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

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,

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

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.

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

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

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)

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 )

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)

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.

ACP Survivorship Curves at UCR Biocontrol Grove Summer: About 50% of ACP reach adulthood when exposed to Tamarixia only. 70-80% 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

% 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

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 0.01542 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)

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.

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

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

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

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)

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