Diaphorina citri

Normal routes of transmission Vectors (Psyllids Diaphorina citri Kuwayama and Trioza erytreae). 

Solution Develop an Effective Natural Repellent to Control Diaphorina citri and... 

Diaphorina citri, this pest is now present in all major citrus-producing states in the United States. The HLB pathogen invariably follows the vector as it expands its range, with trees showing signs of the disease approximately 1-3 years after infection. Citrus trees infected with HLB produce unmarketable fruit and will nltimately die from the disease. 

Careful supplementation of nutrients does not cnre the disease but enables continued fruit production despite HLB infection. This, in tnrn, allows growers to maintain their productivity during the HLB epidemic. However, growers discovered that supplemented plants produce more and better fruit if they are not reinfected with HLB so effective suppression of Diaphorina citri populations remains crucial, even in orchards where most of the plants are already infected with HLB and are being treated with supplemental nntrition. 

Based on recent innovations in research that have shown great potential for use in Diaphorina citri management, we developed a botanically derived repellent, identified from guava leaves. This compound, dimethyl disulfide (DMDS), was formulated into SPLAT and used to successfully... 

We examined the effect of a series of potential botanical repellents on Diaphorina citri in behavioral assays. Repellents were also evaluated in combination with citrus odors to verify their repellency in the presence of these attractive compounds. Finally, we examined the repellent effects of a select number of plant volatiles formulated in SPLAT. 

A minimum of 120 adult female Diaphorina citri were examined per treatment combination (four replications with 30 psyllids per replication). Diaphorina citri females were released individually into the inlet adapter at the base of the olfactometer and given 300 seconds to show a behavioral response by entering either olfactometer arm. The number of adults entering the treatment arm or control arm or remaining in the inlet adapter (release port) or below the T-maze division was recorded. A treatment or control arm choice was recorded when an insect moved into either... 

Behavioral bioassays with synthetic compounds. Allyl methyl trisulflde, diallyl trisulfide, DMTS, ADS, AMDS, DMDS, diallyl sulfide, and AMS were evaluated for their effect on Diaphorina citri behavior at 0.25%, 0.5%, and 1.0% concentrations, both individually and in combination with citrus leaves. The chemical samples were dissolved in 1 mL ethylene glycol (EG), to slow the release rate of the volatile sulfur compounds during the bioassays," " and pipetted onto a 5-cm Richmond cotton wick (Petty John Packaging Inc., Concord, North Carolina). The treated wick was then wrapped in laboratory tissue and placed in SPME chambers. The control treatment contained cotton wicks impregnated with 1 mL EG only. For evaluations of chemicals in the presence of citrus odors, approximately 2 g of fresh citrus leaves were placed in both chemical treatment and control arms of the olfactometer. 

For assays in which putative repellent treatments were presented in the T-maze olfactometer with or without citrus and versus clean air, the number of Diaphorina citri remaining at the release point and not entering the olfactometer was compared between treatments using one-way analysis of variance, followed by Tukey s honest significant difference test (p <. 05). For psyllids leaving the release arm, the number of psyllids choosing the control arm versus the treatment arm was compared with chi-square (/ ) analysis at p <. 05. The data from all four replicates were combined for the analysis. 

Significantly more Diaphorina citri remained at the release point in treatments where DMTS (at 0.25% concentration) was copresented with clean air or citrus odors than when clean air and citrus were presented simultaneously in both arms of the olfactometer (Figure 16.8a). No other synthetic... 

Figure 16.8 Responses of female adult Diaphorina citri presented with sulfur volatiles at (a) 0.25%, (b) 0.5%, or (c) 1.0% concentrations with or without citrus odors. Allyl methyl sulfide (AMS), allyl disulfide (ADS), allyl methyl disulfide (AMDS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS). Black bars followed by same letters are not significantly different (Tukey s honest significant difference, p <.05).

Using a simple, randomized block design with two treatments, (1) insecticide followed by SPLAT ACP Repel and (2) insecticide only, all treatment plots received a label rate (40.0 oz./ha) application of the pyrethroid insecticide Danitol (Valent USA, Walnut Creek, California) at the start of the experiment to knock down Diaphorina citri population. After 2 weeks, half of the... 

Figure 16.9 Reduction in Diaphorina citri popuiations foiiowing treatment with SPLAT containing dimethyi disuifide (DMDS). Resuits suggest that appiioation of DMDS to an infested orchard can cause existing Diaphorina citri popuiations to disperse away from treated trees.

Figure 16.11 Delayed immigration of Diaphorina citri into insecticide-treated plots following application of SPLAT with dimethyl disulfide (DMDS). In untreated plots, populations of Diaphorina citri began to rebound 6 weeks after treatment, with populations becoming equivalent to pretreatment levels by week 7. In plots that received the SPLAT treatment 2 weete after the insecticide spray, Diaphorina citri populations did not return to pretreatment levels for the entire 10 weeks of study 8.

This work indicates that the guava-derived semiochemical, DMDS, is an effective repellent for Diaphorim citri at concentrations as low as 10% in SPLAT AGP Repel. When incorporated into SPLAT, the resulting matrix demonstrated the capacity to extend the release period of this extremely volatile compound, prolonging the repellent s efficacy in the field. Field trials have shown that SPLAT AGP Repel with DMDS alone significantly reduces Diaphorina citri captures in infested orchards, indicating the potential for this formulation to reduce HLB infection rates in areas treated with SPLAT AGP Repel. 

Michaud, J. R, Biological control of Asian citrus psyllid, Diaphorina citri (Hemiptera PsyUidae) in Florida A preliminary report. Entomol. News 113 216-222, 2002. 

Zaka, S. M. et al., RepeUent effect of guava leaf volatiles on settlement of adults of citrus psyUa, Diaphorina citri Kuwayama, on citrus. Insect Sci. 17 39-45, 2010. 

Mann, R. S. et al., SnUur volatiles from Allium spp. affect Asian citrus psyUid, Diaphorina citri Kuwayama (Hemiptera PsyUidae), response to citms volatiles. Bull. Entomol. Res. 101 89-97, 2011. 

Onagbola, E. O. et al., Gnava leaf volatUes and dimethyl disulfide inhibit response of Diaphorina citri Kuwayama to host plant volatiles. J. Appl. Entomol. 135 404-414, 2011. 

Boina, D. R. et al.. Quantifying dispersal of Diaphorina citri (Hemiptera PsyUidae) by inunnnomarking and potential impaet of nnmanaged groves on commercial citius management. Environ. Entomol. 38 1250-1258, 2009. 

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