Spatial dispersion and sampling of citrus whitefly,Dialeurodes citri,for control decisions in a citrus orchard

1 Monitoring the citrus whitefly Dialeurodes citri (Ashmead) in citrus orchards in Israel is necessary for control decisions in IPM in the period before the establishment of natural enemies. The main damage caused by D. citri is due to sooty mould, which colonizes the sweet secretions of this pest. 2 Using Taylor’s Power Law to describe the variance–mean relationship, the dispersion of the citrus whitefly was found to be aggregated at all developmental stages. The action threshold was estimated using regression of sooty mould level on egg or larval counts. 3 Two-stage sampling plans were constructed in different pest generations, for eggs and larval stages, on the basis of the variance between leaves on a tree and the variance between trees in a plot. 4 Fixed sample size plans were prepared, with possible numbers of trees and the numbers of leaves per tree to be sampled, in order to attain a given precision level. 5 Sequential sampling plans were also drawn up, on the basis of four leaves per tree, where trees are sampled until a decision can be reached. The maximum number of trees to be sampled was set according to the corresponding fixed sample size plan. 6 Simulation of the sequential sampling plans showed them to be highly reliable in terms of the decision reached with economy in sample size for high and low infestation levels.     

华南地区柑橘木虱与柑橘粉虱内共生菌检测及其Wolbachia共生菌的系统发育关系分析

【目的】探明不同地理种群的柑橘木虱Diaphorina citri Kuwayama和柑橘粉虱Dialeurodes citri Ashmead体内昆虫内共生菌的种类及其感染率,并以Wolbachia共生菌为代表,对其系统发育关系进行分析,为今后自共生菌角度研发柑橘木虱和柑橘粉虱的新型防控技术奠定基础。【方法】以16S r DNA、23S r DNA以及wsp为目标基因,利用PCR技术检测采自于广州、湛江、南宁、桂林、厦门的柑橘木虱以及采自广州的柑橘粉虱体内共生菌的种类及其感染率;利用多位点序列分型(MLST)技术和MEGA 5.0软件对不同昆虫样本中的Wolbachia进行系统发育关系分析。【结果】本研究采集的柑橘木虱和柑橘粉虱均含有原生共生菌Portiera和次生共生菌Wolbachia、Cardinium、Rickettsia,但该3种次生共生菌在不同木虱与粉虱种群的感染率有所不同;Arsenophonus只在广州和湛江种群的柑橘木虱中检出。基于wsp基因及MLST基因序列的Wolbachia系统发育分析表明,华南地区柑橘木虱和柑橘粉虱体内的Wolbachia均属于Wolbachia的B大组Con亚组。【结论】不同地理种群的柑橘木虱与柑橘粉虱体内感染的共生菌种类及其感染率不同;Wolabchia共生菌与柑橘木虱寄主不存在协同进化关系,在同一采集点存在Wolbachia通过柑橘寄主在柑橘木虱之间、柑橘木虱与柑橘粉虱之间水平传播的可能性。     

Recent advances in the understanding of Xanthomonas citri ssp. citri pathogenesis and citrus canker disease management

Taxonomic status : Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadaceae; Genus Xanthomonas; Species Xanthomonas citri ssp. citri (Xcc). Host range : Compatible hosts vary in their susceptibility to citrus canker (CC), with grapefruit, lime and lemon being the most susceptible, sweet orange being moderately susceptible, and kumquat and calamondin being amongst the least susceptible. Microbiological properties : Xcc is a rod‐shaped (1.5–2.0 × 0.5–0.75 µm), Gram‐negative, aerobic bacterium with a single polar flagellum. The bacterium forms yellow colonies on culture media as a result of the production of xanthomonadin. Distribution : Present in South America, the British Virgin Islands, Africa, the Middle East, India, Asia and the South Pacific islands. Localized incidence in the USA, Argentina, Brazil, Bolivia, Uruguay, Senegal, Mali, Burkina Faso, Tanzania, Iran, Saudi Arabia, Yemen and Bangladesh. Widespread throughout Paraguay, Comoros, China, Japan, Malaysia and Vietnam. Eradicated from South Africa, Australia and New Zealand. Absent from Europe.     

Twelve polymorphic microsatellite loci from the Asian citrus psyllid,Diaphorina citri Kuwayama,the vector for citrus greening disease,huanglongbing

Twelve polymorphic microsatellite markers were developed from microsatellite‐enriched DNA libraries and mined from an expressed sequence tags library of Diaphorina citri, the vector of the citrus greening disease (huanglongbing). Analysis of 288 individuals from Florida, Texas, and Brazil showed that allelic diversity ranged from three to eight alleles per locus and observed and expected heterozygosities ranged from 0.014 to 0.569 and from 0.052 to 0.653, respectively. These variable microsatellite loci can provide means for assessing overall genetic variation and migration patterns for this agriculturally important pest species. This information can be used to aid in developing successful management strategies.     

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and huanglongbing disease do not exist in the Stapleton Station area of the Northern Territory of Australia

Abstract  A series of specimens of the Asian citrus psyllid, Diaphorina citri , collected from the Northern Territory (NT) in 1915 was recently rediscovered in the Natural History Museum, London. Surveys were conducted in 2002 on suitable hosts in the locality of the 1915 collections to see if the infestation had persisted. These failed to detect either D. citri or the bacterium that it transmits and that causes huanglongbing disease in citrus. It is presumed that D. citri was eradicated fortuitously by the removal of all citrus plants above latitude 19°S during an eradication program for citrus canker in the NT from 1916 until 1922.     

Predation of the apefly,Spalgis epius (Lepidoptera: Lycaenidae) on citrus mealybug,Planococcus citri (Hemiptera: Pseudococcidae)

The citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae) is a serious pest of economically important crops worldwide. The apefly, Spalgis epius (Westwood) (Lepidoptera: Lycaenidae) is a potential predator of various species of mealybugs. Earlier investigation on its daily preying capacity and preference for prey stages on P. citri is incomplete. Hence, a study was conducted to find out the daily prey consumption ability and preference for prey stages by different larval instars of S. epius reared on P. citri in the laboratory. Through the 8-day developmental period with four larval instars, the daily prey consumption of S. epius increased from the first to the seventh day and decreased on the eighth day prior to the prepupal stage. Generally, there was a significant difference in the prey consumption on different days. When the prey stages were offered separately, the first to fourth instar larva of S. epius consumed, respectively, a mean of 199.6, 722.6, 1908.8, and 4625.6 eggs or 21.5, 77.0, 168.5, and 670.5 nymphs or 3.2, 7.2, 16.0, and 35.1 adults of P. citri. When an S. epius larva was fed on P. citri eggs, nymphs and adults separately, it consumed a mean of 7456.7 eggs, 937.6 nymphs, or 62.3 adults during its entire development. When the prey stages were offered all together, a single S. epius larva consumed 2618.4 eggs, 170.4 nymphs, and 39.7 adults of P. citri throughout its entire development. The study revealed that S. epius is a voracious predator of P. citri and thus could be utilized as a major biological control agent.     

Stability in the host-parasitoid relationship of Dialeurodes citri and Encarsia lahorensis in the citrus orchard

The citrus whitefly, Dialeurodes citri (Ashmead), a citrus pest, has been prevalent in Israel since 1975. The parasitic wasp Encarsia lahorensis (Howard) has been successfully used for its biological control since 1980 and thehost-parasitoid system is stable. This studyuses field data from four and a half years inorder to examine whether heterogeneity ofparasitism and risk aggregation can explain thestability. After establishing that theprobability of parasitism is not constant overpatches, we examined the question of parasitoidaggregation, dependent or independent of thehost, at different patch levels. At the treelevel we found an inverse relationship betweenthe proportion of parasitism and host density.At the leaf level, taking the tree effect intoconsideration, the host density dependence wasweak and non-significant. At the leaf level, acombined examination of both types ofheterogeneity in parasite distribution – hostdensity dependent heterogeneity (direct orindirect) and host density independentheterogeneity, was performed using the (CV)² > 1 criterion. The mean (CV)² value over different sampling dateswas greater than one. Host density independentheterogeneity had the greater contribution tostability. The (CV)² findings atleaf level in the plot, combining leaf and treeeffects, represent both aggregation at the treelevel (inverse density dependence) andaggregation at the leaf level (host densityindependence). The heterogeneity findings forparasitoid distribution, together with thestability, which was directly observed, supportour hypothesis that aggregation of risk is animportant mechanism in the stabilisinginteraction between the citrus whitefly and itsspecific parasitoid, E. lahorensis.     

Repellent effect of guava leaf volatiles on settlement of adults of citrus psylla, Diaphorina citri Kuwayama, on citrus

Abstract  The Asiatic citrus psyllid ( Diaphorina citri Kuwayama [Hemiptera: Sternorrhyncha: Psyllidae]) is a vector of huanglongbing (citrus greening), a devastating disease of citrus caused by phloem-limited bacteria. Growing guava ( Psidium guajava ) as an intercrop appears to be a successful means of reducing psyllid numbers within citrus orchards; however, the mechanism by which such a reduction is achieved is unknown. To determine the repellent effect of guava leaf and factors attributed to this activity, responses of adult psyllids to guava leaf and its odor were evaluated in cage tests and Y-tube olfactometer test. The results showed that guava leaf possessed a repellent effect against the adult citrus psyllids. Fewer psyllids were found on citrus leaves in the presence of guava foliage than in its absence. Young and old guava leaf showed equal repellent activity. By covering the guava shoots with net cloth, it was revealed that the repellent effect of guava leaf against adult psyllids on citrus was attributed to the volatile compounds, rather than physical factors. The olfactometer response of adult psyllids to guava leaf odor was dosage-dependent. Between guava odor and control, only 35.00%, 25.00% and 16.25% of the psyllids moved toward guava odor when presented with 5.0, 10.0 and 15.0 g of guava shoots, respectively. The olfactometer experiments also showed that both male and female psyllids responded similarly to the guava leaf odor.     

Host selection and sex allocation in Leptomastidea abnormis, a parasitoid of the citrus mealybug Planococcus citri

Leptomastidea abnormis (Girault) and Leptomastix dactylopii (Howard) [Hymenoptera: Encyrtidae] are the two parasitoid species frequently used for biological control of the citrus mealybug Planococcus citri (Risso) [Homoptera: Pseudococcidae]. As part of a programme to determine the best control practice, host size selection and sex allocation were studied in L. abnormis, and compared with those of L. dactylopii. L. abnormis showed a preference for the second size class, but also attacked third and fourth size class and adult mealybugs, while in previous studies L. dactylopii was found to prefer the third and fourth size class and adults, and never attacked second size class mealybugs. Female L. abnormis reared from parasitized mealybugs had a higher mean body mass than males, as is predicted by Charnov's theory on sex allocation. However, sex ratios of emerging L. abnormis did not differ between mealybug size classes. These results imply possibile coexistence of the two parasitoids. As field evidence suggests a more complex interaction between the two species, studying direct competition would be a useful next step.     

Leaf age preference for oviposition by three species of whitefly on lemon

The leaf age preferences for oviposition by three species of whitefly (Dialeurodes citri [Ashmead],Aleurothrixus floccosus [Maskell], andParabemisia myricae [Kuwana]) were tested on lemon,Citrus limon (L.). Four categories of leaf age were tested (I: incompletely expanded, growing leaves; II: young leaves that are completely expanded but not yet dark green; III: completely mature leaves [dark green]; IV: completely mature leaves judged to be older than III as determined by the age of the twigs to which they were attached). Paired choice experiments were conducted in the laboratory using excised leaves and in the field using intact leaves. In both laboratory and field tests,P. myricae preferred I over all other leaf ages. It rarely oviposited on II and never oviposited on III or IV, even when they were the only two choices. The order of preference forD. citri in laboratory and field tests was II>I>III>IV. In laboratory tests,A. floccosus exhibited the same order of preferences asD. citri, but in the field, II was preferred over all others, III was slightly preferred over IV, and I varied greatly among replicates in comparisons against III or IV. In related experiments, the choice between I & III byA. floccosus andD. citri was not affected by confining the whiteflies to either I or III for three days prior to testing.

---

Sélection pour la ponte des feuilles deCitrus limon en fonction de l'âge par trois espèces d'aleurodes

Résumé Des feuilles de 4 tranches d'âges appartenant àCitrus limon L.: 1) en cours de croissance et incomplètement développées; 2) développées mais pas encore vert sombre; 3) complètement développées (vert sombre) 4) plus âgées que le lot 3 d'après l'âge du rameau, ont été proposées pour pondre à 3 espèces d'aleurodes (Dialeurodes citri Ashmead,Aleurothrixus floccosus Maskell,Parabemisia myricae Kuwana). Les femelles étaient isolées dans des cages dont les ouvertures sur deux côtés opposés étaient obstruées par la face inférieure de feuilles de citronniers d'âges différents. Les feuilles utilisées au laboratoire étaient coupées, les expériences dans la nature étaient faites avec des feuilles intactes. Récoltées au bout de 2 jours, leurs ufs étaient dénombrés.Dans les 2 cas,P. myricae a préféré significativement le lot 1, les pontes sur lot 2 étaient rares, et nulles sur les lots 3 et 4 même en l'absence de choix. Les préférences significativement différentes deD. citri au laboratoire et dans la nature étaient les suivantes: 2>1>3>4.A. floccosus a présenté au laboratoire les mêmes préférences queD. citri (P0,0004), mais certains résultats étaient contradictoires. Au laboratoire et dans la nature, le lot 2 était préféré; de même le lot 3 était préféré au lot 4. Cependant de nombreuses expériences de choix dans la nature entre les lots 1 et 3 et 1 et 4 ont montré la même tendance qu'au laboratoire, mais pour d'autres, les résultats étaient inversés. Après regroupement des résultats dans la nature, le lot 3 a été préféré au lot 1 (résultats à la limite du seuil de validité); aucune différence significative n'est apparue entre les lots 1 et 4. Les choix deA. floccocus etD. citri entre les lots 1 et 3 n'ont pas été modifiés par la présence de l'un des lots pendant les 3 jours précédant l'expérience.

     

Distribution and sampling of the whiteflies Aleurothrixus floccosus, Dialeurodes citri, and Parabemisia myricae (Homoptera: Aleyrodidae) in citrus in Spain

From 1993 to 1995 data sets were collected from four citrus groves in Valencia, Spain, to determine the distribution patterns of eggs and nymphs of Aleurothrixus floccosus (Maskell), Dialeurodes citri (Ashmead), and Parabemisia myricae (Kuwana) on leaves, and to develop reliable sampling plans for estimating densities of immature whiteflies. A. floccosus showed higher aggregation than the other two species. The dispersion index b from the Taylor power law did not vary between different developing stages for A. floccosus and D. citri, reaching overall values of 1.70 and 1.53, respectively. In P. myricae, b was 1.60 for eggs and N1, and 1.46 for the remaining nymphs. The minimum number of leaves to estimate the population density with a coefficient of variation of 0.25 for densities above 10 immature whiteflies per leaf was 40 for D. citri and P. myricae, and 250 for A. floccosus. Binomial sampling programs for the three species were rejected for pest management purposes due to the high sample sizes required. The enumerative procedure of counting the number of insects per leaf appears to be the most suitable method for D. citri and P. myricae. For A. floccosus an index of occupation (from 0 to 10) linearly related to the proportion of the leaf undersurface occupied by this insect was found to be reliable and time-saving. Examining 150 leaves with this index achieves the desired relative variation level of 0.25 for most population densities usually found in commercial groves.     

Population dynamics of the citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae) in Japanese pear orchards

In spring a population of the citrus red mite (Panonychus citri),a non-diapausing species, migrated to a Japanese pear orchard, mainly from nearby Japanese holly trees, but in autumn most of the mites starved to death while the rest returned to the holly trees. In the Japanese holly trees, the population of mites reached their maximum density in late May1993 and in mid-June 1994 on overwintered leaves and moved to newly opened leaves in mid-June 1993 and late June 1994. The mites tended to disperse abruptly in early June or mid-June and again towards the end of June. The mites inhabiting the holly trees appeared to migrate to the Japanese pear trees in June but their densities on pear leaves remained low until mid-August. In the pear orchard, the mites initially tended to increase on pear leaves near the holly trees and then gradually spread to other leaves farther away from the holly trees. Their highest density in the pear orchard occurred in mid-October. When pear leaves were inoculated with two or five female adults at different times from May to September, the leaves inoculated before mid-August showed no increase in the number of mites. A possible cause for the suppression of the population increase on pear leaves from June to mid-August is discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

螺旋粉虱在海南的分布与寄主植物种类调查

螺旋粉虱Aleurodicus disperses Russell是新入侵海南的外来有害生物,2006年4月在海南陵水已发现该虫传入。作者于2006年9月至2007年9月对螺旋粉虱在海南的分布与为害情况进行调查。调查结果,显示螺旋粉虱目前已分布至除昌江县和东方市以外的全岛其它15个市县,在吊罗山和尖峰岭保护区的林业局生活区也有分布;调查显示,螺旋粉虱寄主植物达47科120种,其中包括热带果树、蔬菜、热带作物、粮食作物、观赏与园艺作物,印度紫檀、榄仁树、番石榴、番木瓜、木薯、番荔枝、香蕉、茄子、四季豆等作物及美人蕉、飞扬草、野甘草等受害最为严重。对不同寄主植物的受害程度进行了初步划分,并对防控工作进行讨论。     

Effect of imidacloprid on the sivlerleaf whitefly, Bemisia argentifolii Bellows and Perrring (Homoptera: Aleyrodidae), and whitefly parasitism

Bioassays were conducted under greenhouse conditions to determine the effect of imidacloprid on adult and nymphal stages of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and parasitism by Encarsia formosa (Gahan). A flowable formulation (24Oglitre^-1) of imidacloprid at six rates (0.09, 0.04 and 0.02 g a.i. litre^-1 pot volume for experiments 1 and 2; 0.009, 0.004, and 0.002 g a.i. litre^-1 pot volume for experiment 3) was evaluated. After a 48 h exposure to treated plants, high mortality of adult whitefly (>94%) was observed. Adults exposed to poinsettias treated 150 days earlier also had significantly greater mortality (>79%) than the adults on control plants. When exposed to treated plants for only 6 h, >65% of adults were killed. All three rates of imidacloprid caused >97% mortality of immature whiteflies by day 19. When treated plants were continually exposed to adult whiteflies, immature mortality was 100% for the three higher rates of imidacloprid up to and including 88 days after treatment. During the same time, emerging adults were reduced significantly. Immatures reinfested on plants treated 161 days earlier, incurred 80% mortality at the higher rate 0.09 g a.i. litre^-1 pot volume and 38% mortality at 0.02 g a.i. litre^-1 pot volume. At lower treatment rates, results varied. At 0.009 g a.i. litre^-1 of pot volume, mean percentage whitefly mortality (65%) 25 days after treatment was significantly higher than the controls; however, whitefly mortality at 0.004 and 0.002 g a.i. litre^-1 pot volume was not significantly different from controls or plants treated with the higher rate. Parasitoids could develop to the adult stage on whiteflies infesting imidacloprid treated plants. Parasitism occurred at low levels (< 10%), doe to high levels of whitefly mortality on treated plants. No phytotoxicity was observed for any treatment throughout the length of the trials that lasted through flowering.     

Design and use of a simulation model to evaluate germplasm for antibiotic resistance to the greenhouse whitefly (Trialeurodes vaporariorum) and the sweetpotato whitefly (Bemisia tabaci)

SARAH (Software for theAssessment of antibioticResistance toAleyrodidae inHost plants) is a deterministic simulation model of whitefly population growth based on whitefly life-history components determined on individual plants. The life-history components recorded were oviposition rate, adult survival, pre-adult survival, developmental period, and sex ratio. The simulation model serves as a tool to combine these components and to obtain a single criterion for (antibiotic) resistance. The criterion used was the decrease in simulated intrinsic population growth rate, r _s , relative the r _s value determined on a susceptible control genotype. This model-based evaluation method was tested using the greenhouse whitefly,Trialeurodes vaporariorum Westwood, on tomato and the sweetpotato whitefly,Bemisia tabaci Gennadius, on tomato, eggplant, collard, and pepper. To study its consistency over time, the evaluation method was repeated six times forT. vaporariorum on a susceptible and a resistant tomato cultivar. Simulated intrinsic population growth rate was more consistent in indicating resistance than any of the individual life-history components. Of tenL. hirsutum accessions tested for resistance toT. vaporariorum, three exhibited r _s values that were significantly lower than those for the susceptible control. In addition, on these tenL. hirsutum accessions, a significant positive correlation was observed between r _s and sex ratio (# females/# males). Four host plant species (tomato, collard, eggplant, and pepper) were evaluated for resistance toB. tabaci. All life-history components and r _s values varied among host species, while a negative r _s value was observed forB. tabaci on pepper. A high correlation was found between results from a sensitivity analysis of SARAH and results from a sensitivity analysis of a validated whitefly population simulation model by Yanoet al. (1989a). Significant correlations were found for the relationships between oviposition rate, adult survival, or pre-adult survival and r _s , indicating that none of these life-history components can be omitted from the test procedure. This model-based evaluation method offers a standardized way to quantify levels of antibiotic resistance to whiteflies and will enhance efficiency in breeding programs.     

Studies on the flight activity of the Viburnum whitefly, a reluctant flyer

Dispersal of adult Viburnum whitefly,Aleurotrachelus jelinekii (Frauenf.) was assessed over a period of 6 years, both in the field and in the laboratory. Flight activity did not appear to be strongly affected by normal variation in either temperature or windspeed. The aerial density of flying adults decreased rapidly with distance from the host plant. Movement up to 5 m from the host plant was found to be density dependent, although there is no suggestion that longer flights become more frequent at higher population densities. More males were caught at the beginning of the season and the number of males flying increased as the population density rose. Insects were flight mature after about 3 h, but flew readily only after 2 days. Longer flights were observed from younger females at a time when they would move from old to young leaves. Landing site preference was not recorded, which contrasts with the behaviour of the cabbage whitefly. Flight in the Viburnum whitefly appears to redistribute the population within the immediate habitat, but migration did not appear to be a significant demographic factor in the isolated populations studied.

---

Etude de l'activité de vold d'Aleurotrachelus jelinekii peu enclin au vol

Résumé La dispersion des adultes d'Aleurotrachelus jelinekii Frauenf, tant dans la nature qu'au laboratoire, a été estimée sur une période de 6 ans. L'activité de vol n'a pas paru être fortement modifiée par les variations de la température et de la vitesse du vent. Le nombre d'adultes en vol a diminué rapidement jusqu'à 5 m de la plante hôte, et il était density-dependent, bien que rien ne prouve que les vols les plus longs deviennent plus fréquents à des densités de population plus élevées. Plus de mâles ont été capturés au début de la saison et le nombre de mâles en vol s'est accru avec la densité de la population. Les insectes étaient aptes au vol 3 heures après la mue imaginale, mais ne volaient normalement que 2 jours après. Les vols les plus longs ont été observés chez les plus jeunes femelles au moment où elles devaient migrer de feuilles âgées à des feuilles jeunes. Les lieux d'atterrissage préférés n'ont pas été décelés. Le vol chezA. jelinekii semble redistribuer la population dans l'habitat immédiat et la migration n'apparaît pas être un paramètre démographique significantif dans les populations isolées étudiées.

     

The movement and distribution of citrus tristeza virus and citrus exocortis viroid in citrus seedlings1

The systemic movement of citrus tristeza virus (CTV) in sour orange (Citrus aurantium) seedlings and of citrus exocortis viroid (CEVd) in Etrog citron (C. medica) seedlings was studied. The movement of the two pathogens was analysed by detection in sections of roots and stems at different time intervals. Both pathogens were detected initially in the basal parts and the roots and subsequently spread to the shoot. CTV and CEVd moved in young citrus seedlings at similar rates. The findings are consistent with long distance phloem transport of the virus and the viroid. The practical implications of the pattern of systemic movement for diagnosis of infected trees are discussed.     

Primers based on the rpf gene region provide improved detection of Xanthomonas axonopodis pv. citri in naturally and artificially infected citrus plants

AIMS: To have a PCR-based detection method for Xanthomonas axonopodis pv. citri (Xac) using primers designed in a specific region of its genome. METHODS AND RESULTS: A Xac-specific region was identified inside the rpf gene cluster of strain IAPAR 306 in an analysis of its complete genomic sequence. Two primers were designed, Xac01 and Xac02, which, when used in a standard PCR assay, direct the amplification of a 581 bp fragment from DNA of strains belonging to Xac from different regions around the world including unusual American and Asian strains. This product was not observed when DNA from strains of the closely related X. a. aurantifolli and X. a. citrumelo were used as templates. Extracts prepared from 28 xanthomonads of other species, and epiphytic bacteria isolated from citrus also failed to produce products with these primers. Amplification was obtained from cells grown in vitro, from extracts of both fresh and dried citrus canker lesions and from washes of inoculated but asymptomatic leaf surfaces. In sensitivity tests, this PCR technique detected as few as 100 cells. CONCLUSIONS: Primers Xac01 and Xac02 provide specific and sensitive detection of Xac in all citrus tissues where the pathogen is found. SIGNIFICANCE AND IMPACT OF THE STUDY: This PCR-based diagnostic test is suitable for monitoring asymptomatic plants in areas where the bacteria is endemic, in plant quarantine and regulatory situations, and also for obtaining an accurate diagnosis in a very short time. These are important characteristics for any assay to be used for the management of citrus canker disease.     

Increasing distribution and damage to palms by the Neotropical whitefly,Aleurotrachelus atratus (Hemiptera: Aleyrodidae)

In recent years, the coconut whitefly, Aleurotrachelus atratus Hempel, has been recorded from various islands in the southwestern Indian Ocean. Field surveys in La Réunion, the Seychelles, the Comoros and glasshouses in Paris have allowed us to record this whitefly on 56 palm species, some of which are endemic and/or threatened species. Most of trees showed low infestation levels, except for the coconut palm that is its main host plant. Such a wide host range has facilitated the rapid geographical dissemination of this whitefly. A field study was conducted in 2006 in La Réunion, to gain a better understanding of the bioecology of A. atratus in a tropical insular ecosystem. The whitefly was found throughout the island, from sea level to 800‐m altitude. Five parasitoid species (Hymenoptera: Aphelinidae) were found associated with the populations of this pest, with Eretmocerus cocois Delvare being the dominant one. A laboratory study showed that the pre‐imaginal development of A. atratus is around 48 days at 25–27°C, which is relatively long compared to other whitefly species. With a sex ratio of one male per 1022 females collected in La Réunion, it appears that the whitefly reproduces by thelytoky. It represents a threat to ornamental and agricultural palms as well as to natural palm ecosystems in the absence of effective parasitoids.