Insect Science (2010) 17, 39–45, DOI 10.1111/j.1744-7917.2009.01271.x
Repellent effect of guava leaf 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 Plant 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 (Psidium 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 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 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, tree dieback, China. Tel: +86 20 85284925; email: [email protected] and eventual death of infected trees (McClean & Schwarz,