Impact Of Host Plant Xylem Fluid On Xylella Fastidiosa Multiplication ...

Table 2. Mortality and flight performance of GWSS males after a 24-hour exposure to untreated grape or grape
with imidacloprid applied at 1/4 th or 1/32 nd of a standard dose (3.2 mg/500 g soil) 10 days previously.
Performance characteristic
(Males Only)
Sample
size
Range Average * Stand. dev.
Mortality 1/4 th dose 57 0- 100% 33% a 0.34
1/32 nd dose 48 0 - 25% 9% b 0.09
untreated 48 0 - 20% 3% b 0.08
Percentage of surviving non-fliers
1/4 th dose 38 0 - 100% 59% a 0.38
1/32 nd dose 44 0 - 22% 7% b 0.09
untreated 46 0 - 20% 3% b 0.08
*Numbers in a column followed by the same letter were not significantly different using chi-squared with Yates’ correction
and ANOVA.
The flight performance assays of GWSS exposed to 1/8 th and 1/16 th dilutions of the standard dosage of imidacloprid are still
in progress. Preliminary indications are that the 1/8 th dilution may reduce average flight activity but with some individuals
flying as far as fliers from untreated plants.
Unreported Results that were Pending Last Year.
The effects of the insect-repellent kaolin clay (Surround) and Admire applied to potted grapevines were assessed in cages for
possible repellency effects to GWSS and BGSS (Purcell 2003). In general Surround was repellent, whereas Admire was not.
The test plants used in these behavioral experiments were saved for diagnosis for PD, as all sharpshooters used in the
experiments had been exposed to plants infected with X. fastidiosa. Unfortunately, transmission rates in all treatments
(including untreated controls) were too low (3% per plant for GWSS, 9-21% for BGSS) to be of value in assessing the effects
of Admire or Surround applications on the vector transmission of X. fastidiosa where the insects had a choice of treated vs.
untreated plants. This lower than normal transmission rate was probably due to low populations of X. fastidiosa in the PDgrapes
used for acquisition feeding.
CONCLUSIONS
GWSS flew on flight mills for up to 4. 2 miles (6.8 km), averaging over 1.5 miles in a 4 hr period. Soil-applied imidacloprid
(Admire) dosages that caused 33% mortality during a 24-hr exposure to treated plants reduced average flight performance of
surviving GWSS, but some of the insects that survived this exposure flew almost normally. Dosages that caused about 10%
mortality and that have been shown to drastically reduce GWSS feeding did not significantly reduce flight on flight mills.
Admire treatments probably reduce long distance movements of GWSS from treated crops having sap concentrations of
imidacloprid that kill at least 30% of the GWSS within 24 hours.
Sep 11, 2004; Control # 3 Male, 8078 rev (5.08km)
140
120
100
80
60
40
20
0
1 61 121 181
Figure 2A. Flight (flight mill rotations per minute) of a control GWSS (no insecticide); horizontal axis = minutes.
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