Establishment and Dispersal ofUrophora affinis(Diptera: Tephritidae) andMetzneria paucipunctella(Lepidoptera: Gelechiidae) in Southwestern Virginia

Two European gall-producing insects,Urophora affinisFrfld. (Diptera: Tephritidae) andMetzneria paucipunctella(Zeller) (Lepidoptera: Gelechiidae) were introduced into Virginia in 1986 for biological control of spotted knapweed (Centaurea maculosaLam.). Adults ofU. affinis(n = 2625) andM. paucipunctella(n = 450) were released at two sites in Montgomery County, Virginia, and their populations were monitored yearly by dissecting spotted knapweed flower heads. Beginning in 1992, knapweed samples collected at various distances from the release sites were checked for dispersal.U. affinisis well established and is spreading slowly. The number of larvae per flower head and the seed numbers are inversely related as plants with the greatest number of larvae per spotted knapweed head had the lowest number of seeds. Knapweed density has declined at one of the release sites which had the highest rate of infestation byU. affinis.Establishment of the moth,M. paucipunctella,is less certain as it has been recovered at a very low level from only one site.     

Influence of seed head-attacking biological control agents on spotted knapweed reproductive potential in western Montana over a 30-year period

Five insect biological control agents that attack flower heads of spotted knapweed, Centaurea stoebe L. subsp. micranthos (Gugler) Hayek, became established in western Montana between 1973 and 1992. In a controlled field experiment in 2006, seed-head insects reduced spotted knapweed seed production per seed head by 84.4%. The seed production at two sites in western Montana where these biological control agents were well established was 91.6-93.8% lower in 2004-2005 than 1974-1975, whereas the number of seed heads per square meter was 70.7% lower, and the reproductive potential (seeds/m(2)) was 95.9-99.0% lower. The average seed bank in 2005 at four sites containing robust spotted knapweed populations was 281 seeds/m(2) compared with 19 seeds/m(2) at four sites where knapweed density has declined. Seed bank densities were much higher at sites in central Montana (4,218 seeds/m(2)), where the insects have been established for a shorter period. Urophora affinis Frauenfeld was the most abundant species at eight study sites, infesting 66.7% of the seed heads, followed by a 47.3% infestation by Larinus minutus Gyllenhal and L. obtusus Gyllenhal. From 1974 to 1985, Urophora spp. apparently reduced the number of seeds per seed head by 34.5-46.9%; the addition of Larinus spp. further reduced seed numbers 84.2-90.5% by 2005. Path analysis indicated that both Larinus spp. and U. affinis contributed significantly to reduction of seed production over the 30-yr period. Spotted knapweed density may not decrease significantly until the seed bank falls below a critical threshold.     

Interactions and effects of multiple biological control insects on diffuse and spotted knapweed in the Front Range of Colorado

Abundances and interactions among biological control insects and their effects on target invasive plants were monitored within the flower heads and roots of diffuse knapweed, Centaurea diffusa, and in spotted knapweed, Centaurea stoebe, along the Colorado Front Range. Flower weevils, (Larinus species) and root-feeders (Cyphocleonus achates and Sphenoptera jugoslavica) were released on knapweed that already supported biological control gall flies (Urophora species). At a single monitoring site, seed production by C. diffusa declined from 4400 seeds m⁻² in 1997 to zero seeds m⁻² on the monitoring sites in 2006, while the flowering stem density of C. diffusa declined from a peak of almost 30 stems m⁻² in 2000 to zero stems m⁻² in 2006. The average abundance of Urophora and Larinus in flower heads fluctuated independently during the 2001–2006 interval, while the relative abundance of C. achates and S. jugoslavica in roots exhibited a weak inverse relationship that appeared driven by climate effects. The relative abundance of insects on a population of C. stoebe was monitored for five years as Larinus species and C. achates became established on spotted knapweed that already supported Urophora species. Spotted knapweed seed production on our monitoring site declined from 4600 seeds m⁻² in 2003 to zero seeds m⁻² in 2006. Unlike C. diffusa, substantial numbers of rosettes of C. stoebe remained present. Larinus consumed almost all Urophora encountered in C. diffusa, and consumed about 40% of the Urophora in co-infested flower heads of C. stoebe (ca. 10–15% of the total Urophora population). No negative correlations between the relative densities of flower head and root-feeding insects were observed. The effects of these insects on target plants have produced results consistent with the ‘cumulative stress hypothesis’ for biological control of Centaurea species.     

A knapweed biological control perspective

Diffuse and spotted knapweed (Centaurea diffusa Lam. and C. stoebe micranthos (Gugler) Hayek) are Eurasian plants that devastate dry and mesic North American grasslands. They have a mutualistic association with arbuscular mycorrhizal fungal (AMF) phylotypes with hyphal links to nearby plants and a nutrient flux to the strongest sink, usually knapweed. They displace many AMF beneficial to grass and affect knapweed nutrient allocation, biology, knapweed insects and probably root necrosis and emergence of ant buried seed. AMF determined nutrient root or shoot allocation determines nutrient shoot and root allocation and the benefit to root or seed-head insect species and whether C. diffusa is an annual–biannual or a semelparous perennial needing 5 or more years to flower. Both knapweeds do well without its AMF phylotypes without competition in fertile soil. In grass in Eurasia, they have a community of seven seed-head species segregated by head development stage. Prolonged seed dormancy buffered knapweed decline that resulted in release of a surfeit seed-head species. The presence of an eliasome on the seed and vigorous seedling clumps suggests burial by myrmecochorous ants with AMF supplied carbon supporting their growth. The root species community is segregated by habitat, climate, root part, and size. With larval induced compensatory growth and AMF nutrient sharing, the growth of plants with and without a larva was the same. On feeding completion, a nutrient out flux from the attacked plants reduced growth; but without killing. This needs a dual species or a repeated single species attack. Root species packing increases knapweed utilization; but the four approved species are insufficient for maximum utilization. Two additions are suggested. The aim of the paper is to provide enough understanding of the AMF and its plant and insect interactions to facilitate knapweed biological control and avoid past mistakes.     

The lesser of two weevils: physiological responses of spotted knapweed (Centaurea stoebe) to above- and belowground herbivory by Larinus minutus and Cyphocleonus achates

The physiological responses of plants to variable levels of root and shoot herbivory in the field may yield valuable insights regarding potential compensation or tolerance responses for herbivory. In an infestation of Centaurea stoebe (spotted knapweed) located in the Colorado foothills, we measured physiology, biomass, and flower production of individual plants undergoing a natural range of herbivory by the above- and belowground biological control insects, Larinus minutus and Cyphocleonus achates. Over the growing season, net carbon assimilation rate, transpiration, stomatal conductance, and intercellular leaf [CO₂] (C _i) all decreased, while water use efficiency increased. The decrease in these physiological traits was due to an increase in the intensity of L. minutus damage over time; effects of C. achates root damage to plant physiology, including transpiration were only marginally significant. The effects of these two species on plant physiology were not interactive, and Larinus minutus was found to exert larger negative effects on this invasive plant in terms of plant physiology and potential reproductive output than C. achates. While previous studies have shown C. achates to have significant negative effects on population densities of spotted knapweed, the addition of Larinus minutus to the suite of insects used in biological control of spotted knapweed should facilitate continued or enhanced reduction in densities of this noxious weed.     

How do biological control and hybridization affect enemy escape?

Two mechanisms often linked with plant invasions are escape from enemies and hybridization. Classical biological control aims to reverse enemy escape and impose top-down population control. However, hybridization has the potential to alter interactions with enemies and thus affect biological control. We examined how introductions of biological control agents affect enemy escape by comparing specialist enemy loads between the native and introduced ranges of two noxious weeds (spotted and diffuse knapweed; Centaurea stoebe L. and C. diffusa Lam.) that have been the targets of an extensive biological control program. Hybrids between spotted and diffuse knapweed are often found within diffuse knapweed sites in North America, so we also compared enemy loads on plants that appeared morphologically like diffuse knapweed and hybrids. Finally, we tested the preference for diffuse knapweed, hybrids, and spotted knapweed of one of the agents thought to be instrumental in control of diffuse knapweed (Larinus minutus; Curculionidae). In North America spotted knapweed has largely escaped its root herbivores, while seedhead herbivore loads are comparable in the introduced and native ranges. Diffuse knapweed exhibited seedhead herbivore loads five times higher in the introduced compared to native range. While this pattern of seedhead herbivory is expected with successful biological control, increased loads of specialist insect herbivores in the introduced range have rarely been reported in the literature. This finding may partially explain the better population control of diffuse vs. spotted knapweed. Within North American diffuse knapweed sites, typical diffuse knapweed and hybrid plants carried similar herbivore loads. However, in paired feedings trials, the specialist L. minutus demonstrated a preference for newly created artificial hybrids over North American diffuse knapweed and for European diploid spotted knapweed over North American tetraploid spotted knapweed. Overall though, hybridization does not appear to disrupt biological control in this system.     

Impact of clear-cutting and prescribed burning on microbial diversity and community structure in a Jack pine (Pinus banksiana Lamb.) clear-cut using Biolog Gram-negative microplates

Three isolates ofFusarium avenaceum are pathogenic on spotted knapweed(Centaurea maculosa), a major weed plant of pasturelands and rangelands of the Pacific Northwestern USA. One isolate (no. 1) obtained from the European centre of origin of knapweed and isolate no. 365 native to Montana, did not significantly affect knapweed seed germination. However,F. avenaceum no. 1003, another Montana native isolate, caused a 100% decrease in seed germination and hence, no seedling emergence. When formulated, isolate no. 1003, could be recovered from treated soils after 7 days and caused a significant reduction in seedling emergence or seedling dry weight. This organism had no effect on the germination ofTriticum aestivum orMedicago sativa, but did affect the germination of other plant species.F. avenaceum appears to be a candidate for the biocontrol of spotted knapweed, however, a native isolate is potentially more effective than an isolate obtained from the centre of origin ofC. maculosa.     

Non-target effects of an introduced biological control agent on deer mouse ecology

Release of exotic insects as biological control agents is a common approach to controlling exotic plants. Though controversy has ensued regarding the deleterious direct effects of biological control agents to non-target species, few have examined the indirect effects of a ”well-behaved” biological control agent on native fauna. We studied a grassland in west-central Montana infested with spotted knapweed (Centaurea maculosa) to examine the effects of knapweed invasion and two gall flybiological control agents (Urophora affinis and U. quadrifasciata) on the native deer mouse (Peromyscus maniculatus). Stomach-content analysis revealed that Urophora were the primary food item in Peromyscus diets for most of the year and made up 84–86% of the winter diet. Stomach contents indicated that wild-caught mice consumed on average up to 247 Urophora larvae mouse^–1 day^–1, while feeding trials revealed that deer mice could depredate nearly 5 times as many larvae under laboratory conditions. In feeding trials, deer mice selected knapweed seedheads with greater numbers of galls while avoiding uninfested seedheads. When Urophora larvae were present in knapweed seedheads, deer mice selected microhabitats with moderately high (31–45% cover) and high knapweed infestation (≥46% cover). After Urophora emerged and larvae were unavailable to Peromyscus, mice reversed habitat selection to favor sites dominated by native-prairie with low knapweed infestation (0–15%). Establishment of the biological control agent, Urophora spp., has altered deer mouse diets and habitat selection by effecting changes in foraging strategies. Deer mice and other predators may reduce Urophora populations below a threshold necessary to effectively control spotted knapweed. Received: 04 May 1999 / Accepted: 14 August 1999     

Distribution of Insect Attacks in Biological Control of Weeds: Infestation of Centaurea virgata Flowerheads by a Gall Fly

The success of biological control efforts to reduce weed density through release of insects may depend as much on the distribution of insect attacks among individual plants or plant parts as on the mean level of infestation. We used an index of dispersion to describe the distribution of Urophora quadrifasciata (Diptera: Tephritidae) galls among squarrose knapweed (Centaurea virgata) flowerheads at 18 west central Utah sites in the first 5 years following introduction of the biological control agent. Two thirds of the samples showed a significantly aggregated distribution of galls among flowerheads. Statistical analysis showed that site and year accounted for relatively small proportions of the variance in the index of dispersion. The degree of gall aggregation among flowerheads was positively correlated with the mean flowerhead quality (mean number of seeds per flowerhead; P = 0.013) and tended to be negatively correlated with the mean fly density per flowerhead at a site in a given year (P = 0.097). Our data suggest that higher quality flowerheads, and possibly higher quality plants, are preferentially attacked by U. quadrifasciata and therefore are more heavily subject to reduced reproductive potential through biological control. However, an aggregated distribution of fly attacks may undercut the potential of the fly to reduce seed production by the weed population as a whole. Understanding both the distribution of insect attacks among individual plants and the behavioral mechanisms producing such distribution patterns is important to the biological control of weeds.     

Invasion of an exotic forb impacts reproductive success and site fidelity of a migratory songbird

Although exotic plant invasions threaten natural systems worldwide, we know little about the specific ecological impacts of invaders, including the magnitude of effects and underlying mechanisms. Exotic plants are likely to impact higher trophic levels when they overrun native plant communities, affecting habitat quality for breeding songbirds by altering food availability and/or nest predation levels. We studied chipping sparrows (Spizella passerina) breeding in savannas that were either dominated by native vegetation or invaded by spotted knapweed (Centaurea maculosa), an exotic forb that substantially reduces diversity and abundance of native herbaceous plant species. Chipping sparrows primarily nest in trees but forage on the ground, consuming seeds and arthropods. We found that predation rates did not differ between nests at knapweed and native sites. However, initiation of first nests was delayed at knapweed versus native sites, an effect frequently associated with low food availability. Our seasonal fecundity model indicated that breeding delays could translate to diminished fecundity, including dramatic declines in the incidence of double brooding. Site fidelity of breeding adults was also substantially reduced in knapweed compared to native habitats, as measured by return rates and shifts in territory locations between years. Declines in reproductive success and site fidelity were greater for yearling versus older birds, and knapweed invasion appeared to exacerbate differences between age classes. In addition, grasshoppers, which represent an important prey resource, were substantially reduced in knapweed versus native habitats. Our results strongly suggest that knapweed invasion can impact chipping sparrow populations by reducing food availability. Food chain effects may be an important mechanism by which strong plant invaders impact songbirds and other consumers.     

Field cage assessment of interference among insects attacking seed heads of spotted and diffuse knapweed

Field studies were conducted to determine the competitive interactions between introduced biological control agents that attack the seed heads of spotted knapweed (Centaurea stoebe ssp. micranthos) and diffuse knapweed (Centaurea diffusa). Two weevils, Bangasternus fausti and Larinus minutus (Coleoptera: Curculionidae), were each paired with the previously established fly, Urophora affinis (Diptera: Tephritidae). Each species was released either alone or in pair-wise combinations inside screen cages placed over existing knapweed plants at six field sites in Montana and one in Oregon. Larinus minutus produced almost three times as many progeny on diffuse knapweed as on spotted knapweed. Larinus minutus reproduction was not affected by competition with U. affinis, but U. affinis reproduction was reduced by the presence of L. minutus (by 71% on spotted and 77% on diffuse knapweed). Bangasternus fausti reproduction generally was not affected by competition with U. affinis, nor was U. affinis affected by B. fausti on either host plant. There were extremely few cases of successful production of both weevil and fly in the same capitulum, which was probably because weevil larvae consume the developing flies. Both weevils increased the total proportion of seed heads infested on diffuse knapweed, and B. fausti increased it on spotted knapweed. However, the release of either weevil did not significantly further reduce seed production on either plant. The results and experimental design are discussed in light of the subsequent establishment and impact of these agents.     

Flowering phenology of <Emphasis Type="Italic">Ulex europaeus</Emphasis>: ecological consequences of variation within and among populations

Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of long-flowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.     

Impact of two shoot-galling biological control candidates on Russian knapweed, Acroptilon repens

Russian knapweed, Acroptilon repens, is one of the most serious exotic invaders of temperate grasslands in North America. Here we present results from a field experiment in which we quantified the impact of two potential biological control agents, the gall wasp Aulacidea acroptilonica V.Bel. (Hymenoptera, Cynipidae) and the gall midge Jaapiella ivannikovi Fedotova (Diptera, Cecidomyiidae), on A. repens under field conditions in the plant’s native range in Uzbekistan. Attack by A. acroptilonica reduced shoot length by 21%, above-ground biomass by 25% and seed output by 75%, while attack by J. ivannikovi reduced shoot length by 12%, above-ground biomass by 24%, and seed output by 92%. The results of these field experiments are likely to accurately reflect the potential of these two gall formers to reduce above-ground biomass and sexual reproduction of A. repens shoots, since the shoots were part of a clonal network. Despite this, the attacked shoots were not able to compensate for the reallocation of plant resources to gall formation. Moreover, the mean number of galls per shoot obtained in the experiments was within the range of observed gall incidences in the native range. The impact of these two gall-forming insects on Russian knapweed in North America will depend on the population size the species reach and on the timing of attack. The highest impact is likely to occur when the insects attack shoots that have not yet started producing flower-buds.     

Plant community changes after the reduction of an invasive rangeland weed, diffuse knapweed, Centaurea diffusa

The expected outcome of weed control in natural systems is that the decline of a dominant weed will result in an increase in diversity of the plant community but this has seldom been tested. Here we evaluate the response of the plant community following the decline of diffuse knapweed (Centaurea diffusa) in six different pastures at White Lake, BC, Canada over five years. This period followed the establishment, spread and high levels of attack by the introduced European weevil, Larinus minutus, as part of a biological control program. Knapweed declined immediately before and during the study period, but, contrary to expectations, the species richness and diversity of the rangeland plant community did not increase. The absolute cover of native and introduced forbs and grasses increased following knapweed decline, but only the introduced grasses showed a consistent increase in cover relative to the other life-forms. However, unlike in other studies, the native plants dominated the study site. We conclude that the changes in plant communities following successful biological control are variable among programs and that the impact of replacement species must be evaluated in assessing the success of ecological restoration programs that use biological control to manage an undesirable weed.     

Effects of different Beauveria bassiana isolates on field populations of Lygus lineolaris in pigweed (Amaranthus spp.)

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is a pest of various fruit, vegetable, fiber, and seed crops; including cotton. Lygus spp. populations often build on alternate host plants before moving to cotton, and in the midsouthern U.S. wild host plants, such as pigweed (Amaranthus spp.), play a major role in L. lineolaris population development. Three isolates of the entomopathogenic fungus Beauveria bassiana (Balsamo) were evaluated for L. lineolaris control in redroot pigweed (Amaranthus retroflexus L.): one from L. lineolaris in Mississippi (TPB3); one from Lygus hesperus (Knight) in California (WTPB2); and one commercial isolate from Mycotrol^® (GHA). Fungal applications resulted in moderate to high mycosis in adults (33 to 80%) and moderate mycosis in nymphs (36 to 53%) that were collected from field plots at 2 days post-treatment and incubated under laboratory conditions. Although TPB3 was previously found to be more pathogenic in laboratory bioassays, there was not a consistent separation of this isolate from the other two isolates in field trials. Where differences in adult mycosis or mortality were observed, TPB3 was the most pathogenic. However, in one field trial 7 day mortality for nymphs treated with GHA was higher than those treated with TPB3 or WTPB2. Infection rates at 2, 7, and 14 days post-treatment from caged and non-caged adults suggested that movement of adults among plots occurred, which could have masked some treatment effects. Fungal treatments did not significantly reduce populations relative to controls. This may have been caused by delayed mortality rates under field conditions and/or difficulties with estimating population change under field conditions characteristic of wild host plant populations (e.g., heterogeneous populations, adult movement, and small plot size). Further work evaluating time–dose–mortality over dynamic temperatures, spring and fall field trials on this and other wild hosts, and improved methods for estimating populations on wild hosts are needed.     

Increased seed consumption by biological control weevil tempers positive CO2 effect on invasive plant (Centaurea diffusa) fitness

Predicted increases in atmospheric CO₂ and temperature may benefit some invasive plants, increasing the need for effective invasive plant management. Biological control can be an effective means of managing invasive plants, but the anticipated range in responses of plant–insect interactions to climate change make it difficult to predict how effective biological control will be in the future. Field experiments that manipulate climate within biological control systems could improve predictive power, but are challenging to implement and therefore rare to date. Here, we show that free air CO₂ enrichment in the field increased the fitness of Centaurea diffusa Lam., a problematic invader in much of the western United States. However, CO₂ enrichment also increased the impact of the biological control agent Larinus minutus (Coleoptera: Curculionidae) on C. diffusa fitness. C. diffusa plants flowered earlier and seed heads developed faster with both elevated CO₂ and increased temperature. Natural dispersal of L. minutus into the experimental plots provided a unique opportunity to examine weevil preference for and effects on C. diffusa grown under the different climate change treatments. Elevated CO₂ increased both the proportion of seed heads infested by L. minutus and, correspondingly, the amount of seed removed by weevils. Warming had no detectable effect on weevil utilization of plants. Higher weevil densities on elevated CO₂ plants reduced, but did not eliminate, the positive effects of CO₂ on C. diffusa fitness. Correlations between plant development time and weevil infestation suggest that climate change increased weevil infestation by hastening plant phenology. Phenological mismatches are anticipated with climate change in many plant–insect systems, but in the case of L. minutus and C. diffusa in mixed-grass prairie, a better phenological match may make the biological control agent more effective as CO₂ levels rise.     

Host Range of,and Plant Reaction to,Subanguina picridis

The host range of the knapweed nematode, Subanguina picridis (Kirjanova) Brzeski, under controlled environmental conditions was extended to include, in addition to Russian knapweed, Acroptilon repens (L.) DC., plant species within the Centaureinae, and Carduinae subtribes of the Cynareae tribe of the Asteraceae family. Examination of host response to nematode infection revealed that Russian knapweed was the only highly susceptible host plant. Diffuse knapweed (Centaurea diffusa Lam.) was moderately susceptible, and other plants which formed galls were resistant to S. picridis.     

Effects of inoculation methods on the incidence of ear-cockle and ‘tundu’ on wheat under field conditions

Wheat,Triticum aestivum L. cv. Mexipak was artificially inoculated withAnguina tritici (Steinb.) under field conditions. Nematode inocula: 0, 0.1, 0.2 and 0.3 g of seed galls/50 seeds or, germinated seeds of wheat (sown in a 1-m long row) were either added as intact seed galls or as a suspension of 2nd stage juveniles. Inoculation of ungerminated seeds with juveniles produced the highest incidence of ear-cockle disease. Whereas, intact seed galls inocula produced the highest incidence of tundu disease. Ear-cockle incidence was always greater than that of tundu at all treatments. The highest reduction in grain yield was associated with the treatments that caused the highest incidence of tundu disease.     

Epidemiology of Anguina agrostis on Highland Colonial Bentgrass

The epidemiology of Anguina agrostis was investigated in field plots of Colonial bentgrass (cv. Highland), Agrostis tenuis, near Corvallis, Oregon. Each October from 1990-92, nylon mesh pouches, each containing 10 galls, were buried in the field or placed on the soil surface in microplots. Pouches were collected monthly or bimonthly between December and June and nematodes per gall counted. Nematode egression from galls began in late March and was completed by mid-May, corresponding to the period of floral initiation in bentgrass. In 1991 and 1992, 0.09-m² plots were inoculated with 0, 1, 5, 15, 50, 120, or 200 galls/plot. The disease severity (number of galls) and disease incidence (% seed heads with galls) increased linearly at inoculum densities below 50 galls/ plot. At higher inoculum densities, disease increase approached an asymptote. In 1991, plots were established to determine the characteristics of disease spread. Disease foci were established by placing 0, 5, 50, or 500 galls along 30-cm sections of row in the fall. In July 1992, seed heads were harvested at 30 and 60 cm from each focus within and across plant rows. Most infestations were found within 30 cm of foci at all inoculum levels. At high inoculum densities, the distribution of galls was aggregated with the majority of galls located on less than 10% of the seed heads. These disease spread and incidence data suggest populations of A. agrostis increase slowly in bentgrass in Oregon.     

Development of transgenic sorghum for insect resistance against the spotted stem borer (Chilo partellus)

Transgenic sorghum plants expressing a synthetic cry1Ac gene from Bacillus thuringiensis (Bt) under the control of a wound-inducible promoter from the maize protease inhibitor gene (mpiC1) were produced via particle bombardment of shoot apices. Plants were regenerated from the transformed shoot apices via direct somatic embryogenesis with an intermittent three-step selection strategy using the herbicide Basta. Molecular characterisation based on polymerase chain reaction and Southern blot analysis revealed multiple insertions of the cry1Ac gene in five plants from three independent transformation events. Inheritance and expression of the Bt gene was confirmed in T₁ plants. Enzyme-linked immunosorbant assay indicated that Cry1Ac protein accumulated at levels of 1–8 ng per gram of fresh tissue in leaves that were mechanically wounded. Transgenic sorghum plants were evaluated for resistance against the spotted stem borer (Chilo partellus Swinhoe) in insect bioassays, which indicated partial resistance to damage by the neonate larvae of the spotted stem borer. Reduction in leaf damage 5 days after infestation was up to 60%; larval mortality was 40%, with the surviving larvae showing a 36% reduction in weight over those fed on control plants. Despite the low levels of expression of Bt -endotoxin under the control of the wound-inducible promoter, the transgenic plants showed partial tolerance against first instar larvae of the spotted stem borer.