Flight in Female Asian Spongy Moths

Photo Credit

USDA Forest Service photo by Melody Keena

Large spongy moth caterpillars eating all but the main veins of oak leaves.

Key areas of past Asian spongy moth research have included:

1. Genetics. Identifying the genetic differences between Asian and European spongy moths.
2. Phenology. Studying the life stages of spongy moths to predict their development and behavior over time.
3. Host utilization and defenses in conifers. Examining how spongy moths use conifer trees as hosts and how these trees defend themselves against the moths.
4. Dietary issues and temperature tolerance. Testing the dietary needs and issues of spongy moths in order to more successfully grow larvae in laboratories, and looking at how factors like temperature and food availability might affect spongy moth growth, survival, and fertility.

Genetics research

Although there were molecular tests to distinguish between spongy moth subspecies, these tests were not good at tracing the geographic origins of Asian spongy moths found on foreign ships. Knowing where these moths come from would help authorities understand how they are being introduced and prevent further introductions.

Northern Research Station scientists and colleagues tested the use of single nucleotide polymorphism (SNP) markers obtained through a method called genotyping by sequencing (GBS) to determine the geographic origins of spongy moth samples. They used GBS on eight lab-reared spongy moth populations from different parts of the world.

The analysis showed strong differences among the populations, allowing clear identification of subspecies and geographic variants. This method revealed some genetic mixing near the boundaries between subspecies. Using 2,327 SNPs, researchers could accurately assign moths to their original populations 100% of the time. These results show that genome-wide SNP markers have the potential to identify the geographic origins of intercepted spongy moth samples.

Phenology research

Managing the European spongy moth in North America has been successful due to over a century of research. However, Asian spongy moths present new challenges. These moths have multiple subspecies, live in diverse habitats, and there is limited data on their life cycles, which affects risk assessment.

To tackle these challenges, researchers used existing data on the life cycles of eight Asian spongy moth populations to create specific models for each strain. These models were tested at 47 ports in East Asia where the Asian spongy moth is native. The results were compared with trap data to see how well the models predicted moth flight times in different locations and years.

The study found that:

• Life cycle data varied among the eight populations, leading to different predicted flight times at the 47 ports.
• Using data from “local” populations did not always improve the accuracy of the models, which varied significantly among different ports and years.
• The models are useful for estimating flight periods at some ports, but the variation in model quality suggests that there may be unsampled moth populations and other factors that need to be studied further.

In a related study, scientists looked at how temperature and exposure time affect when Asian spongy moth eggs hatch. Egg hatching is a crucial event in controlling spongy moth populations and limiting their spread. The scientists created new model parameters for the Asian spongy moth phenology model. The new parameters made the model predictions much more accurate, reducing errors from 7,818 to 178. The predicted egg hatch times were very close to the observed times, differing by only 0-7 days.

Research on host utilization and defenses in conifers

Understanding which trees spongy moths can use as hosts is important for predicting which forests and which regions are at risk. This study compared how well spongy moths from three subspecies developed and survived on 13 North American conifers and three broadleaf trees.

The study found that:

• Spongy moth larvae from different regions showed different abilities to survive and grow on North American conifers. This variation was not consistent within subspecies but depended more on the specific population’s origin and traits.
• In general, European and North American spongy moths gained weight faster and survived better than Asian spongy moths.
• Spongy moth development was slower and survival rates were lower on several conifers. Some Asian spongy moths did well on certain conifers.
• First instar larvae (the earliest stage) could feed on conifers unless the needles were tough or had chemical substances that deterred feeding.
• The timing of new foliage or buds was crucial since early-stage larvae preferred to feed on these parts.

Research on dietary issues and temperature tolerance

In order for Asian spongy moths to establish themselves in new areas, their larvae need to survive long enough to find suitable food. Therefore, scientists studied the survival and development of newly hatched larvae from nine different Asian spongy moth populations at seven temperatures. They tested larvae with and without food, using summer foliage from a preferred broadleaf or conifer tree.

This study found that:

• Larvae survived about a month at 5 degrees Celsius (°C) without food, but only a few days at 30°C.
• At 1°C, survival was lower than at 5°C, likely because of death by freezing.
• Larvae from one population fed and gained weight on summer foliage, especially conifers, at 10-15°C. However, less than 20% survived for 14 days at 20-30°C.
• Newly hatched larvae from all eight populations fed at 10-30°C and developed at 15-30°C on summer foliage from both broadleaf and conifer trees.
• Survival on conifers was highest for one Chinese and two European populations of spongy moths, indicating that the ability to use conifers depends on the population, not the subspecies.

These findings suggest that larvae can find enough food to survive even if they hatch at different times than the onset of new leaves in the spring in a new habitat.

In a separate study, researchers tested how different temperatures affected spongy moth development, survival, and fertility. They found that the larvae developed faster as the temperature increased, peaking at 29°C. However, they had molting problems at both the highest (30°C) and lowest (10°C) temperatures. In addition, at 30°C, females had reduced fertility and fewer offspring. This suggests that high summer temperatures in the southern United States may limit their survival.

Collaborators

• Gwylim S. Blackburn, Canadian Forest Service and Department of Wood and Forest Sciences, Laval University

• Christopher I. Keeling, Canadian Forest Service and Department of Biochemistry, Microbiology, and Bioinformatics, Laval University

• Julien Prunier, Department of Biochemistry, Microbiology, and Bioinformatics and Institute of Integrative Biology and Systems, Laval University

• Catherine Béliveau, Canadian Forest Service

• Richard Hamelin, Forest Sciences Centre, University of British Columbia

• Francois Olivier Hebert, Institute of Integrative Biology and Systems, Laval University

• Roger C. Levesque, Institute of Integrative Biology and Systems, Laval University

• Michel Cusson, Canadian Forest Service and Department of Biochemistry, Microbiology, and Bioinformatics, Laval University

• Ilga Porth, Department of Wood and Forest Sciences, Centre for Forest Research, and Institute of Integrative Biology and Systems, Laval University