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Gypsy Moth Research in Northern Mongolia

Tuulaikhuu Baigal-Amar

One of the completely unexpected findings of this project has been the discovery of an outbreak of the Asian Gypsy Moth in the study area. In addition to posing the question of whether the moth has only recently moved into the Hövsgöl watershed (local people have not seen it previously), its discovery and study has led to a very fruitful collaboration with Dr. Paul Schaefer of the U. S. Department of Agriculture’s Exotic Pest Control Laboratory.

Research Objectives

  • Identification of the important pest insects (Lepidoptero and Coleoptera) in the taiga forests of Hövsgöl region
  • Identify the distribution of the pest species, and correlate with forest density, forest-age structure and microclimate conditions
  • Define extent of damage to Siberian larch trees (Larix sibirica) caused by the Asian gypsy moth (AGM)
  • Study the biology, ecology and behavior of the Asian gypsy moth, identify its population dynamics and movements northward into Hövsgöl National Park area,
  • Define causative agents, if possible for the eruptions or outbreaks and migration movements northward, and find biological control mechanisms for the AGM

Research Activities

  • Identification general parameters: to define period of population increase. Survival, weight, color, parasite infection rate and species are identified in all stages (egg, larvae, pupae and adults), every year.
  • Laboratory Development: AGM eggs are collected in Ulaanbaatar and shipped to U.S. Department of Agriculture, ARS. There eggs are hatched and reared under constant conditions (76°F, 60-70% R.H. and 16:8 Light/Dark photoperiod). The larvae are fed foliage of Japanese larch, Larix leptolepis until pupation, at which time their sex was determined.
  • Phenology: Phenology of larval development is monitored during collection of larvae for parasitism assessment. Collected larvae are scored by instar frequency within each sample. Phenology of moth flight is monitored using:
    • on-going seasonal insect monitoring Malaise traps for both males and females
    • disparlure baited milk carton gypsy moth traps for males only.
  • Egg Capacity and Morphometrics: Among larvae of those reared in the laboratory, pupal weight, wing expanse and female ova count are recorded.
  • An investigation of dendrochronology: To determine whether the history of insect and gypsy moth attacks is recorded in the pattern of tree rings.
  • Sex Pheromone: As a follow-up to experiment conducted in northern Japan, we deployed the same experiment in Dalbay Valley, Lake Hövsgöl, on 10 August 2003 to confirm the importance of a second component to the long established concept that disparlure or (7R, 8S)-cis-7,8-Epoxy-2-methyloctadecane was the only component of the sex pheromone communication system in Lymantria dispar. One experiment (4 treatments, 10 replications) was conducted testing disparlure and compound X both alone and in combination.
  • Perform graphical and statistical analysis of all data and relate to other studies (forest fire, forest regeneration and meteorology).
  • Collaborators:
    • Dr. Paul W Schaefer, Research Entomologist, U.S. Department of Agriculture, Beneficial Insect Introduction Laboratory,
    • Dr. Clyde Goulden, Hovsgo GEF project International Consultant.
Figure 1: Baigal-Amar and Paul W. Schaefer

Figure 1: Paul Schaefer and Baigal-Amar

Initial Results

The distribution of the Gypsy moth larvae was determined in relation to mountain slopes and wind direction. When gypsy moths lay eggs, their preference is for a shelter in shady but warm areas, particularly on rocky outcrops. They primarily deposit eggs on the surface of rocks at the top of the mountains. The larvae hatch in May and spread silk over the rocks.

Figure 2

Figure 2: Dalbay gypsy moth silking on rocks

From here, they distribute themselves in a southeastward direction, or up valley, for a distance of as much as 1150 m. The first outbreak occurs on south-facing slopes of the forested mountains that are exposed directly to the sun.

Figure 3

Figure 3: Gypsy Moth Spread Direction From Rock to Forest

Gypsy moth development was studied in relation to air temperature, air humidity and precipitation. Larval feeding activity is related to air temperature. We presently have evidence that gypsy moth development and maturation occurs when summer average air temperature passes a critical point, air temperature appears to regulate the Hövsgöl gypsy moth population.

Gypsy moth impacts on larch forest have been defined with a leaf area index meter (LAI-2000); LAI readings are negatively correlated with larval number. For saplings, gypsy moth impact is high (saplings have less than half of their needles) the height of growth is decreased, while un-eaten saplings’ height growth in same plots, increase. We presently estimate that the annual growth of Siberian larch was decreased by about 40% by gypsy moth damage.

Figure 4

Figure 4: Gypsy Moth Effect on Larch Sapling

We found six species of food plants, included in four plant families that the moths fed on. Eight species of birds feed on gypsy moths in our study sites.

The important situation was density dependent charactristics during the time period of outbreak and decreasing. Female body size increased from year to year throughout the three years and, at the same time, the number of eggs carried increased respectively. Egg hatching rate decreased from 2002 to the end of the outbreak in 2004.

Figure 5

Figure 5: Some Parameters of Gypsy Moth Population in Recent Years

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