Asian citrus psyllid (Diaphorina citri Kuwayama) and citrus greening disease: Understanding the vector-pathogen interaction for disease management

Transcription

1 Asian citrus psyllid (Diaphorina citri Kuwayama) and citrus greening disease: Understanding the vector-pathogen interaction for disease management Michael E. Rogers, Timothy A. Ebert, Rosana H. Serikawa, Kirsten S. Pelz-Stelinski and Ronald H. Brlansky University of Florida / IFAS / Citrus Research & Education Center, Lake Alfred

2 Citrus IPM Programs in Florida (past 20 yrs) Scale insect pests under complete biological control Relied mostly on use of petroleum oils for pest / disease management Processed oranges 1-3 oil applications per season (eriophyid mites, fungal diseases) Little use of broad-spectrum insecticides

3 Asian citrus psyllid (Diaphorina citri) Florida Direct feeding damage insignificant Vector of bacterial pathogen of citrus!!!

4 Citrus greening pathogen found in Florida in August 2005 Now spread to all major citrus growing areas of the state Recently found in LA

5 Citrus Greening Disease Huanglongbing (HLB) yellow shoot disease

6 Greening Effects on Citrus Production Bitter-tasting, lopsided fruit, small in size May not color properly with portions remaining green

7 Reduction in fruit size Mosambi sweet orange India (Oct 08)

8 Greening Effects on Citrus Production Overall tree decline, loss of production

9 Current Psyllid Control Programs In the presence of HLB use of broad-spectrum insecticides targeting adult psyllids winter dormant sprays significantly reduce psyllid populations on spring flush Additional broad-spectrum sprays prior to new flush Florida grower average 5-7 sprays / yr; $300/A increase in production costs

10 Psyllid Control in Florida Where do we go from here? repeated use of broad-spectrum insecticides is not a long-term solution Disruption of established biocontrol agents Pesticide resistance likely High cost of applications Need to develop sustainable psyllid management programs Better understanding of pathogen transmission by psyllids

11 Goal: Refine psyllid management programs to reduce insecticide applications to those periods when most benefit will be received

12 Current Research Focus Basic pathogen transmission studies Acquisition, latency, inoculation, transovarial Past studies used symptoms Improved pathogen detection (real time PCR) Seasonality of transmission Can we target psyllid control to specific times of year Effects of insecticides on transmission Reduction or prevention of pathogen transmission

13 Psyllid Acquisition Rates (laboratory studies) Psyllids which fed as adults on HLB (+) plants Average acquisition rate of 20-30% Detection of pathogen in adult ACP % Las positive Feeding Time (days)

14 Psyllid Acquisition Rates (laboratory studies) Adult psyllid reared on HLB (+) plants (nymphs fed entire time on infected plant) Percentage of HLB (+) adult psyllids ranged from 11.6% to 100%

15 Psyllid Acquisition Rates (field studies) Caging Studies Acquisition by adults vs nymphs

16 Psyllid Acquisition Rates (field studies) Adult psyllids caged on HLB (+) plants 1 out of 1,000+ psyllids tested HLB (+) Adult psyllids reared from nymphs on HLB (+) plants Percentage of adults testing HLB (+) ranged from 0% to 100% Variation due to differences in pathogen levels in different parts of the plant

17 Seasonal Psyllid Infection Rates Monthly collections of wild psyllid populations DNA extraction / real time PCR to detect presence of HLB pathogen in psyllids 8 grove sites in 5 Florida counties including: DeSoto, Highlands, Okeechobee, Polk and St. Lucie counties HLB (+) trees have been found in all of these locations

18 Pathogen detection in natural populations (Jan-Jul 2008) Psyllid Infection rate and sample size averaged for all Florida sites. Infection Rate % Total # psyllids sampled 0.5% Sample Size (N) Small sample size Jan Feb Mar Apr May Jun Jul Aug the highest monthly infection rate found in a single grove thus far was 1.6%; high number of HLB (+) trees present Infected psyllids were NOT found in most groves where HLB management programs were in place

19 Summary of Results to date Pathogen acquisition rates by adult psyllids is low High rates of pathogen detection in adults which acquired as nymphs completing development on HLB (+) plants

20 Summary of Results to date Appears to be some fluctuation in abundance of infected psyllids throughout the year (1 year of data) Overall psyllid infection rates in the field are likely less than 1% Rates >1% only where HLB infected trees were still present

21 Implications for HLB Management Importance of tree removal Elimination of source of inoculum Grower reluctance Cost of scouting and tree removal % of trees infected could result in removal of entire grove Some now choosing insecticide only approach

22 Vector Management using insecticides Reducing overall psyllid populations Disruption of pathogen transmission

23 Can insecticides prevent pathogen transmission? Soil-applied systemic and foliar insecticides Vector mortality prior to transmission? If insecticides can prevent transmission, how long does such protection last? Effects of residue degradation?

24 Ongoing studies: imidacloprid treated and untreated plants challenged with HLB (+) psyllids

25 Ongoing studies: Currently holding more than 100 plants; no PCR positives to-date Positive transmission results could take 8-12 months Early symptoms can be a bit confusing

26 EPG Studies Determine exact feeding time required for pathogen transmission / acquisition Determine whether insecticides can disrupt feeding prior to transmission Determine how long insecticides (residues) provide disruption of psyllid feeding / pathogen transmission

27 Electrical Penetration Graph (EPG) measure psyllid feeding

28 Final Thoughts on HLB Management Intensive psyllid control is a short-term solution Buying time until sustainable solutions developed Successful management will require: Resistant (tolerant) citrus varieties Changes in cultural practices Development of sustainable citrus IPM practices

29 Acknowledgements Rogers Lab Members: Harry Anderson Sr. Biol. Sci. Percivia Peaches Mariner Research Assistant Rhonda Schumann Sr. Chemist Dalia Shawer Ph.D. Visiting Entomologist Tim Ebert Post-doctoral Research Assoc. Antonios Tsagkarakis Post-doctoral Research Assoc. Rosana Serikawa Ph.D. Student