1. Erica J. Kistner and Mark S. Hoddle Applied Biocontrol Research
Life Table Analyses to Determine Natural Enemy Impact on Asian citrus psyllid in southern CA
This is a story about an Invasive Plant Pathogen-Vector system
Erica J. Kistner and Mark S. Hoddle
UC-Riverside
Dept of Entomology
Applied Biocontrol Research

2. Asian citrus psyllid (ACP) Diaphorina citri (Hempitera: Liviidae)
Eggs
Nymphs
Adult
Efficient vector of the bacterium responsible for the deadly citrus disease Huanglongbing (HLB)
Feeds on most citrus varieties (Rutaceae)
Thrives in both urban and agricultural areas
Fast developmental time (egg to adult in 2-3 weeks)
Adults act like flying contaminated syringes (good dispersers)
The Vector,

3. Huanglongbing - HLB “Citrus Greening Disease”
Most severe of all citrus diseases
Caused by phloem dwelling bacterium, Candidatus Liberibacter asiaticus (CLas)
Found in all major citrus growing regions worldwide
Disease affects most plants in citrus family (Rutaceae)
Symptoms: foliage dieback, malformation of seeds, premature fruit drop, and ↓ fruit yield
All infected trees die (3-5 yrs)
Currently no cure or resistant citrus variety in US
CLas
Photo by Mike Irey
HLB infected tree in FL

4. US Citrus Industry in Peril
US citrus industry is valued at ~ $13 billion ($3 billion in CA and $10 billion in FL)
FL Case Study:
ACP and HLB discovered in FL in 1998 and 2005, respectively
Both are widespread throughout the state
~ 75% of Florida’s citrus trees are likely infected
ACP-HLB ↓ FL citrus production to its lowest output rate since the 1960s
Cost FL citrus industry $2 billion in estimated net losses
CA (the jury is still out):
ACP and HLB discovered in CA in 2008 and 2012, respectively
ACP is widespread throughout CA’s residential landscape
HLB has NOT established in commercial orchards
Pesticides are employed in commercial grooves
Classical biological control is utilized in urban
residences
60% of all CA homeowners have a citrus tree
Industry, Academia and Government are all working on this problem.

5. Classical Biological Control: Tamarixia radiata (Hymenoptera: Eulophidae)
Most commonly utilized biocontrol agent of ACP
Solitary ecto-endoparasitoid (host specific)
Attacks 3rd, 4th, & 5th instar ACP
Kills ACP via host feeding too
Sourced from Punjab, Pakistan (70% climate match with SoCal)
Since 2011, over 1,000,000 wasps have been released across SoCal
Wasps have established multiple populations and are doing quite well

6. ACP Phenology on Citrus in LA
Tamarixia
detected at
site
Our tiny parasitic wasp is now well established in southern California
However this is all speculative, does not take generalist predators, mutualism by argentine ants, and density dependent/ independent factors into account.
Ongoing ACP surveys suggest that Tamarixia may be limiting ACP population growth in some urban areas

7. ACP Life Table Studies
Life tables can be used to assess mortality and survivorship rates for the different immature life stages of ACP
Eggs
Small nymphs
Large nymphs
Mortality can be assigned to different causes
Parasitism
Predation
Bad luck!
Life tables are mortality and survivorship schedules
Accounting system originally designed to study human mortality and to identify vulnerable stages and probability of death due to certain causes
Life insurance companies use “life tables” to figure out your premiums based on age risk etc!
Bad luck (born in the winter months, where it is cold and there is not enough fresh flush to feed on)

8. Developing Life Tables for ACP
2. No walking insects (sticky barrier)
3. T. radiata only (156 holes per inch2 )
4. All insects (No treatment)
Similar studies have been conducted in FL by Qureshi and Stansly (2009), set out potted orange jasmine with -150 ACP eggs
1. No enemies (Density dependent effects), 2 Parasitism 3, all flying predators 4 all mortality effects
1. ACP only (625 holes per inch2 )

9. Lochmoor (private property) Jurupa (private property)
ACP Life Table Studies
ACP Cohorts that are “born” at the same time are studied across sites and through time
Three different sites in Riverside, CA
Differ significantly in flora composition
Life tables for ACP cohorts being developed for populations in:
Spring
Summer
Fall
Winter
UC-R Biocontrol Plot
Lochmoor (private property)
Tamarixia is currently being released and has been recovered from all three sites. On 4th cohort at Biocontrol
Jurupa (private property)

10. Collecting Survivorship and Mortality Data
Every other day ACP life stages are counted on experimental plants:
Number entering each stage is recorded
Determine survivorship rates to adulthood
Determine parasitism rates
Identify predators on ACP patches and trapped on sticky barrier
Methods adopted from Qureshi and Stansly 2009 who developed field life tables in FL
Ro (based on egg to adult survival and fecundity assuming 1:1 sex ratio, fecundity at the temperature range determined by Lui and Tsai 2000)
These experiments will be repeated over the Sept and Octobers 2014 as well as May-Oct 2015.

11. ACP Survivorship Curves at UCR Biocontrol Grove
Summer: About 50% of ACP reach adulthood when exposed to Tamarixia only % ACP die when exposed to flying and walking natural enemies. 90% ACP only survive
Fall: About 30% ACP die when exposed to Tamarixia only. 100% ACP die when all natural enemies can access cohorts. 70% ACP only survive
Winter: Nearly all ACP die because of cold weather and long developmental times expose them to natural enemies for longer. 20% of ACP survive
Despite reduced Tamarixia activity in winter months, colder temperatures limit ACP population growth in two ways: 1) reduce survival of less fit individuals 2) extend ACP developmental periods giving predators ample opportunities to consume slowly growing nymphs.
Oct 20th-Nov 30th 2014
Sept 20th -Oct 16th 2014
ACP survival ↓ substantially when exposed to natural enemies and cold temperatures

12. % Mortality of ACP by Life Stage
Summer cohort – ants excluded
ACP Life Stage
No. Entering Stage
No. Dying in Stage
Cause
of Death
% Dying in Stage
Eggs
215 38
Disappeared: 10
Unknown: 28 5%
18%
1st-3rd instars
177 26
Eaten: 17
Disappeared: 9
10%
4-5th instars
151
108
Eaten: 36
Parasitism: 72
24%
47%
Adults 43
% Survivorship = 20% % Mortality = 80%
Both Tamarixia and generalist predators limit ACP populations

13. UC-R Biocontrol plot life table parameters
Cohort
Treatment Ro MT rm Td
Summer
ACP only
259.56
25.9
0.21
3.22
No walking insects
172.35
21.6
3.26
All insects
71.36
21.9
0.19
3.56
Tamarixia only
98.99
23.4
0.22
3.14
Fall
198.6
28.5
0.18
3.7 -
1.18
20.3
0.01
85.05
195.4
27.8
3.65
Winter
12.09
55.9
0.045
15.54  -
2.26
52.94
44.95
Assumes all adult females reproduce and fecundity is based on temperature. If Ro is greater than 1, the populations is growing.
Ro, net reproductive rate, (per capita rate of population growth), MT, mean generation time (in days) rm, instristic rate of increase, Td, doubling time (in days) for population.
Surviving female ACP exhibited ↑ net reproductive rates when protected from natural enemies (P < 0.001) and during warm months (P < 0.01)

14. Common Insects on ACP Life Table Cohorts
Invasive Argentine ants tend ACP nymphs and protect them from natural enemies
Enemies vary across site and time.

15. Management Implications
Both generalist predators and T. radiata ↓ experimental ACP numbers (double the biocontrol)
Impact affected by:
Type of natural enemies and interactions
Time of year (flush growth, ACP infestation levels)
flora diversity and yard care at study sites
Argentine ants likely have a very disruptive effect on all ACP natural enemies and should be controlled
IPM practices should be
employed during hot months
when both ants and ACP flourish

16. Acknowledgements
Hoddle Lab Members: Christina Hoddle, Ruth Amrich, Martin Castillo, Michael Lewis (photos), Kelsey Schall, Allison Bistline-East
CRB: MaryLou Polek
USDA: Greg Simmons
CDFA: David Morgan, Grace Radabaugh
UC-Riverside, Dept of Entomology: Matt Daugherty
Field help: Nagham Melhem, Elizabeth Carpenter, Kathryn Vega

17. Parasitism rates decrease when exposed to other insects
Sept-Nov 2014

18. Common ACP predators: chrysopid and syrphid larvae
ACP mortality rates from these larvae ranged from 35% to 93%
Green Lacewing larvae (Chrysopidae)
Hoover fly larvae (Syrphidae)

19. Background Measurements
Taken monthly at each site:
Ant density and activity
% Flush
% Flush infested by ACP life stage
Temperature and relative humidity
Urban flora and ground substrate