Foliage Consumption Research Articles

PHYSIOLOGICAL ADAPTATION TO TEMPORAL VARIATION IN CONIFER FOLIAGE BY A CATERPILLAR

AbstractLarvae of the hemlock looper, Lambdina fiscellaria fiscellaria (Guenée) (Lepidoptere: Geometridae), consume both new and old foliage within the crowns of their host, balsam fir, Abies balsamea (L.) Miller (Pinaceae), despite the poor nutritional quality generally ascribed to old tissues. Laboratory studies evaluated whether the consumption of old foliage by hemlock looper larvae could be an adaptation to the relative paucity of new versus old foliage, and to the limited temporal window during which young foliage remains high in nutritional quality. Access to new foliage was critical to hemlock looper survival; 55% of larvae fed an exclusive diet of new foliage survived, whereas only 5% and 0% of larvae fed exclusively 1-or 2-year-old foliage survived, respectively. Moreover, larvae reared on branches in synchrony with bud flush were more than twice as likely to survive than those whose emergence was delayed by 2 weeks. Despite the reliance by the hemlock looper upon new foliage for survival, larvae given access to both new and old foliage survived better and were heavier than those restricted to new foliage. By incorporating older foliage into their diet, the hemlock looper can circumvent the limited availability of new foliage, thereby gaining access to more abundant tissues.

Consumo foliar de cultivares de arroz irrigado por Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

O consumo médio de área foliar da lagarta-da-folha Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), em função do sexo e do ínstar, foi determinado em condições de laboratório em folhas de arroz, das cultivares BR-IRGA 410 e Embrapa 6-CHUÍ. Não houve diferença significativa no consumo total de área foliar das duas cultivares pelas lagartas que resultaram em machos e fêmeas. Ocorreram diferenças significativas entre ínstares, sendo o maior consumo constatado no 7º ínstar. A duração do estágio larval não diferiu para machos e fêmeas nas duas cultivares, entretanto houve diferença significativa na duração dos ínstares, independente do sexo. O 7º ínstar foi o mais longo, onde concentrou-se o maior consumo foliar diário. No consumo médio diário foram observados valores muito próximos tanto para machos como para fêmeas dentro dos cinco ínstares analisados nas duas cultivares testadas, constatando-se um aumento considerável a partir do 5º ínstar.

Deletion of the Lymantria dispar Multicapsid Nucleopolyhedrovirus Ecdysteroid UDP-Glucosyl Transferase Gene Enhances Viral Killing Speed in the Last Instar of the Gypsy Moth

Abstract The Lymantria dispar multicapsid nucleopolyhedrovirus (Ld M NPV) is used on a limited basis as a gypsy moth ( L. dispar ) control agent. In an effort to improve the efficacy (i.e., killing speed) of the Ld M NPV, we generated a recombinant viral strain (vEGT-) that does not produce the enzyme ecdysteroid UDP-glucosyltransferase (EGT). We compared the potency and efficacy of vEGT- to wild-type virus (A21-MPV) and the impact of vEGT- and A21-MPV on larval weight gain. Bioassay of L. dispar 1st, 4th, and 5th instars showed no significant difference in the LC 50 values in larvae infected with vEGT- or A21-MPV. The LT 50 values of 1st and 4th instar larvae infected with either virus were similar, but the LT 50 value of 5th instar larvae infected with vEGT- was significantly lower by ca. 33% compared with larvae infected with A21-MPV. Female 4th and 5th instar larvae infected with vEGT- gained significantly less weight than those infected with A21-MPV, whereas male 4th and 5th instar larvae infected with either virus showed no significant difference in weight gain. Larval weight gain was also used as an indicator of feeding activity through generation of FT 50 values (time when 50% of larvae ceased feeding). Fifth instar larvae infected with vEGT- exhibited a decrease in the FT 50 of ca. 32% compared with A21-MPV-infected larvae. Comparison of the total number of polyhedra produced in vEGT- or A21-MPV infected larvae showed that significantly more polyhedra were produced in 5th instars infected with A21-MPV. Deletion of the Ld M NPV egt gene generated an improved virus strain since the killing speed of vEGT- is significantly faster than wild-type virus in 5th instar L. dispar larvae, and larvae infected with vEGT- stopped gaining weight earlier than larvae infected with wild-type virus. Because the majority of foliage consumption by L. dispar larvae occurs in the 5th instar, the use of vEGT- may offer better foliage protection than wild-type virus in the field.

Food consumption of Rhammatocerus schistocercoides Rehn (Orthoptera: Acrididae) infected by the fungus Metarhizium flavoviride Gams & Rozsypal

Foliage consumption by nymphs and adults of the grasshopper Rhammatocerus schistocercoides Rehn infected with the fungus Metarhizium flavoviride Gams & Rozsypal was evaluated. Sixth and eighth instar nymphs and female adults consumed on average (±SEM) 6.9 ± 0.36 cm² (60.7 ± 2.92 mg of dry matter), 11.0 ± 1.35 cm² (74.9 ± 9.24 mg d.m.), and 16.0 ± 0.50 cm² (126.5 ± 6.35 mg d.m.) of sugarcane leaves per day, equivalent to 85.4, 35.9 and 41.9% of the insect body weights, respectively. Eighth instar nymphs and female adults inoculated with M. flavoviride (5,000 conidia / insect) ingested less food from day three onward and showed at day 10 an average consumption 74.5 and 45.6% lower than control insects, respectively. Adult females topically treated with a sub-lethal dosage (3 ml of a 8 ppm suspension / insect) of the chemical insecticide diflubenzuron showed consumption rates comparable to untreated insects (P=0.065). The combination fungus + chemical did not show results different from those obtained with the fungus alone (P=0.405). A strong correlation (r²=0.998) between production of fecal pellets by R. schistocercoides and food consumption was observed. These results confirmed the high voracity of R. schistocercoides and showed a remarkable adverse effect of the fungus on food intake by infected nymphs and adults.

Genetic transformation of potato with nptII-gus marker genes enhances foliage consumption by Colorado potato beetle larvae

Little is known about the effect of transgenic plants containing commonly used marker genes, such as aph(3′)II (nptII encoding neomycinphosphotransferase) and uidA (gus encoding β-glucuronidase) on insect feeding behaviour. We report here, for the first time, that transgenic potato plants containing only nptII and gus marker genes enhance foliage consumption by the Colorado potato beetle (CPB, Leptinotarsa decemlineata S.). Transformation of potato cultivar Desiree was performed with Agrobacterium tumefaciens. Internode explants were inoculated with different strains of bacteria, carrying either nptII-gus or nptII alone. A total of 180 transgenic and untransformed control plants were grown in the greenhouse for the analysis of food consumption by CPB. For each transformed and untransformed line tested, four bioassays were conducted each consisting of 10 second-instar larvae feeding independently on a 2 cm diameter leaf disc for 20 h. Our data show up to 50% increase of mean foliage consumption on plants transformed with the nptII-gus construct, indicating that transgenic plants containing these marker genes can affect the feeding behaviour of the insects. These results were obtained from the ‘primary regenerants’ (R0 lines) as well as from tuber-derived plants (R1 lines). Further tests with transgenic plants containing the nptII marker gene only, showed no significant difference in feeding when compared to untransformed control plants, allowing us to rule out a direct effect of this marker gene on foliage consumption by the insect larvae. It is suggested that gus protein is involved in the increase of foliage consumption by CPB.

Caterpillar guts and ammonia volatilization: retention of nitrogen by gypsy moth larvae consuming oak foliage

The gypsy moth (Lymantria dispar L.), a major defoliator of hardwood forests in the eastern U.S., has a highly alkaline midgut pH. We hypothesized that the high pH would cause high rates of ammonia (NH3) volatilization as larvae consumed foliage, leading to potentially large losses of N from the ecosystem to the atmosphere during gypsy moth outbreaks. We measured NH3 emission during the consumption of oak foliage by larvae in the laboratory. Surprisingly, we found very low amounts of NH3 release of about 0.1% of the N consumed in foliage. We speculate that digestive mechanisms may limit NH3 production in the midgut, and that the acidic environment of the hindgut traps most of the small amount of NH3 that is produced, effectively preventing a potentially very large N loss from both larvae and ecosystem. The estimated rate of NH3 emission from a defoliated forest is small compared to other inputs and outputs of N from the ecosystem, but could potentially enhance the neutralization of atmospheric acidity during the defoliation period.

Oviposition Response of Cotesia plutellae (Hymenoptera: Braconidae) to Sterile and Normal Diamondback Moth (Lepidoptera: Plutellidae) Larvae

Augmentative release of the endoparasitoid Cotesia plutellae (Kurdjumov) to control diamondback moth, Plutella xylostella (L.), in cabbage. Brassica oleracea variety capitata (L.), would be expensive for growers if done continually during a growing season. A method for establishing released parasitoids would be very beneficial in the control of this pest. One method under consideration is to use sterile diamondback moth larvae deposited on 'nursery' collard plants as hosts for C. plutellae to allow the parasitoid to build up in numbers and spread into adjacent cabbage fields. Therefore, the ability of C plutellac to accept and develop successfully in normal and sterile diamomlback larvae was evaluated, C. plutellae does not discriminate between normal larvae and larvae from parents sterilized by gamma radiation, and both sets of larvae served as suitable hosts for the parasitoid. Parasitism, foliage consumption, and survivorship were similar for the 2 types of larvae. Adult female F 1 parasitoids developed from sterile diamondback larvae were as fit as those from normal larvae. In laboratory bioassays, sterile and normal diamondback larvae traversed similar distances before pupation. Field cage assays showed less distance traversed by both types of larvae compared with the laboratory studies. Survivorship for both types of larvae was very low under field conditions. Results indicate that sterile diamondback moth larvae are acceptable hosts for C. plutellae and suggest that the nursery approach toward establishment and build up of numbers would be a viable approach to in-field production of the parasitoid with little chance for harm to nearby cabbage because of spread of sterile larvae from the nursery plants. This approach could be a cost effective way to augment naturally occurring parasitoids and predators in diamondback moth management programs.

Systemic Induction of Terpenoid Aldehydes in Cotton Pigment Glands by Feeding of Larval Spodoptera exigua

Pigment glands in cotton contain terpenoid aldehydes that are toxic and deterrent to feeding of several generalist lepidopteran insects. We hypothesized that previously observed systemically induced feeding deterrence may be associated with pigment glands. We conducted experiments to determine the dynamics and chemical nature of inducible feeding deterrents in leaves of cotton, Gossypium hirsutum L, to larvae of the beet armyworm, Spodoptera exigua. Production and/or filling of pigment glands was influenced by physiological age of Deltapine 90 cotton plants. In undamaged plants, successively formed leaves contained more pigment glands, up to the seventh or eighth true-leaf developmental stage. Feeding choice tests conducted one or seven days after initial feeding damage revealed that third instars of S. exigua consumed more of the two youngest leaves from control cotton plants than from plants whose two oldest leaves had been fed on previously for 24 hr by S. exigua. The preference for leaves from control plants was significant one day after initial damage and highly significant seven days after damage. Consumption of mature foliage (leaf immediately above initially damaged leaves) from control plants and damaged plants did not differ. More pigment glands were counted on the youngest leaf of damaged plants than on the youngest leaf of control plants one day after initial damage. HPLC analysis revealed greater amounts of hemigossypolone, heliocides 1 and 2 (H1 and H2), and total terpenoid aldehydes per gland in young foliage of damaged plants than control plants one day after initial injury. By seven days after initial injury, greater quantities of hemigossypolone and all heliocides except H4 were detected in young foliage from damaged plants compared to control plants. Concentrations of H1 per gland in young leaves from damaged plants increased the most of all terpenoid aldehydes measured (3.4× the amount found in leaves from control plants). Mature leaves from damaged plants did not contain more terpenoid aldehydes than mature leaves from control plants. We suggest that systemically induced feeding deterrence to S. exigua in young leaves of glanded cotton was due to increased amounts of terpenoid aldehydes in pigment glands.

Development and evaluation of a method for the design of spray applications: aerial tebufenozide applications to control the eastern spruce budworm, Choristoneura fumiferana (Clem.)

A novel approach to the design of insecticide spray applications was developed and evaluated in field trials to assess the efficacy of the insect moulting hormone analog tebufenozide (Mimic ®) against the eastern spruce budworm, Choristoneura fumiferana (Clem.). The pest biology, and habitat and pesticide characteristics were used as a basis to derive the required active ingredient (a.i.) and deposit density. Ingestion is the primary exposure route; an LD 95 acquisition through foliage consumption by fourthinstar larvae was used to establish a target dose of 15 ng a.i. cm −2 in one drop per needle (2.5 cm −2). A range of a.i. and volume application rates were selected based on the required densities, canopy leaf area index and projected spray losses to the understorey and by drift; application rates of 35, 70 and 140 g a.i. 1 ha −1 were employed, with volume application rates of 1, 2 and 4 L ha −1. Coniferous forest plots were aerially treated, resulting in average deposit densities (droplets cm −2) on artificial foliage between 0.8 and 3.7, with averge volumetric deposits between 7 and 30% of volume application rates. Population control was satisfactory, except for those applications at 35 g a.i. in 2 L and 70 g in 4 L ha −1 for which low deposit densities were observed. This approach to spray application design was found to be of scientific value and is adaptable to other insecticide applications.

Aerial and Surface Fuel Consumption in Crown Fires

An empirical model is presented which relates fractional reduction in loading to fuel element diameter and moisture content for surface and aerial fuels consumed near the fire front in a spreading crown fire. The model is based upon data from a series of experimental crown fires in immature jack pine. Its intended use is to permit calculation of fuel consumption per unit area (kg/m2) needed to estimate edge intensity (kW/m) from the spread rate of a crown fire. Model predictions of small fuel component fractional loading reduction had a root-mean-square error of almost 0.2 for our calibration data set. Most of the error arises from the model prediction of complete consumption of crown foliage, some of which was not exposed to flame in the fires of our data set. The model does not address the longer term burning of duff and large woody fuels.

Low Temperature Effect on Viability of Diadegma insulare (Hymenoptera: Ichneumonidae) Pupae and Effect of This Parasitoid on Feeding Rate of Diamondback Moth Larvae (Lepidoptera: Plutellidae)

Laboratory tests with Diadegma insulare (Cresson), a parasitoid of the diamondback moth (Plutella xylostella (L.)), were conducted to evaluate the viability of cocoons stored at 4°C for varying lengths of time and also the effects of parasitism by D. insulare on the feeding rate of diamondback moth larvae. The percentage of adults emerging from cocoons declined steadily with time spent in storage at 4°C and was predictable (r2=0.9603; Y=98.3-2.06X; P<0.01). No emergence of D. insulare was observed after 49 d in storage. There was a significant difference in feeding rate of parasitized larvae and non-parasitized larvae. Consumption of collard foliage by parasitized larvae (86.25% of them were parasitized) the first day after stinging was about the same as for non-parasitized larvae; but the parasitized larvae then became sluggish and fed very little on days 2-5 when the experiment was terminated.

Phenylpropenoid phenolics in sweetbay magnolia as chemical determinants of host use in saturniid silkmoths (Callosamia)

Host plant chemistry can play an important role in determining the evolution of host use patterns in herbivorous insects by influencing host selection, consumption, and assimilation of foliage. We used a comparative approach to test the hypothesis that specialist herbivores of sweetbay magnolia (Magnolia virginiana) possess adaptations that allow them to overcome chemical deterrents or toxins that prevent herbivory by unadapted herbivores. The three silkmoth species in the genusCallosamia can be collectively regarded as specialists on magnoliaceous hosts; however, only the monophagousC. securifera is able to complete development on sweetbay magnolia, its natural host. In laboratory assays with intact foliage, bothC. angulifera and the polyphagousC. promethea fed readily on sweetbay but were unable to survive past the third instar. Two neolignan compounds, magnolol and a biphenyl ether, were found to reduce neonate growth and survival of unadapted herbivore species when painted on acceptable host leaves at concentrations similar to those found in sweetbay foliage. Both compounds significantly reduced neonate growth ofC. angulifera andC. promethea but had no effect on the sweetbay specialist,C. securifera, indicating that the latter species possesses the unique ability in the genus to tolerate, metabolize, or otherwise circumvent the phytochemical defenses of this host.

A model for testing hypotheses of gypsy moth, Lymantria dispar L., population dynamics

A model for simulating long-term gypsy moth ( Lymantria dispar L.) population dynamics in North America has been developed. Simulated ecological processes include larval dispersal, foliage consumption on different host trees, reproduction, and mortality due to natural enemies (virus, 4 guilds of parasitoids, and 2 guilds of predators). Population dynamics in several forest stands can be simulated taking into account the migration of gypsy moth and its natural enemies. The model fits well to the following observations and data: (1) quasi-periodic outbreaks at approximately 10-year intervals, (2) life-tables in different outbreak phases, (3) increased parasitism in artificially augmented gypsy moth populations, and (4) phase plots of population dynamics. Simulated survival curves are intermediate between those reported by J.S. Elkinton et al. and by J.R. Gould et al. It is shown that low-density gypsy moth populations can be stabilized by immigration from high-density areas without any density-dependent local processes. The model supports the following hypotheses about gypsy moth population dynamics: (1) density fluctuations of small mammal predators is the most probable synchronization factor in gypsy moth populations; (2) the outbreak frequency depends on the proportion of susceptible tree species and the density of small mammal predators; (3) bacterial insecticide can be applied less frequently for gypsy moth control than can a chemical insecticide of the same killing power because the bacterial insecticide spares invertebrate natural enemies; (4) the success of gypsy moth eradication programs depends on the initial gypsy moth population density and on the type of functional response of predators. An alternative form of population bimodality hypothesis is suggested, according to which there are two types of gypsy moth population dynamics: eruptive in susceptible stands and stable in resistant stands.

Leaf dynamics and insect herbivory in a Eucalyptus camaldulensis forest under moisture stress

Abstract The influence of soil moisture content on leaf dynamics and insect herbivory was examined between September 1991 and March 1992 in a river red gum (Eucalyptus camaldulensis) forest in southern central New South Wales. Long‐term observations of leaves were made in trees standing either within intermittently flooded waterways or at an average of 37. 5m from the edge of the waterways. The mean soil moisture content was significantly (P≤0.05) greater in the waterways than in the non‐flooded areas. Trees in the higher soil moisture regime produced significantly larger basal area increments and increased canopy leaf area. This increase in canopy leaf area was achieved, in part, through a significant increase in leaf longevity and mean leaf size. Although a greater number of leaves was initiated and abscissed per shoot from the non‐flooded trees, more leaves were collected from litter traps beneath the denser canopies of the flooded trees. Consumption of foliage by insects on the trees subjected to flooding compared to the non‐flooded trees was not significantly different. However, the relative impact of insect herbivory was significantly greater on the non‐flooded trees. Leaf chewing was the most common form of damage by insects, particularly Chryso‐melidae and Curculionidae. No species was present in outbreak during this study. Leaf survival decreased as the per cent area eaten per leaf increased. In addition, irrespective of the level of herbivory, leaf abscission tended to be higher in E. camaldulensis under moisture deficit. The influence of soil moisture content on the balance between river red gum growth and insect herbivory is discussed.

FEEDING BY COLORADO POTATO BEETLE LARVAE (COLEOPTERA: CHRYSOMELIDAE) IN FIELD CAGES: MEASUREMENTS AND A MODEL

AbstractFeeding rates of Colorado potato beetle larvae were measured in 24-h trials in small field cases on potato leaflets that remained attached to the plants. Four models were constructed to explain the results; these differed by including or excluding the effect of insolative heating on larval body temperature, and by including or excluding thermoregulatory behavior, in all combinations. In all instars, observed feeding was independent of mean body temperature during the trial as estimated by each model, and less than the amount predicted using this mean to drive constant-temperature feeding rate functions.The four models were assessed by regressing model predictions on observed feeding rates. For first and second instars, there was no relationship between observed feeding and the amount predicted by any of the models, probably because the feeding rate was small relative to the precision of the measurements. For third and fourth instars, predictions from the model that included both insolative heating and behavioral thermoregulation did not differ significantly from observations. Simulations using this model suggested that daily mean body temperature fails to predict foliage consumption because this mean cannot account for the effects of transient occurrences of suboptimal temperatures.

Foliage Consumption and Larval Development of Three Noctuid Pests on Soybean and Cotton1

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Alan T. Wier, David J. Boethel; Foliage Consumption and Larval Development of Three Noctuid Pests on Soybean and Cotton. Journal of Entomological Science 1 July 1995; 30 (3): 359–361. doi: https://doi.org/10.18474/0749-8004-30.3.359 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest Search

Feeding, Growth, and Survival of Soybean Looper (Lepidoptera: Noctuidae) in Response to Nitrogen Fertilization of Nonnodulating Soybean

Feeding activity, growth, and survival of soybean looper, Pseudoplusia includens (Walker), larvae fed foliage from nonnodulating soybean, Glycine Max (L.) Merrill, plants supplied with different rates of nitrogen (N) fertilizer were examined. Foliage was obtained from the non–nodulating isoline ‘Lee’ soybean beginning at the V8 growth stage (46 d after planting) and continuing through initiation of bloom. Plants were grown in pots fertilized with four sequential applications of five rates of N fertilizer (5.25, 21, 42, 84, and 168 kg N/ha as NH4NO3) and from nonfertilized plants. These six treatments resulted in foliage N concentrations that ranged from 10 to 33 mg/g dry weight and chlorophyll concentrations that ranged from 0.5 to 1.7 mg/g fresh weight (51–50 d after planting) during the feeding bioassay. Foliage from nonfertilized control plants and those fertilized with 5.25 and 21 kg N/ha were low in N(≤12 mg/g) and caused 100% mortality when fed to soybean looper larvae. Foliage from plants fertilized with 42 kg N/ha contained 17 mg N/g dry weight and resulted in moderate levels of mortality (55%), whereas the higher N rates (84 and 168 kg N/ha) resulted in foliage N concentrations of 22 and 33 mg/g dry weight and ≥90% survival. Although the highest three foliage N concentrations were sufficient for survival of soybean looper larvae, differential effects on development of larvae were observed. Greater number of stadia, lengthened duration of the larval development period, and greater foliage consumption were observed with each reduction in foliage N from 33.4, to 22.4, to 16.9 mg/g, but ultimately, similar maximum larval weights were achieved. These three factors appear to be mechanisms tbat allow the soybean looper to compensate for reduced N and may explain how this species maintains itself on such a wide range of hosts (73 plant species in 29 families) including noncultivated species.

Direct and Indirect Effects of Prior Grazing of Goldenrod upon the Performance of a Leaf Beetle

A plant's grazing history can influence the nutritional quality of its leaves and directly affect herbivore performance. In addition, leaf nutritional quality can indirectly affect herbivore performance by influencing food consumption. We examined the direct and indirect influences of prior grazing of Solidago missouriensis upon leaf nutritional quality and the growth and fecundity of Trirhabda canadensis (Coleoptera: Chrysomelidae). We fed leaves from both previously grazed (during 1988 and 1989) and ungrazed goldenrod plots derived from a single S. missouriensis clone to larvae and adults of T. canadensis in laboratory performance trials. We computed standard insect performance indices and used structural equation modeling and path analysis to interpret the results of these trials. Prior grazing of goldenrod had a direct negative impact upon the growth of T. canadensis larvae in spring of 1990; a concomitant reduction in foliage consumption accentuated this effect. Larvae fed leaves from grazed plots accumulated biomass and N more slowly, used them less efficiently, and reached a lower final mass than did larvae fed leaves from plots without prior folivory. Goldenrods produced a new flush of leaves following larval grazing in the spring of 1990. Therefore, adults feeding in plots defoliated by larvae ate younger leaves than those feeding in undefoliated plots. Leaves from defoliated plots had direct positive impacts upon growth and egg production of adult T. canadensis. Adults converted these young leaves into biomass with greater efficiency and preferred them to older leaves from ungrazed plots in choice tests. However, negative indirect effects of prior grazing upon initial adult mass and total foliage consumption negated any positive influence that these more nutritious leaves had upon growth, and made the overall impact of prior grazing upon egg production negative. These results indicate that impacts of food availability and quality must be considered jointly to understand how prior grazing influences herbivore performance.

The diet of introduced brushtail possums Trichosurus vulpecula in a low-diversity New Zealand Nothofagus forest and possible implications for conservation management

We evaluate the diet of introduced brushtail possums Trichosurus vulpecula in a relatively low-diversity New Zealand Nothofagus forest. Although possums only invaded this area 30–40 years ago, densities (0·5–1·0 ha −1) are similar to those recorded for other Nothofagus forests. Thirty-three food types are eaten by possums, but the four most important contribute 68·4% of annual diet. Preference indices show that foliage consumption is non-random, with some species being highly favoured, particularly short-lived ‘seral’ tree species. Although possums rely heavily on foliage, the type of food consumed is strongly influenced by seasonal shifts in availability of key food types. Invertebrates and fruit are seasonally important in the diet and are probably taken opportunistically to supplement the staple foliage diet. Possum damage is less obvious in Nothofagus forests than in floristically more diverse forests as palatable species form only a small proportion of the biomass. However, these species make a major contribution to overall forest diversity and, through selective browsing, possums reduce diversity and accentuate the strong bias towards unpalatable biomass. These changes have significant implications for forest birds, as there is considerable overlap between possum and bird diet. If possum browsing continues, it is likely to restrict food supply for some birds. Most concern in possum control has gone into more diverse mixed-species forests, but even in low-diversity Nothofagus forests with few possums, these animals can have a disproportionately large impact on forest composition. Possum control in these forests is therefore likely to have considerable long-term benefits for ecosystem health.

Feeding Activity, Growth, and Survival of Soybean Looper on Low‐Nitrogen Nonnodulating Soybean

AbstractFeeding and larval development of several lepidopteran species are influenced by reduced foliage N of host plants. Nonnodulating soybean [Glycine max (L.) Merr.] isolines have exhibited foliar symptoms typical of N deficiency in field plots in absence of supplemental N. Under these chlorotic conditions, reducedefoliation and larval development of soybean looper [Lepidoptera:Noctuidae, Pseudoplusia includens (Walker)] have been observed. This study was conducted to evaluate the influence of foliage N level of nodulating and nonnodulating soybean isolines on feeding and development of the soybean looper. Two feeding studies involving the soybean looper and foliage of nodulating and nonnodulating isolines of #x2018;Clark’ soybean were conducted using foliage collected from plants in full bloom (R2) and in the beginning seed stage (R5). The foliage N level of the nonnodulating isoline was not significantly lower than that of the nodulating isoline when collected at R2 and, consequently, only slight effects on feeding and development were attributable to consumption of nonnodulating isoline foliage. However, chlorosis and a 43% reduction in the foliage N level of the nonnodulating isoline occurred by R5, resulting in limited compensatory feeding, extended larval development, and reduced survival when soybean loopers consumed this isoline. Foliage N concentrations of ≈40 mg g−1 leaf dry weight were sufficient for soybean looper development from the neonate to the adult stage, while concentrations of 23 mg g−1 leaf dry weight were inhibitory.