J. Mark Scriber

Seasonal patterns in the phytochemistry of three Populus species

Abstract We monitored seasonal changes in the leaf quality characteristics of three native species of Populus during 1986. Leaf water and nitrogen contents of each species declined during the growing season. The phenolic glycosides salicin, salicortin, tremuloidin and tremulacin occurred in Populus tremuloides and P. gradidentata ; all but tremulacin occurred in P. deltoides . Levels of salicin and tremuloidin were low throughout the growing season in all three species. Among the tree species, concentrations of salicortin and tremulacin were highest, and exhibited the least among-plant variation and strongest seasonal declines in P. grandidentata . Levels of salicortin and tremulacin were intermediate in P.tremuloides , varied greatly among individual trees, and did not significantly decrease during the growing season. Levels of salicortin were relatively low, varied considerably among trees, and did not decline seasonally in P. deltoides . Spatial and temporal variation in these constituents produces plant parts, individuals and species with differential resistance to insect herbivores.

THE BEHAVIOR AND NUTRITIONAL PHYSIOLOGY OF SOUTHERN ARMYWORM LARVAE AS A FUNCTION OF PLANT SPECIES CONSUMED IN EARLIER INSTARS

Few differences were observed in biomass digestibility (AD) as related to previous instar feeding experience of the polyphagous southern armyworm, Spodoptera eridania, on leaves of paper birch, Betula papyrifera; mountain ash, Sorbus americana; and black cherry, Prunus serotina. However, significant improvements of nitrogen utilization efficiencies (NUEs) were observed with previous feeding experience for larvae fed paper birch and mountain ash. For larvae fed black cherry, the assimilation efficiency of biomass and nitrogen utilization efficiency in all treatments were greater than for paper birch and mountain ash, however, final instar growth rates were lowest. In addition, pupae for all replicates of certain cherry‐fed treatments were deformed and died. This physiological stress was manifested in the pre‐pupal stage as an elongated, bloated appearance, yet the nutritional indices for biomass or nitrogen budgets provided no premonition of any such irregularity. Possible biochemical mechanisms which might be involved (e.g., induction of digestive enzymes and/or detoxication enzymes and their interaction with hormone systems) remain to be analyzed.

Sequential diets, metabolic costs, and growth of Spodoptera eridania (Lepidoptera: Noctuidae) feeding upon dill, lima bean, and cabbage

SummaryThis 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.

Characterization of phenolic glycosides from quaking aspen

Abstract A crude extract quaking aspen Populus tremuloides exhibits differential bioactivity against subspecies of the eastern tiger swallowtail Papilio glaucus. Components were isolated and identified on the basis of NMR and IR spectra, and chemical methods, as the phenolic glycosides salicin, salicortin, tremuloidin, and tremulacin.

Effects of hydrolyzable and condensed tannin on growth and development of two species of polyphagous lepidoptera: Spodoptera eridania and Callosamia promethea

SummaryThe 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 (RGRs) of Spodoptera eridania Cram. were due to the suppressed relative consumption rates (RCRs) and decreased conversion efficiencies (ECDs) 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.

Larval developmental rates of three putative subspecies of tiger swallowtail butterflies, Papilio glaucus, and their hybrids in relation to temperature

SummaryThe 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).

HOST‐PLANT UTILIZATION BY HYALOPHORA CECROPIA AS AFFECTED BY PRIOR FEEDING EXPERIENCE

Hyalophora cecropia larvae were switched at the beginning of the penultimate stadium from one host‐plant species to another to test whether prior feeding on one host‐species alters the ability of larvae to utilize a new host‐species. Larvae accepted the new hosts, survived and grew normally. Although there were no dramatic effects on larvae from being switched from one host‐species to another, several subtle effects on subsequent food consumption and food utilization efficiencies were noted.

Neonate larval survival of European corn borers, Ostrinia nubilalis, on high and low dimboa genotypes of maize: Effects of light intensity and degree of insect inbreeding

Abstract Neonate (newly eclosed) larvae of the European corn borer, Ostrinia nubilasis Hubner, were studied in regard to their feeding responses on 9 different genotypes of field corn, Zea mays L., which were grown under two different light intensity regimes (high and low). Larval feeding rates were greatest on the DIMBOA A-less mutant (lacking the cyclic hydroxamate) and the low-DIMBOA inbred WF9 and lowest for the high-DIMBOA U.S. inbred B49 and the tropical genotype, San Juan × Antigua, under both light regimes. Significantly greater feeding rates were observed under the low-light-intensity compared to the high-light-intensity regime for all 4 Caribbean genotypes tested and WF9. The biochemical mechanism responsible for the reduced consumption rates of larvae on these varieties under the high-light regime is unlikely to be DIMBOA (2,4 dihydroxy-7-methoxy-1,4 benzoxazine-3-one) since its concentrations in leaves of the high-intensity regime were lower in all cases in which significant differences were observed. Leaf nitrogen concentrations were greater in the low-intensity regime and may be at least partially responsible for the greater feeding rates of larvae in this regime. Another study was conducted to determine the relative magnitude of insect inbreeding on larval consumption rates using two corn genotypes from the “susceptible” (WF9 and DIMBO A-less) and two from the “resistant” (B49 and San JUan) ends of the spectrum. Laboratory-reared European corn borer larvae of two ages (1 year = 10 generations and 6 years = 52 generations) exhibited no significant differences in 72-h survival nor 72-h consumption rates on any particular corn genotype. This suggests that insect inbreeding through extended laboratory rearing does not necessarily render insects ineffective as bioassay organisms (at least during this critical neonate stage).

THE RELATIONSHIP BETWEEN RESTRICTION OF HOST PLANT CONSUMPTION, AND POST-INGESTIVE UTILIZATION OF BIOMASS AND NITROGEN IN HYALOPHORA CECROPIA

The growth rate and food utilization efficiencies of penultimate instar Hyalophora cecropia are affected by restrictive feeding regimens which simulate the case of behaviorally induced larvae encountering a new food, and which entail an initial period of reduced consumption. Our data suggest that any effects on post‐ingestive utilization of a new host plant or diet onto which larvae have been switched may not only be the result of a lack of physiological adaptation to the new food, but may also be caused by deterrent effects (e.g. when behaviorally induced larvae encounter and initially reject a new food).

Allelochemicals and Alimentary Ecology: Heterosis in a Hybrid Zone?

Proper interpretation of differential survival, growth, and reproduction of phytophagous insects on various host plants depends on our ability to discriminate between a large number of plant characteristics, insect characteristics, and environmental factors that influence the preingestive acceptability (Ahmad, 1983; Miller and Strickler, 1984) and post-ingestive suitability of food plants (Scriber and Slansky, 1981; Berenbaum, 1985, 1986). Research over the last several years has addressed these various concerns in considerable detail for leaf-chewing Lepidoptera and has made it more feasible to differentiate between environmental and/or food plant effects and heritable physiological adaptations (Scriber, 1983, 1984a; Rausher, 1984; Whitham et al., 1984; Slansky and Scriber, 1985; Mattson and Scriber, 1985).