Distribution and Inheritance of Female Flight

Research Issue

Female flight capability is the key trait that regulatory agencies are using to determine their response to introductions of gypsy moth from other world areas.  The biggest concern with flight-capable females in the introduced strains (and possibly in hybrids between them and the existing flightless strain) is that they might increase the potential rate of spread and complicate procedures for detecting and delimiting isolated populations.  Since there had been no comprehensive survey of female flight across the gypsy moth’s native range it was uncertain what areas were of concern other than those where female flight was already documented in the literature.  In addition, since the mode of inheritance of female flight was not known we could not predict how much flight would be retained with hybridization.

Our Research

We crossed individuals from a North American population where no females are capable of flight with a Russian population where > 90% of the females are capable of sustained ascending flight.  We characterized female propensity to initiate flight, capability for flight, muscle strength, morphometric wing and body measurements, and pre-flight behaviors in the parental, reciprocal F1 hybrids, reciprocal backcrosses to both parental strains, and double reciprocal F2 hybrids.  Additionally, female and egg mass weights were compared to determine if there was a detectable negative trade-off between flight and fecundity.  We also documented female flight capability and the traits that affect it (wing length, muscle strength, and flight behaviors) for 46 strains of gypsy moth from throughout its range.

Expected Outcomes

Biological basis for predicting female flight capability in hybrids.  Documentation of variation in female flight across the gypsy moth native range.

Research Results

A clinal female flight polymorphism exists in the gypsy moth, Lymantria dispar L., where female flight diminishes from east to west across Eurasia.  A Russian population where females are capable of sustained ascending flight and a North American population with females incapable of flight were crossed: parentals, reciprocal F1 hybrids, double reciprocal F2 hybrids, and all possible backcrosses to both the parental lines were compared.  Heritability of female flight capability measured using a free flight test was at least 0.60, and variation in wing size, muscle strength, and flight behaviors contributed to the flight polymorphism.  Relative wing size varied continuously and had a heritability of 0.70.  Environmental variation accounted for > 90% of the variation in female pre-flight weight and relative flight muscle strength, as estimated by an inverted female’s ability to right herself.  Pre-flight walking behavior and early deposition of eggs were each inherited through a single gene with two co-dominant alleles.  There was no evidence for sex-linkage or maternal effects in female flight capability or associated traits.  Continued vigilance to exclude and eradicate introductions of strains capable of female flight in North America is warranted even in areas where no females fly, because some of the alleles required for full flight capability may not be present in the North American populations and some flight capability is maintained in the hybrids which could increase the rate of spread of L. dispar.  

Female gypsy moth, Lymantria dispar L., from 46 geographic strains were evaluated for flight capability and related traits.  Females capable of strong directed flight were found in strains that originated from Asia, Siberia, and the northeastern parts of Europe, but flight capability was not fixed in most strains.  No flight-capable females were found in strains from the United States or southern and western Europe.  Wing size and musculature were shown to correlate with flight capability and potentially could be used in predicting female flight capability.  Gene flow or barriers to it are important in determining the current distribution of flight-capable females.  Larval food source also was found to affect female flight capability.  Other factors, such as illumination source and intensity, temperature, and pheromone-mediated activity patterns, have been found to affect female flight timing in all three Lymantriid  species.

Melody A. Keena, Marie-Jose Côté, Phyllis S. Grinberg, and William E. Wallner. 2008 World Distribution of Female Flight and DNA Variation in Lymantria dispar (Lepidoptera: Lymantriidae).  Environ. Entomol. 37(3):636-649. 

Keena MA, Grinberg PS, and Wallner WE.  2007. Inheritance of Female Flight in Lymantria dispar(Lepidoptera: Lymantriidae).  Environ. Entomol. 36(2):484-494. 

Keena MA, Wallner WE, Grinberg PS, and Cardé RT.  2001.  Female flight propensity and capability in Lymantria dispar (Lepidoptera: Lymantriidae) from Russia, North America, and their reciprocal F1 hybrids.  Envrion. Entomol. 30(2): 380-387. 

Charlton, R.E. , Cardé, R.T. , Wallner, W.E. 1999. Synchronous crepuscular flight of female Asian gypsy moths: Relationships of light intensity and ambient and body temperatures J Insect Behavior, 12(4):517-531.

Cardé, R.T. , Charlton, R.E. , Wallner, W.E. , Baranchikov, Y.N. 1996. Pheromone-mediated diel activity rhythms of male Asian gypsy moths (Lepidoptera: Lymantriidae) in relation to female eclosion and temperature. Annals Ent. Soc. Am.,89(5):745-753. 

Wallner, W. E., L. M. Humble, R. E. Levin, Y. N. Baranchikov, and R. T. Cardé. 1995. Response of adult lymantriid moths to illumination devices in the Russian Far East. J. Econ. Entomol. 88:337-342.

Research Participants

Principal Investigator

• Melody Keena, USDA Forest Service- Northern Research Station Research Entomologist 
• William Wallner, USDA-Forest Service- NRS Retired Research Entomologist
• Phyllis Grinberg, USDA-Forest Service- NRS Retired 
• Ralph Charlton, Kansas State University
• Ring Cardé, University of California Riverside

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