Performance and host association of spotted lanternfly (Lycorma delicatula) among common woody ornamentals

Abstract

Lycorma delicatula (spotted lanternfly) has a broad host range with a strong preference for the invasive host plant from its native range, tree of heaven (Ailanthus altissima); it had long been speculated that L. delicatula could not develop or reproduce without access to tree of heaven. In 2019, we found that this assumption was incorrect, but fitness was reduced in the absence of A. altissima in that the number of egg masses laid was dramatically fewer for insects reared on suitable non-A. altissima host plants that had recently been established. We hypothesized that longer established, larger trees (of the same species) would improve the fitness of L. delicatula in the absence of tree of heaven. In spring 2020, we examined insect performance with and without access to A. altissima by tracking development, survival, host tree association and oviposition in large enclosures with trees planted two years prior to the study. Each enclosure included one each of Juglans nigra, Salix babylonica and Acer saccharinum along with either one A. altissima or one Betula nigra; these trees had twice the diameter of the same trees the previous year. We reared nymphs with and without access to A. altissima, released them into the corresponding large enclosures as third instars, and monitored them from early July 2020 through November 2020. We also determined whether lack of access to A. altissima by parents of L. delicatula have any fitness effects on offspring performance. To ensure adequate adult populations for comparing fecundity between treatments, third instars were released into the multi-tree enclosures due to high mortality in earlier instars that occurred in a similar study in 2019. Insect survival was higher and development faster with access to A. altissima. Third and fourth instar nymphs were most frequently observed on A. altissima when it was present, while adults were equally associated with A. saccharinum and A. altissima. In the absence of A. altissima, nymphs were most frequently found on S. babylonica, while adults were most often on A. saccharinum. Females with access to A. altissima deposited nearly 7-fold more egg masses than those without access to A. altissima, which is consistent with the difference in egg mass numbers between the two treatments the previous year; thus, our hypothesis was rejected. The offspring of parents that had been reared without access to A. altissima showed similar survival and development time from egg to adult as offspring from parents that never had access to A. altissima. These findings suggest that managers need to be aware that even in the absence of A. altissima in the landscape, several hardwood host trees can be utilized by L. delicatula to develop and reproduce, but fitness without A. altissima is likely to still be reduced.

Figure 1

Mean (± SE) trunk diameter (mm) of tree species in enclosures with Ailanthus (A) and without Ailanthus (B) (n = 5 enclosures) in 2019 and 2020. Measurements were made on October 31, 2019 and November 3, 2020. Means within a column followed by different letters are significantly different (Bonferroni post hoc test: P < 0.05). Black walnut trees were not included in the analysis because most died during the 2019 studies and had to be replaced in spring of 2020.

Figure 2

Proportion of Lycorma delicatula (nymphs and adults combined) that survived in enclosures with planted Ailanthus altissima, Acer saccharinum, Juglans nigra and Salix babylonica (‘Ailanthus,’ n = 5 enclosures) or enclosures with the same tree species except for the presence of Betula nigra in place of A. altissima (‘without Ailanthus,’ n = 5 enclosures) from July 15 to November 4, 2020. Fitted binomial regression lines are shown, with shaded areas indicating 95% confidence intervals for predicted regression means. In total, 120 third-instar nymphs were released in each enclosure and their numbers and host tree associations were recorded weekly.

Figure 3

Proportion of L. delicatula that developed from the third to the fourth instar over time, with fitted logistic regression lines, in enclosures with and without Ailanthus altissima.

Figure 4

Proportion of L. delicatula that emerged as adults over time, with fitted logistic regression lines, for enclosures with and without Ailanthus altissima.

Figure 5

Mean (± SE) proportion of Lycorma delicatula third instars (A) fourth instars (B) and adults (C) present on each tree species in enclosures with Ailanthus (Ailanthus altissima), silver maple (Acer saccharinum), black walnut (Juglans nigra) and willow (Salix babylonica) (n = 5 enclosures) from July 15 to November 4, 2020. Nymphs and adults found on annual plants (2%) within the enclosure or on enclosure walls (98%) are included as ‘Others.’ Means within a column followed by different letters are significantly different (Bonferroni post hoc test: P < 0.05). No adults were found on black walnut and no third instar nymphs were found on other surfaces.

Figure 6

Mean (± SE) proportion of Lycorma delicatula third instars (A), fourth instars (B) and adults (C) present on each tree species in enclosures with silver maple (Acer saccharinum), black walnut (Juglans nigra), willow (Salix babylonica) and river birch (Betula nigra) (without Ailanthus altissima, n = 5 enclosures) from July 15 to November 4, 2020. Nymphs and adults found on other plants (2%) within the enclosure or on enclosure walls (98%) are included as ‘Others.’ Means within a column followed by different letters are significantly different (Bonferroni post hoc test: P < 0.05). No adults were found on black walnut and no third instar nymphs were found on other surfaces.