Asian Gypsy Moth

Egg Chill Requirements and Inheritance

Research Issue

Diapause of the mature embryonic larva within the egg is a lengthy (8-9 mo/yr) and a critical portion of the life cycle of the gypsy moth.  Diapause enhances survival during the winter and synchronizes hatch with bud burst of preferred host plants in the spring.  Strains of gypsy moth from different geographic areas have been reported to have heritable differences in requirements for completing diapause and hatching.  These strain differences are likely adaptational to the natural environments where the strains were found.  Therefore, it is very likely that the gypsy moths introduced from Asia will have different requirements for diapause completion and hatch than do the moths already present in the United States.  Knowledge of the temperature requirements for egg hatch of the Asian strain is required to parameterize correctly predictive models. 

Our Research

These studies document differences in thermal requirements for egg hatch between gypsy moths from North America and other world areas. Percentage hatch of embryonated eggs, days to first hatch after incubation at warm temperature, and temporal distribution of hatch are used to compare hatch of the different strains under various controlled laboratory conditions. Genetic crossing experiments between populations with different thermal requirements for hatch and between diapausing and non diapausing strains were done to determine the inheritance of these traits.

Expected Outcomes

Data needed to parameterize predictive models so that egg hatch for strains from other world areas can be accurately predicted.

Research Results

[photo:] Long larva from Honshu, Japan.

Key Finding: Heritable variation in the chill required for egg hatch was found in gypsy moth populations from all geographic regions and subspecies.

Eggs from two Far East Russian gypsy moth populations can hatch with reduced chilling requirements relative to other populations and this characteristic is retained when hybridized with other populations. Eggs from two Russian gypsy moth strains required less exposure to low temperature to be able to hatch than did eggs from a North American strain. Hatch took longer to begin and proceeded more slowly in eggs held at constant 15°C and 20°C. Hatch did not occur for over 99% of North American and Russian eggs held at a constant 25°C. Variation in diapause requirements within a strain and between strains can be assessed and compared by holding eggs for 60 d at 5°C followed by incubation at 25°C.

Eggs from 43 geographic populations were evaluated for hatch characteristics after being held for 60 d at 5°C followed by incubation at 25°C. There was considerable variation both within and among the populations in the proportion able to hatch, time to first hatch, and average time to hatch. Egg masses with reduced requirement for low temperatures before the eggs were ready to hatch were present in all subspecies of L. dispar, not just in the Asian subspecies, and the phenotype was not fixed in most populations. The populations clustered into 3 distinct groups and climatic variables were found to be rough predictors of those groups.  Variation in hatch phenotypes between populations is likely an adaptation to local climate and within a population provides a bet-hedging strategy to ensure that at least some hatch synchronizes with host leaf-out. 

Mode of inheritance of hatch traits in Lymantria dispar L. were determined by crossing populations nearly fixed for the phenotypic extremes. The non-diapausing phenotype was inherited via a single recessive gene and the phenotype with reduced low temperature exposure requirements before hatch was inherited via a single dominant gene. There was no evidence for sex-linkage or cytoplasmic effects with either gene. Continued vigilance to prevent movement of populations both within and between countries is warranted, because some of the alleles that confer non-diapause or reduced low temperature requirements before egg hatch are not be present in all populations and their introduction would increase variation in egg hatch within a population. Greater variation in egg hatch can make a gypsy moth population able to adapt to a wider range of climatic conditions and may alter management protocols for a given area.

Keena, M.A. 2016. Inheritance and world variation in thermal requirements for egg hatch in Lymantria dispar (Lepidoptera: Erebidae). Environmental Entomology. 45(1): 1-10. https://doi.org/10.1093/ee/nvv163.

Keena, Melody A. 1996. Comparison of the Hatch of Lymantria dispar (Lepidoptera: Lymantriidae) Eggs from Russia and the United States After Exposure to Different Temperatures and Durations of Low Temperature. Annals of the Entomological Society of America. 89(4): 564-572.

Research Participants

Principal Investigator

  • Melody Keena, USDA Forest Service- Northern Research Station Research Entomologist
  • Last modified: May 18, 2020