Sizing up spotted lanternfly nymphs for instar determination and growth allometry

A major ongoing research effort seeks to understand the behavior, ecology and control of the spotted lanternfly (SLF) ( Lycorma delicatula ), a highly-invasive pest in the U.S. and South Korea. These insects undergo four nymphal stages (instars) before reaching adulthood, and appear to shift host plant preferences, feeding, dispersal and survival patterns, anti-predator behaviors, and response to traps and chemical controls, with each stage. However, categorizing SLF lifestage is challenging for the first three instars, which have the same coloration and shape, because no comprehensive allometric datasets exist. We present a dataset of body mass and length for SLF nymphs throughout a growing season and compare our results with published ranges of instar body lengths based on small samples. An ontogenetic allometric analysis found that SLF nymph body mass scales isometrically with body length (exponent c = 3.05 [2.95,3.15]). An analysis using two clustering methods also revealed that first through third instar body mass and length fell into distinct clusters (Dyar’s rule), supporting using these two metrics to stage nymphs during a single growing season. The ranges for 2nd and 3rd instars were not consistent between our results and those from earlier studies for diverse locations. Using previously-published data, we also found that tarsal claw and arolia (adhesive footpad) dimensions scale in proportion to body length and mass, respectively, indicating that adhesive ability does not decrease with age, as posited in some previous studies. Conversely, mouthpart dimensions do not correlate with body length, consistent with predictions that these features should reflect preferred host plant characteristics rather than body size. We suggest extending these methods to study how SLF instar development depends on factors such as hatch date, host plant, temperature, and geographic location, using citizen scientist networks to collect morphometric data for a wide range of locations and environmental conditions. ### Competing Interest Statement The authors have declared no competing interest.