Insect Science (2010) 17, 39–45, DOI 10.1111/j.1744-7917.2009.01271.x

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

Syed Muhammad Zaka1, Xin-Nian Zeng1, Paul Holford2 and George Andrew Charles Beattie2 1Key Laboratory of Natural Pesticide and Chemical Biology of the Ministry of Education, South China Agricultural University, Guangzhou, China, 2 Centre for and Food Science, University of Western Sydney, Locked Bag 1797, Penrith South DC, New South Wales 1797, Australia

Abstract The Asiatic citrus psyllid (Diaphorina citri Kuwayama [Hemiptera: Sternor- rhyncha: Psyllidae] is a vector of huanglongbing (citrus greening), a devastating disease of citrus caused by phloem-limited bacteria. Growing guava ( guajava)asaninter- crop 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 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 fac- tors. 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. Key words Asiatic citrus psyllid, huanglongbing (HLB), insect behavior, Psidium gua- java, volatile compounds

Introduction cretes copious amounts of honeydew on which sooty mould may grow (Reynolds, 1999). However, the Asiatic The Asiatic citrus psyllid, Diaphorina citri Kuwayama citrus psyllid is a major pest mainly because it is the major (Hemiptera: Sternorrhyncha: Psyllidae) is a major pest of vector of huanglongbing (HLB) or citrus greening, a dev- citrus (Halbert & Manjunath, 2004; Yang et al., 2006). astating disease caused by phloem-limited, Gram-negative The psyllid prefers to feed on the phloem of tender shoots liberibacters (α-Proteobacteria). In several Asian coun- and leaves and can induce abnormal growth and shoot tries, in Papua New Guinea and the USA, the disease is dieback (Husain & Nath, 1927; Bove,´ 2006; Halbert & caused by Candidatus Liberibacter asiaticus (Bove´ et al., Manjunath, 2004; Michaud, 2004). The insect also ex- 1996; Garnier & Bove,´ 1996; Weinert et al., 2004); in Africa by Ca. L. africanus; in Mauritius and Reunion´ by Ca. L. asiaticus and Ca. L. africanus (Garnier et al., 1996); Correspondence: Xin-Nian Zeng, Key Laboratory of Natu- and in Brazil by Ca. L. asiaticus and Ca. L. americanus ral Pesticide and Chemical Biology of the Ministry of Educa- (Yamamoto et al., 2006). The disease leads to unmar- tion, South China Agricultural University, Guangzhou 510642, ketable fruit, reduced yield and fruit quality, dieback, China. Tel: +86 20 85284925; email: [email protected] and eventual death of infected (McClean & Schwarz,

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1970; da Grac¸a, 1991; Bove,´ 2006). The host range of any disease or pest. Fresh new shoots of both guava and D. citri includes species and varieties of Citrus and Cit- citrus were collected at the same time from the field for rus relatives including Murraya paniculata (L.) Jack and experimental use. M. exotica L. (both known as orange jasmine) of the tribe Aurantieae [Sapindales: Rutaceae: Aurantioideae], Berg- Repellent effect of guava shoot era koenigii L. (curry leaf), and some species of Clausena including Cl. lansium (Lour.) Skeels (wampee or huangpi) The responses of mixed populations of adult male and of the tribe Clauseneae [Aurantioideae]. female psyllids to guava and citrus shoots (15.0 cm in Using insecticides for the control of D. citri limits, but length) with fresh leaves were observed in ‘no-choice’ does not prevent, the spread of the disease, and biologi- experiments in which adult psyllids were released into cal control is not feasible given the serious nature of the cages (60.0 cm × 30.0 cm × 60.0 cm) containing the disease and the effectiveness of disease transmission. In same treatment. Vietnam it has been observed that citrus orchards planted In the first test, one guava shoot was placed aside a citrus with guava (Psidium guajava L. [: ]) shoot as a treatment in a 50-mL flask moistened inside showed much lower psyllid infestation levels and low inci- with some tap water. Five flasks containing the guava and dence of HLB compared to citrus orchards lacking guava citrus shoots were placed in one cage and five containing (Beattie et al., 2006). Although raising guava as an inter- citrus shoot only were placed in another cage as control. crop appears to reduce psyllid numbers in orchards, the The flasks were positioned randomly, but equidistant from mechanism by which this occurs is unknown. The effects each other, within the cage. Fifty adults (25 males and 25 of guava on citrus psylla could be due to physical disrup- females) were released into each cage and kept at ambient tion on host recognition, repellent effect of volatile com- laboratory conditions. The number of adults settled on pounds from guava or chemical alteration of the volatile citrus leaves was recorded after 12 h and 24 h. Each assay compounds emitted by citrus reacting with guava com- was replicated five times. pounds. The present study was conducted to determine if In the second test, the repellent effect of mature and guava has a repellent effect on adults of Asiatic citrus psyl- immature guava shoots on the settlement of adults on lids, the attributions (chemical or physical) of repellence, citrus was measured by using guava shoots with leaves dose response of adults to guava volatiles, and whether fully hardened and expanded, and leaves soft and not fully the volatile compounds from guava alone, or by reacting expanded. with that of citrus, play the role. Also, in order to determine that the repellent effect of guava is attributed to the odor (volatiles) instead of phys- Materials and methods ical factors (leaf color, shape and structure), the response of adults to covered and uncovered guava shoots was mea- Insects sured using the method mentioned above. Guava shoots were covered with fine white net cloth, allowing volatile Adults of D. citri were collected daily from 4-year- compounds to go through and preventing psyllids from old sweet orange (Citrus × aurantium L.) trees in the being affected by the color, shape or structure of guava botanical garden of South China Agricultural University, leaves. Guangzhou, China. High psyllid populations were main- tained by pruning the trees regularly to encourage new growth favored by the psyllid. Adults were collected with Repellent effect of guava leaf volatiles a mechanical aspirator each morning and held in small plastic cups for use later in the day. Males and females To confirm the repellent effect of guava leaf volatiles were separated on the basis of their morphology. The tip on adult psyllids, Y-tubeolfactometer responses of adults of the abdomen of an adult male is bent upwards while to guava leaf odor were measured based on the methods the abdomen of the female is straight. of Horton & Landolt (2007). The arms were 21.0 cm long and 2.5 cm in diameter. Charcoal-filtered and dis- tilled water-moistened air was vacuumed through the sys- tem at a rate of 50 mL/min. The choice combinations of Four-year-old guava (Psidium guajava L. cv. Pearl) and odor sources of guava, guava plus citrus, citrus (control), sweet orange trees from the university campus were used moist air (blank) were tested. A line was drawn on each as the source of plant materials. These plants were regu- of the two arms at 10.0 cm distance from the arm junc- larly irrigated and fertilized and were visually free from tion. Psyllids crossing the line within 10 min spells were

C 2009 The Authors Journal compilation C Institute of Zoology, Chinese Academy of Sciences, Insect Science, 17, 39–45 Repellent effect of guava leaf volatiles 41 considered to have made a choice. Each combination was Table 1 Effect of guava shoot on the number of adult psyllids measured using 10 psyllids individually and was repeated settling on citrus shoot. eight times by changing new materials and shifting arm ± positions alternately. All the experiments were done un- Mean adult no. s.e. per shoot = der laboratory conditions at temperatures of 26–30◦C and (n 5) 2 lamp-light intensity of 282 mW/cm . Treatment 12 h 24 h In the dosage response experiment, choices of mixed populations of male and female psyllids to volatiles from Citrus shoot + 9.0 ± 0.71 a† 7.0 ± 0.55 a 2.5 g, 5.0 g, 10.0 g, and 15.0 g of guava leaves were guava shoot compared to a blank. Also, the choices to volatiles from Citrus shoot 14.2 ± 0.66 b 14.8 ± 0.73 b the same series amount of guava leaves plus 5.0 g of † citrus leaves were compared to volatiles from 5.0 g of Means in the same column followed by same letter are not = citrus leaves. significantly different according to Tukey’sHSD test at P 0.05. Response of adult males and females to volatiles ema- Table 2 Effect of guava shoot maturity on the number of adult nating from 15.0 g of guava leaves versus blank was also psyllids settling on citrus shoot. evaluated separately using the same methods. Mean adult no. ± s.e. per shoot (n = 5) Statistical analysis Treatment 12 h 24 h Differences between treatments were determined using repeated-measures analysis of variance (ANOVA) with Citrus shoot + mature 4.2 ± 0.20 a† 4.8 ± 0.20 a the time of assessment being the repeated measure using guava shoot Statistica (Version 7, StatSoft, Inc., Tulsa, OK, USA). All Citrus shoot + 4.4 ± 0.24 a 4.6 ± 0.24 a data sets were homoscedastic according to Levene’s test immature guava and means were separated using Tukey’sHonestly Signifi- shoot cant Difference (HSD) test. Contingency χ 2 tests (includ- Citrus shoot 6.8 ± 0.37 b 7.4 ± 0.40 b ing Yates’correction) were used to determine whether the †Means in the same column followed by the same letter are not numbers of psyllids moving toward either of the two arms significantly different according to Tukey’sHSD test at P = 0.05. of the olfactometer were significantly different. Table 3 Effect of covered guava shoot on the number of adult Results psyllids settling on citrus shoot. Mean adult no. ± s.e. per shoot Repellent effect of guava shoots (n = 5)

The results showed that significantly fewer psyllids Treatment 12 h 24 h were found on citrus leaves in the presence of guava fo- liage than in its absence (F = 810; P < 0.001) (Table 1). Citrus shoot + covered 2.8 ± 0.37 a† 3.2 ± 0.20 a The percentage reductions of adult numbers were 36.62% guava shoot and 52.70%, respectively, after 12-h and 24-h treatments. Citru shoot + 3.2 ± 0.37 a 3.2 ± 0.20 a It indicates that guava shoots possess repellent effects uncovered guava against the adults of citrus psyllids. shoot There was a significant difference in the mean number Citrus shoot 7.2 ± 0.58 b 7.4 ± 0.51 b of adult psyllids settled on the citrus leaves between the †Means in the same column followed by the same letter are not treatments having guava and no guava (Table 2). However, significantly different according to Tukey’sHSD test at P = 0.05. no significant difference could be seen between the mean number of psyllids on citrus with immature and mature shoots, showing that they had equal repellent activity. and uncovered guava showed no significant difference By covering the guava shoots with net cloth, it was in the mean number of psyllids present on the citrus revealed that the repellent effect of guava shoots to leaves, although a highly significant difference (F = 4.0, adult psyllids on citrus was attributed to the volatile P < 0.001) occurred between both guava treatment and compounds, rather than physical factors. The covered the no-guava control (Table 3).

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= 10 in the two arms was found (P 0.350 6, Fig. 1A) at A 8 2.5 g treatment. It was suggested that low concentrations 6 of guava have no repellent effect on adult psyllids. When 4 the amount reached 5.0 g of guava leaves, a highly signif- 2 0 icant difference between the mean number of psyllids in 2 the two arms (P < 0.000 1, Fig. 1B) was observed. The 4 percentages of psyllids moving toward guava odor were 6 35.00%, 25.00% and 16.25%, respectively, in treatments 8 Number of adult psyllids of Number psyllids adult 10 Blank of 5.0, 10.0 and 15.0 g of guava shoots. Guava leaves (2.5 g) When guava plus citrus and citrus leaf odors were pro- vided in the two arms, similar, but stronger repellent ac- 10 B tivities were obtained. All treatments showed significant 8 differences between the mean numbers of psyllids in the 6 4 two arms (Fig. 2). The percentages of adults moving to- 2 ward the arm having both citrus and guava odors were 0 38.75%, 33.75%, 17.50% and 13.75%, respectively. This 2 might indicate that the repellent activity of volatiles from 4 guava leaf would be increased by interacting with those 6 Number of adult psyllids psyllids adult of Number from citrus leaf. 8 Blank 10 Results shown in Fig. 3 reveal that the response of males Guava leaves (5.0 g) and females to guava leaves (15.0 g) were similar. C 10 8 6 Discussion 4 2 Citrus HLB has become a great threat to the world citrus 0 2 industry (Bove,´ 2006; Zhao, 2008). So far, no success- 4 ful cure for it has been reported. The key measures for 6 limiting its epidemic spread are the use of disease-free

Number of adult psyllids of Number psyllids adult 8 Blank seedlings and the suppression of psyllid populations to 10 Guava leaves (10.0 g) reduce pathogen transmission. Observations in Viet Nam suggested that citrus groves interplanted with guava trees

10 D showed low populations of citrus psylla and low incidence 8 of HLB-infected trees (Beattie et al., 2006). Understand- 6 ing the mechanism by which guava affects citrus psylla 4 may lead to the proper use of guava in the control of HLB. 2 0 The results obtained in the present study revealed that 2 volatile compounds, instead of color and shape of the 4 leaves, played a role in reducing citrus psylla populations 6

Number of adult psyllids psyllids adult of Number on citrus, although it is possible that other factors such Blank 8 as the masking of citrus volatiles may contribute to the 10 Guava leaves (15.0 g) response of the psyllid. It indicates that certain volatile R1 R2 R3 R4 R5 R6 R7 R8 Mean compounds in guava leaf could be developed as repel- Fig. 1 Response of adult psyllids to volatiles emanating from lents for the management of citrus psylla. Guava fruits and different quantities of guava foliage. leaves produce a wide range of volatile compounds, such as sesquiterpenes (Sagrero-Nieves et al., 1994; Ogun- Repellent effect of volatiles from guava leaf wande et al., 2003), aldehydes and alcohols (Idstein & Schreier, 1985; Begum et al., 2002, 2004; Soares et al., The olfactometer response of adult psyllids to guava 2007). Some of these aldehydes and alcohols are the so- leaf odor was dosage-dependent (Fig. 1). When guava called ‘green leaf volatiles’ that have been shown to have leaf odor and moist air (blank) were provided, no sig- repellent effects on insects (Jang & Light, 1991). Further nificant difference between the mean number of psyllids studies are required to determine the active compounds in

C 2009 The Authors Journal compilation C Institute of Zoology, Chinese Academy of Sciences, Insect Science, 17, 39–45 Repellent effect of guava leaf volatiles 43

10 A A. Male adults 8 10 6 8 4 6 2 4 0 2 2 0 4 2 6 4 8 Number of adult psyllids psyllids of adult Number 6 10 Citrus leaves (5.0 g) 8 Citrus leaves (5.0 g) + Guava leaves (2.5 g) psyllids of adult Number Blank Guava leaves (15.0 g) 10

10 B B. Female adults 8 6 10 4 8 2 6 0 4 2 2 4 0 6 2 Number of adult psyllids psyllids adult of Number 8 4 Citrus leaves (5.0 g) 10 6 Citrus leaves (5.0 g) + Guava leaves (5.0 g) Number of adult psyllids psyllids adult of Number 8 Blank Guava leaves (15.0 g) 10 10 C 8 R1 R2 R3 R4 R5 R6 R7 R8 Mean 6 4 Fig. 3 Repellent effect of guava leaf volatiles on male and 2 female adult psyllids. 0 2 Number of adult psyllids psyllids of adult Number 4 Pre-alighting discrimination of a potential host plant 6 8 Citrus leaves (5.0 g) implies that the relevant characteristics are perceived at 10 Citrus leaves (5.0 g) + Guava leaves (10.0 g) a distance. As such, these cues are expected to influ- ence orientation and choice by the insect. To investigate 10 D the chemical basis of pre-alighting discrimination, olfac- 8 6 tometers that deliver volatiles to test insects while they 4 are airborne have been developed and used with success 2 (Eigenbrode & Bernays, 1997). With psyllids, Horton & 0 Landolt (2007) used a Y-tube olfactometer to show that 2 males of the pear psylla, Cacopsylla pyricola (Forster)¨ 4 6 [Psyllidae], are attracted to volatile odors from female- Number of adult psyllids psyllids adult of Number 8 Citrus leaves (5.0 g) infested or previously infested shoots. Cen et al.usinga 10 Citrus leaves (5.0 g) + Guava leaves (15.0 g) four-arm olfactometer demonstrated that D. citri females

R1 R2 R3 R4 R5 R6 R7 R8 Mean were strongly repelled by odors from essential oil of guava leaf and freshly ground guava leaf, but were not repelled Fig. 2 Choice response of adult psyllids to volatiles emanating by odor of essential oil of guava fruit (Cen et al., pers. from citrus foliage alone and from citrus foliage plus different comm., 2007). In the present study, the olfactometer re- quantities of guava foliage. sults revealed that the repellent action of guava against citrus psylla is dose-dependent, with very low doses hav- guava leaves repelling D. citri and their efficacy. Research ing little effect on citrus psylla. This result indicates that is also required to determine how guava, other plants that to control citrus HLB by interplanting guava trees in cit- may produce volatiles that repel citrus psyllids, or perhaps rus groves, sufficient numbers of guava trees are needed synthetic repellents, can best be used to reduce the impact to keep the dosage of volatile compounds emitted from of HLB in citrus orchards. guava at an effective level in the entire grove. In China,

C 2009 The Authors Journal compilation C Institute of Zoology, Chinese Academy of Sciences, Insect Science, 17, 39–45 44 S. M. Zaka et al. observations revealed that even in the presence of guava Bove,´ J.M. (2006) Huanglongbing: a destructive, newly- trees scattered inside or around the groves, citrus psylla emerging, century-old disease of citrus. Journal of Plant populations are high. This could be due to the fact that the Pathology, 88, 7–37. guava trees present did not release enough active volatile Bove,´ J.M., Chau, N.M., Trung, H.M., Bourdeaut, J. and Garnier, compounds. In Vietnam, it was suggested that guava trees M. (1996) Huanglongbing (greening) in Viet Nam: Detection are interplanted prior to citrus at a ratio of one guava tree of Liberobacter asiaticum by DNA-hybridization with probe to one citrus tree (Beattie et al., 2006). Besides, guava In2.6 and PCR amplification of 16S ribosomal DNA. Pro- interplanting may increase severity of fruitfly damage to ceedings of the 13th Conference of the International Organi- citrus (Xie & Zhang, 2005; Xu et al., 2005). Under these zation of Citrus Virologists, 16–23 November 1995, Fuzhou, circumstances, fruit-removing or bagging would be ade- Fujian, China. International Organization of Citrus Virolo- quate before guava fruits ripen to block the food chain of gists, University of California, Riverside, California, United fruitfly in groves and to protect citrus fruits from fruitfly States of America. pp. 258–266. damage. da Grac¸a, J.V.(1991) Citrus greening disease. Annual Review of Guava is a widely planted tropical and subtropical fruit. Phytopathology, 29, 109–136. Guava leaf is traditionally used as an antidiarrheal drug. Eigenbrode, S.D. and Bernays, E.A. (1997) Evaluation of factors The oral acute toxicology of leaf extract to mice is low affecting host plant selection, with an emphasis on studying with a LD50 of more than 20.0 g/kg (Aimmanas et al., behaviour. Methods in Ecological and Agricultural Entomol- 1995). This suggests that use of guava chemicals as in- ogy (eds. D.R. Dent & M.P. Walton), pp. 147–169. CAB In- secticides will be safe to mammals. ternational, Cambridge. Garnier, M. and Bove,´ J.M. (1996) Citrus greening disease. Proceedings of the Twelfth Conference of the International Acknowledgments Organization of Citrus Virologists, 23–27 November 1992, Our research was supported by special funds from the New Delhi, India. International Organization of Citrus Virol- National Science Foundation of China (30471169), the ogists, University of California: Riverside, California, United President’s Foundation of South China Agricultural Uni- States of America. pp. 212–219. versity (2007G003), and the Department of Education, Garnier, M., Jagoueix, S., Toorawa, P., Grisoni, M., Mallessard, Science and Training of the Commonwealth of Australia R., Dookun, A., Saumtally, S., Autrey, J.C. and Bove,´ (CH060068). We thank Dr. Yi-Jing Cen and Mr. Ke- J.M. (1996) Both huanglongbing (greening) liberobacter Cheng Huang for their kind cooperation during the study. species are present in Mauritius and Reunion. Proceed- ings of Thirteenth Conference of the International Organi- zation of Citrus Virologists, Department of Plant Pathology, References Riverside, California, United States of America. pp. 392– 394. Aimmanas, A.P., Chavalittumrong, P.R. and Pranee, C. (1995) Halbert, S.E. and Manjunath, K.L. (2004) Asian citrus psyllids Toxicity study of Psidium guajava Linn. leaves. Bul- (Sternorrhyncha: Psyllidae) and greening disease of citrus: A letin of the Department of Medical Sciences, 37(4), 289– literature review and assessment of risk in Florida. Florida 305. Entomologist, 87, 330–353. Beattie, G.A.C., Holford, P., Mabberley, D.J., Haigh, A.M., Horton, D.R. and Landolt, P.J. (2007) Attraction of male pear Bayer, R. and Broadbent, P. (2006) Aspects and insights psylla, Cacopsylla pyricola, to female infested pear shoots. of Australia–Asia collaborative research on huanglongbing. Entomologia Experimentalis et Applicata, 123, 177–183. Proceedings of an International Workshop for Prevention of Husain, M.A. and Nath, D. (1927) The citrus psylla (Diaphorina Citrus Greening Diseases in Severely Infested Areas, 7–9 citri, Kuw.) [Psyllidae: Homoptera]. Memoirs of Department December 2006, Ishigaki, Japan (Multilateral Research Net- of Agriculture in India, 10, 5–27. work for Food and Agricultural Safety. Japanese Ministry of Idstein, H. and Schreier, P. (1985) Volatile constituents from Agriculture, Forestry and Fisheries; Tokyo, Japan). pp. 47– guava (Psidium guajava L.) fruit. Journal of Agricultural and 64. Food Chemistry, 33, 138–143. Begum, S., Hassan, S.I., Ali, S.N. and Siddiqui, B.S. (2004) Jang, E.B. and Light, D.M. (1991) Behavioral responses of fe- Chemical constitutes from the leaves of Pisidium guajava. male oriental fruit flies to the odor of papayas at three ripeness Natural Product Research, 18, 135–140. stages in a laboratory flight tunnel (Diptera: Tephritidae). Begum, S., Siddiqui, B. and Hassan, S.I. (2002) Triterpenoids Journal of Insect Behaviour, 4, 751–762. from Psidium guajava leaves. Natural Product Research, 16, McClean, A.P.D. and Schwarz, R.E. (1970) Greening or blotchy- 173–177. mottle disease in citrus. Phytophylactica, 2, 177–194.

C 2009 The Authors Journal compilation C Institute of Zoology, Chinese Academy of Sciences, Insect Science, 17, 39–45 Repellent effect of guava leaf volatiles 45

Michaud, J.P. (2004) Natural mortality of Asian citrus psyllid Xie, Q. and Zhang, R.J. (2005) Study advance on biology and (Homoptera: Psyllidae) in Central Florida. Biological Con- ecology of Bactrocera dorsalis (Hendel) and its control. Eco- trol, 29, 260–269. logical Science, 24(1), 52–56. Ogunwande, I.A., Olawore, N.O., Adeleke, K.A., Ekundayo, O. Xu, Y.J., Zeng, L., Lu, Y.Y. and Lin, J.T. (2005) Ovipositional and Koenig, W.A. (2003) Chemical composition of the leaf selection of Bactrocera dorsalis (Hendel) to different fruits. volatile oil of Psidium guajava L. growing in Nigeria. Flavour Journal of Huazhong Agricultural University, 24(1), 25–26. and Fragrance Journal, 8, 36–138. Yamamoto, P.T., Filippe, M.R., Garbim, L.F., Coelho, J.H.C., Reynolds, D.R. (1999) Capnodium citri: The sooty mold fungi Ximenes, N.L., Martins, E.C., Leite, A.P.R., Sousa, M.C., comprising the taxon concept. Mycopathologica, 148, 141– Abrahao,˜ D.P. and Braz, J.D. (2006) Diaphorina citri 147. (Kuwayama) (Hemiptera: Psyllidae): vector of the bac- Sagrero-Nieves, L., Bartley, J.P. and Provis-Schwede, A. (1994) terium Candidatus Liberibacter americanus. Proceedings of Supercritical fluid extraction of the volatile components from the Huanglongbing-Greening International Workshop,July, the leaves of Psidium guajava L. (guava). Flavour and Fra- 2006, Ribeirao˜ Preto, SP, Brazil. pp. 96–97. grance Journal, 9, 135–137. Yang, Y.P., Huang, M.D., Beattie, G.A.C., Xia, Y.L., Ouyang, Soares, F.D., Pereira, T., Marques, M.O.M. and Monteiro, A.R. G.C. and Xiong, J.J. (2006) Distribution, biology, ecology and (2007) Volatile and non-volatile composition of the white control of the psyllid Diaphorina citri Kuwayama, a major guava fruit (Psidium guajava) at different stages of maturity. pest of citrus: a status report for China. International Journal Food Chemistry, 100, 15–21. of Pest Management, 52, 343–352. Weinert, M.P., Jacobson, S.C., Grimshaw, J.F., Bellis, G.A., Zhao, X.Y. (2008) A general review on citrus Huanglong- Stephens, P.M., Gunua, T.G., Kame, M.F. and Davis, bing. Program and Abstracts of the 11th International Citrus R.I. (2004) Detection of huanglongbing (citrus green- Congress, 26–30 October, 2008, Wuhan, China. p. 19. ing disease) in Timor-Leste (East Timor) and in Papua New Guinea. Australasian Plant Pathology, 33, 135– 136. Accepted March 17, 2009

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