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

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

Report Date: 10/01/2015
Project: 853   Year: 2015
Category: ACP Vector
Author: Stephen Lapointe
Sponsor: Citrus Research and Development Foundation

Antennal responses of psyllids to citrus volatiles and degradation products of citrus volatiles were studied using EAG and GC-EAD recordings. The antennal responses showed that psyllid olfactory system can detect and respond to the degradation products of citrus volatiles. Behavioral experiments using Y-tubes to study the choice behavior of psyllids elicted poor responses to these antennally active odorants. The poor behavioral response may correspond to the ineffectiveness of these odorants in eliciting a long range odorant detection. So we performed experiments to study the short range odorant detection of these same citrus volatiles using a SPLAT probing assay to assess the probing behavior of psyllids. SPLAT probing choice assay measured both insect orientation from several cm to the source of volatiles (olfaction) and subsequent probing behavior that may result from a combination of olfaction and gustation upon contact with a wax substrate containing odorants. Experiments were performed using response surface methods to identify primary drivers in a 4-component mixture design to identify an optimal blend of the primary drivers for maximum probing by D. citri. Different odorant blends were prepared based on the results of the EAG studies. The proportion of different odorants in each blend were calculated using a Design Expert program. Test compounds were incorporated in a slow-release wax matrix for volatiles (SPLAT´┐Ż, ISCA Technologies Inc., Riverside, CA) and offered to caged D. citri adults. Treatments (SPLAT plus odorants) were applied as 1 ml narrow strips or beads (2.0 x 0.5 x 0.1 cm) to 6 glass cover slips and air-dried. Cohorts of 200 5- to 8-d-old D. citri adults were starved for 6 h and then released into each cage and allowed to probe for 21 h under temperature and humidity controlled conditions. To visualize stylet sheaths produced by feeding attempts on the SPLAT beads, the cover slips were removed from the cages and beads were stained with Coomassie blue dye, washed in water and allowed to air-dry. The number of salivary sheaths in each bead was counted under a stereomicroscope at 4X magnification. SPLAT beads containing odorant blends received more probes (salivary sheaths) compared to single odorants. Male and female psyllids responded consistently to formic and acetic acids by EAG and GC-EAD. Incorporation of those compounds into the feeding assay slow-release matrix allowed us to examine behavioral response to odorant blends. Probing by D. citri of the feeding substrate increased with the addition of a blend of formic and acetic acids compared with the unscented control. A 2:1 proportion of formic: acetic acids received the highest number of probes compared to single odorants including formic acid, acetic acid, ocimene and citral. We are now pursuing the hypothesis that additional odorant compounds, not stimulatory by themselves, may augment the probing response when combined with formic and acetic acids. The addition of these odorant blends can increase the probing behavior of psyllids. This research finding will have important practical use of being used as a phagostimulant, which could improve the efficacy of pesticides and other pest management strategies.


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