Age differences in the behavioural economics of cannabis use: Do adolescents and adults differ on demand for cannabis and discounting of future reward?

BACKGROUND: Adolescence is a period of psychological and neural development in which harms associated with cannabis use may be heightened. We hypothesised that adolescent who use cannabis (adolescentsWUC) would have steeper delay discounting (preference for immediate over future rewards) and greater demand (relative valuation) for cannabis than adults who use cannabis (adultsWUC). METHODS: This cross-sectional study, part of the 'CannTeen' project, compared adultsWUC (n = 71, 26-29 years old) and adolescentsWUC (n = 76, 16-17 years old), and gender- and age-matched adolescent (n = 63) and adult (n = 64) controls. AdolescentsWUC and adultsWUC used cannabis 1-7 days/week and were matched on cannabis use frequency (4 days/week). The Monetary Choice Questionnaire assessed delay discounting. A modified Marijuana Purchase Task (MPT) assessed cannabis demand in adolescentsWUC and adultsWUC. The MPT yielded five indices: intensity (amount of cannabis used at zero cost), Omax (total peak expenditure), Pmax (price at peak expenditure), breakpoint (cost at which cannabis demand is suppressed to zero) and elasticity (degree to which cannabis use decreases with increasing price). Analyses were adjusted for covariates of gender, socioeconomic status, other illicit drug use. RESULTS: Both adolescentsWUC and adultsWUC had steeper delay discounting than controls (F, (1,254)= 9.13, p = 0.003, ηp2= 0.04), with no significant age effect or interaction. AdolescentsWUC showed higher intensity (F, (1,138)= 9.76, p = 0.002, ηp2= 0.07) and lower elasticity (F, (1,138)= 15.25, p < 0.001, ηp2= 0.10) than adultsWUC. There were no significant differences in Pmax, Omax or breakpoint. CONCLUSION: Individuals who use cannabis prefer immediate rewards more than controls. AdolescentsWUC, compared to adultsWUC, may be in a high-risk category with diminished sensitivity to cannabis price increases and a greater consumption of cannabis when it is free.

The CannTeen study: verbal episodic memory, spatial working memory, and response inhibition in adolescent and adult cannabis users and age-matched controls.

BACKGROUND: Preclinical and human studies suggest that adolescent cannabis use may be associated with worse cognitive outcomes than adult cannabis use. We investigated the associations between chronic cannabis use and cognitive function in adolescent and adult cannabis users and controls. We hypothesised user-status would be negatively associated with cognitive function and this relationship would be stronger in adolescents than adults. METHODS: As part of the 'CannTeen' project, this cross-sectional study assessed cognitive performance in adolescent cannabis users (n = 76; 16-17-year-olds), adolescent controls (n = 63), adult cannabis users (n = 71; 26-29-year-olds) and adult controls (n = 64). Users used cannabis 1-7 days/week. Adolescent and adult cannabis users were matched on cannabis use frequency (4 days/week) and time since last use (2.5 days). Verbal episodic memory (VEM) was assessed using the prose recall task, spatial working memory (SWM) was assessed using the spatial n-back task, and response inhibition was assessed with the stop-signal task. Primary outcome variables were: delayed recall, 3-back discriminability, and stop signal reaction time, respectively. RESULTS: Users had worse VEM than controls (F(1,268) = 7.423, p = 0.007). There were no significant differences between user-groups on SWM or response inhibition. Null differences were supported by Bayesian analyses. No significant interactions between age-group and user-group were found for VEM, SWM, or response inhibition. CONCLUSIONS: Consistent with previous research, there was an association between chronic cannabis use and poorer VEM, but chronic cannabis use was not associated with SWM or response inhibition. We did not find evidence for heightened adolescent vulnerability to cannabis-related cognitive impairment.

The effects of cannabidiol on impulsivity and memory during abstinence in cigarette dependent smokers.

Acute nicotine abstinence in cigarette smokers results in deficits in performance on specific cognitive processes, including working memory and impulsivity which are important in relapse. Cannabidiol (CBD), the non-intoxicating cannabinoid found in cannabis, has shown pro-cognitive effects and preliminary evidence has indicated it can reduce the number of cigarettes smoked in dependent smokers. However, the effects of CBD on cognition have never been tested during acute nicotine withdrawal. The present study therefore aimed to investigate if CBD can improve memory and reduce impulsivity during acute tobacco abstinence. Thirty, non-treatment seeking, dependent, cigarette smokers attended two laboratory-based sessions after overnight abstinence, in which they received either 800 mg oral CBD or placebo (PBO), in a randomised order. Abstinence was biologically verified. Participants were assessed on go/no-go, delay discounting, prose recall and N-back (0-back, 1-back, 2-back) tasks. The effects of CBD on delay discounting, prose recall and the N-back (correct responses, maintenance or manipulation) were null, confirmed by a Bayesian analysis, which found evidence for the null hypothesis. Contrary to our predictions, CBD increased commission errors on the go/no-go task. In conclusion, a single 800 mg dose of CBD does not improve verbal or spatial working memory, or impulsivity during tobacco abstinence.

Psilocybin with psychological support improves emotional face recognition in treatment-resistant depression.

RATIONALE: Depressed patients robustly exhibit affective biases in emotional processing which are altered by SSRIs and predict clinical outcome. OBJECTIVES: The objective of this study is to investigate whether psilocybin, recently shown to rapidly improve mood in treatment-resistant depression (TRD), alters patients' emotional processing biases. METHODS: Seventeen patients with treatment-resistant depression completed a dynamic emotional face recognition task at baseline and 1 month later after two doses of psilocybin with psychological support. Sixteen controls completed the emotional recognition task over the same time frame but did not receive psilocybin. RESULTS: We found evidence for a group × time interaction on speed of emotion recognition (p = .035). At baseline, patients were slower at recognising facial emotions compared with controls (p < .001). After psilocybin, this difference was remediated (p = .208). Emotion recognition was faster at follow-up compared with baseline in patients (p = .004, d = .876) but not controls (p = .263, d = .302). In patients, this change was significantly correlated with a reduction in anhedonia over the same time period (r = .640, p = .010). CONCLUSIONS: Psilocybin with psychological support appears to improve processing of emotional faces in treatment-resistant depression, and this correlates with reduced anhedonia. Placebo-controlled studies are warranted to follow up these preliminary findings.

Acute memory and psychotomimetic effects of cannabis and tobacco both 'joint' and individually: a placebo-controlled trial.

BACKGROUND: Cannabis and tobacco have contrasting cognitive effects. Smoking cannabis with tobacco is prevalent in many countries and although this may well influence cognitive and mental health outcomes, the possibility has rarely been investigated in human experimental psychopharmacological research. METHOD: The individual and interactive effects of cannabis and tobacco were evaluated in 24 non-dependent cannabis and tobacco smokers in a randomized, placebo-controlled, double-blind, 2 (cannabis, placebo) × 2 (tobacco, placebo) crossover design. Verbal memory (prose recall), working memory (WM) performance including maintenance, manipulation and attention (N-back), psychotomimetic, subjective and cardiovascular measures were recorded on each of four sessions. RESULTS: Cannabis alone impaired verbal memory. A priori contrasts indicated that tobacco offset the effects of cannabis on delayed recall. However, this was not supported by linear mixed model analysis. Cannabis load-dependently impaired WM. By contrast, tobacco improved WM across all load levels. The acute psychotomimetic effects and ratings of 'stoned' and 'dizzy' induced by cannabis were not altered by tobacco. Cannabis and tobacco had independent effects on increasing heart rate and interacting effects on increasing diastolic blood pressure. CONCLUSIONS: Relative to placebo, acute cannabis impaired verbal memory and WM. Tobacco enhanced performance on WM, independently of cannabis. Moreover, we found some preliminary evidence that tobacco may offset the effects of cannabis on delayed, but not immediate, verbal recall. In contrast, the psychotomimetic and subjective effects of cannabis were unaffected by tobacco co-administration. By reducing the cognitive impairment from cannabis, tobacco co-administration may perpetuate use despite adverse health consequences.

Are adolescents more vulnerable to the harmful effects of cannabis than adults? A placebo-controlled study in human males.

Preclinical research demonstrates that cannabinoids have differing effects in adolescent and adult animals. Whether these findings translate to humans has not yet been investigated. Here we believe we conducted the first study to compare the acute effects of cannabis in human adolescent (n=20; 16-17 years old) and adult (n=20; 24-28 years old) male cannabis users, in a placebo-controlled, double-blind cross-over design. After inhaling vaporized active or placebo cannabis, participants completed tasks assessing spatial working memory, episodic memory and response inhibition, alongside measures of blood pressure and heart rate, psychotomimetic symptoms and subjective drug effects (for example, 'stoned', 'want to have cannabis'). Results showed that on active cannabis, adolescents felt less stoned and reported fewer psychotomimetic symptoms than adults. Further, adults but not adolescents were more anxious and less alert during the active cannabis session (both pre- and post-drug administration). Following cannabis, cognitive impairment (reaction time on spatial working memory and prose recall following a delay) was greater in adults than adolescents. By contrast, cannabis impaired response inhibition accuracy in adolescents but not in adults. Moreover, following drug administration, the adolescents did not show satiety; instead they wanted more cannabis regardless of whether they had taken active or placebo cannabis, while the opposite was seen for adults. These contrasting profiles of adolescent resilience (blunted subjective, memory, physiological and psychotomimetic effects) and vulnerability (lack of satiety, impaired inhibitory processes) show some degree of translation from preclinical findings, and may contribute to escalated cannabis use by human adolescents.

Salience attribution and its relationship to cannabis-induced psychotic symptoms.

BACKGROUND: Cannabis is a widely used drug associated with increased risk for psychosis. The dopamine hypothesis of psychosis postulates that altered salience processing leads to psychosis. We therefore tested the hypothesis that cannabis users exhibit aberrant salience and explored the relationship between aberrant salience and dopamine synthesis capacity. METHOD: We tested 17 cannabis users and 17 age- and sex-matched non-user controls using the Salience Attribution Test, a probabilistic reward-learning task. Within users, cannabis-induced psychotic symptoms were measured with the Psychotomimetic States Inventory. Dopamine synthesis capacity, indexed as the influx rate constant K i cer , was measured in 10 users and six controls with 3,4-dihydroxy-6-[18F]fluoro-l-phenylalanine positron emission tomography. RESULTS: There was no significant difference in aberrant salience between the groups [F 1,32 = 1.12, p = 0.30 (implicit); F 1,32 = 1.09, p = 0.30 (explicit)]. Within users there was a significant positive relationship between cannabis-induced psychotic symptom severity and explicit aberrant salience scores (r = 0.61, p = 0.04) and there was a significant association between cannabis dependency/abuse status and high implicit aberrant salience scores (F 1,15 = 5.8, p = 0.03). Within controls, implicit aberrant salience was inversely correlated with whole striatal dopamine synthesis capacity (r = -0.91, p = 0.01), whereas this relationship was non-significant within users (difference between correlations: Z = -2.05, p = 0.04). CONCLUSIONS: Aberrant salience is positively associated with cannabis-induced psychotic symptom severity, but is not seen in cannabis users overall. This is consistent with the hypothesis that the link between cannabis use and psychosis involves alterations in salience processing. Longitudinal studies are needed to determine whether these cognitive abnormalities are pre-existing or caused by long-term cannabis use.

Nitrous oxide speeds the reduction of distressing intrusive memories in an experimental model of psychological trauma.

BACKGROUND: Post-traumatic stress disorder (PTSD) involves maladaptive long-term memory formation which underlies involuntary intrusive thoughts about the trauma. Preventing the development of such maladaptive memory is a key aim in preventing the development of PTSD. We examined whether the N-methyl d-aspartate receptor (NMDAR) antagonist gas nitrous oxide (N2O) could reduce the frequency of intrusive memories by inhibiting NMDAR-dependent memory consolidation in a laboratory analogue of psychological trauma. METHOD: Participants were randomized to inhale N2O (N = 25) or medical air (N = 25) after viewing a negatively valenced emotional film clip ('trauma film'). Participants subsequently completed a daily diary assessing frequency of intrusive thoughts relating to the film clip. A week later, participants completed an explicit memory recall task related to the film. RESULTS: Post-encoding N2O sped the reduction in intrusive memory frequency, with a significant reduction by the next day in the N2O group compared to 4 days later in the air group. N2O also interacted with post-film dissociation, producing increased intrusion frequency in those who were highly dissociated at baseline. Sleep length and quality the night after viewing the film did not differ between the groups. CONCLUSION: N2O speeds the reduction of intrusive analogue trauma memory in a time-dependent manner, consistent with sleep-dependent long-term consolidation disruption. Further research with this drug is warranted to determine its potential to inoculate against enduring effects of psychological trauma; however, caution is also urged in dissociated individuals where N2O may aggravate PTSD-like symptomatology.

AKT1 genotype moderates the acute psychotomimetic effects of naturalistically smoked cannabis in young cannabis smokers.

Smoking cannabis daily doubles an individual's risk of developing a psychotic disorder, yet indicators of specific vulnerability have proved largely elusive. Genetic variation is one potential risk modifier. Single-nucleotide polymorphisms in the AKT1 and catechol-O-methyltransferase (COMT) genes have been implicated in the interaction between cannabis, psychosis and cognition, but no studies have examined their impact on an individual's acute response to smoked cannabis. A total 442 healthy young cannabis users were tested while intoxicated with their own cannabis-which was analysed for delta-9-tetrahydrocannbinol (THC) and cannabidiol content-and also ± 7 days apart when drug-free. Psychotomimetic symptoms and working memory were assessed on both the sessions. Variation at the rs2494732 locus of the AKT1 gene predicted acute psychotic response to cannabis along with dependence on the drug and baseline schizotypal symptoms. Working memory following cannabis acutely was worse in females, with some suggestion of an impact of COMT polymorphism on working memory when drug-free. These findings are the first to demonstrate that AKT1 mediates the acute response to cannabis in otherwise healthy individuals and implicate the AKT1 pathway as a possible target for prevention and treatment of cannabis psychosis.

Examining the profile of high-potency cannabis and its association with severity of cannabis dependence.

BACKGROUND: Cannabis use is decreasing in England and Wales, while demand for cannabis treatment in addiction services continues to rise. This could be partly due to an increased availability of high-potency cannabis. METHOD: Adults residing in the UK were questioned about their drug use, including three types of cannabis (high potency: skunk; low potency: other grass, resin). Cannabis types were profiled and examined for possible associations between frequency of use and (i) cannabis dependence, (ii) cannabis-related concerns. RESULTS: Frequent use of high-potency cannabis predicted a greater severity of dependence [days of skunk use per month: b = 0.254, 95% confidence interval (CI) 0.161-0.357, p < 0.001] and this effect became stronger as age decreased (b = -0.006, 95% CI -0.010 to -0.002, p = 0.004). By contrast, use of low-potency cannabis was not associated with dependence (days of other grass use per month: b = 0.020, 95% CI -0.029 to 0.070, p = 0.436; days of resin use per month: b = 0.025, 95% CI -0.019 to 0.067, p = 0.245). Frequency of cannabis use (all types) did not predict severity of cannabis-related concerns. High-potency cannabis was clearly distinct from low-potency varieties by its marked effects on memory and paranoia. It also produced the best high, was preferred, and most available. CONCLUSIONS: High-potency cannabis use is associated with an increased severity of dependence, especially in young people. Its profile is strongly defined by negative effects (memory, paranoia), but also positive characteristics (best high, preferred type), which may be important when considering clinical or public health interventions focusing on cannabis potency.

Attentional bias and treatment adherence in substitute-prescribed opiate users.

BACKGROUND: Attentional bias (AB) is implicated in the development and maintenance of substance dependence and in treatment outcome. We assessed the effects of attentional bias modification (ABM), and the relationship between AB and treatment adherence in opiate dependent patients. METHOD: An independent groups design was used to compare 23 opiate dependent patients with 21 healthy controls. Participants completed an AB task before either a control or an ABM task designed to train attention away from substance-related stimuli. Pre- and post-ABM AB and craving were assessed to determine any changes. Relationships between treatment adherence ('using on top' of prescribed opiates or not) and AB, craving and psychopathology were also examined. RESULTS: There was no baseline difference in AB between patients and controls, and no significant effect of ABM on AB or substance craving. However, treatment adherent patients who did not use illicit opiates on top of their prescribed opiates had statistically significantly greater AB away from substance-related stimuli than both participants using on top and controls, and reported significantly lower levels of craving than non-treatment adherent patients. CONCLUSION: Whilst we did not find any significant effects of ABM on AB or craving, patients who were treatment adherent differed from both those who were not and from controls in their attentional functioning and substance craving. These findings are the first to suggest that AB may be a within-treatment factor predictive of adherence to pharmacological treatment and potentially of recovery in opiate users.

The effects of nicotine dependence and acute abstinence on the processing of drug and non-drug rewards.

RATIONALE: Drug addiction may be characterised by a hypersensitivity to drug rewards and a hyposensitivity to non-drug rewards. This imbalance may become further polarised during acute abstinence. OBJECTIVES: (i) Examine the differences between dependent and occasional smokers in choices for, motivation for and self-reported wanting and liking of cigarette and non-drug rewards. (ii) Examine the effects of 12-h nicotine abstinence on these metrics. METHODS: Dependent (n = 20) and occasional, non-dependent smokers (n = 20) were tested after ad libitum smoking and ≥12-h of nicotine abstinence. A novel task was developed (Drug, Reward and Motivation-Choice (DReaM-Choice)) in which different rewards (cigarettes, music and chocolate) could be won. In each trial, participants chose between two rewards and then could earn the chosen reward via repeated button-pressing. Participants subsequently 'consumed' and rated subjective liking of the rewards they had won. RESULTS: Compared with occasional smokers, dependent smokers made more choices for (p < 0.001), pressed more for (p = 0.046) and reported more wanting (p = 0.007) and liking (p < 0.001) of cigarettes, and also made fewer choices for chocolate (p = 0.005). There were no differences between the groups on button-pressing for chocolate or music. However, the balance between drug and non-drug reward processing was different between the groups across all metrics. Twelve-hour nicotine abstinence led to more cigarette choices (p < 0.001) and fewer music choices (p = 0.042) in both groups. CONCLUSIONS: Nicotine dependence was associated with a hypersensitivity to cigarette rewards, but we found little evidence indicating a hyposensitivity to non-drug rewards. Our findings question the moderating influence of dependence on how acute nicotine abstinence affects reward processing.

Tobacco smoking in schizophrenia: investigating the role of incentive salience.

BACKGROUND: Smoking is highly prevalent in people diagnosed with schizophrenia, but the reason for this co-morbidity is currently unclear. One possible explanation is that a common abnormality underpins the development of psychosis and independently enhances the incentive motivational properties of drugs and their associated cues. This study aimed to investigate whether incentive salience attribution towards smoking cues, as assessed by attentional bias, is heightened in schizophrenia and associated with delusions and hallucinations. METHOD: Twenty-two smokers diagnosed with schizophrenia and 23 control smokers were assessed for smoking-related attentional bias using a modified Stroop task. Craving, nicotine dependence, smoking behaviour and positive and negative symptoms of schizophrenia were also recorded. RESULTS: Both groups showed similar craving scores and smoking behaviour according to self-report and expired carbon monoxide (CO), although the patient group had higher nicotine dependence scores. Attentional bias, as evidenced by significant interference from smoking-related words on the modified Stroop task, was similar in both groups and correlated with CO levels. Attentional bias was positively related to severity of delusions but not hallucinations or other symptoms in the schizophrenia group. CONCLUSIONS: This study supports the hypothesis that the development of delusions and the incentive motivational aspects of smoking may share a common biological substrate. These findings may offer some explanation for the elevated rates of smoking and other drug use in people with psychotic illness.

Sub-chronic impact of cannabinoids in street cannabis on cognition, psychotic-like symptoms and psychological well-being.

BACKGROUND: Cannabis varies considerably in levels of its two major constituent cannabinoids - (delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Recently, we found evidence that those who smoked cannabis containing detectable levels of CBD had fewer psychotic-like symptoms than those whose cannabis had no CBD. The present study aimed, first, to replicate those findings and, second, to determine whether protective effects of CBD may extend to other harms of cannabis, such as memory impairment and reduced psychological well-being. METHOD: A total of 120 current cannabis smokers, 66 daily users and 54 recreational users were classified into groups according to whether analysis of their hair revealed the presence or absence of CBD and high versus low levels of THC. All were assessed on measures of psychosis-like symptoms, memory (prose recall; source memory) and depression/anxiety. RESULTS: Lower psychosis-like symptoms were found in those whose hair had CBD compared with those without. However, this was seen only in recreational users, who had higher levels of THC in their hair. Higher THC levels in hair were associated with increased depression and anxiety. Prose recall and source memory were poorer in daily users with high THC levels in hair while recognition memory was better in individuals with CBD present in hair. CONCLUSIONS: CBD attenuates the psychotic-like effects of cannabis over time in recreational users. Higher THC negatively impacts on memory and psychological well-being. These findings raise concerns for the harms stemming from use of varieties such as 'skunk' (sensimillia), which lack any CBD but currently dominate the supply of cannabis in many countries.

Drug cue induced overshadowing: selective disruption of natural reward processing by cigarette cues amongst abstinent but not satiated smokers.

BACKGROUND: Addicts show both reward processing deficits and increased salience attribution to drug cues. However, no study to date has demonstrated that salience attribution to drug cues can directly modulate inferences of reward value to non-drug cues. Associative learning depends on salience: a more salient predictor of an outcome will 'overshadow' a less salient predictor of the same outcome. Similarly, blocking, a demonstration that learning depends on prediction error, can be influenced by the salience of the cues employed. METHOD: This study investigated whether salient drug cues might interact with neutral cues predicting financial reward in an associative learning task indexing blocking and overshadowing in satiated smokers (n=24), abstaining smokers (n=24) and non-smoking controls (n=24). Attentional bias towards drug cues, craving and expired CO were also indexed. RESULTS: Abstaining smokers showed drug cue induced overshadowing, attributing higher reward value to drug cues than to neutral cues that were equally predictive of reward. Overshadowing was positively correlated with expired CO levels, which, in turn, were correlated with craving in abstainers. An automatic attentional bias towards cigarette cues was found in abstainers only. CONCLUSIONS: These findings provide the first evidence that drug cues interact with reward processing in a drug dependent population.

H-gene-mediated resistance to Hessian fly exhibits features of penetration resistance to fungi.

Features shared by host-specific phytophagous insects and biotrophic plant pathogens include gene-for-gene interactions and the ability to induce susceptibility in plants. The Hessian fly shows both. To protect against Hessian fly, grasses have H genes. Avirulent larvae die on H-gene-containing resistant plants but the cause of death is not known. Imaging techniques were used to examine epidermal cells at larval attack sites, comparing four resistant wheat genotypes (H6, H9, H13, and H26) to a susceptible genotype. Present in both resistant and susceptible plants attacked by larvae were small holes in the tangential cell wall, with the size of the holes (0.1 microm in diameter) matching that of the larval mandible. Absent from attacked resistant plants were signs of induced susceptibility, including nutritive tissue and ruptured cell walls. Present in attacked resistant plants were signs of induced resistance, including cell death and fortification of the cell wall. Both presumably limit larval access to food, because the larva feeds on the leaf surface by sucking up liquids released from ruptured cells. Resistance was associated with several subcellular responses, including elaboration of the endoplasmic reticulum-Golgi complex and associated vesicles. Similar responses are observed in plant resistance to fungi, suggesting that "vesicle-associated penetration resistance" also functions against insects.

First Report of Beet black scorch virus in the United States.

In October of 2005, sugar beet (Beta vulgaris L.) plants exhibiting symptoms of rhizomania caused by Beet necrotic yellow vein virus (BNYVV) (3) were observed in a production field near Greeley, CO. The roots of seven plants exhibiting moderate to severe symptoms characteristic of this disease were tested using double-antibody sandwich enzyme-linked immunosorbent assay with anti-BNYVV antiserum from rabbits. Of these, only two roots exhibiting the mildest symptoms tested positive for BNYVV (all roots tested negative for the presence of the related Beet soilborne mosaic virus (BSBMV). 'Hairy' lateral roots characteristic of the disease were combined from the remaining five roots, ground in phosphate buffer, and the supernatant from the suspension was mechanically applied to leaves of Chenopodium quinoa in an effort to isolate an infectious agent. Five days postinoculation (dpi), yellow lesions with necrotic centers were visible on inoculated leaves, well in advance of those typically observed for BNYVV or BSBMV. Lesions exhibiting a similar rate of development on C. quinoa subsequently were induced from extracts of root vascular tissue prepared from four of seven additional beet roots tested from this location. Transfer of the infection from the C. quinoa lesions to 32 healthy C. quinoa and 10 sugar beet plants (hybrid ACH9369; American Crystal Sugar Co., Moorhead MN) resulted in 100% infection. Inoculated leaves of C. quinoa exhibited a high density of necrotic local lesions within 3 dpi, whereas inoculated leaves of sugar beet exhibited pinpoint, necrotic to diffuse, chlorotic local lesions evident by 5 dpi. Electron microscopic examination of fixed, ultra-thin sections of symptomatic C. quinoa leaf tissue revealed aggregates of virus-like particles of icosahedral symmetry within the cell cytoplasm. Following a virus minipreparation procedure, nucleic acid extracted from the partially purified virus was found to be single-stranded RNA by ribonuclease digestion and alone was infectious when inoculated to C. quinoa leaves. The apparently monopartite RNA genome was 3.5 kb long and a candidate for the single coat protein (CP) had a mass of ˜25 kDa. The sole reference set found in the literature for a virus naturally occurring on sugar beet with similar characteristics was that for Beet black scorch virus (BBSV), a virus recently accepted by the ICTV into the genus Necrovirus within the family Tombusviridae (2). Prior to this communication, BBSV has only been reported in China where it was first documented affecting sugar beet in the late 1980s (1). Using the published sequence of BBSV (Genbank Accession No. AY626780), DNA primers directed to the 3' half of the BBSV genome were used in reverse transcription-polymerase chain reaction to produce an amplicon from the unknown virus. Sequencing the amplicon revealed 88.8% nucleotide sequence identity to the BBSV CP gene and 97% amino acid sequence identity to the predicted CP gene product. Combined, the nucleotide sequence and physical characteristics confirm the presence of BBSV in a U.S. sugarbeet field for the first time. To our knowledge, this is the first report of the occurrence of BBSV outside of China. References: (1) Y. Cao et al. Arch. Virol. 147:2431, 2002. (2) C. M. Fauquet et al. Eighth Report of the International Committee on the Taxonomy of Viruses. Academic Press, New York, 2005. (3) C. M. Rush. Ann. Rev. Phytopathol. 41:567, 2003.

Cuticular lipids and silverleaf whitefly stage affect conidial germination of Beauveria bassiana and Paecilomyces fumosoroseus.

Beauveria bassiana and Paecilomyces fumosoroseus are generalist entomopathogenic fungi that infect the silverleaf whitefly (Bemisia argentifolii). We found second and third instar whiteflies to be the most susceptible larval stage to both fungi. Conidia of B. bassiana germinated most readily on the cuticle of second instars (54% germinated) and P. fumosoroseus germination was highest on third instar cuticle (45%). Fourth instars (the ultimate instar) had low susceptibility to these pathogens, and spore germination on the cuticle of fourth instars was very low for B. bassiana (7%) and intermediate for P. fumosoroseus (33%). Cuticular lipids were found to have toxic or inhibitory effects on conidia of B. bassiana and P. fumosoroseus when the spores were germinated on nutrient agar in the presence of the lipids. In the absence of added nutrients, P. fumosoroseus conidial germination increased in the presence of the lipids. To test if the inhibitory effects of the lipids were due solely to hydrophobicity (preventing water from coming into contact with the conidia) we tested the effects of synthetic long-chain wax esters. The synthetic wax esters inhibited germination of P. fumosoroseus to a degree that was similar to the effect of the cuticular lipid extracts, but the synthetic lipids did not have a significant effect on B. bassiana. Thus, the thick coating of long-chain wax esters produced by whitefly nymphs affect spore germination of fungal pathogens, but whether they play a significant role in defense against disease is not clear.