Why is Poncirus trifoliata resistant to colonization by Asian citrus psyllid?

Why is Poncirus trifoliata resistant to colonization by Asian citrus psyllid?

Report Date: 02/01/2016
Project: 853   Year: 2015
Category: ACP Vector
Author: Stephen Lapointe
Sponsor: Citrus Research and Development Foundation

Volatile compounds often serve as cues for orientation by phytophagous insects to their host plants. However, all citrus volatiles studied to date in Y-tube olfactometer tests or field tests have elicited little to no orientation from the Asian citrus psyllid (ACP). We devised a probing choice assay to measure short range orientation and subsequent probing behavior by ACP on a wax substrate containing odorants. ACP probing increased with addition of a blend of formic and acetic acids compared with a control. A 2:1 blend of formic:acetic acids received the highest number of probes compared to single odorants including formic acid, acetic acid, ocimene and citral. Our results demonstrated that acetic and formic acids (and perhaps others compounds) act as phagostimulants for ACP. These novel results have been accepted for publication in the journal Chemical Senses and will be more fully described in the next report. We also studied the effect of incorporating additional compounds into multiple component blends to increase the stimulatory effect of acetic and formic acids on probing behavior of adult ACP. Compounds identified as stimulatory to olfactory receptors by single-cell recordings from neurons in ACP antennae were selected as candidate compounds. Experiments were performed using geometric mixture designs and response surface methods to identify primary drivers in 5- and 3-component mixtures to identify an optimal blend of odorants to maximize probing by ACP. We also studied the interaction between visual attraction to yellow and olfaction or gustation. Test compounds were incorporated into a slow-release wax matrix (SPLAT´┐Ż, ISCA Technologies Inc., Riverside, CA) and offered to caged ACP adults. Treatments (white or yellow SPLAT with or without odorants) were applied as 1 ml wide strips or beads to glass cover slips and arrayed on the floor of a cubical cage. Cohorts of ACP adults were starved for 6 h and released into each cage and allowed to move freely and probe on beads for 21 h. The beads were stained with Coomassie blue dye to visualize stylet sheaths produced by feeding attempts on the wax beads. There was a strong interaction between color and odorant. The yellow beads always received more probes compared with white beads. Addition of 1 (formic acid), 2 (formic and acetic acids) or 3 (formic acid, acetic acid and para-cymene) resulted in progressively more probing behavior on yellow beads, but not on white beads. Ethyl-butyrate and myrcene had no effect or a negative effect on probing behavior. The optimal 3-component blend will be reported as a phagostimulant blend in a manuscript under preparation. This blend will be further tested in greenhouse and field trials. This phagostimulant may be used in an attract-and-kill strategy for ACP control.


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