2023 SLF Summit Q and A - Day 2

Compiled by Jerrie Haines, Northeastern IPM Center

Morgan Dube | morgan.dube@agr.nh.gov | NH Department of Agriculture

Q. Does this support the hypothesis that egg laying is triggered by photoperiod rather than temperature?

A. But yes, this supports egg laying is triggered by photoperiod. Melody Keena reported that too, and Tracy Leskey has seen that in her lab reared SLF.

Julie Urban | jmu2@psu.edu | Penn State

Q. 246 DD less in 2020 versus 2019 is how many % less (Total DD)?

A. Paul — I haven’t computed that based on total DD for the whole year. But they are beginning to lay just short of 2000 DD. So that is about 12% of the DD needed for egg laying.

Q. If host plant is cuing egg laying, then could their egg laying adapt to northern range expansion?

A. I think it might be able to — esp. with the variation or phenotypic plasticity that Melody Keena is seeing in terms of developmental differences in different areas of the Northeast. I need to look at her results in more detail.

Q. How about the site in southern Indiana, they were seeing adults quite early, but egg laying seemed to be delayed — due to day length?

A. Yes, it seems like it. From what Greg Parra said, they saw egg laying at about the same time in North Carolina as up north.

Q. Lab specimens: do you mean reared on potted trees in a pop-up?

A. The ones that I measured were from bugs from the two published studies that Laura Nixon led in Tracy’s lab. I would like to include from any captive reared SLFs to compare across types (in QT lab, in semi-field, in your enclosures, etc.).

Q. www.usanpn.org email alerts for SLF Alerts — Is this a useful tool for GDD alerts?

A. I haven’t used that but will check it out. Thank you!

Q. But will SLF go to these crops if preferred hosts are present?

A. THAT is the multi-million-dollar question. The answer depends upon what else is in the landscape. So maybe not. But if that is all they have access to (e.g., they hatch out on egg masses in a nursery), those plants could potentially suffice as a temporary food source to fuel them on to move onto other plants.

Q. Do we know if SLF can lay more than one egg mass? If so, do they have similar numbers of eggs and viability as the first or typical egg mass? Thanks.

A. I am looking for indicators in my dissections. B/c it looks like the females have to break up the crystal of the spermatophore, their bursa copulatrix when they are older and have a spermatophore (crumbled bits) has dark marks on it. But I have SLF from the late season preserved in fixative (rather than ethanol) to try to home in on whether I can find any reliable indicator of having laid before.

A. For the second part of your question, don’t know. But it could be interesting to see as a function of time — Brian’s data where he marked when egg masses were laid. But I think I’d need to collect females just after they laid and if I collected the mass and had the indicator internally (presuming I can establish one) that she laid already — that could do it. Lab reared could be laying fewer eggs b/c are less fit.

Q. Will you be doing the LLT and CTmin for the other life stages — esp. the adults.

A. Yes. Just not as part of Liz’s thesis.

Q. Is it possible they may survive colder temperatures through huddling together at night like we see them do?

A. It could be. Even individuals go down “in the duff” at the base of grapevines at night. So, they can also keep warmer by moving down into that area.

Q. I think the point is that SLF can prosper in areas that experience very cold temps, way below freezing, but not develop populations in areas that are relatively cool from spring to fall.

A. Yes — the temp. work is just about exposure limits.

Q. If day length turns out to be a factor in reaching reproductive maturity, do you expect latitude to be a major limiting factor in northern range limitations?

A. It could be but there are other factors at play so not sure that it would only ever come down to just one factor.


  • Host cues is a really interesting question! Thanks, Amanda.
  • I was thinking about this yesterday, and it seems that it would allow SLF to tune their development to the local environment, and given that trees use photoperiod and temperature for senescence, then it is a reasonable hypothesis. Amanda Roe.
  • Will you be doing the LLT and CTmin for the other life stages — esp. the adults. We would like to chat with you and Liz at some point bc we would like to use some of these approaches to assess whether winter experienced by the egg masses impacts 1st instar thermal tolerance. These data would be a great baseline. Amanda Roe.

Kelli Hoover | kxh25@psu.edu | Penn State

Q. Do we know if SLF can lay more than one egg mass? If so, do they have similar numbers of eggs and viability as the first or typical egg mass? Thanks.

A. Tracy Leskey has had SLF lay up to 3 egg masses by the same female in her studies.

Stephanie Lewkiewicz | lewkiewicz@temple.edu | Temple University

Q. The R0 map you showed seemed like it was saying that SLF couldn’t establish in the parts of Pennsylvania where it currently is, was I reading that right?

A. Some of the R0 maps we have made throughout our modeling efforts predict population establishment in southeastern PA while some predict population collapse. (For instance, when using different types of temperature data.)

Sebastiano De Bona | sebastiano.debona@temple.edu | Temple University

Q. How long were the eggs exposed to those temps that killed the eggs?

A. J, those were daily mortality rates. They represent the daily exponential mortality rate at a given temperature.

Q. Have you found that now a) the public is highly aware of SLF and b) businesses are supportive of treatment & permits?

A. Yes, the public is very aware of SLF now in NJ! All locations where we plan to treat have to sign our treatment agreement. By and large they are all supportive. A few have concerns about staff being on the property and sometimes ask about indemnity agreements. We have a letter that we typically give out that usually alleviates that concern.

Q. Have you gotten much criticism for militaristic language or accusations of xenophobia regarding an insect from “China”?

A. I have not encountered any xenophobia about China, and I have responded to countless phone calls. Militaristic language hasn’t come up either to my knowledge thankfully. We ask nicely for permission to access the property and treat. If anything, we get folks asking us to come spray but we can’t go away from our priority locations.

Q. Are the county treatments done by the same folks that do mosquito control or is it completely different people?

A. Each county is different. Definitely mosquito control departments are doing some of the work but also parks people and DPW staff can do it. They are allowed to even hire a spray company if they choose.

Matt Helmus | mrhelmus@temple.edu | Temple University

Q. Was that a rating of risk in connection with different modes of transportation that you had towards the end of your presentation?

A. Yes, you can find it here: docs.google.com/spreadsheets/d/107ZHyursbXE6W2_C8MKQYjC-PZvt_G-Y-c5dbPaZtkU/edit#gid=0

Q. The historic range prediction includes southern Canada, the rough map suggests only extreme southern Canada is suitable. Which prediction is more “accurate” or is the truth simply that there is significant uncertainty?

A. I am happy to discuss this more (send me an email if you like) but briefly, there is significant uncertainty, so as a manager I would look at all models, before deciding how conservative you want to be. 1. We do not yet have enough data to know how far north they will spread. 2. SLF adapt. 2. The climate is changing 3. The thermal tolerances are based on very little data. 4. As a rule of thumb, anywhere that grapes or TOH grow can likely also grow SLF.

Matthew Travis | matthew.a.travis@usda.gov | USDA

Q. Great talk! I agree from what I’ve heard, railroads pose the most significant risk for SLF dispersal events (especially if there is Ailanthus tree near railroad tracks). From my understanding, in PA at least, there has been some pushback from railroad companies to get an SLF permit and be inspecting their trains, due to the logistical challenges of doing so. Can anybody speak to if there are efforts being made to work with railroad companies?

A. Great question. Yes, USDA APHIS has a continuous dialogue with the major Tier 1 railroads and also the smaller short lines. USDA has been working to gain permits and access for survey and treatments throughout many states.

Q. They fly off the tree onto the passing trains so that might not matter, depends on what trees are along the RR.

A. Rail has been associated with multiple state detections and established populations. This continues to be a focus for analysis and the risk for long range dispersal. Potential host presence along the rail is certainly also a factor. Rail yards with railcars sitting for long periods of time during egg laying periods is a concern and warrants analysis.

Patrick Gilkey | pgilkey@pa.gov

Q. Great talk! I agree from what I’ve heard, railroads pose the most significant risk for SLF dispersal events (especially if there is Ailanthus tree near railroad tracks). From my understanding, in PA at least, there has been some pushback from railroad companies to get an SLF permit and be inspecting their trains, due to the logistical challenges of doing so. Can anybody speak to if there are efforts being made to work with railroad companies?

A. Thank you! I was doing outreach in Erie the other week with wineries and vineyards. It was a bit surreal . . . acres upon acres of vineyards, and then right next to them, railroads. I hope APHIS is able to work with those railroads before SLF gets to Erie.

  • I would also add that PDA has done great work with rail in Pennsylvania and has been conducting treatments and survey on many rail lines in PA. (Matthew Travis)
  • I’ve heard that too! Treatment and survey is being implemented for railroads, and that certainly is effective. The pushback I have heard about is more about them getting an SLF permit and inspecting their trains, as it is admittedly very difficult to regularly inspect entire trains for SLF. (Patrick Gilkey)

Brian Ruether | brianfr@vt.edu | Virginia Tech

Q. Are there any studies that anybody knows of where lavender field border and/or prairie strip plantings have been done as preventative planting against SLF? We in SE MI have confirmed populations in neighboring counties.

A. No, there haven’t been any studies published with SLF to date. There may be some in the context of other pests, but I’m not aware of them.


  • I grow lavender on my balcony, and they laid egg masses still.
  • Hmm . . . Perhaps then there is quantity threshold needed to be SLF deterrent.
  • I agree. It’s all about identifying if the repellent can outweigh the effect of the attractant (for your deck, I suppose the fact that it’s a tall object attractive for egg laying plus any host plants you might be growing).

Houping Liu | hliu@pa.gov | PA Dept of Conservation and Natural Resources

Q. This is a random question for anyone to please answer. Has there been any evidence that SLF will feed on pawpaw (Asimina triloba)?

A. We saw a lot of egg masses on pawpaw at one of our sites but not sure whether young nymphs feed on it. We did not see adults feeding on this species.

Julie Lockwood | julie.lockwood@rutgers.edu | Rutgers University

Q. Where would you say NY State as a whole is on the cost of inaction continuum?

A. Million-dollar question. I’m not sure we know enough to be certain.

Q. Have you considered crossing into Canada?

A. Good question. We are moving our surveys north in the Fall of 2023 toward Canada, but we have not had anyone contact us to do surveys within Canada yet.

Q. Very interesting talk! Is it possible to use one sample to monitor for more than one species? Or would you need to collect a sample for each species you’re interested in monitoring?

A. Absolutely. If it was just 2 or 3 species, you could do three qPCR analyses. Once you get to more than about 5 species that are of interest, the lab work switches to meta-barcoding. That approach is used regularly within fisheries and aquatic eDNA work, and our lab and others have shown it also works for terrestrial insects.

Q. Understand tree of heaven tends to grow around railways, were you able to get cooperation from rail companies to survey, as well as airports.

A. We have not surveyed around railways yet, but based on Matt’s results that seems logical. The trick will be getting permission to enter these areas, but I think it would be a very good test to see if we can detect early infestations at these high-risk sites.

Q. Is there any possibility of false positive results from sampling areas where non-SLF, native Fulgoridae?

A. We have tested against several other plant hopper species and shown no evidence that the genetic assay we have will amplify another species’ DNA. But, it is always good practice to continuing to “challenge” eDNA assays to be sure they are species-specific.

Q. Is there a threshold for the amount of DNA you need to find in order to mark a positive?

A. There is. I would have to look up the exact amount, but the lower limit is 10 or so copies of their DNA or just a few femtograms. It’s very low, which is consistent across all eDNA uses (aquatic and terrestrial).

Q. I think you said plants retain DNA evidence for up to 2 days — is that right? Does this mean detections indicate something about when the insects were present?

A. Yes, from previous research where we tested how long the “signal” of DNA lasts on plants exposed to rain and sun last we found that the signal pretty much fades within about 2 days to a week. So, we can pick up DNA left days before our arrival at a site.

Q. Julie — can you talk about your visual survey that it is different than how PPQ and states visually survey for SLF.

A. We did standardize 15-minute visual surveys within a set spatial area around where we sampled for DNA. We relied on information from our Rutgers fruit ag folks for this, but if you can share the PPQ protocols we’ll do that this coming fall so that we can do a more pertinent comparison.


Joy Goforth | joy.goforth@ncagr.gov | NCDA&CS

Q. Does your plan cover at what threshold you will throw in the towel on eradication?

A. Without knowing what future resources will be available, it is impossible to predict. Our plan is to continue with suppression in areas where eradication is not possible, but there may be a tipping point if more established populations are found.

Q. That was great Joy. Do you think eradication is still possible? Do you have a cut off point for changing to slow the spread? Thanks.

A. Thank you! Anything is possible, but we are probably looking at suppression until there are new methods of control.

Q. Joy, does that photo of the egg mass indicate that you have hatch in NC at present?? Or is that from hatch 2022?

A. We believe that egg mass was the first for this season. There was a long period of egg laying last season and we are wondering if this was the first to hatch because it was one of the first to be laid.

Q. Joy, what area in NC was the emergence egg mass found? Forgive me if you mentioned it when presenting.

A. Our active population is in Kernersville which is pretty centrally located in the state. The egg mass was there.

Robert Miller | millerr35@michigan.gov | MI Dept. of Ag and Rural Development

Q. When you are scraping egg masses, are you squishing and scraping, or scraping into alcohol, or what’s the technique?

A. Our folks in the field had both options to scrape into a bottle of soapy water to squish them. Most folks prefer to squish the egg masses.

Q. Do you find that after a rain, even late-season egg masses are more visible?

A. Yes, I believe so. Robert Miller.

Q. It looks like you used a 1/4 x 1/4 mi delimit grid size — did you find this was a good cell size from a boots on the ground standpoint?

A. Our grid cells were around 100' x 100'. That is a good size. Keep in mind that as folks work in a grid they should be within line of site of their partner.

Scott Schirmer | scott.schirmer@illinois.gov | IL Department of Agriculture

Q. Can you repeat those host species you said you tend to find egg masses on?

A. Maple, styrax, willow, and river birch I believe it was.

Frank Buccello | frank.buccello@agriculture.ny.gov | NY Department of Agriculture

Q. Where did you purchase the backpack vacuums?

A. Without naming the store, we purchased them from the two main box stores.

Q. How long can the battery last?

A. The batteries last approximately 45–60 minutes on one charge. Our inspectors carry 3–4 batteries with them and recharge them overnight.

Q. How noisy are these vacuums? I don’t see any ear protection on the operators.

A. They are not so noisy to require ear protection, but we do have it available if necessary. They are quieter than we expected.

Q. Which life stage are you finding the vacuum works best for?

A. Not really much difference between nymph or adult.

Q. What kind of maintenance is required?

A. We empty and clean them regularly, but other than recharging the batteries, not much more maintenance.

Q. Have you tried out different brands/models of vacuums? Does that Milwaukee model you showed seem to work best?

A. We stayed with the Milwaukee model because we started with it and experienced good results, but from what I have seen available, I am sure there are other brands & models that would work.

Jacob Henry | jachenry@pa.gov | PA Department of Agriculture

Q. Are you combining the bifenthrin with systemic treatment as a foliar spray or doing foliar spray and basal trunk spray.

A. A typical treatment will be basal spray application of dinotefuran followed by a broadcast application of bifenthrin.

Q. Are you using pyrethroids for the powered applications?

A. We exclusively us bifenthrin as a contact spray.