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. 

Expected Outcomes

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

Research Results

Eggs from some Far East 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.  Eggs from all of the North American populations required more than 60 days at 5ºC for eclosion; eggs from European and Asian populations varied in the percentage able to eclose after only 60 days at 5ºC.  No geographical pattern of requirements for hatch was obvious.  Substantial variation in hatch in response to low temperature exists both within and between gypsy moth strains, making adaptation to a wide range of climates possible.  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.

Keena MA.  1996. Comparison of hatch of Lymantria dispar (Lepidoptera: Lymantriidae) eggs from Russia and the United States after exposure to different temperatures and durations of low temperature.  Ann. Entomol. Soc. Am. 89(4): 564-572. 

Keena MA.  1994. Genetics of diapause in the gypsy moth: a review.  In Logan JA, ODell TM, Gray DR, eds. Diapause and gypsy moth management: status, applications and research; 1991 October 2-3; Blacksburg, VA. U.S. Dep. Agric. For. Serv., Northeast. For. Exp. Sta. Gen. Tech. Rep. NE-193, p 89-97. 

Research Participants

Principal Investigator

• Melody Keena, USDA Forest Service- Northern Research Station Research Entomologist 

Last Modified: 10/01/2009

For further details log on website :
https://www.nrs.fs.fed.us/disturbance/invasive_species/asiangm/biology_ecology/egg_chill/