Abstract
Novel, suitable and sustainable alternative control tactics that have the potential to reduce migration of Diaphorina citri into commercial citrus orchards are essential to improve management of huanglongbing (HLB). In this study, the effect of orange jasmine (Murraya paniculata) as a border trap crop on psyllid settlement and dispersal was assessed in citrus orchards. Furthermore, volatile emission profiles and relative attractiveness of both orange jasmine and sweet orange (Citrus × aurantium L., syn. Citrus sinensis (L.) Osbeck) nursery flushes to D. citri were investigated. In newly established citrus orchards, the trap crop reduced the capture of psyllids in yellow sticky traps and the number of psyllids that settled on citrus trees compared to fallow mowed grass fields by 40% and 83%, respectively. Psyllids were attracted and killed by thiamethoxam-treated orange jasmine suggesting that the trap crop could act as a ‘sink’ for D. citri. Additionally, the presence of the trap crop reduced HLB incidence by 43%. Olfactometer experiments showed that orange jasmine plays an attractive role on psyllid behavior and that this attractiveness may be associated with differences in the volatile profiles emitted by orange jasmine in comparison with sweet orange. Results indicated that insecticide-treated M. paniculata may act as a trap crop to attract and kill D. citri before they settled on the edges of citrus orchards, which significantly contributes to the reduction of HLB primary spread.
Highlights
Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) is considered the main threat to orange production due to its ability to transmit the putative causal agents (‘Candidatus Liberibacter spp.’) of huanglongbing (HLB), the most destructive citrus disease worldwide[1]
Recent results showed that D. citri could not acquire Candidatus Liberibacter asiaticus’ (CLas) upon feeding and developing on CLas-quantitative polymerase chain reaction (qPCR) positive orange jasmine seedlings[22]. These results indicate that orange jasmine is a poor host for CLas and suggest that it may be used as a potential trap crop, attracting psyllids which could be controlled in these plants by insecticides, limiting spread of HLB
A, Fig. 1a) reduced incidence of D. citri in the orchard, when compared to the control, over a 45-month survey (d.f. = 1; P = 0.0030). In this area significantly fewer psyllids were captured on yellow sticky traps placed in citrus trees bordered on the east side by the trap crop compared to identical traps placed in control trees bordered on the east side by fallow mowed grass (F = 5.74; d.f. = 1, 38; P = 0.0216) (Fig. 1a)
Summary
Diaphorina citri Kuwayama (Hemiptera: Liviidae) is considered the main threat to orange production due to its ability to transmit the putative causal agents (‘Candidatus Liberibacter spp.’) of huanglongbing (HLB), the most destructive citrus disease worldwide[1]. Current management of HLB is based on the prevention of citrus tree infection through planting of healthy nursery trees, inspections and eradication of symptomatic trees and control of its vector D. citri using insecticides[3]. Despite the intensification of chemical control of D. citri on grove borders in recent years, concomitant reductions of HLB infections is limited because of the intense and constant influx of migrating psyllids[9,11]. The trap cropping tactic has been studied for the integrated pest management of many insect pests, including aphids, leafhoppers, planthoppers, and whiteflies, which are important hemipteran vectors of plant diseases[12]. Trap crops are plants used to attract insects or other organisms in order to protect important economic crops from direct damage or indirect damage related to vector-transmitted diseases[13]. Borders of transgenic Rainbow papaya (Carica papaya L.) plants resistant to the Papaya ringspot virus were used as trap crop to reduce the spread of viruliferous aphid vectors to non-transgenic papaya plants in Hawaii[16]
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