Progress report for GNE22-287
Project Information
Spotted lanternfly (Lycorma delicatula, SLF) is an invasive sap-feeding insect that poses a serious threat to several agricultural and ornamental industries, especially grapes, fruit and walnut trees, and hops. The invaded range that started in one county in PA in 2014 has expanded to 11 states in the Northeast, Midwest and Mid-Atlantic regions. To prevent losses from this pest, it is necessary to find control methods that are sustainable and cost effective, for which biocontrol shows great promise. A potential source of biocontrol agents that has yet to be explored are predatory insects that are endemic to the U.S. For this project, I will identify the most effective predators of different SLF life stages through field surveys and further assess predation efficiency of commercially available or easily collected predators (e.g., Chinese praying mantises, Carolina mantises, convergent ladybugs, harlequin ladybugs, green lacewings, brown lacewings, wheel bugs, and spined soldier bugs). I will also determine functional response relationships between these predators and increasing SLF density to determine the most effective predators. A functional response is when the rate of predation increases with increasing prey density. My findings will be shared through direct interactions with stakeholders by our PSU Extension collaborator and PSU Extension Educators, posts on the Penn State Extension webpages (https://extension.psu.edu/spotted-lanternfly; https://extension.psu.edu/spotted-lanternfly), Penn State News, social media, and presentations I will give at grower meetings (e.g., PA Wine Marketing and Research Board, Ag Progress Days, and the PA Farm Show). I also expect to publish at least one peer-reviewed paper from this project.
- Survey for insect predators that are consuming different SLF life stages in the field.
Justification: While we have a great deal of data on predators of adult SLF from a citizen science project, we did not receive many reports of predators of earlier life stages, including eggs and nymphs, likely due to their inconspicuous nature. Identifying wild predators that feed on different life stages will indicate which species to encourage through conservation biocontrol or release for augmentation biocontrol.
- Identify which insect predators have the highest rate of SLF consumption by life stage over time.
Justification: By identifying which insect predators already present in the introduced range have the highest rate of SLF consumption, I will collect information that is useful for the development of a biocontrol program for the sustainable management of SLF. Predators that feed at higher rates than others will have the most promise and should be the foci for future work. I will test species that are commercially available or can easily be collected and reared for use in augmentation or supported through conservation biocontrol. For this project, I will test convergent ladybugs (Hippodamia convergens), harlequin ladybugs (Harmonia axyridis), brown lacewings (Micromus variegatus), and green lacewings (Chrysoperla rufilabris) to determine if they will feed on SLF eggs and early instar nymphs (1sts and 2nds) since they are generalist predators that feed on insect eggs and small soft-bodied insects. We will also test Chinese praying mantises (Tenodera sinensis), Carolina mantises (Stagmomantis carolina), wheel bugs (Arilus cristatus) and spined soldier bugs (Podisus maculiventris) against the nymphs and adults since these predators feed on larger mobile insects. Wheel bugs are not commercially available but frequently attack SLF in the field (Johnson pers. obs). We have also observed wheel bug egg masses laid next to SLF egg masses and received reports of nymphal wheel bugs feeding on SLF nymphs and adults.
- Determine which predators display a functional response to SLF density.
Justification: The most effective biocontrol agents typically show a functional response to their prey, increasing their consumption rate as prey density increases (Jeschke et al., 2004). Determining which of the predators tested in Objective 2 show a functional response to SLF is useful for the selection of the most effective biocontrol agents for further evaluation. This information will also guide initial predator to prey ratios to test for efficacy in a crop setting for control of SLF (such as in an orchard or vineyard).
The purpose of my project is to identify the most efficient native and naturalized predators of SLF in the mid-Atlantic and Northeastern regions of the U.S. as well as those that are commercially available or can be collected and reared for potential augmentative biocontrol of SLF. SLF was first found in the U.S. in 2014 in Berks County, Pennsylvania and now has established populations in 11 states in the region (NYS IPM, 2022). It is a highly polyphagous pest with the potential to damage many agricultural crops such as grapes, hops, and tree fruits. Grapes are currently the crop of greatest economic concern, as there have been reported losses of yield and fruit quality and occasionally vine death in vineyards with high levels of SLF, with one vineyard reporting a yield loss of 90% (Urban, 2020). This has led to increased pest management costs for growers, with some spray records showing that the average cost of insecticide treatments nearly tripled through increased applications (Urban, 2020), which can also have negative effects on beneficial arthropods, other wildlife, and human health (Bale et al., 2007). In addition to the detrimental effects on the ecosystem, SLF control in agriculture relies primarily on two classes of insecticides, neonicotinoids and pyrethroids (Leach et al. 2019), to which SLF could develop insecticide resistance, making it vital to find alternative control methods. Research into more sustainable control methods for SLF that can be applied in an agricultural setting is needed and biocontrol shows great promise.
Biocontrol is the management of a pest through its natural enemies, including pathogens, parasitoids, and predators. It can be more sustainable environmentally and economically than pesticide treatments and is divided into 3 types: classical, augmentation, and conservation biocontrol (Bale et al., 2007). Classical biocontrol is the introduction of a natural enemy from the native range of the pest, but assessments for environmental impacts, including non-target testing, to obtain approval for release usually takes over a decade (Borowy, 2021). This is not an issue for augmentation biocontrol, where natural enemies already found in the invaded range are released. Conservation biocontrol is often employed in combination with augmentation, which is where measures are taken to support natural enemy populations already present by modifying the environment, which might include intercropping or hedgerows of plants that provide shelter and/or sustenance for natural enemies. Thus, by focusing on endemic natural enemies, biocontrol can be implemented sooner by growers. However, not all native predators will be equally effective at controlling SLF. A natural enemy’s ability to control a pest is dependent on its functional and numerical responses to pest population levels; a functional response is the change in predation rate with changes in prey density and a numerical response is an increase in the predator population with increases in prey density (Lester & Harmsen, 2002). While both are important metrics in realizing the impact of predators on prey, assessing functional responses in this system will allow us to find which predators should be our priority in augmentative releases.
Research
The SLF lifecycle begins with eggs laid in a mass of 30-50 that they cover with wax. After overwintering as eggs, hatch begins in late April to mid-May with 4 nymphal instars. In August, adults begin to appear and feed heavily on host trees, especially tree of heaven, to reach sexual maturity. Egg laying can last from September into November until remaining adults die from a hard freeze. As is the case with most natural enemies, each predator is likely to feed on only one or a few life stages of its prey, depending on its size in relation to its prey, its efficiency in searching and catching prey and its spatial and temporal overlap with prey in the field.
Objective 1. To determine which predatory insects have the most potential for biocontrol of SLF, I will begin by conducting a survey in an area with high SLF populations to document which predators in the invaded range are already feeding on SLF, especially on eggs and nymphs. I will target host plants infested with a large number of SLF and record all interactions between predators and prey for 3 hours, one session in the morning and one in the evening. I will survey once a week in the fall of 2022 (adults and eggs) and again once a week in the spring, summer, and fall of 2023 (nymphs, adults, and eggs) for a total of approximately 60 observation sessions as SLF pass through each life stage. I will record the species of the host plant, species and life stage of the predator, life stage of SLF it fed on, how many SLF were eaten, and feeding behavior of the predators. I will attempt to vary what host plants I use to observe predation to see if this influences the composition of the predator community. I will use these observations to create a list of the most common predators of each life stage with information on how pest managers can encourage these species. These species will also be tested for use in augmentation biocontrol in future projects.
Objective 2. To determine which predatory insects are the most promising for control of SLF, I will set up 5 enclosures in the field for each predator species and SLF life stage. Enclosures will be 1 cubic meter in size, containing potted grape and strawberry for nymphs, and grape plus a potted tree of heaven for adults due to changes in SLF preferred hosts over their life cycle (Dara et al., 2015). These plants are easy to grow, are preferred by SLF, and provide diet mixing, which maximizes SLF fitness (Nixon et al., 2021). Predator density per enclosure will be according to the recommendation of the seller or using the density for a similar commercially available predator. I will provide each predator with 10 egg masses, 50 nymphs, or 25 adult field-collected SLF. The number of SLF eaten will be recorded every day over 2 weeks, adding additional prey as needed. This will allow me to calculate the mean rate at which each predator feeds on SLF, which can be compared among predator species using a one-way repeated measures ANOVA to determine if there is a significant difference in the number of SLF eaten among the tested predators over the 2-week period.
Convergent ladybugs, harlequin ladybugs, brown lacewings, and green lacewings will be tested against SLF eggs and 1st and 2nd instar nymphs, while wheel bugs and spined soldier bugs will be tested against all nymphal stages and adults since these bugs can consume prey larger than themselves with their piercing/sucking mouthparts along with the Chinese and Carolina mantises which are large enough to handle SLF. Convergent ladybugs and brown lacewings are commercially available as adults, and we will establish colonies this summer so that we will have larvae to test in these experiments. Both species of ladybug larvae and green lacewing larvae are more voracious predators than the adults and thus larvae will be used in experiments. For the remaining insect predators, adults will be primarily used in experiments and larvae will also be used when available.
Objective 3. To determine which predators show a functional response to SLF population density, I will set up 5 enclosures in the field for each predator and SLF life stage, 1 m3 in size, containing potted grape and strawberry for nymphs, and grape plus a potted tree of heaven for adults. Each enclosure will contain the number of predators recommended by the seller recommendation or using the recommendations for the most similar commercially available predator. I will add SLF egg masses, 1st instar nymphs, 4th instar nymphs, or adults that are field collected at two densities: 15 or 20 egg masses, 60 or 75 nymphs, and 35 or 50 adults. The number of SLF eaten will be recorded every day for 2 weeks, adding additional prey as needed to maintain these densities. By combining these results with those obtained in Objective 2, I will have three different prey densities to determine which predator(s) exhibit a functional response to SLF density. I will compare the daily and weekly rate of predation with increasing prey density using multiple regression with predator species and time as explanatory variables and number of prey consumed per day (and per week) as the dependent variable. Convergent ladybugs, harlequin ladybugs, brown lacewings, and green lacewings will be tested against SLF eggs and 1st instar nymphs, while wheel bugs and spined soldier bugs will be tested against 1st instar nymphs, 4th instar nymphs, and adults. See the attached Table outlining all experiments in this submission.
Expected Outcomes: I expect that we will see predation of SLF by many arthropod species, including praying mantids, spiders, ants, wasps, and predatory true bugs, in our observational survey, as this would align with results from my citizen science project. I expect that lacewings will be the best egg predators and wheel bugs will be the best nymphal and adult predators, as this would align with what I’ve observed and had reported to me from the citizen science project. I suspect that spined soldier bugs and wheel bugs are most likely to increase their feeding rate as SLF density increases, which would be consistent with findings with similar species tested against another aggressive invasive species, the cotton bollworm (Parajulee et al., 2006).
Potential Problems and Solutions: We may experience some difficulty finding enough wheel bugs to collect and test in these experiments. I am currently looking into ways to rear these insects in a colony, which could provide us with a steady supply. It may also be difficult to build enough enclosures for the testing of SLF eggs in time for the experiment to start, but we already have many pop-ups that could be substituted for the planned enclosures. As this is a single-year study, one limitation I will face is that I will not be able to test if predators continue to attack SLF when other prey items are available, but that question will be addressed during the following season.
Objective 1. So far, I have not observed any predators feeding on SLF, but I did see many insects such as flies, ants, yellow jackets, and red paper wasps feed on the honeydew produced by the adult SLF observed in 2022. Red paper wasps were also seen attempting to grab adult SLF during an observation period on September 29th, 2022, which may have been attempts at predation, but the wasps would leave the SLF alone as soon as they moved. This may also be an indication that the wasps were more interested in feeding on the honeydew produced by the SLF than the SLF themselves, and were perhaps looking for easier access to the source of the honeydew.
Objective 2. Preliminary testing done in 2022 on convergent ladybugs, harlequin ladybugs, brown lacewings, and green lacewings have shown them to be relatively ineffective predators of SLF as they did not feed on the eggs or nymphs offered to them. This has led to an interest in looking at other commercially available or easily collected predators, notably Chinese and Carolina mantises, as based on results from the community science project I ran as well as lab testing with Chinese mantises as predators of SLF, these are far more likely to be effective predators.
Education & Outreach Activities and Participation Summary
Participation Summary:
I will convey my results through presentations for growers and at outreach events, such as Penn State’s Ag Progress Days, the PA Wine and Marketing Board, and the Pennsylvania Farm Show. Since one of our collaborators has a large PSU Extension appointment at the Fruit Research and Extension Center in Biglerville, PA, we will be able to inform the public of our results through Penn State Extension activities (webpages, trade journal publications, and social media posts). In addition, we have ongoing relationships with Penn State News’ journalists who continue to provide an avenue for conveying new information to a broad audience. I will post key findings on my Facebook page created for our citizen science project (Birds Biting Bad Bugs, http://facebook.com/birdsbitingbadbugs), allowing people who have shown an interest in predators of SLF to see how this information may be applied for SLF management. I will also publish my results in an open access journal and give presentations at conferences on this project.