Host Shrubs Research Articles

A new whitefly of quarantine importance infesting a native and invasive plant, Rubus ellipticus Sm. (Rosaceae) in the Western Himalaya, India

Pealius kufriensis Dubey sp. nov. is described from a native and invasive plant, Rubus ellipticus Sm. (Rosaceae) from the Western Himalaya, India. Puparial characteristics of the genus Pealius Quaintance and Baker are discussed. The new species and its associated plant are considered of quarantine importance. Pealius kufriensis Dubey sp. nov. , puparium on Rubus ellipticus Sm. • Pealius kufriensis Dubey sp. nov. infesting Rubus ellipticus Sm. is described. • Puparial characteristics of the genus Pealius Quaintance and Baker are discussed. • The new species is of quarantine importance along with its associated plant species. Puparia of Pealius kufriensis Dubey sp. nov. found infesting a native and highly invasive plant, Rubus ellipticus Sm. (Rosaceae) are described. The host shrub was found highly infested with the new whitefly on the underside of leaves. Puparial characteristics of the genus Pealius Quaintance and Baker shared with Aleyrodes Latreille and Bemisia Quaintance and Baker are discussed.

Invasive Japanese Barberry, Berberis thunbergii (Ranunculales: Berberidaceae) Is Associated With Simplified Branch-Dwelling and Leaf-Litter Arthropod Communities in a New York Forest.

Arthropod food webs can be indirectly impacted by woody plant invasions, with cascading consequences for higher trophic levels. There are multiple bottom-up pathways by which invasive plants can alter food webs: above-ground interactions based on plant-herbivore associations and below-ground at the interface of leaf-litter and soil food webs. We compared arthropod community composition in these two food web dimensions in a New York forest that has been heavily invaded by nonnative Japanese barberry. Using two sampling protocols, we compared arthropod community composition on Japanese barberry shrubs to multiple species of native host shrubs and then compared leaf-litter arthropod assemblages between forest patches with exceptionally high Japanese barberry densities and those with relatively little to no Japanese barberry present. Fitting with trends in other woody shrub invasions, arthropod species richness was significantly lower in the leaf litter around Japanese barberry and on Japanese barberry plants themselves. Although overall arthropod abundance was also significantly lower on and in the leaf litter around Japanese barberry than on and around native shrubs, total biomass did not differ due to the taxa associated with Japanese barberry tending to be larger-bodied. We observed a dramatic reduction in predatory arthropods in response to both bottom-up pathways, particularly among ants and spiders. Our results show that Japanese barberry-invaded habitats may be experiencing trophic downgrading as result of lower numbers of generalist predators like spiders and ants, which may have rippling effects up the food web to insectivorous animals and their predators.

Abundance and Distribution of Blue Elderberry (Sambucus nigra ssp. caerulea) on Lower Cache Creek: Implications for Adaptive Floodplain Management

Author(s): Rayburn, Andrew P.; Rogner, Michael; Frank, Paul | Abstract: Many western U.S. landscapes are managed for multiple objectives, including biological conservation, commodity production, human welfare, and recreation. Effective conservation of special-status species in managed landscapes is challenging when species protection must be balanced with broader land-management objectives. In managed river systems, actions such as channel maintenance, bank stabilization, dam operation, and habitat enhancement are often implemented to achieve objectives related to water delivery, flood control, protection of adjacent lands, public recreation, and biological conservation. However, these actions are often constrained by the presence of special-status species because of regulatory requirements that may supersede implementation of other measures. Strategies to balance special-status species conservation with broader management objectives are directly informed by robust data sets on species abundance and distribution. On lower Cache Creek in Yolo County, California, multi-objective management seeks to balance protection of the federally-threatened Valley elderberry longhorn beetle (Desmocerus californicus dimorphus) and its sole host shrub, blue elderberry (Sambucus nigra ssp. caerulea), with channel maintenance, bank stabilization, and habitat enhancement actions. We conducted a comprehensive field survey from 2015 to 2016 to map all elderberry shrubs across the 904-ha Cache Creek Resource Management Plan area. An estimated 10,296 shrubs that spanned small, medium, and large size classes were mapped, strongly suggesting that the local population has been increasing since in-channel mining ceased in 1996. Analyses of shrub distribution relative to floodplain inundation zones, and associated vegetation, slope, and aspect revealed that most shrubs occurred in association with other woody riparian vegetation and within the ≤ 10-yr floodplain inundation zone. In addition, shrubs occurred more often than expected on intermediate slopes and both westerly and northwesterly aspects. The results of this study are guiding adaptive management and informing project planning and permitting on lower Cache Creek, demonstrating the importance of spatially-explicit abundance and distribution data for special-status species in managed landscapes.

Influence of Holoparasitic Plant Cuscuta japonica on Growth and Alkaloid Content of Its Host Shrub Catharanthus roseus: A Field Experiment

Japanese dodder (Cuscuta japonica) is a flowering, parasitic weed that causes major yield losses on crop and forest production. In the present field study, the influence of Cuscuta on the growth and secondary metabolite of its host medicinal shrub Madagascar periwinkle (Catharanthus roseus) was investigated. Vegetative and reproductive growth of the host plant Catharanthus was measured at intervals from 0 to 60 days after inoculation (DAI), and content of three alkaloids, naturally produced by the host, in the host and parasite were measured by HPLC at intervals from 15 to 45 DAI. Dodder infection significantly inhibited biomass accumulation and reproductive growth of Catharanthus, and aerial parts of the host died by 60 DAI. Levels of alkaloids vinblastine, vindoline and catharanthine in the inoculated Catharanthus were lower than in uninoculated control plants, both in immature leaf and in mature leaf, except the alkaloids contents were elevated in host immature leaf compared with uninoculated control plants immature leaf at 15 days. The host plant thus actively responded to dodder infection by accumulating alkaloids acts as a defense molecule at 15 DAI. The alkaloids produced by host plants accumulated in dodder at 15–45 DAI, and the alkaloid content in dodder reached a maximum at 45 DAI. The alkaloids transported from host to parasite act as a sink, the high content of alkaloids in dodder be cytotoxic and accelerated the onset of senescence.

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. However, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear. We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans-Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect, and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the centre of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on the vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands.

Diminished fitness in an endemic Hawaiian snail in nonnative host plants

Hawaii’s diverse achatinellid tree snails occur almost exclusively in host trees and shrubs that are native to the Hawaiian Archipelago. A few exceptions to this pattern are known, where an arboreal gastropod population has persisted in introduced plants. On Oahu, Hawaii, the last known population of the single-island endemic snail Auriculella diaphana has persisted in nonnative plants for multiple decades, leading to the following question: are there differences in the relative fitness of native gastropods in native versus nonnative host plants? To address this we conducted laboratory trials with A. diaphana in three treatment groups, one with the two dominant nonnative host plants from their current distribution, another group with two primary native host plant species, and a third treatment maintained in cages with a mixture of equal parts of both the nonnative and native plants. Trials were replicated in two 16-week intervals, with 100 snails. Relative fitness was assessed among treatments as survival and reproductive output (number of eggs produced). Results demonstrated that while survival of adult snails was equivalent across treatments (100%), fecundity was significantly higher in cages where native plants were available. Egg production was 20.05-fold and 14.95-fold greater in treatments with 100% and 50% native host plants, respectively, than in treatments with nonnative plants only. These results suggest that native snails persisting in nonnative host plants experience sublethal stress, reflected in a dramatic reduction in reproductive output. Snails in treatments with mixed native and nonnative plants also showed significantly higher reproduction than those in nonnative plant cages. We suggest that the observed decreased fecundity was due to the poor nutritional value of the microbial phyllosphere of nonnative vegetation, and that translocation of this and related species occurring in nonnative habitat to nearby native host plants will be beneficial in terms of relative fitness.

Conspecific Pollen Loads on Insects Visiting Female Flowers on ParasiticPhoradendron californicum(Viscaceae)

Desert mistletoe, Phoradendron californicum (Viscaceae), is a dioecious parasitic plant that grows on woody legumes in the Mojave and Sonoran Deserts, produces minute flowers during winter, and is dispersed by birds defecating fruits. Pollination of desert mistletoe has not been examined despite the species' reliance on insects for transporting pollen from male to female plants. I investigated the pollination of P. californicum parasitizing Acacia greggii (Fabaceae) shrubs at 3 sites at different elevations in the Mojave Desert of southern Nevada during February 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted pollen grains in insect pollen loads. Desert mistletoe's tricolpate pollen differed from a previous description by being oblate instead of subprolate in equatorial view. Female flowers were visited by 13 species of Diptera in 10 genera and 6 families and 3 species of Hymenoptera in 3 families. Almost all (98.5%) of the pollen carried by insects was from desert mistletoe. Five species of phytophagous fruit flies in Tephritidae were frequently found on flowers, comprising 53% of the insects collected, but carried low amounts of P. californicum pollen. Two species of blow flies in Calliphoridae, both larval decomposers of animals, were also relatively abundant on flowers and carried moderate to high pollen loads. Flies in Syrphidae, 2 predators and 1 plant-decomposer, carried varying amounts of conspecific pollen. Conspecific pollen loads also varied on a species of native bee in Halictidae and on naturalized honey bees in Apidae. Desert mistletoe appears to be pollinated mostly by tephritids, due to their abundance on female flowers, and by calliphorids. Blow flies would be more likely than fruit flies to carry pollen between male and female plants on different host shrubs due to their larger size and stronger flight. Parasitic, dioecious P. californicum plants appear to rely on a web of mutualism between fruit-eating birds and flower-fertilizing insects.

Sunbird pollination of the dioecious root parasite Cytinus sanguineus (Cytinaceae)

Cytinus (Cytinaceae) is an enigmatic lineage of parasitic plants distributed in the Mediterranean, Africa and Madagascar, and exhibits variation in floral traits suggestive of multiple pollinator shifts. The flowers of Cytinus sanguineus, a dioecious South African species, are sturdy, bright scarlet, and scentless - a combination of floral characteristics that suggests pollination by nectarivorous birds. However, the emergence of flowers at soil level underneath host shrubs and the absence of perches are not typical features of plants pollinated by sunbirds, which are generally averse to foraging on the ground. We studied the pollination system of C. sanguineus using camera traps, analysis of floral nectar and scent, and spectrophotometry of floral surfaces. We observed that C. sanguineus is pollinated by sunbirds, which readily forage on the ground and transfer pollen on their beaks while drinking copious, diluted nectar from narrowly tubular floral nectaries. High fruit set regardless of spatial separation of male and female flowers indicates efficient pollination. Rodents and insects rarely visit C. sanguineus flowers, likely due to the absence of attractive floral volatiles, and the inaccessibility of nectar for rodents. The pollination system of C. sanguineus is clearly distinguished from those of the rodent-pollinated Cytinus visseri and the ant-pollinated Cytinus hypocistis, where pollinator attraction is achieved through production of specific floral volatiles. Our documentation of bird pollination in Cytinus contributes to understanding of the diversity of pollination systems in this genus.

Availability of ectomycorrhizal fungi to black spruce above the present treeline in Eastern Labrador.

Ectomycorrhizal fungi (ECMF) are an important biotic factor in the survival of conifer seedlings under stressful conditions and therefore have the potential to facilitate conifer establishment into alpine and tundra habitats. In order to assess patterns of ectomycorrhizal availability and community structure above treeline, we conducted soil bioassays in which Picea mariana (black spruce) seedlings were grown in field-collected soils under controlled conditions. Soils were collected from distinct alpine habitats, each dominated by a different ectomycorrhizal host shrub: Betula glandulosa, Arctostaphylos alpina or Salix herbacaea. Within each habitat, half of the soils collected contained roots of ectomycorrhizal shrubs (host+) and the other half were free of host plants (host−). Forest and glacial moraine soils were also included for comparison. Fungi forming ectomycorrhizae during the bioassays were identified by DNA sequencing. Our results indicate that ECMF capable of colonizing black spruce are widespread above the current tree line in Eastern Labrador and that the level of available inoculum has a significant influence on the growth of seedlings under controlled conditions. Many of the host− soils possessed appreciable levels of ectomycorrhizal inoculum, likely in the form of spore banks. Inoculum levels in these soils may be influenced by spore production from neighboring soils where ectomycorrhizal shrubs are present. Under predicted temperature increases, ectomycorrhizal inoculum in soils with host shrubs as well as in nearby soils without host shrubs have the potential to facilitate conifer establishment above the present tree line.

Reproduction and dispersal in an ant‐associated root aphid community

Clonal organisms with occasional sex are important for our general understanding of the costs and benefits that maintain sexual reproduction. Cyclically parthenogenetic aphids are highly variable in their frequency of sexual reproduction. However, studies have mostly focused on free-living aphids above ground, whereas dispersal constraints and dependence on ant-tending may differentially affect the costs and benefits of sex in subterranean aphids. Here, we studied reproductive mode and dispersal in a community of root aphids that are obligately associated with the ant Lasius flavus. We assessed the genetic population structure of four species (Geoica utricularia, Tetraneura ulmi, Forda marginata and Forda formicaria) in a Dutch population and found that all species reproduce predominantly if not exclusively asexually, so that populations consist of multiple clonal lineages. We show that population viscosity is high and winged aphids rare, consistent with infrequent horizontal transmission between ant host colonies. The absence of the primary host shrub (Pistacia) may explain the absence of sex in three of the studied species, but elm trees (Ulmus) that are primary hosts of the fourth species (T.ulmi) occurred within a few km of the study population. We discuss the extent to which obligate ant-tending and absence of primary hosts may have affected selection for permanent parthenogenesis, and we highlight the need for further study of these aphids in Southern Europe where primary hosts may occur close to L.flavus populations, so that all four root aphid species would have realistic opportunities for completing their sexual life cycle.

Insect herbivory in climber-host shrubs associations: Benefit or detriment?

Spatial proximity between different plant species could modify the sign (positive or negative) of plant–herbivore interaction. The chance of a plant being detected and colonized by herbivorous insects depends not only on the plant's own traits but also on the identity of the neighbouring plants that grow with it. The closest proximity between plants occurs in climbers and their host. We conducted a field experiment to assess the effect of spatial association between a climber plant, Vicia nigricans (Fabaceae), and two host shrubs, Berberis buxifolia (Berberidaceae) and Schinus patagonica (Anacardiaceae), on insect herbivory levels, reproductive output and growth. The presence and identity of the host shrubs affected the herbivory levels of the climber V. nigricans, but not the reproductive output. For the climber, the probability of being attacked by insects could depend on the characteristics of the host shrub. Taking the opposite perspective, climber association affected different traits of the host shrubs. The association with the climber decreased leaf damage (positive), tended to decrease leaf production (negative) and did not affect reproductive output (neutral). Our findings suggest that spatial association between plant species could change the sign of the interactions between plants and insects affecting different traits. By taking into account the perspective of both plants involved in the association, this study shows and emphasizes that plant–animal interactions strongly depend on the community context.

The Effects of Long-Term Drought on Host Plant Canopy Condition and Survival of the Endangered Astragalus jaegerianus (Fabaceae)

Astragalus jaegerianus Munz (the Lane Mountain milkvetch) is a federally endangered species that exists in only four fragmented populations within and adjacent to the U.S. Army's National Training Center, Fort Irwin, CA. Since 1999, our monitored A. jaegerianus populations have consistently declined, and are now 12% of their previous size. A number of subpopulations are in danger of local extinction. The decline of A. jaegerianus has occurred simultaneously with severe drought in the Mojave Desert. These drought conditions began in 1999 and are predicted to continue for decades, or may continue indefinitely under warmer temperature conditions projected by global climate change-type drought. Our results suggest that drought has direct and indirect affects on A. jaegerianus by killing or degrading its host shrubs. Astragalus jaegerianus host shrubs have decreased in shrub volume and cover by roughly 10 percent since the onset of drought, and shrub mortality has been high. Our results show that canopy condition has a profound affect on the microclimate within host shrubs. Furthermore, our results show a significant increase in survival of A. jaegerianus among host plants with more intact canopies. These results support our study hypothesis that drought-related changes to host plant canopies affect A. jaegerianus survival, and represent an indirect negative effect of long-term drought on A. jaegerianus populations.

Take Me to Your Leader: Does Early Successional Nonhost Vegetation Spatially InhibitPissodes strobi(Coleoptera: Curculionidae)?

The spatial influences of host and nonhost trees and shrubs on the colonization patterns of white pine weevil Pissodes strobi (Peck) were studied within a stand of planted interior hybrid spruce [Picea glauca (Moench) Voss x Picea engelmannii (Parry) ex Engelm.]. Planted spruce accounted for one third of all trees within the stand, whereas the remaining two thirds were comprised of early-successional nonhost vegetation, such as alder (Alnus spp.), paper birch (Betula papyrifera Marsh.), black cottonwood [Populus balsamifera ssp. trichocarpa (T. Ng.) Brayshaw], lodgepole pine [Pinus contorta (Dougl.) ex Loud.], trembling aspen (Populus tremuloides Michx), willow (Salix spp.), and Canadian buffaloberry [Shepherdia canadensis (L.) Nutt.]. Unlike the spruce trees, nonhost vegetation in the stand was not uniformly distributed. Spatial point process models showed that Canadian buffaloberry, paper birch, black cottonwoood, and trembling aspen had negative associations with damage caused by the weevil, even though the density of the insects' hosts in these areas did not change. Moreover, knowing the locations of these nonhost trees provided as much, or more, inference about the locations of weevil-attacked trees as knowing the locations of suitable or preferred host trees (i.e., those larger in size). Nonhost volatiles, the alteration of soil composition, and overstory shade are discussed as potential explanatory factors for the patterns observed. New research avenues are suggested to determine whether nonhost vegetation in early successional stands might be an additional tool in the management of these insects in commercially important forests.

Facilitative and competitive effects of a N-fixing shrub on white fir saplings

In Sierra Nevada forests, shrubs are considered strong soil moisture competitors with regenerating trees, reducing seedling establishment, and slowing growth. Recent studies, however, suggest that in some circumstances shrubs can facilitate tree establishment and growth by modifying harsh microclimate conditions; increasing acquisition of water, carbon, and/or nutrients via shared mycorrhizal connections; or enhancing soil fertility, particularly under nitrogen-fixing shrubs such as Ceanothus spp. We examined the establishment dates and growth rates and patterns of white fir saplings growing in greenleaf manzanita, whitethorn ceanothus, and bare patches to examine whether establishment was correlated with past wet years, whether saplings growing in ceanothus had nitrogen-enriched foliage or faster growth rates than in the other two patches, and whether saplings in shrub patches experienced competition for light. Sapling establishment was not correlated with high precipitation or heavy snowpack years, suggesting shade-tolerant saplings do not need wet years to become established. Soils under ceanothus were nitrogen enriched, but white fir sapling foliage did not have higher nitrogen concentrations and saplings did not grow faster in ceanothus than in the other two patches. Because growth rates of saplings were comparable in all patch types examined despite significantly different edaphic and abiotic conditions, we inferred that the various competitive and facilitative interactions affecting tree growth are in net balance across the patch types examined. However, competition for light is important—a significant percentage of growth release events occurred after saplings emerged above their host shrubs. Where shrubs are present, shade-tolerant species (i.e., white fir) are favored over drought-tolerant (pine) species. Our results may help interpret changes in understory conditions that are contributing to mixed conifer's compositional shift toward more shade-tolerant species after a century of fire-suppression.

Conservation biological control in urban landscapes: Manipulating parasitoids of bagworm (Lepidoptera: Psychidae) with flowering forbs

Abstract We conducted field experiments to test the hypothesis that regulation of herbivorous pests in urban landscapes can be enhanced with forbs that provide floral resources for adult natural enemies. The herbivore was bagworm, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), which is attacked by a guild of hymenopterous parasitoids. We established host shrubs in common garden plantings, encircling some with flowering forbs, released bagworm larvae on shrubs, and assessed survivorship. The hypothesis was supported: parasitism rates of bagworm were 71% higher in shrubs that were surrounded by flowering forbs than in shrubs that lacked flowers. This study also suggested that white-footed mice and European sparrows were important predators of bagworms. The most abundant parasitoid species was the exotic ichneumonid Pimpla (=Coccygominus) disparis (Vierick), an introduced biological control agent of gypsy moth. In a second experiment, parasitism rates were at least three times higher in shrubs encircled by a high density of forbs compared to those having fewer or no forbs. In a third experiment, parasitism rates exceeded 70% in shrubs that were adjacent to a central bed of flowering forbs, but less than 40% in shrubs that were farther away. We conclude from these studies that flowering forbs have a localized effect on host-searching behavior of female parasitoids, encouraging them to parasitize bagworms in the immediate vicinity. This study provides further evidence that ecological methods of pest management can be integrated into the design of urban landscapes to improve regulation of herbivorous pests.

Patterns of shrub-dwelling arthropod diversity across a desert shrubland–grassland ecotone: a test of island biogeographic theory

This study tested the applicability of Island Biogeographic Theory to arthropod assemblages on ‘islands’ of creosotebush (Larrea tridentata) across a desert shrubland-grassland ecotone in central New Mexico, U.S.A. We assumed that herbivorous arthropod taxa that specialize on creosotebush view these shrubs as ‘islands’ of suitable habitat in a ‘sea’ of grassland, and used the Island Biogeographic Theory to examine the observed plant and arthropod patterns. Specifically, we addressed predictions concerning the relationship among arthropod species richness and (1) shrub ‘island’ area, (2) distance between ‘island’ and ‘continent’, and (3) ‘island’ isolation. Using a pyrethrum insecticide, we defaunated 36 shrubs within three ecotonal areas (12 shrubs per area), defined as ‘continental’ (high shrub density), ‘archipelago’ (medium shrub density, close to the ‘continent’), and ‘oceanic’ (low shrub density, far from the ‘continent’). We assessed the initial arthropod distribution and then repeated the defaunation after two weeks to assess immigration patterns. The arthropods from both samples were catalogued and related to ‘island area’ (shrub volume), ‘island’ distance from the defined ‘continent’, and ‘island’ isolation (density). We found that in the initial sample, specialist herbivore species richness was (1) positively related to shrub volume, (2) negatively related to shrub distance from the ‘continent’, but (3) not significantly related to shrub density. Following the recolonization period, we found that specialist herbivore species richness was again significantly positively related to shrub volume, but was not significantly related to shrub distance from the ‘continent’ or to shrub density. We also examined the relationship between generalist predator arthropod (spiders and mantids) populations and shrub ‘island’ characteristics as well as specialist prey abundances on the shrubs. We found that predator abundances on individual shrubs were positively related to shrub volume prior to and following defaunation, negatively related to shrub density both initially and following recolonization, and positively related to the architectural complexity of host shrubs initially. We also found that predator population sizes on shrubs were positively correlated with abundances of specialist prey species. We concluded that our model conformed fully to the species richnes·island area and species richnes·island distance relationships of Island Biogeographic Theory, but only in part to the species richnes·island isolation relationship. We also found that species-specific dispersal ability was a critical factor with regard to the observed species distribution patterns.

Survival of Arbuscular Mycorrhizal Fungi Following Reciprocal Transplanting Across the Great Basin, USA

Mycorrhizal fungi are transplanted into exotic habitats to aid in agriculture and land restoration. However, different taxa have different effects on hosts, and little is known about their survival or spread. The fate of arbuscular mycorrhizal fungi was examined in a reciprocal transplant experiment of a single host shrub species, Artemisia tridentata subspecies tridentata between two semiarid sites. The sites were located near Reno, Nevada, and San Diego, California, in the western United States. The experiment was a complete factorial design: two plant populations, A. tridentata ssp. tridentata from the Reno and the San Diego sites, and five fungal treatments (Acaulospora elegans from San Diego, Scutellospora calospora from Reno, a whole‐soil inoculum from San Diego, a whole‐soil inoculum from Reno, and uninoculated soil). Based on fluorescein isothiocyanate‐labeled antiserum studies, neither fungus declined over three growing seasons at the site of origin with the plant population of origin. Survival of the fungi always declined in association with the exotic host population and at the exotic site. Spore density of fungi that had been inoculated was generally very low. However, when significant differences between treatments were observed, spore density of the fungus was higher in association with plants that had been inoculated with it than with uninoculated plants, and the fungus had higher survivorship in the site and with the host of its origin. Both fungi usually sporulated more often under inoculated than uninoculated host plants. Over three growing seasons, both A. elegans and S. calospora survived in their sites of origin and in the exotic location with both plant populations. The fungi spread throughout the root systems and between plants of the different treatments. These results show that, while there was higher survival by the arbuscular mycorrhizal fungi at the site and with the host of origin, these fungi survived and spread for at least three growing seasons, although they declined significantly at the exotic site and with exotic hosts.

Influence of Host Phenology and Vegetation on the Abundance of Tamalia coweni Galls (Homoptera: Aphididae) on Arctostaphylos insularis (Ericaceae)

Tamalia coweni formed galls on immature leaves of Arctostaphylos insularis during the wet season on Santa Cruz Island, California. Because immature leaves were absent from twigs with fruit, the more nonfruiting twigs on a shrub, the more aphid galls on its leaves. Plant species richness, host plant size, host plant abundance, and proximity of neighboring host shrubs were not significantly related to gall abundance. Thus, a resource concentration effect was evident for the exploited host organ (immature leaves), but not for whole host plants. This effect was overridden by the presence of chaparral vegetation. Excluding fruiting twigs from consideration, Arctostaphylos insularis shrubs within chaparral had a lower mean percentage of infested leaves (8.5 vs. 32.9) and averaged fewer galls per leaf (0.12 vs. 0.67) than did shrubs within grassland. The mechanisms that produced these patterns are unknown.

Bionomics of an Oak Defoliating Grasshopper, Dendrotetlix quercus1 in Wisconsin2,3

The acridid grasshopper, Dcndrotettix quercus Packard, has been found widely in Wisconsin. Preferred hosts were species of oaks, Quercus spp., and hazelnut, Corylus americana Walt. Foliage from trees of the red oak group was preferred to that of the white oak group. Red maple, Acer rubrum L., was not fed upon. Most individuals of a population appeared during the same year, but biennially. A few individuals could be found during the intervening summers. Both brachypterous and apparently flightless macropterous individuals, including a rare intermediate form, were found. Two forms of dark-phase adults occurred, both estimated to comprise less than 1% of the total. Eclosion began in late May or early June and grasshoppers became mature near the first of July. Both morphological and morphometric systems were utilized to separate the 5 nymphal instars. Oviposition began in mid-July with most egg pods deposited near the margins of the oak woods. Nymphs and adults spent most of their lives in the host trees or shrubs. Although adults sometimes wandered appreciably from known hosts, no dispersal or migratory tendencies were evident. Rain and frost accounted for high mortality of 1st-stage nymphs. Two pathogenic fungi, Aspergillus sp. and Beauvaria sp. (probably bassiana ) were isolated from laboratory stock. Two sarcophagid parasites, one tentatively identified as Blaesoxipha sp. and the other Heliocobia rapax (Walker), were collected. Nematode parasites of the genus Agamermis (Mermithidae) were found in 18% of adults. Grasshoppers infected with nematodes had lower fecundity and longevity. Both vertebrate and invertebrate predators were observed.