Orange jasmine as a trap crop to control Diaphorina citri

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.

Figure 1

(Miranda) Cumulative number of Diaphorina citri collected on yellow stick traps placed in citrus trees located in plots with or without (control) orange jasmine trap crop on the border over a 45-month survey. Data from two experimental areas, (a) area A (new planting, 6 months old) and (b) area B (established orchard, 7 years old). Bar graphics represent the cumulative mean number of D. citri (±standard error) after 45 months of survey. Means followed by the same letter in the small bar graphics do not differ statistically (P < 0.05).

Figure 2

(Miranda) Number of marked Diaphorina citri (mean ± standard error) found on ‘Pera’ sweet orange trees located on plots with orange jasmine trap crop or fallow field (control) over time (DAR). Means followed by the same letter at each time did not differ statistically (P < 0.05).

Figure 3

(Miranda) Diaphorina citri infestation maps at 1, 3 and 7 days after release (DAR). Data were obtained with the sum of psyllids found on citrus trees in the first, second and third replicate of the experiment to assess the effect of orange jasmine as a trap crop on D. citri settlement and dispersal. Each black dot represents a citrus tree. Black squares at the right side of map are the insect release platforms. The three groups of thick black lines represent the orange jasmine trap crop. Numbers at the bottom and left side of map are the Universal Transverse Mercator (UTM) coordinates from 22 k zone.

Figure 4

(Miranda) Number of marked psyllids found on orange jasmine trees according to the plots in which the insects were released: trap crop + control, trap crop and control. Visual assessments were performed at 1, 3 and 7 days after release (DAR). Observed data were fitted to Gaussian models (lines) with the equations y = 165.90 × exp(−0.50 × ((x-2.47)/1.71)²), y = 137.3 × exp(−0.50 × ((x-2.53)/1.68)), and y = 28.88 × exp(−0.50 × ((x-2.14)/1.87)) for psyllids released on trap crop + control, trap crop and control plots, respectively.

Figure 5

(Miranda) Mortality (%) (mean ± standard error) of Diaphorina citri adults confined on orange jasmine trees previously treated with systemic insecticide (thiamethoxam) or untreated (control) over time after psyllid confinement (DAC). Means followed by the same letter at each time do not differ statistically (P < 0.05).

Figure 6

(Miranda) Responses of Diaphorina citri females, tested in a 4-arm olfactometer, to volatiles of two sets of odor sources [orange jasmine × control (clean air)] (a) and [‘Pera’ sweet orange × control (clean air)] (b). Bars represent the mean time spent by D. citri in each odor source (±standard error).

Figure 7

(Miranda) (a) Representative Principal Component Analysis (PCA) of MetAlign output scan peak values resulting from GC-MS of orange jasmine and sweet orange flushes. + corresponds to orange jasmine, X to orange and dots (•) to quality control samples (mixtures of flushes from both genotypes). PC1 explained at least 75% of the variance at two independent replicate dates. (b) Heatmap, generated with ClustVis, showing the corrected areas of selected volatile compounds emitted by orange jasmine (AM1, AM2, AM3, BM1, BM2, BM3) and sweet orange (AC1, AC2, AC3, BC1, BC2, BC3) flushes. Representation corresponds to three biological replicates (named 1, 2, 3) for each genotype (M, orange jasmine; C, orange) at two different sampling dates (A and B).

Figure 8

(Miranda) Schematic view of the experimental area used to evaluate the effect of orange jasmine as a trap crop on Diaphorina citri settlement and dispersal. Each black dot represents a citrus tree; and black squares at the right side of map are the insect release platforms. The three groups of thick black lines represent the orange jasmine trap crop. Letters “T” and “C” in each plot represent the trap crop and control treatments, respectively. Numbers at the bottom and left side of map are the Universal Transverse Mercator (UTM) coordinates from 22 k zone.