Spotted Lanternfly Survivorship and Damage to Specialty Agricultural Crops 2021

Spotted lanternfly, a new invasive insect in the Northeastern U.S., has continued to spread throughout Pennsylvania and to neighboring states for 6 years. SLF has a broad host range and can feed on over 70 different plant species, although some plants, including important agricultural and ornamental plants, are more strongly preferred hosts. Research done in 2020 has focused on evaluating the risk spotted lanternfly may pose to a variety of agricultural crops. This research includes assessing SLF survivorship, or host suitability of the crop, and potential specialty crop damage. Although SLF has been observed to feed on other specialty crops (e.g., apple, stone fruit), to date, grapevine is the only agricultural commodity on which we have observed feeding damage from SLF. The information presented below is preliminary data to establish early predictions of SLF risk to avocado, fig, kiwi, cucumber, hemp, hops, peach, and raspberry. Please note that this is ongoing research and the information may change, particularly as more research is conducted and as SLF establishes in new areas.

Survivorship Studies

Survivorship was tested on avocado, fig, and hardy kiwi in response to concern from the industry. SLF survivorship on all three of these agricultural commodities was comparable to survival on tree-of-heaven, one of SLF's preferred hosts. Because these studies only tested forced feeding, we do not yet know if SLF would choose these hosts in the field. However, these results do show that these crops are potentially suitable hosts. Crop damage was not assessed in these survivorship studies.

Avocado

4^th instar spotted lanternfly feeding on avocado. Photo: Heather Leach.

Survivorship studies on 4^th instar spotted lanternfly were conducted on potted avocado plants in 2020. Beginning on July 20, 50 field-collected 4^th instar nymphs were added to each of two avocado plants in 5-gallon pots in pop-up mesh cages. Mortality was checked twice weekly. The study ended on August 5. In addition to the two avocado plants used for this study, two tree-of-heaven were set up identically to compare survival. SLF 4^th instar survivorship on fig (95.1%) was comparable to the tree-of-heaven control (98.9%). While high survivorship does not necessarily indicate a high likelihood of damage to this crop, this is a viable SLF host and therefore, the threat that SLF poses to avocado should be investigated further.

Fig

4^th instar spotted lanternfly feeding on fig. Photo: Heather Leach.

Survivorship studies on 4^th instar spotted lanternfly were conducted on potted fig plants in 2020. Beginning on July 20, 50 field-collected 4^th instars were added to each of two fig plants in 5- gallon pots in pop-up mesh cages. Mortality was checked twice weekly. The study ended on August 5. In addition to the two fig plants, two tree-of-heaven were set up identically to compare survival. SLF 4^th instar survivorship on fig (94.9%) was comparable to the tree-of-heaven control (98.9%). While high survivorship does not necessarily indicate a high likelihood of damage to this crop, the threat that SLF poses to fig should be investigated further because this is a viable host for SLF.

Kiwi Berry

Adult and 4^th instar spotted lanternfly feeding on young and mature kiwi berry vines (respectively). Photo: Heather Leach.

Two 2-year-old kiwi berry plants field-planted in spring 2020 were used for this study. Because of the small plant size, only 20 SLF were introduced to each of the two plants. 4^th instar survivorship was evaluated from July 29 to August 5 and adult survival was evaluated from August 20 to August 26. Mortality was checked every two days. Survivorship for 4^th instars was 93.7% and for adults was 76.6%. In field observations, adult spotted lanternfly have been observed feeding on mature kiwi berry plants (commercial U-pick production) in low numbers (5-10 per plant) during late September (H. Leach, personal observation). While high survivorship does not necessarily indicate a high likelihood of damage to this crop, it is a viable host for SLF and therefore the threat that SLF poses to both kiwi fruit and kiwi berries should be investigated further.

Survivorship and Damage Studies

SLF survivorship and feeding damage or effects on quality of hosts has been assessed for grapevine, cucumber, raspberry, hemp, peaches, and hops. Most studies below are preliminary assessments to discern if SLF is capable of causing damage to plants from forced feeding assays. In these assays, the majority of crops tested were affected by SLF feeding, but this was variable. The level of SLF feeding damage observed is likely highly dependent on overall plant health and the presence of other stressors (e.g. diseases, weather, etc.). Generally, grape appears to be the most affected, though cucumber should also be watched closely for potential damage.

Grapevine

Beginning in 2017, research at Penn State has focused on evaluating the damage of spotted lanternfly on grapevine as significant populations have been observed in vineyards. More information on damage and management of SLF in grapevines can be found at "Spotted Lanternfly Management in Vineyards."

Cucumber

The relationship between yield and SLF feeding levels on cucumber (left) and the caged cucumber used in this trial (right). Photo: Heather Leach

4^th instar SLF were introduced to in-ground cucumber at different levels (i.e., numbers of SLF) beginning on July 27, 2020. In this study, 4 sets of 2 plants were covered in mesh cages and SLF were added at the following levels: 0, 25, 50, or 100. Insect mortality was counted weekly and the dead bugs were replaced with living bugs each week to maintain the same level of feeding on the plants. The trial ended on August 4. Average weekly survival of 4^th instars on the cucumber plants was 96.8%. On August 21, all mature cucumbers were harvested from the plants. The total number of fruit and weight of each fruit were recorded. Note that during the trial, the mesh bags prevented other insects from entering, including bees for pollination services. There was a negative relationship with the total yield (combined weight of all fruit) produced per plant and the number of 4^th instar spotted lanternfly exposed. To our knowledge, SLF have not been reported as a significant pest of cucumber in commercial production, but backyard growers have reported infestations, particularly with nymphal SLF. This data suggests that SLF may have the ability to reduce yield of cucumber plants if infestation is severe.

Hemp

The number of SLF observed feeding on field-grown hemp plants (left) and an adult SLF feeding on the stem of a hemp plant. Photo: Lauren Briggs.  

This study had two parts: a forced feeding study where nymphs were introduced to young potted hemp plants, and a field study during which scouting was conducted to record late-season adults feeding on field-planted mature hemp plants. In the forced feeding study, 4^th instar nymphs were introduced to six potted hemp plants in netted cages at six different population levels: 0, 5, 10, 20, 40, and 80 SLF per plant. Survivorship of nymphs feeding on hemp was low-medium, ranging from 32% to 43% on average across the 4 weeks of feeding. This low survivorship could be, in part, related to plant health and the fact that this trial was conducted using potted plants. Hemp bud quality and quantity were not assessed in this trial. From scouting data, adult SLF were observed in hemp fields (Landisville, PA), however at 2 or less SLF per plant (19 total plants observed per week), with the highest total number of SLF occurring in the first week of October. Altogether, the preliminary data from this study indicates that SLF can feed and survive on hemp, but hemp does not currently appear to be a preferred host plant. To our knowledge, hemp growers in Pennsylvania have not reported spotted lanternfly-related damage to hemp production.

Hops

The relationship between hop yield (total cone weight) and the number of SLF exposed to the plant.

Five hop plants (cv. 'Cascade') were used for this study where SLF survivorship and SLF effects on hop quality and yield were tracked. Note that these hops plants were at a maximum trellis height of 10 feet. Each hop plant was fitted with a large mesh enclosure, enclosing the entire plant, and randomly assigned a different level of SLF feeding (0, 25, 50, 100, or 200). 4^th instars and adult SLF (ratio dependent on field collections) were introduced to the plants on July 20 and the trial ended on August 26^th. Survival of SLF was counted weekly and dead individuals were replaced to maintain the same feeding pressure on the plants. Average weekly SLF survival was 81.8%. Hops were harvested on August 15^th, and the total number of cones and weight of the cones were recorded. Average weight of each cone across the treatments was similar (average 0.34 grams wet weight), but there was a slight decreasing trend for total yield produced per plant as SLF infestation increased. A subset of the harvested cones was sent for quality analysis; there was no difference in beta/alpha acids or cohumulone of the cones across the treatments. In field scouting, nymph and adult SLF have been observed feeding on hop plants but in low numbers (5-10 per plant or less). To our knowledge, no backyard or commercial hop growers have reported damage to their hops due to SLF feeding or honeydew deposition, however low populations (5-10 per plant) have been observed. Hop plants have been a particular concern to watch for SLF feeding damage and we will continue to follow this crop to learn more about potential risks associated with SLF.

Peach

Evidence of fruit abortion on peach after SLF feeding. Photo: Heather Leach.

Five 6-foot potted peach plants were used for this study, all of which had fruit. On each tree, two similarly sized branches with the same number of fruits were selected, and each was enclosed in a mesh bag. 50 4^th instar SLF were introduced into one bag, chosen randomly, and the other bag was left with no SLF. 4^th instars were introduced on June 29 and the trial ended on August 9. Each week, mortality was counted and dead SLF were replaced with living SLF to maintain consistent feeding pressure. Average weekly survival for 4^th instars was 60%. Of the 13 total fruit assessed for each treatment (SLF vs. no SLF), 2/13 fruit were aborted from the SLF treated where no fruit were aborted from the no SLF treatment (0/13). On average, the size of the mature fruit was 8% smaller (diameter) in the shoots exposed to SLF. Shoot length between the two treatments was similar both at the beginning and end of the trial. Continued research should focus on the potential of SLF feeding damage on peach or other tree fruit to cause fruit abortion. Additionally, no long-term studies have investigated how SLF feeding could affect tree fruit planting and establishment on younger trees, and this should be looked at further. To our knowledge, few growers have reported sustained high populations on their tree fruit, particularly in peach, though occasional outbreak periods of SLF appear to be somewhat common.

Raspberry

Mesh bags used to enclose raspberry canes for SLF feeding trial (left) and the growth of raspberry canes after exposure to SLF (right). Photo: Heather Leach.

Raspberry plants (planted in the ground in 2019) at Penn State Berks were used for this study. On each plant, 2 sets of 2 canes of similar height were covered in a mesh bag. One of the bags on each plant was randomly selected to have 50 4^th instar introduced beginning on June 24, 2020, and the trial continued through August 9^th. Survival of nymphs was counted weekly and new 4^th instars were added to replace any dead individuals so that the plant maintained the same level of SLF feeding. Average weekly survival of 4^th instars was 52.6%. This was generally lower than other plants tested, however high heat is thought to have contributed to some of this mortality in July. Before SLF exposure and 21, 33, and 46 days after SLF exposure began, each cane length was measured. Cane length was variable between plants but those that were exposed to SLF had slightly (8%) reduced growth. To our knowledge, SLF have not been reported as a pest in bramble production, however nymphal SLF have been observed feeding on wild brambles.

Acknowledgements

The researchers thank Dave Jackson of Kiwi Berry Organics Co. for providing plant material and John Rost at Penn State Berks for maintaining plants.