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Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/19/1995 Publication Date: N/A Citation: N/A Interpretive Summary: The gypsy moth, Lymantria dispar, is the major insect pest of deciduous hardwood forest and shade trees in the United States. In spite of the application of improved technology and quarantine effort the pest continues to spread and infest new areas. Its ability to quickly establish in different geographical areas is due primarily to a genetically diverse egg diapause that can rapidly adjust to new environmental conditions. The purpose of this study was to evaluate variability of the diapause response in a laboratory colonized strain of the gypsy moth. Results of the study showed a high degree of variation among egg masses in response to KK-42, an anti-hormonal compound previously shown to be effective in preventing diapause in gypsy moth eggs. It was also found that resistance (R) of susceptibility (S) to KK-42 was associated with egg mass hair color. Thus extremely light and dark forms were significantly more resistant than an intermediate color group. Also, the darker haired egg masses terminated diapause faster and required less chilling for synchronous egg hatch. Removal of egg mass hairs resulted in 50% reduction in egg hatch after chilling for 6 months showing that the attached hairs enable better survival in cold environments. Larvae from KK-42 susceptible egg masses gained weight more rapidly than the slower developing resistant group. These findings are important for subsequent development of a susceptible strain for more efficient manipulation of diapause for laboratory rearing and to determine the mode of action of KK-42 in disrupting the diapause program in the gypsy moth. Technical Abstract: Eggs from 30 different egg mass families were treated with KK-42, a novel, insect anti-hormonal compound that averts embryonic diapause in the gypsy moth, Lymantria dispar. The test population included three egg mass groups (10 masses/group) differing in the degree of pigmentation (coloration) of egg mass hairs and were classified as light, intermediate and dark haired. The incidence of KK-42 induced development without diapause showed a high degree of variation (8 to 89 percent) among the different families of egg masses. Also, egg masses with light or dark hairs showed a significantly lower response to KK-42 than egg masses with intermediate hair coloration. Samples of non-treated eggs from intermediate and dark-haired masses chilled (7 degrees C) for 7-10 weeks terminated diapause and hatched earlier than those from light colored egg masses, suggesting differences in quality or intensity of diapause associated with hair coloration). There was no difference in the rate or incidence of egg hatch in the color groups chilled for 3, 5 and 6 months. Viability and hatching of dehaired eggs chilled for 6 months were significantly lower than with intact egg masses suggesting that the hairs have an insulating effect with increased cold tolerance. Female larvae from egg masses that showed high resistance to KK-42 had a significantly lower weight gain compared to those from susceptible egg masses. Results show both KK-42 resistant and susceptible egg masses of the gypsy moth, and suggest a linkage to egg mass hair coloration, differences in diapause and growth of female larvae. Further studies could lead to highly susceptible strains for more efficient manipulation of diapause, and to a better understanding of the mechanism by which KK-42 disrupts the diapause program. |
