Abstract
Simple SummaryIncrease in abundance of the vector Diaphorina citri Kuwayama population is mostly influenced by the cyclic flushing of citrus. Relative degree of aggregation index for D. citri adults increased during periods of cyclic production of new flush as females aggregated to lay eggs, and the adult migration and dispersal was influenced by flushing cycles. Horticultural mineral oil (HMO) can reduce the spread of HLB as HMO produced significantly lower level of 11.43% of diseased citrus trees compared to 42.20% in untreated control plots.Diaphorina citri Kuwayama transmits a destructive citrus disease caused by a fastidious bacterium ‘Candidatus Liberibacter asiaticus’ (CLas) designated as Huanglongbing (HLB) which posed a risk of detrimental threat to the Malaysian citrus industry. All D. citri life stages show a lumped habit on young flushes and its population fluctuations was closely related to accessibility of young flushes. The study aimed to investigate if the appearance of young flush shoots on citrus influences ACP population fluctuation and if horticultural mineral oil (HMO) could reduce spread of HLB transmission by ACP in a commercial healthy orchard. Field research was carried out from 1 April 2011 to 1 December 2014 in a 2-year-old 1 ha citrus farm that consisted of 200 PCR-certified disease-free grafted non-bearing honey tangerine (Citrus reticulata L.) in southwestern Sarawak, Malaysia. The experiment had two treatments namely control (unsprayed) and nC24 HMO with four replications arranged in a simple randomized block design. ACP eggs, nymphs, and adults per flush shoot was assessed and HLB incidence was monitored for visual inspection of the citrus trees for the current existence of usual signs of characteristic symptoms of HLB such as yellowing shoots, leaf mottling, and corky or enlarged veins on leaves. HLB-specific primer was employed in 16S rDNA polymerase chain reaction to detect the CLas gene in diseased trees. Increase in abundance of D. citri is mainly affected by the citrus flushing cycles and their life stages are completed on these flush shoots. Relative degree of aggregation index for D. citri adults increased during periods of cyclic production of new flush. HMO-treated plots produced a significantly lower percentage up to 11.43% of diseased trees against 42.20% in untreated control plots. HMO is effective against D. citri and recommended to be incorporated in the IPM program to prevent infection and reduce the spread of HLB.
Highlights
The Asian citrus psyllid (ACP), Diaphorina citri (Insecta: Hemiptera: Psyllidae), is an economically important pest insect of citrus as it is one of the two known effective vectors of a bacterium called Huanglongbing (HLB) disease, designated as citrus greening [1,2,3]
Milosavljevic et al [30] who synthesizes datasets of five globally distributed D. citri populations (Brazil, California, China, Florida, and Japan) reared on six different host plants reported that daily thermal fluctuations had significant effects on growth times of D. citri nymphs, which differed across experimental temperatures
The emergence of a new flush cycle initiates a surge in adult number of D. citri and a drop was noted while flush shoots reach maturity, and availability of young flushing shoots are reduced in the citrus orchard
Summary
The Asian citrus psyllid (ACP), Diaphorina citri (Insecta: Hemiptera: Psyllidae), is an economically important pest insect of citrus as it is one of the two known effective vectors of a bacterium called Huanglongbing (HLB) disease, designated as citrus greening [1,2,3]. HLB, being one of the ultimate devastating and fastidious citrus diseases produced by ‘Candidatus Liberibacter asiaticus’ (CLas) (α-Proteobacteria), is a phloem-limited Gramnegative bacterium [4] attacking sweet orange and mandarin varieties in Asia [5]. It has caused the majority of economic loss in the citrus blossoming in Asia [6], South Africa, and USA [7]. Despite homogeneity of citrus trees, all life stages of D. citri show an aggregated habit on young flushes, where oviposition, and growth of immature nymphs take place [11]. Temperature, can influence the development of D. citri populations (all life stages) in citrus orchards [28,29,30]
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