Factors affecting the distribution and survival of an endemic and an introduced species of operophtera (lepidoptera : geometridae)
Date
1989
Authors
Hale, Margaret Angela
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Abstract
The purpose of this study was to compare the effects of physiological and biochemical factors on the recently introduced European winter moth, Operophtera brumata (L.) (Lepidoptera:Geometridae) with the endemic Bruce spanworm, Q. bruceata (Hulst) using breeding experiments, laboratory tests of the effect of temperature and humidity on development and biochemical analysis of protective molecules. The results of these studies were used to make predictions regarding the future spread of the introduced species in North America and to supply evidence that water binding molecules such as glycerol may have a protective role in preventing desiccation during the aestival pupal stage. Q. bruceata males can freely interbreed with females of Q. brumata because 94 % of breeding trials resulted in fertile eggs. The reciprocal cross was not as successful due to anatomical incompatibility, with 23% of trials producing fertile eggs. There is evidence that hybridization occurs in the field.
The results of this study suggest that the introduced Q. brumata is at least as cold-hardy and desiccation resistant as the native species. Pupal duration was not affected by relative humidity and the effect of temperature was the same for both species of Operophtera. The highest pupal mortality occurred at the lowest humidity tested (38% RH) and at the high, constant temperature treatment, with slightly higher mortality experienced by Q. bruceata pupae. The water content of the pupal stage of both species was measured using the independent methods of freeze drying and heat extraction. Both methods showed that Q. bruceata had higher water content (70.7 %,69.7 %) than Q. brumata (65.5%,66.1%) and that the water was more readily extracted from Q. bruceata. Supercooling ability increased significantly during the pupal stage of both species and the degree of supercooling ability was greater in Q. brumata (Mean scp = -19.6 °C). Q. brumata probably could expand its range anywhere in temperate North America where Q. bruceata is already established. The sugar fraction of the insect samples was extracted and derivatised along with standard aldoses and alditols for identification and quantification using gas-liquid chromatography.
Analysis of the sugar fraction of the insect samples using gas-liquid chromatography detected glucose, galactose and glycerol. In samples extracted from Q. brumata, levels of glycerol increased and levels of glucose decreased in the pupal stage which had the lowest supercooling point.