Lycorma delicatula White (Hemiptera: Fulgoridae), spotted lanternfly, is an invasive planthopper first detected in Berks County, Pennsylvania, USA, in 2014 that now has spread to an additional 13 states in the US. This invasive pest is univoltine with 4 nymphal instars developing between late spring and early fall to the adult stage. Adult populations feed heavily in the late summer and reproduce throughout fall before succumbing during hard frost events (Barringer et al. 2015; Lee et al. 2019; Liu 2019a). Lycorma delicatula is considered a threat to a range of specialty crops and, in particular, grape vine, Vitis vinifera L. (Vitaceae), with heavy feeding related to yield reductions and vine death (Leach et al. 2019; Leach & Leach 2020).

Because L. delicatula is invasive, there is strong interest in developing a classical biological control program. The egg and nymphal parasitoid species, Dryinus sinicus Olmi (Hymenoptera: Dryinidae) and Anastatus orientalis Yang & Choi (Hymenoptera: Eupelmidae), respectively, are both from the same native range as L. delicatula and currently are being evaluated via host range testing programs (Liu 2019b; Malek et al. 2019; Broadley et al. 2020). If these parasitoids are approved for release in the US, then a classical biological control program will require large numbers of L. delicatula eggs and nymphs to be available for rearing these biological control agents. In nature, most egg masses generally harbor less than 50 eggs per mass with large numbers of egg masses recorded on host plants such as Ailanthus altissima Mill. (Swingle) (Simaroubaceae) as well as Prunus L. (Rosaceae) and Acer L. (Sapindaceae) spp. among others (Liu 2019a).

Recently, a rearing procedure for L. delicatula was developed. This methodology requires both suitable plant material, namely A. altissima plants and logs, and controlled environmental conditions for successful rearing in greenhouses or growth chambers (Nixon et al. 2022). While this approach does generate both egg masses and nymphs, there may be a possibility of using egg masses collected from nature as a source for rearing biological control agents. High densities of egg masses have been recorded in the field (up to 75 egg masses per m²) on natural host substrates (Liu 2019a; Liu & Hunter 2021). However, removal from these host substrates requires a great deal of time and careful handling (Nixon et al. 2022) because egg masses become brittle as the winter season progresses, with the protective waxy coating flaking away and exposing egg masses to potential damage or dislodgement when removed from the substrate.

One approach to obtaining large numbers of egg masses inexpensively may be to deploy suitable substrates in areas with reproducing L. delicatula populations at high densities. Indeed, L. delicatula oviposit on human-made objects such as metal fence posts (Liu 2019a), cut stone, cinder blocks, vehicles, and rail cars (Urban 2020). While this behavior may contribute to human-assisted spread (Urban et al. 2021), it also points to the opportunity to use removable substrates to gather egg masses. Here, we evaluated a range of available materials to determine if they were suitable substrates for L. delicatula oviposition; when deployed in the field, substrates could be used for detection of reproductive L. delicatula populations and as a means for collecting egg masses for research.

We evaluated 9 potential substrates including roofing shingles, Sorbus spp. L. (Rosaceae) (Ash) bark, roof caps, landscaping fabric, corrugated plastic, mylar bubble wrap, white mesh, vinyl siding, and wooden planks as potential removable oviposition substrates for L. delicatula; for sizes and product information of all substrates, see Table 1. Substrates were deployed on 1 Oct 2019. Substrates were deployed directly on A. altissima trees with some larger trees hosting multiple treatments at 5 sites within 1.6 km of each other (1 replicate per site with the exception of roof cap and wood treatments, which were deployed only at 4 locations) in Frederick County, Virginia, USA. Rigid substrates (bark, roof caps, corrugated plastic, vinyl siding, and wooden planks) were affixed to tree trunks with 2 screws in the center of the material area; flexible substrates (shingles, landscape fabric, mylar wrap, and white mesh) were wrapped loosely around the tree trunk and stapled into place. Deployment height ranged from 1 to 2 m, and tree diameter ranged from 25 to 60 cm diameter at breast height. Materials were removed and egg masses counted on 16 Dec 2019. In total, 68 L. delicatula egg masses were recovered. The number of egg masses per m² was calculated for each material; these data followed a non-normal distribution, therefore a non-parametric Kruskal-Wallis Rank Sum Test was performed to compare the number of egg masses per m² on each material type with a Steel-Dwass post hoc analysis for all pairs. Data analysis was performed using JMP 16.0 (SAS Institute Inc., Cary, North Carolina, USA). Significantly more egg masses were recovered from roofing shingles, roof caps, and ash bark compared with all other treatments (χ² = 26.69; df = 8; P = 0.0008) (Fig. 1). Egg masses laid in 2019 on ash bark and roof shingles were cut out using plant pruners; those sections of substrate were stored in Ziploc bags (S. C. Johnson & Son, Racine, Wisconsin, USA) and transported to a quarantine facility in Fort Detrick, Maryland, USA, in accordance with APHIS permit P526P-18-03369. Roof caps with egg masses were sealed in larger bags and transported whole. The 42 egg masses that were laid on the roof shingles and the 7 that were laid on the roof caps were all physically damaged during this process due to the flexibility of the substrate. Thus, we were not able to conduct egg hatch studies for substrates. Egg masses deposited on ash bark fared better, and this substrate has been used previously to acquire field-derived egg masses (Nixon et al. 2022).

Table 1.

Sizes (m²) and product information for all removable substrates deployed for oviposition of Lycorma delicatula. Mention of a concept, idea, trade name, or commercial product in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.

Fig. 1.

Egg masses deposited per m² of removable substrates deployed in direct contact with Ailanthus altissima in 2019. Kruskal-Wallis analysis with Steel-Dwass post hoc applied: bars (means ± SE) sharing a letter were not significantly different from each other. Total egg masses collected from each substrate type is specified above each bar.

In 2020, 3 replicates of 7 of these materials were deployed with the same protocol; roof caps and ash bark were not evaluated in 2020 due to a lack of availability. Substrates were deployed on 1 Oct 2020 and removed for counting on 18 Dec 2020. A total of 9 egg masses across 3 substrate items were recorded: 7 on a single roofing shingle and 2 on vinyl siding treatments each receiving 1 egg mass. Additionally, in 2020, we evaluated the most effective substrate from 2019, roof shingles, either in direct contact with the vertical tree trunk or suspended horizontally between trees. Three replicates of the direct and suspended shingles were deployed on 1 Oct 2020 at 3 sites (1 replicate per site) within 1.6 km of each other in Frederick County, Virginia, USA. Direct contact shingles were attached vertically to A. altissima trees 1 m from the ground as described above, and suspended shingles were folded lengthwise and the long edges affixed to either side of a 5 × 5 cm wooden post. This wooden post was then suspended in a level horizontal orientation at either end to 2 A. altissima trees 1 m from the ground. These shingles were removed on 1 Mar 2021 and the number of egg masses on each recorded. A total of 7 L. delicatula egg masses were laid on direct contact shingles (1, 1, 5) and 1 was laid on the suspended shingles (0, 0, 1). In general, L. delicatula relative densities were much lower in 2020 compared with 2019, leading to deposition of far fewer egg masses.

Based on these results, it is possible to gather egg masses using removable oviposition substrates under field conditions. Roofing shingles, roof caps, and ash bark resulted in L. delicatula oviposition when in direct contact with A. altissima trees. However, care must be taken in handling flexible materials like roofing shingles to ensure egg masses are not damaged or dislodged. Additionally, this same approach may provide an opportunity for monitoring L. delicatula oviposition in newly invaded regions, because egg masses are cryptically colored, and may be more easily observed on removable substrates.

Mention of a concept, idea, trade name, or commercial product in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. The USDA is an equal opportunity employer. This work was funded, in part, by USDA-ARS Project 8080-21000-032-00-D and National Institute of Food and Agriculture, US Department of Agriculture, Specialty Crop Research Initiative under award number 2019-51181-30014.