JOSH MOSIONDZ, HANNAH FRASER, DENISE BEATON, WENDY McFADDEN-SMITH & CASSIE RUSSELL

Spotted lanternfly (SLF), Lycorma delicatula, is a sap-feeding planthopper with a love of grapevines. Native to China and Vietnam, SLF is invasive to Japan, South Korea, and most recently the United States (U.S.). The first North American population was confirmed in Berks County, Pennsylvania, in 2014, and despite eradication and quarantine efforts, it has spread to at least 17 states. This includes populations in both New York and Michigan, right across the border from grape-producing regions in Niagara and Essex.  An interactive map of the distribution is available https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/whats-bugging-you/spotted-lanternfly/spotted-lanternfly-reported-distribution-map.

As of the time of writing, despite several 2023 sightings and interceptions of SLF on imports and vehicles in Ontario, the pest has not been detected in Canada. “Detected” refers to confirmed finds of live, established SLF in the environment.

To learn more about SLF from those working with and managing the pest, a team of Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) specialists (Figure 1) traveled to Reading Pennsylvania and surrounding areas in fall 2023 to participate in hands-on training. Over the course of four days, the team was able to meet with a wide range of extension specialists, researchers, and industry personnel, including those from Penn. State University, the Fruit Research and Extension Center, the United States Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS), the US Army Corps of Engineers, Pennsylvania Department of Agriculture (PDA) and commercial growers. Through these visits, the team was able to discuss ongoing containment and various management strategies attempted for this invasive insect. From this, three main takeaways were identified following our stay.

1. Egg masses, detection difficulties, and interesting behaviours

Figure 2: (Left) An adult female deposits a white waxy coating upon a newly laid eggmass atop of a previous generation’s eggmass. (Right) a newly laid eggmass with fresh white waxy coating (approximately 1-2 hours old) vs. an older egg mass 3-4 days old which has its waxy coating faded to a light brown.

The reason that SLF has been such a successful invader is because it is an excellent hitchhiker, and it isn’t a picky eater. More than 70 host plants have been identified in the U.S., many of which are common agricultural and landscape plants in Eastern North America. Long-distance spread to new geographic areas is attributed to the movement of egg masses, which can survive long-distance transport and cold temperatures. For example, SLF is suspected to have entered the U.S. in the egg-mass stage on a shipment of landscaping stone.  Females lay their eggs on virtually any flat surface, including both host plants and non-plant material such as landscaping stones, outdoor furniture, pots, firewood and vehicles. Eggs are covered by a protective substance that, once dried, makes them difficult to detect. They look like splotches of mud, especially when on vehicles, campers, trailers, railcars, garden equipment, or other materials. When egg masses are deposited on the bark of certain tree species, it can be very difficult to distinguish an egg mass from the actual bark, especially as SLF often lay eggs high in the canopy of trees, several feet or more above eye level.

Movement of adults on vehicles is also possible. The observed spread in the U.S. closely follows the distribution of major highways and railways, possibly from mated females jumping off along the way. Disturbed habitats often include preferred hosts such as the invasive tree of heaven and wild grapevines, which also help facilitate establishment and subsequent local spread.

Beyond this, an interesting observation we made was that females often returned to the same general location to lay their egg masses as previous generation. We also frequently observed fresh egg masses laid on or near areas of the tree where the previous year’s egg masses had been scrapped off (and with it a thin layer of tree bark). Both old and new egg masses were typically found in tree cracks, crevices, branch crotches, on the underside of branches or any other protected portion of the tree (Figure 2). Researchers and extension specialists have also found that in the Reading, PA region, egg laying typically starts on or close to the timing of the fall equinox, perhaps suggesting that this is triggered by photoperiod.

2. Ecosystem and plant effects – direct and indirect damage

Swarms of nymphs and adults damage plants directly by feeding on sap from the stems and trunks, and indirectly by excreting large amounts of sugary honeydew that promotes the development of sooty mould, which in turn interferes with photosynthesis. Large, concentrated populations of SLF are sometimes known to create a “rain effect” as honeydew falls to the ground during periods of heavy feeding – some of which we were also able to experience firsthand. The honeydew that falls on plants and other substrates and develops the black sooty mould will appear black in colour and will often look as if it were burned (Figure 3). Besides causing issues with the plant’s photosynthesis, it is also not aesthetically pleasing. The honeydew buildup additionally attracts other insects which like to feed on the sugary mixture – often bees, wasps, or other stinging insects. Aggregations of adults and the messy, sticky honeydew they excrete are significant nuisance factors, with impacts to homeowners, tourism, businesses, and overall quality of life. 

Figure 3: (Left) Sooty mould buildup (approximately 3-4mm thick) on a tree branch following honeydew accumulation. (Right) Sooty mould build up on understory plants beneath a mature tree of heaven on which SLF have fed.

The spotted lanternfly is considered a plant stressor, contributing to the long-term weakening of established vines, shrubs and trees. Prolonged swarm feeding (hundreds to thousands of individuals can occur together) has led to the death of grapevines (wild and cultivated), the invasive tree of heaven (a preferred host), and saplings of black walnut and silver maple in infested areas. For large trees, this can lead to the development of deadfall as trees may decline or die, and pose a subsequent safety hazard to anyone around them as branches become brittle and fall.

While there have been some dramatic images of swarms on fruit trees, SLF is understood to be more of a transitory feeder on these crops and numbers are often kept in check with regular insect IPM programs. The long-term impact to other hosts, including understory plants covered with sooty mould, has not been determined.

3)Questions and challenges still remain, and many of them!

Of particular concern to the grape and wine sector, grapevines exhibit decreased vine growth, reduced crop yield, poor winter survivability, and high levels of mortality when SLF populations are not managed. Treatment thresholds are under development in Pennsylvania and other wine-producing states which currently have populations of SLF.  One of the challenges with SLF in vineyards is that populations frequently build up in the landscape around vineyards rather than within. When those alternative hosts start to senesce in the fall, adults move into vineyards in repeated waves, requiring multiple insecticide applications to protect the vines until the adult SLF are killed off by heavy frosts. In the U.S., growers generally use products with short Pre-Harvest Intervals (PHIs) before harvest for management of adults. Products with longer residual activity may be applied earlier in the season when PHIs allow for use, or sometimes post-harvest when populations continue to persist. Nymphs hatching from eggs laid in the fall within the vineyard are generally easily killed in the spring and summer by insecticides used for other pests.   

One significant question to which we still lack a definitive answer is what drives the adults to gather and exhibit their swarm-like behaviour in the fall as they move from their landscape hosts into vineyards. Currently, research has been unsuccessful in identifying consistently effective aggregation or sexual pheromones that could be the cause. Other hypotheses behind these aggregations include visual recognition, honeydew excretions or frequencies.

Our tour guides also explained that they have found certain trees are highly attractive to adults and large numbers can be found on one tree and nearby trees of the same species and similar size and appearance will be left relatively unscathed. The reason SLF is attracted to these “hot trees’ is a phenomenon that is not yet well understood.

Additionally, the “hot trees” may not be so ‘hot’ the next year. Turgor pressure, which helps move the sugary phloem from the roots to the canopy, is a suspected factor but remains unproven thus far.

Finally, there is research underway to identify potential biocontrol options that will help manage this insect. Researchers are looking at native predatory insects and host-specific parasitoids from SLF’s native host range. This work can take many years to complete since non-target effects for non-native biocontrols must be investigated thoroughly to ensure there will be no unintended harm to the environment.

With wholesome integrated pest management (IPM) programs still in the early stages of development, U.S. growers are relying mainly on insecticides to keep numbers at low, manageable levels. Research in the U.S. indicates that perimeter sprays around vineyards can be as effective as full block applications, as most individuals are located along vineyard borders. When making any kind of insecticide application for SLF management, thorough spray coverage and use of effective products with good knock-down is critical to effectively manage populations. Exclusion netting can also be very effective, but very labour intensive, and is often not practical for large blocks or commercial growers. Efficacy can also wane when tall trees are present around the vineyard which allows adults to simply fly above it. Scraping and destroying of egg-masses, most of which are along borders, is time-consuming, and given hatching nymphs are easily killed in-season, is probably of limited value.   

As of January 2024, some pest control products are fully registered by the Pest Management Regulatory Agency (PMRA) for use on Spotted Lanternfly (Table 1) and several additional submissions are currently in review at the Pest Management Regulatory Agency.

Table 1: Summary of current insecticide registrations for SLF in Canada

* Emergency Use Registration currently in effect

All of this may leave you wondering what YOU as a grower, industry member, or citizen can do to prepare for this insect’s arrival.

• Ensure you and any potential staff are properly trained to inspect any imported products from regions with known SLF infestations with extreme diligence.
• Ensure you look for proper life stage according to timing within the year and report any suspected presence of SLF.
• Keep an eye out for educational materials, training workshops, and follow Best Management Practices as they continue to be developed and released.
• Most importantly, should you suspect you’ve found a SLF egg mass, nymph, or adult whether on imported material or outside your operation, immediately snap it (take a picture or video), catch or kill it, and get in touch with the CFIA to report your finding.

For more information on the pest’s life cycle, biology, and how to recognize and identify eggs, nymphs and adults, please visit  www.ontario.ca/spottedlanternfly 

For those attending the 2024 Ontario Fruit and Vegetable Conference, a morning session on Wednesday February 21^st will be dedicated to SLF with speakers from various backgrounds currently scheduled to participate. Also visit the OMAFRA Agriculture Development Branch booth to view specimens in ethanol or pinned in shadow boxes to take in how large these insects are in real life!

Josh Mosiondz is provincial minor use co-ordinator; Hannah Fraser is entomologist – horticulture; Denise Beaton is crop protection specialist; Wendy McFadden-Smith is tender fruit and grape IPM specialist; and Cassie Russell is nursery and landscape specialist. All are with the Ontario Ministry of Agriculture, Food and Rural Affairs.