was the inability of tuliptree lineages of C. promethea to survive on paper birch (Betula papyrifera Marsh), although this may reflect the geographical pattern of adaptation to birch, rather than a negative correlation with adaptation to tuliptree. These results suggest that for C. promethea larvae, growth performance and survival is primarily influenced by plant nutritional quality, rather than physiological adaptations to the locally preferred host plant.

Notes: Summary Papilio glaucus subspecies, hybrids and backcrosses exhibit greatly different abilities to use quaking aspen (Populus tremuloides) and other members of the Salicaceae as host plants. This study was conducted to test the hypotheses that phenolic glycosides account for the differences in larval performance, and that differential performance is correlated with differential larval esterase activities. To test the hypotheses we conducted first instar survival trials and fourth (penultimate) instar feeding trials with tremulacin, a phenolic glycoside. We also conducted assays of β-glucosidase, esterase, and glutathione transferase activities, using midgut enzyme preparations from fifth instars. First instar survival on the tremulacin treated diet generally improved with a higher proportion of Papilio glaucus canadensis genes in the genotype, although survival in one backcross treatment was surprisingly low. Penultimate instars of P.g. glaucus and P.g. australis fed tremulacin treated black cherry leaves experienced a severe reduction in growth rate relative to larvae fed control leaves. This seriously suppressed growth was partially due to reduced consumption rates and reduced conversion efficiencies, however, approximate digestibility was not affected. In contrast, P. g. canadensis and hybrids showed no differences in growth rates between tremulacin treated and control leaves. Reciprocal backcrosses of hybrids with P. g. glaucus resulted in slightly suppressed growth on treated versus control leaves. The results suggest that after a certain threshold, increased proportions of P. g. glaucus genes resulted in poorer growth performance with tremulacin in the diet. Soluble esterase activities generally increased with the proportion of Papilio glaucus canadensis genes in the genotype, and paralleled overall trends in larval survival and feeding performance. We conclude that phenolic glycosides such as tremulacin are responsible for differential performance of Papilio glaucus subspecies, hybrids and backcrosses fed plants in the Salicaceae, and that detoxification of phenolic glycosides by midgut esterase explains why some Papilio glaucus genotypes can effectively utilize these plants.

Notes: Abstract. The gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis, overlap geographically as well as in their host ranges. Adult female swallowtails are incapable of distinguishing between damaged and undamaged leaves, and the opportunities for competition between these two species are numerous. We designed field and laboratory experiments to look for evidence of indirect competition between P. canadensis and L. dispar larvae. Swallowtail caterpillars were reared in the laboratory on leaves from gypsy-moth-defoliated and undefoliated trees to explore host-plant effects. We tested for pathogen-mediated interactions by rearing swallowtail larvae on both sterilized and unsterilized leaves from defoliated and undefoliated sources. In addition, we measured the effects of known gypsy moth pathogens, as well as gypsy moth body fluids, on the growth and survival of swallowtail larvae. Field experiments were designed to detect the presence of parasitoid-mediated competition, as well: we recorded parasitism of swallowtail caterpillars placed in the field either where there were no gypsy moth larvae present, or where we had artificially created dense gypsy moth populations. We found evidence that swallowtails were negatively affected by gypsy moths in several ways: defoliation by gypsy moths depressed swallowtail growth rate and survival, whether leaves were sterilized or not; sterilization significantly reduced the effect of defoliation, and gypsy moth body fluids proved lethal; and swallowtail caterpillars suffered significantly increased rates of parasitism when they were placed in the field near gypsy moth infestations.

Notes: Summary. The ability to perceive and respond to phytochemicals that reliably indicate poor suitability of a potential host plant confers a selective advantage to ovipositing female swallowtail butterflies. Papilio glaucus females are generalists that nonetheless do not oviposit on red bay (Persea borbonia: Lauraceae). Red bay is toxic to P. glaucus neonates but is commonly found in habitats alongside their principal host plant, Magnolia virginiana, in central Florida. The hypothesis that deterrent compounds present in the leaves of red bay mediate its rejection by P. glaucus was evaluated in our study. Florida populations of P. glaucus did not oviposit on host leaves sprayed with the methanol extract of red bay foliage, although they accepted solvent-treated and untreated tulip tree leaves in 3 choice bioassays. Additionally, tulip tree leaves sprayed with methanolic extracts of red bay also deterred oviposition by P. glaucus females from Ohio, Kentucky and Pennsylvania, although these populations do not naturally encounter red bay. Clearly, deterrent compounds found within this non-host are the basis of its rejection by populations of P. glaucus and such recognition is fundamental to the species, not just a reflection of local adaptations.

Notes: Summary This study illustrates the diversity of feeding responses of individually polyphagous southern armyworms, Spodoptera eridania, to plants with differing allelochemics. In spite of the near optimal leaf water and nitrogen contents of the young foliage, it is apparent that vastly different larval growth performance results from dill, lima bean, and cabbage. Cabbage is the poorest food (as measured by larval growth rates and metabolic costs of processing the plant biomass). Unlike the case with certain other plant species or cultivars that are costly to process, with cabbage, S. eridania does not compensate for low efficiencies (E.C.D.'s) with increased consumption rates (R.C.R.'s). Biochemical or physiological reasons for this inability are unknown. A sequence of foods (changed each 18–24 h) apparently did not add sufficient stress upon the MFO system to be detected in the respiratory expenditures of S. eridania larvae, in spite of the fact that dill is known to contain insecticidal and synergistic chemicals (Lichtenstein et al. 1974). The larval growth performances and metabolic expenditures in these sequences were intermediate between the best food (dill) and the worse (cabbage). Significant differences were observed however between the sequential switching sequences, perhaps indicating that particular periods during the instar are especially more sensitive to certain allelochemics. Actual respiratory costs of the lima bean-cabbage-dill (i.e. B-C-D) sequence were 40–50% higher than observed for the other two sequences and more than 50% higher than the theoretical metabolic costs based on the proportions actually eaten and known costs associated with each food. This study and a related one (Scriber 1981a) illustrate how consumption rates, feeding efficiences, and larval growth of Spodoptera eridania are not species, population, or even individual characteristics, (cf. Fox and Morrow 1981), but instead depend largely upon variations in plant allelochemics and plant nutritional quality (Wolfson 1978; Scriber, 1981 b; Scriber and Slansky 1981). More significantly they illustrate that the food consumed in earlier instars (Scriber 1981 a) as well as the food consumed earlier in an instar can be a major influence upon the observed armyworm growth performances under a given set of environmental conditions.